Finding middle ground: environmental conflict resolution.

Background: Saliva of blood-sucking arthropods contains a cocktail of antihemostatic agents and immunomodulators that help blood feeding. Mosquitoes additionally feed on sugar meals and have specialized regions of their glands containing glycosidases and antimicrobials that might help control bacterial growth in the ingested meals. To expand our knowledge on the salivary cocktail of Ædes ægypti, a vector of dengue and yellow fevers, we analyzed a set of 4,232 expressed sequence tags from cDNA libraries of adult female mosquitoes. Results: A nonredundant catalogue of 614 transcripts (573 of which are novel) is described, including 136 coding for proteins of a putative secretory nature. Additionally, a two-dimensional gel electrophoresis of salivary gland (SG) homogenates followed by tryptic digestion of selected protein bands and MS/MS analysis revealed the expression of 24 proteins. Analysis of tissue-specific transcription of a subset of these genes revealed at least 31 genes whose expression is specific or enriched in female SG, whereas 24 additional genes were expressed in female SG and in males but not in other female tissues. Most of the 55 proteins coded by these SG transcripts have no known function and represent high-priority candidates for expression and functional analysis as antihemostatic or antimicrobial agents. An unexpected finding is the occurrence of four protein families specific to SG that were probably a product of horizontal transfer from prokaryotic organisms to mosquitoes. Conclusion: Overall, this paper contributes to the novel identification of 573 new transcripts, or near 3% of the Æ. ægypti proteome assuming a 20,000-protein set, and to the best-described sialome of any blood-feeding insect. Published: 04 January 2007 BMC Genomics 2007, 8:6 doi:10.1186/1471-2164-8-6 Received: 05 August 2006 Accepted: 04 January 2007 This article is available from: http://www.biomedcentral.com/1471-2164/8/6 © 2007 Ribeiro et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background
AEdes aegypti is a highly anthropophagic and cosmopolitan mosquito vector of epidemic dengue and yellow fever. To achieve fast blood feeding, adult female mosquitoes inject a complex salivary mixture into their hosts while probing for blood. Mosquito saliva, like that of other blood-feeding animals, has antihemostatic and antiinflammatory activities that counteract host responses that would otherwise restrict blood flow or call the attention of the host to the feeding site [1,2]. A preliminary transcriptome of adult female salivary glands (SG) has been previously reported [3] where 32 full-length transcripts have been described based on an analysis of 456 expressed sequence tags (EST). Of these putative proteins, ten have been verified by Edman degradation of Coomassie blue-stained bands from sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) of SG homogenates. Most salivary proteins found have no known function.
The genome of AE. aegypti has been recently made available, facilitating further gene discovery. In this paper, we present the analysis of an additional set of 3,776 SG cDNA sequences (total of 4,232 compared with previous set of 456 clones). We describe 573 new transcripts, 136 of which code for proteins of a putative secretory nature, most of which have no known function. We expect this work will contribute to the understanding of the evolution of blood feeding in arthropods and to the discovery of novel pharmacologic agents.

Results and discussion
General description of the salivary transcriptome database A total of 4,232 clones was included in the EST salivary database, including 456 previously described [3]. The average length of the sequences was 752 bp, with 1419 sequences containing a polyA signature (20 contiguous A's). These clones assembled into 1,273 clusters (containing 2-261 sequences per cluster) and singletons (956 sequences). In this paper, we will use the word 'contig' to refer to clusters of one or more sequences. Mitochondrial sequences, identified by their match to sequenced Aedes albopictus and anopheline mitochondrial genomes, accounted for 73 EST from 13 clusters (thus far, the mitochondrial genome of AE. aegypti is unknown). Of interest, several of these mitochondrial sequences mapped to scaffolds named supercont1.593 and also to supercont1.600, supercont1.929, and supercont1.363. Upon close inspections, these genomic scaffolds contain large segments of high similarity to Ae. albopictus mitochondrial genome. Accordingly, these contigs may be assigned to the mitochondrial genome in the final genome assembly, or may represent translocation of Ae. aegypti mitochondrial genes to the nuclear genome. To attempt a functional classification of these unique sequences, we compared them with proteome databases by blastx and with protein motifs by rpsblast (see Methods). Following manual annotation of these contigs, which included assignment of known or putative functions to the translation products, they were further divided into four categories: secreted (Sclass) with 352 contigs and 2,723 sequences; housekeeping (Hclass) with 739 contigs and 1,264 sequences; transposable element (Tclass) with 5 contigs and 9 sequences; and a last category composed of contigs coding for proteins of unknown function (Uclass) with 177 contigs and 234 sequences. The unknown class may contain truncated transcripts mainly mapping to 3' untranslated regions of genes. Although the Sclass corresponds to only 27% of the contigs, it consists of 64% of all EST, reflecting the relatively low complexity and abundance of the secretory material of the SG, as indicated before [3].

Transcribed transposable elements
Nine transcripts in our database possibly derive from transposable elements. Their translation products are similar to those of the sea urchin Strongylocentrotus purpuratus [4] and to Tc1-like transposase [5]. These transcripts may indicate active ongoing transposition activity in AE. aegypti or, more likely, they may represent regulatory elements suppressing transposition of relatively recent genome invasions. To obtain additional information potentially useful to address future functional analysis, we determined the tissue and sex specificity of a selected subset of 73 transcripts encoding secreted proteins and corresponding to a total of 71 genes. These 73 transcripts were selected based on their similarity to transcript families found in diverse mosquito species, and in the presumption that their translated products might play a role either in sugar or blood feeding. Oligonucleotide primers suitable for amplification of corresponding mRNA were employed for reverse transcriptase-polymerase chain reaction (RT-PCR) amplifications using as template total RNA extracted from female SG, female carcasses (i.e. adult females from which SG had been dissected), and whole adult males. Primers amplifying the ribosomal protein S5 were used for normalization and as control. The results of this analysis are summarized in Table 2. We previously used a similar assay for the analysis of the Anopheles gambiae salivary transcriptome [12] and obtained results overlapping very well with the information independently obtained by Marinotti et al. [13] using the Affymetrix microarray chip. The results reported here also fit well with the data obtained comparing salivary versus nonsalivary libraries (Additional File 2) [6,11]. With our assay, it is possible to distinguish three broad classes of genes. First, genes that are female SG specific or whose expression is enriched in the female glands: they are indicated as SG or ENR, respectively, in Table 2.
Products encoded by these genes are likely to play some role in blood feeding, for example as antihemostatics or immunomodulators. Among those genes analyzed, 31 belong to this class; more precisely, 23 were female gland specific, and 8 were enriched in female SG. They include both genes with unknown functions and genes known from previous studies on other mosquito species to be involved in the acquisition of blood meals (see below). A second group is represented by genes expressed in female glands and in adult males, without any expression in female carcasses: these are identified as SG,M in Table 2. It is very likely that most of these genes are gland specific and expressed both in male and female glands. The corresponding products may be involved in sugar feeding, antimicrobial activity, or other gland functions; 24 transcripts are members of this group. Finally, the last class includes genes with ubiquitous expression, i.e. expressed at approximately the same level in the three tissues examined and indicated as Ubiq in Table 2. These genes most likely encode polypeptides involved in housekeeping functions: 16 of the transcripts analyzed belong to this group. The following is a detailed description of the fulllength transcripts found in the SG of adult female AE. aegypti and of their profile of expression.

Secreted salivary proteins
Proteins with some function confirmed or presumed from structure Secreted ligand carrier-like proteins including D7 family D7 salivary proteins The first D7-coding gene was reported 15 years ago, for the mosquito AE. aegypti [14]. It was later found in virtually  Salivary purine nucleosidase X gi|1703351 Salivary apyrase X gi|18568326 Putative adenosine deaminase X Serine proteases gi|94468658 Serine protease X # gi| 94468410 Salivary chymotrypsin-like enzyme X gi|18568306 Putative serine protease X gi|94468372 Trypsin like X

Lectins gi|94468370
Putative salivary C-type lectin X gi|18568318 Putative C-type lectin X # gi|94468698 C type lectin X gi|94468694 C-type lectin X Angiopoietin gi|18568298 Angiopoietin-like protein X # gi|94468352 Angiopoietin-like protein splice variant X Antimicrobial polypeptides gi|48256697 Defensin A1 X gi|18568310 Gambicin X gi|18568288 Putative lysozyme X gi|94468690 Putative salivary peptide with HHH domain X Other gi|94468654 i23M allele X gi|18568294 Gram-negative binding protein X gi|94468610 Peptidoglycan recognition protein X Unknown function, secreted, and ubiquitous Antigen 5 protein family gi|18568284 Antigen 5 member X gi|18568278 Putative secreted protein X gi|18568308 Antigen 5 family member X Other secreted proteins found in nonbloodsucking insects gi|94468620 PAN/APPLE-like domains X gi|94468538 Cysteine-rich venom-like protein X # Unknown function, found in hematophagous Diptera salivary transcriptomes 56.5 kDa gi|18568292 Putative 56.5 kDa secreted protein all mosquito sialotranscriptomes where short (~15 kDa) and long (~30 kDa) forms were recognized [15]. In An. gambiae, this gene family, except for one poorly transcribed gene, appears to be selectively expressed in the female SG [17,18], indicating a role in blood feeding. This protein family is distantly related to the odorant-binding protein (OBP) family, which specializes in binding small ligands [17]. Recently, some mosquito D7 proteins were shown to bind and inhibit the action of biogenic amines such as serotonin, histamine, and norepinephrine, a function that might help blood feeding [18]. Additionally, one short D7 protein from Anopheles stephensi, named hamadarin, was shown to prevent kallikrein activation by Fac-torXIIa [19]. Long D7 forms also exist in sand flies [16] and Culicoides [20], indicating that this gene family was recruited very early in the evolution of hematophagous Nematocera.
In the mosquito An. gambiae, five short and three long D7 proteins are known. Their genes are organized in a inverted tandem repeat [21] where the coding region for the three long proteins is followed by the five genes coding for the short protein in the reverse orientation [12]. In AE. aegypti, three short and two long D7 proteins map to the assembled genome supercontig1.204 (Figure 1), and one short D7 protein maps to supercontig1.253 (not shown). The genomic region coding for the D7 proteins in supercontig1.204 shows three short D7 genes followed by two genes coding for long forms; however, while in Anopheles the frame orientation of the short and long forms is the same (but the short and long forms are in reverse orientation to each other), in AEdes there is no consistent orientation ( Figure 1A). Similarly to An. gambiae, all large AEdes D7 genes contain five exons ( Figure 1B); however, all short AEdes D7 genes have two exons ( Figure  1C), including that in supercontig1.253 (not shown), while in Anopheles, four of the five genes coding for short D7 proteins have three exons. The anopheline gene coding for the two-exon gene is poorly expressed, leading to the suggestion that this two-exon gene may be turning into a pseudogene [18]. The differences between Anopheles and AEdes in the number of D7 coding genes, their exon number, their orientation, and their chromosome location (in Anopheles, all eight genes are clustered, while one AEdes gene is far apart from the main cluster of five genes) are consistent with the ~150 million years of separation between culicines and anophelines [22].
In agreement with the larger genome size of AEdes [23], the five-gene D7 cassette of AEdes spans nearly 80 kb, four times more than the eight-gene cassette of Anopheles. To investigate whether additional genes were expressed within the D7 gene cassette in AE. aegypti, we mapped 220,000 EST to the AE. aegypti genome. No new identifiable expressed genes were revealed in the D7 region; how-ever, in the vicinity of the short D7 cassette, we found two transcripts, both deriving from SG libraries, which map to the intron of D7s3 and to the 3' region of the same gene ( Figure 2). Translations of these two EST do not reveal extended open reading frames. This finding is reminiscent to the D7 short gene region of Anopheles, which also has an apparently noncoding EST mapping to the end of the short cassette, but at its 5' end. We have hypothesized previously that these noncoding transcripts could be associated with transcriptional regulation of the cassette.
Alignment of the D7 sequences from AE. aegypti with those of AE. albopictus, Culex quinquefasciatus, An. gambiae, and one D7 salivary protein from the sand fly Lutzomyia longipalpis indicates, as shown before, that the short D7 proteins appear to be truncated versions of the long D7 proteins, which appear to be the ancestral type ( Figure  3A). The resulting phylogram, using the sand fly sequence as an outgroup, shows three clades without strong bootstrap support; however, the inner tree branches show considerably more conservation of the multiple forms within genus than between genera. For example, the common long D7 clade ( Figure 3B) shows that two of the long D7 proteins of An. gambiae are more closely related to each other as are the Culex or the AEdes pair. Within the AEdes genus, the AE. albopictus and AE. aegypti homologues are distinctly grouped together, indicating that they share a relatively recent common ancestor before the duplication event, as expected from these two mosquitoes of the same subgenus. The same pattern is visible in the culicine short D7 clade ( Figure 3B) where all short D7 proteins are more related to each other within genus than between genera. This is even more remarkable in the short D7 proteins of Anopheles, where all short D7 proteins form a single clade outside of their culicine counterparts. If the gene duplication events that lead to the formation of long and short D7 proteins occurred in the primordial mosquito ancestral to both culicines and anophelines, the tree pattern observed would be one where the orthologous pairs would be more similar to each other between genera than within genus. Two possible explanations may account for the observed tree pattern: either the gene duplications leading to the D7 expansions occurred independently after the division of the culicine and anopheline lineages, or some degree of gene conversion occurred within each species, maintaining the uniformity of the genes within species. This latter scenario is consistent with the proposed primordial role of the D7 proteins, e.g. sequestration of host serotonin released by thrombocytes at the site of bite, a function that would require the D7 proteins to be a major salivary protein constituent [3]. The gene duplication event would be beneficial in allowing increased transcript mass needed to create the substantial amount of protein needed in the mosquito saliva to chelate the near-micromolar concentration of the vasoac-The D7 gene cassette in supercontig1.204 of AEdes aegypti Figure 1 The D7 gene cassette in supercontig1.204 of AEdes aegypti. A, Overview of genomic region containing three short and two long D7 genes. B, Exon-intron structure for gene D7L1. C, Exon-intron structure for gene D7s1. A B C tive amine. Gene conversion events to maintain this function on multiple genes could be beneficial at this earlier stage of blood feeding evolution. This phenomenon would maintain intraspecific copies of the gene family more similar to each other than to the orthologous interspecific copies. With time, other salivary proteins may have taken a similar role of preventing platelet function, allowing the D7 proteins to acquire different functions such as binding other amines or to become anti-bradykinins, a function apparently only acquired in the anophelines, which diverged from the culicines ~150 million years ago [22]. For a review on the evolution of gene families, see references [24,25].
Evidence for synthesis of the two large D7 proteins and for D7s2 was shown before from Edman degradation results of SDS-PAGE gels [3]. Presently, we observed extensive coverage of tryptic fragments for both long D7 proteins (D7l1 and D7l2) as shown by two-dimensional (2D) gel electrophoresis ( Figure 4 and Additional File 2) [14]. This protein family appears polymorphic. The predicted translation products of some of these alleles are shown in Additional File 2. As expected from this protein family, all transcripts described in Additional File 2 are more expressed in the SG cDNA libraries than in the remaining libraries, three of which are significant by the χ 2 test at the 0.05 level. RT-PCR experiments agree with these results, indicating a selective or preferential expression of this gene family in female SG ( Figure 5 and Table 2). It should be noted, however, that transcripts encoding the short D7 were exclusively found in female glands, whereas mRNA encoding the long D7 were also detectable at a lower level in adult males (D7l1, D7l2) and in other female tissues (D7l2). This observation may be connected to an inde-pendent regulation of the short and long D7 cassettes, which are more that 30 kb apart.

Phosphatidylethanolamine binding proteins
We report three members (one possibly truncated) of this very ubiquitous protein family never found before in sialotranscriptomes of blood-sucking arthropods [26,27], two of which have clear signal peptide indicative of secretion. This protein family is known to bind lipids and was also shown to have serine protease inhibitory capacity. Their role in saliva is unknown. No enrichment was found for these transcripts on the SG libraries when compared with other libraries.
Other small molecule binding proteins An OBP and a lipocalin with a juvenile hormone binding motif were found in the sialotranscriptome of AE. aegypti, both containing distinct peptide signal indicative of secretion. The D7 proteins belong to the OBP superfamily. Lipocalins are abundantly expressed in tick and triatomine sialomes, where they act as nucleotide (nt)-and biogenic amine-binding proteins in addition to other functions. Their function in AEdes is unknown. No enrichment was found for these transcripts on the SG libraries when compared with other libraries.

Secreted protease inhibitors Serpins
Two serpins have been described before in AE. aegypti, one of which has been characterized as an inhibitor of Fac-torXa of the clotting cascade [28,29]. We present one allele of the FXa-directed anticoagulant precursor having only 89% identity to the reported protein [30] which originated from the Rockefeller strain of AE. aegypti, and two alleles of a novel salivary serpin mapping to supercontig1.65. The three genes coding for these serpins are not located near each other in the AE. aegypti genome. All three salivary AE. aegypti serpins have corresponding homologues found in Ae. albopictus sialotranscriptome [31]. The novel serpin has abundant tryptic fragment matches recovered by proteomics (band marked Serp2, Figure 4), indicating its expression in the SG, as did gi|18568304 (marked Serp1, Figure 4). Transcripts for all serpins are significantly overrepresented in the SG library when compared with the remaining libraries, in accordance to the RT-PCR experiments shown in Table 2, which indicates that two of the three serpins are female specific and that one may be found also in males but not in carcasses of females not containing SG ( Figure 5).

Other protease inhibitors
A Kazal domain-containing peptide, similar to one described in Ae. albopictus and to several other proteins described as thrombin inhibitors, was found in the AE. aegypti sialotranscriptome. A cystatin was also found, but Numbers on the left indicate molecular weight marker positions in the gel. The + and -signs indicate the anode or cathode side of the isoelectrophocusing dimension, which ranged from pH3-10. Gel bands that were identified to a protein (following tryptic digestion and mass spectrometry) are shown in the gel. In some cases, more than one band accounted for the same protein, possibly due to trailing or multiple isoforms. The proteins found were: D7l1 (gi: 16225992), PNase (purine nucleosidase, gi: 21654712) PDI (protein disulfide isomerase, gi: 94468800), HS70 (heat-shock protein 70  this protein is reported as truncated; we were not successful in searching the genome for the missing exon(s). This could be due to the large intron size observed in Ae. aegypti. Accordingly, no indication of secretion is possible, but it is described in this section due to the importance of this family in inhibiting proteases associated with inflammation. Both transcripts are ubiquitously found in mosquito tissues by RT-PCR and may play a housekeeping role.

Vasodilator Sialokinin
The gene coding for this endothelium-dependent peptide vasodilator [32,33] has been reported earlier and shown to be transcribed specifically in female SG [34]. Although two forms of the peptide have been described earlier differing in the aminoterminal (aspartate or asparagine), only one gene is found coding for this peptide sequence, for which 60 EST were found in the salivary cDNA library. The Asn version may have been an artifact from the modification of the original peptide, which was stored in acidic solution.

Enzymes Nucleotidases
The salivary purinergic degradation machinery of AE. aegypti comprises the enzymes apyrase (a member of the 5' nucleotidase family), adenosine deaminase (ADA), and purine hydrolase [35][36][37], which may serve an antihemostatic and antiinflammatory function by removing nucleotide agonists of platelet aggregation and mast cell degranulation. In addition to these previously described enzymes, we found a second 5' nucleotidase that may function either as an alternative apyrase or as a secreted salivary 5' nucleotidase, as is the case with Lutzomyia longipalpis [38]. The novel 5' nucleotidase has only 38% identity to the previously characterized apyrase form of Aedes aegypti[39] but has a higher identity (52%) to a Culex. quinquefasciatus salivary 5' -nucleotidase/apyrase protein [40]. 5' nucleotidases are typically seen in the external part of the cellular membrane to which they are bound by a inositol phosphate anchor [41][42][43]. Secreted apyrases and 5' nucleotidases have lost either the conserved Ser or the surrounding lipophylic amino acids (aa) (or both) to which the inositol phosphate moiety binds to [35,38]. The novel AEdes 5' nucleotidase, like the previously described salivary apyrase [35], lacks the typical Ser residue surrounded by hydrophobic aa typical of membranebound enzymes, similarly to other mosquito salivary 5' nucleotidase ( Figure 6), supporting their role as secreted 5' nucleotidases. This novel apyrase may contribute to the purinergic degradation machinery found in saliva of AE. aegypti. All these genes are overrepresented in SG libraries and, except for ADA, significantly so. RT-PCR results are somewhat contradictory with the proposed role of these enzymes in blood feeding: with the exception of the ADA coding transcript that was enriched in female SG, the other genes appeared to be SG specific, because they are expressed in SG of females and in whole males, which would suggest a role in sugar feeding, instead. We do not have a good explanation for this observation; however, we should point out that apyrase, purine nucleosidase (PNase), and ADA showed very similar expression profiles by RT-PCR in the related mosquito AE. albopictus (Arcà et al., manuscript in preparation). Evidence of synthesis of these enzymes was found for the ADA, the original apyrase, and the PNase, which provided abundant tryptic fragments ( Figure 4, bands labeled ADA, apyrase, and PNase).
A novel ribonuclease of the T2 family [44] was also characterized. This enzyme has not been previously characterized in sialotranscriptomes. It has a typical signal peptide indicative of secretion and may function in the degradation of extracellular RNA [45].

Serine proteases
Nine secreted serine proteases varying in predicted mature molecular weight between 28 and 43 kDa were found in the AE. aegypti sialotranscriptome, seven of which are being reported for the first time (Additional File 2). Two of these serine proteases (AEA-876 [46]and AEA-562 [47]) contain a CUB domain [48], indicating specialized substrate recognition. Both are found in supercontig1.217 within 63 kb of each other. Some of these enzymes (such as gi|18568334[49]) are possibly related to immunity and are similar to other enzymes annotated as prophenoloxidase (PPO)activators, but they could have been co-opted to function in hydrolyzing specific host proteins. A smaller number of this type of enzymes found in An. gambiae sialotranscriptomes was selectively expressed in the SG of adult females, indicating they may play a role in blood feeding, perhaps by activating antiinflammatory pathways (such as protein C) or deactivating inflammation. One such AEdes enzyme is AE-226 [50], similar to proteins annotated as chymotrypsin, which is overexpressed in AEdes sialotranscriptomes as opposed to the remaining transcriptomes. Three of these serine proteases were significantly underrepresented in the nonsalivarygland libraries. Four serine proteases tested by RT-PCR agreed with the library frequency results: the transcripts were found in female glands and adult males but not in female carcasses deprived of SG.

Sugar hydrolases
Previously reported amylase [51,52] and alpha-glycosidase/maltase [53,54] are abundantly overrepresented in the salivary EST collection. These genes were shown to be expressed in the proximal regions of the female glands, the region associated with sugar feeding.

Other hydrolases
An alkaline phosphatase [55] and a carboxylesterase [56], both containing signal peptides indicative of secretion, are described. Both enzymatic activities in adult female SG have been previously described in AEdes [57], and the esterase activity shown in saliva, but their function in blood feeding can only be speculated upon.

Immunity-related proteins
The SG of mosquitoes produce various antimicrobial polypeptides and other immunity-related products such as bacterial surface-recognizing proteins and lectins that may be important in opsonization and initiation of activation of the PPO enzyme leading to pathogen melanization. The purpose of these products may be to control microbial growth in the sugar solutions stored in the crop or in the gut following a blood meal. Previously, lysozyme [58] was found in both male and female SG of AE.
aegypti, and in the mosquito crop [59] and shown to be secreted by females following either a sugar or blood meal [60]. Indeed, AE. aegypti salivary lysozyme is significantly overrepresented in the SG libraries, and the RT-PCR experiment supports salivary expression in both male and female SG (Table 2 and Figure 5). Anopheline mosquitoes also display a similar pattern of lysozyme expression in the proximal gland region [61]. It is possible that most immunity-related gene products follow the same pattern of expression shown by lysozyme. Some of the enzymes possibly associated with PPO activation have been listed above in the Enzyme section.

C-type lectins
Five C-type lectins are described in Additional File 2, four of which are novel. Expression of AE-189 and gi|18568318 was confirmed by mass spectrometry following tryptic digestion of protein bands (labeled C-Lec1 and Alignment of members of the 5' nucleotidase family deriving from salivary glands of mosquitoes or from Drosophila mela-nogaster, D. pseudoobscura, Bos taurus, or Rattus rattus  Figure 4). These two lectins are also expressed significantly more in sialotranscriptomes than in other AE. aegypti cDNA libraries, indicating that they are possibly salivary-tissue specific. In accordance with this expectation, RT-PCR experiments indicate expression exclusively in female SG (Table 2 and Figure 5). The two genes coding for these salivary-specific lectins were found as an inverted tandem repeat in supercontig1.10, each with a single intron separating the signal peptide gene region from the remaining coding sequence. Two other C-type lectins tested by RT-PCR were ubiquitously expressed.
The C-type lectin family is expressed in most mosquito sialotranscriptomes described thus far. This protein family is implicated in immune recognition phenomena in general and in Plasmodium development in Anopheles in particular [62,63]. Despite these not-yet-demonstrated roles of C-type lectins in salivary immunity, it is interesting that in snake venoms this protein family has been recruited to perform various unrelated functions such as anticlotting, toxin, and platelet aggregation inducer [64,65]. Lectins may also play a role in the colectin pathway of complement activation [66]. Hemagglutinins were described in anopheline SG more than 60 years ago [67]. This activity may help concentration of red blood cells in the mosquito gut [68]. The molecular nature of any anopheline hemagglutinin, however, is unknown. Differently from anophelines, and despite having salivary lectins, AEdes SG homogenates lack hemagglutinins, indicating that the salivary lectins do not recognize vertebrate red blood cells or that they are monomeric in their carbohydrate binding site. Overall, it appears that the two female SG-specific lectins may have a role in hemostasis rather than immunity.
Other proteins with sugar-binding domains AET-12005 and AET-670 are similar to, but shorter than, N-acetylgalactosaminyltransferase and glucuronyltransferase, respectively, appearing to derive from novel genes that arose from gene duplications and partial deletions of ancestral genes coding for carbohydrate binding enzymes, the final products lacking the original carboxyterminal domain. AET-12005 has a partial Pfam Glycos_transf_2 motif that comprises a diverse family transferring sugar from UDP-glucose, UDP-N-acetyl-galactosamine, GDPmannose, or CDP-abequose to a range of substrates including cellulose, dolichol phosphate, and teichoic acids. AET-670 has a weak match to the PFAM UDPGT motif and is similar to proteins in the nonredundant (NR) database annotated as UDP-glucosyl transferase. It is possible that these proteins have a destination in the endoplasmic reticulum or Golgi and do not have a secretory nature. Their function is unknown.
The proteins annotated as imaginal disk growth factor protein 4 [69] and AEA-871BRE were expressed in the sialotranscriptome of AE. aegypti. These proteins have a chitinase domain and are homologous to An. gambiae bacteria responsive protein 1 [70] and bacteria responsive protein 2 [71], which were shown to be immune-responsive chitinase-like proteins that have lost chitin-binding activity [72].

Angiopoietins/ficolins
This group of proteins has the PFAM fibrinogen C motif [73]seen in invertebrate proteins displaying lectin activity toward N-acetylglucosamine residues and implicated in immune function [74]. In An. gambiae, the ficolin family was expanded in comparison to Drosophila melanogaster, where 53 members were seen in its genome as opposed to 20 in the fruit fly [75]. Three proteins belonging to this family are shown in Additional File 2, two of which are novel. Evidence for salivary expression of gi|18568298 and AE-154 was found by mass spectrometry in tryptic digests of protein bands (labeled Ang1 and Ang2, respectively, in Figure 4). Of interest, the two genes for these proteins occur as a tandem repeat in supercontig1.15. EST for these two genes are also overrepresented in the sialotranscriptomes and are indicated to be female-salivary-gland specific by RT-PCR experiments, thus suggesting a blood-feeding rather than an immune role for these proteins.

Antimicrobial peptides (AMP)
The gene products for the AMP gambicin[76], lysozyme [58], and defensin A1 [77] have been previously described in AE. aegypti sialotranscriptomes and are listed in Additional File 2. Transcripts encoding gambicin and defensin A1 were detected by RT-PCR in all tissues examined, indicating ubiquitous expression (Table 2 and Figure 5); however, a significant overrepresentation of the corresponding EST in sialotranscriptomes should be pointed out. We additionally describe three novel peptides that may have an antimicrobial function. AET-590 [78] has GY repeats that are also found in peptides of similar size known to have antimicrobial activity in nematodes [79]. AET-462 [80] and AET-11358 [81] are candidate AMP containing a HHH motif seen in other histidine-rich AMP [82,83]. AET-11358 appears to be SG specific, as a total of 88 EST was found in the combined SG transcriptome, although none were seen in other tissue transcriptomes. RT-PCR confirmed the presence of the transcript in female glands and male bodies but not in female carcasses without SG (Table 2 and Figure 5).
Other immune-related gene products A peptide (named AEA-233 [84]) closely related to a previously described AE. aegypti peptide named i23R[85] potentially involved in Plasmodium susceptibility [86] was found in the sialotranscriptome. We also present an allele to AEA-233a, indicating the polymorphism of this gene. The AE. albopictus sialotranscriptome revealed a homologue that is 63% identical, but no significant matches were found to any other animal or plant proteins in the NR database. This peptide may belong to a not-yet-characterized antimicrobial gene family specific to the AEdes genus. Expression of AEA-233a was ubiquitous by RT-PCR.
Two other gene products are described, both associated with pathogen surface-pattern recognition: the previously described Gram negative binding protein [87], which is significantly overrepresented in sialotranscriptomes and appears expressed both in female SG and in adult males (Table 2, Figure 5), and the novel AE-7210 [88], which is similar to peptidoglycan recognition proteins and was ubiquitously expressed by RT-PCR experiments.

Mucins
Mucins and peritrophins are proteins associated with lining of epithelia or inert extracellular structures, such as chitin. Mucins are highly glycosylated proteins containing Ser or Thr modified with N-acetylgalactosamine residues.
Their expression in the SG may have a function of lining the chitin surfaces of the mouthparts, but they may also assist in antimicrobial functions.
We present 12 mucins in Additional File 2, 11 of which are novel, including one allele. These proteins have an average Ser+Thr equal to 13.8% of their total aa, as opposed to 0.9% observed as the average of all proteins found in Additional File 2. We additionally report on a polypeptide (AE-466, mucin-like peritrophin) containing three glycosylation sites and one chitin-binding domain, which may be involved in proximal lining of the cuticular duct. All other proteins have 11-69 glycosylation sites.
Putative secreted proteins without functional classification Belonging to ubiquitous protein families Antigen5 (AG5) family AG5-related salivary products are members of a group of secreted proteins that belong to the CAP family (cysteinerich secretory proteins; AG5 proteins of insects; pathogenesis-related protein 1 of plants) [89]. Members of this protein family are found in the SG of many blood-sucking insects [3,90,91]. Most of these animal proteins have no known function; in the few instances to the contrary, they diverge from proteolytic activity in Conus [92], to smooth muscle-relaxing activity [93,94] in snake venoms, to salivary neurotoxin in the venomous lizard Heloderma horridum [95]. Three members of this gene family were previously described in the sialotranscriptome of AE. aegypti. EST's for all three genes are overrepresented in the sialotranscriptome as compared with the combined tran-scriptomes, indicating they may be preferentially expressed in the SG. In accordance with these results, gi|18568284 was exclusively transcribed in female glands as indicated by RT-PCR, suggesting an antihemostatic function for the gene product, while the other two genes are transcribed in female glands and male bodies but not in female carcasses.
Differently to An. gambiae, which has four salivary AG5 members, three of which cluster in chromosome arm 2 L [12], the salivary AG5 proteins of AEdes do not appear to cluster in the genome, mapping to different supercontigs.

Other secreted proteins of unknown function found in nonbloodsucking insects
Eight putative secreted proteins have similarities to proteins or protein domains found in non-bloodsucking insects. One of these proteins (AE-796) [96] is a truncated fragment where it is not possible to identify whether it has a signal peptide indicative of secretion, but it has a weak CDD domain PAN_AP_HGF [97], which is found in plasminogen/hepatocyte growth factor proteins, and various proteins found in Bilateria, such as leech antiplatelet proteins; however, the mRNA encoding this protein was found ubiquitously expressed by RT-PCR and may not have a unique salivary role in blood feeding. AE-389[98] has a TIL [99] domain (trypsin inhibitor like) and is significantly overexpressed in sialotranscriptomes. RT-PCR indicates both male and female SG may be the target tissue of expression of this peptide ( Figure 5 and Table 2). Peptides containing a TIL domain were also found in the An. stephensi[100] and An. gambiae adult male sialotranscriptomes[101 -103]. The finding of this type of peptide being overexpressed in male An. gambiae SG indicated a possible antimicrobial function rather than a function as a host serine protease inhibitor during blood feeding. Indeed, a tick TIL domain containing peptide named ixodidin[104] was found to have an antimicrobial function in addition to inhibiting serine proteases [105]. The remaining six polypeptides have similarities to Drosophila or other species, and their structure does not hint at any particular function.

Belonging to families only found in blood-sucking diptera 56-kDa family
This protein family has been found to date only in salivary transcriptomes of adult mosquitoes, including adult male An. gambiae. The SG specificity of this gene transcript in AE. aegypti is supported by significant overrepresentation of EST on the sialotranscriptome and by RT-PCR ( Figure 5 and Table 2). All family members have a signal peptide indicative of secretion and a predicted molecular weight near 56 kDa. BLAST comparisons [106] also show weak similarity to bacterial proteins but to no other eukaryotes. Following 4 iterations of PSI-BLAST [107], only mosquito and bacterial proteins are retrieved [108], suggesting that this family of proteins may have originated as a lateral transfer from a bacterial genome to the ancestral mosquito genome. The single exon structure of the gene [109] -unusual in eukaryotes, particularly for a protein of this size, but the rule in prokaryotes -supports this hypothesis. The An. gambiae homologue also displays a single exon gene structure [110], as reported previously [12]. The bacterial proteins retrieved by PSI-BLAST are mostly annotated as phage-associated proteins, suggesting the lateral transfer might have occurred via a phage-associated mechanism.  Figure  5). The function of any member of this protein family is unknown.

30-kDa GE-rich family
This acidic, Gly/Glu-rich protein family is abundantly expressed in adult female mosquito SG, where they appear to be involved in allergic reactions to mosquito bites [114]. In AE. aegypti, two proteins of this family have been previously reported, and we now report two additional splice variants and alleles. Evidence for expression was found in bands labeled 30 ag (for gi|14423642 [115] and gi|18568322[116]) in the 2D gel experiment shown in Figure 4. The two proteins are coded by an inverted tandem repeat in supercontig1.464 separated by only 363 base pairs. The sialotranscriptome is significantly overrepresented in EST coding for this protein family, indicating it is salivary specific. RT-PCR confirms the female SG specificity of these transcripts. Based on the public sequences available, it appears that in anopheline mosquitoes (An. gambiae, An. stephensi, An. albimanus, An. dirus), only one polymorphic gene exists for this protein family per genome.

29-kDa family
Two different transcripts [117] in AE. aegypti are possibly obtained from the same genomic region coding for the basic (pI = 9.4) salivary protein AE-236 and for the alternative shorter transcript AE-236A, which was not found on the salivary EST but rather as one contig assembled from four EST deriving from nonsalivary libraries [118]. BLAST comparison of the deducted salivary protein with the NR database shows similarities to other culicine and anopheline salivary proteins, including weak similarities to some members of the 30 kDa protein family. Four iterations of Psi-blasT [119] are able to assemble only salivary proteins of mosquitoes, Culicoides, and Phlebotomus, including all 30-kDa proteins discussed above, suggesting that either this unique protein family was co-opted as salivary proteins independently by these different families of Diptera or that they have a common blood-feeding ancestor. ClustalW alignment of the sequences shows that following the signal peptide region, a subset of the proteins have a Ser/Thr/Gly-rich region, poor in aliphatic aa as shown in Figure 7 by the richness in brown residues. The carboxyterminal region is marked by the alternation of polar and aliphatic residues. A subset of Culicoides proteins does not have this domain. The phylogenetic tree shows a robust mosquito clade (marked I in Figure 8) with three members of the family per AEdes species (two 30-kDa genes, one 29-kDa gene, plus alleles) and one member (plus alleles) per Anopheline species, which have only a single 30-kDa member. A single Cx. pipiens sequence is also part of this clade. CladeII has two very similar Culicoides proteins. CladeIII has very divergent Culex and Phlebotomus sequences, and CladeIV has solely Culicoides sequences, representing those lacking the Ser/Thr/Gly-rich aminoterminal domain. It is tempting to speculate that these data support a common origin of blood feeding for these three Dipteran families, where two genes are found in Culicines, a single in Anophelines and possibly Phlebotomus, and a rather large gene expansion in Culicoides, which has at least seven genes in the family. Notice that CladeIII, containing mosquito and sand fly sequences, roots with Culicoides CladeIV and that Culicoides cladeII roots with the mosquito cladeI, indicating that Culicoides may have shared a common ancestor with mosquitoes that had two genes of this unique family. Alternatively, convergent evolution may have shaped these genes to produce similar proteins. AE-236A was enriched in the SG of adult females, while AE-236 was significantly underrepresented in non-SG libraries, suggesting a salivary specificity for this protein family, as is the case with the related 30-kDa family discussed above.
Other mosquito-or Diptera-specific peptides Additional File 2 also includes 14 additional polypeptides, one of which is an allele, showing sequence similarities to putative proteins from other hematophagous Diptera including, in a few cases, some weak similarities to Drosophila; 13 of these are novel. Among this class of polypeptides, nine were analyzed by RT-PCR ( Figure 5 and Table 2), and seven are significantly underrepresented in the non-sialotranscriptomes, as follows: AE-212 [120], which is similar to Drosophila and Culicoides proteins of unknown function and was ubiquitously expressed by RT-PCR experiments; two alleles (AE-165 [121] and AE-163 [122]) coding for basic (pI = 9.

Genes belonging to protein families found to date only in AEdes genus
Nineteen genes were found expressed in the sialotranscriptome of AE. aegypti coding for polypeptide families known only in the AEdes genus, as follows:

62-kDa family
Two single exon [129] genes separated by ~20 kb in supercontig1.15 code for proteins with signal peptides and mature mass of 62-63 kDa. Transcripts for these genes are significantly overrepresented in the sialotranscriptome and are shown to be adult female SG specific by RT-PCR ( Figure 5 and Table 2). They are similar to homologous salivary protein sequences seen in Ae. albopictus [130] and, to a much smaller degree, to rhoptry proteins of Plasmodium. Repeated Leu and Glu residues provide similarities to myosin[131], indicating this protein family may be involved in adhesion phenomena. Their uniqueness among metazoan and single-exon structure indicates possible horizontal acquisition of this gene family in AEdes. Both genes are abundantly expressed in the SG as evidenced by bands labeled 62 k by 2D gel electrophoresis MS/MS (Figure 4).

34-kDa gene family
Seven transcripts coding for related proteins were found mapping to supercontig1.92. After locating the corresponding genomic regions, these 7 transcripts were anno-tated as truncated forms or alleles of three genes found as a tandem repeat (Figure 9). We additionally found one possible related gene in the most distal region of the 34-kDa cassette (Putative_34 kDa in Figure 9). Except for the first gene on the cassette, which codes for a 16-kDa protein and has two exons[132], the remaining genes are single exonic [133] and code for proteins of ~34 kDa. The two central genes, each with a single exon, are abundantly expressed as evidenced by MS/MS sequencing of tryptic digested bands (34k1 and 34k2 in Figure 4). All transcripts matching this gene region are significantly overexpressed in the SG transcriptome when compared with the remaining libraries. RT-PCR indicates they are enriched or exclusive of adult female SG ( Figure 5). Protein products of these genes match significantly only Ae. albopictus proteins [134]. PSI-BLAST for each transcript against the NR protein database reveals cytoskeletal proteins such as actin and myosin, mainly due to the presence of repeated charged aa. This indicates that this protein family may be associated with adhesion phenomena (not shown). The single-exon nature of most members of this gene family and their uniqueness among Metazoa points to a horizontal acquisition of this gene.

30.5-kDa family
Two genes coding for proteins of ~30.5-kDa (not to be confused with the 30 kDa/GE-rich protein family) are found as a tandem repeat on supercontig1.280. The gene coding for gi|61742033 is abundantly expressed as evidenced by MS/MS of tryptic digested band labeled 30.5 in Figure 4. These proteins are similar only to homologues[135] found in Ae. albopictus [136]. Both genes are significantly overtranscribed in the sialotranscriptome when compared with other transcriptomes. RT-PCR indicates enrichment in the female SG or exclusive expression in the same organ.

9-kDa family
Two genes[137] having 80% sequence similarity and coding for mature peptides of 8.5 and 9.5 kDa are found as a tandem repeat in supercontig1.18. They are similar only to salivary peptides of Ae. albopictus [138]. Both genes are significantly overexpressed in sialotranscriptomes. RT-PCR suggests that these genes occur in both male and female SG.
Other salivary polypeptides Additional File 2 lists an additional 11 full-length transcripts originating from 10 genes coding for proteins found to date only in the genus AEdes. Six of these genes have overrepresentation in the sialotranscriptome, as follows: AE-376 [139] [143], and AE-214 [144]. RT-PCR in 10 of the 11 transcripts show enrichment or female specificity for 5 transcripts and ubiquitous expres-sion for 2 genes, while 3 appear to be transcribed in both male and female SG ( Figure 5, Table 2, and Additional File 2). Their function is unknown.

Proteins of possible housekeeping function Function possibly predicted Transporter function and storage proteins
Being a secretory organ, mosquito SG are involved in active ion and water transport associated with their function. V-ATPases are generic 'batteries' that generate a proton gradient across membranes that can be coupled with ion exchangers and are used in eukaryotic cells for transport purposes [145]. This multi-subunit enzyme complex has been extensively studied in insects, in particular in Lepidotera larvae midgut [146] and in the malpighian fluid transport in mosquitoes [147]. A role for V-ATPases in mosquito SG secretion has been previously proposed [148]. Additional File 2 reports 22 gene products including 9 subunits of the V-ATPase complex, 3 aquaporins (water channels), 2 chloride channels, and the enzyme carbonic anhydrase, which is associated with proton transport in epithelia to speed intracellular pH regulation via the CO 2 +H 2 O↔bicarbonate + H + reaction.

Probable signal transduction function
Thirty-eight proteins, 35 of which are novel, are described in Additional File 2 as possibly associated with signal transduction events. Included are four proteins associated with inhibition of apoptosis, four enzymes associated with juvenile hormone metabolism, one associated with ecdyesteroid metabolism, and a gamma-amino butyric (GABA) receptor-associated protein, in addition to protein kinases and phosphatases.

Nuclear regulation, transcription factors, and transcription machinery
Twelve (all novel) proteins are associated with nuclear function including histones, zinc finger proteins, and proteins associated with cell division. Additionally, we found 9 possible transcription factors and 21 proteins involved in the transcription machinery, only one of which has been previously reported (Additional File 2). Eighteen proteins (14 novel) were possibly associated with the translation machinery, including elongation factors, tRNA synthases, and translation initiation factors. Elongation factors 2, 2 alpha, and 2 beta were significantly overexpressed in the SG.

Protein modification and protein export machinery
Forty-four proteins (43 novel) were possibly associated with the protein modification machinery including enzymes associated with proline isomerization, disulfide bridge formation, glycosylation, and several chaperones. Thirty-six proteins (35 novel) are possibly associated with the protein export machinery, including signal peptidase complex, endoplasmic reticulum, Golgi, and vacuole proteins. The putative cargo transport protein EMP24 is overexpressed in the sialotranscriptome, although also found in other nonsalivary libraries. Evidence for expression of a protein disulphide isomerase was found by MS/MS results of the tryptic digestion of band labeled PDI in Figure 4.

Oxidant metabolism
One peroxiredoxin, one thioredoxin, two superoxide dismutases, one cytochrome P-450 enzyme, and one truncated catalase are among ten proteins associated with oxidant metabolism (eight of which are novel). The cytochrome P-450 enzyme has a signal peptide indicative of secretion and is a member of the CYP4 family (based on the nomenclature of related proteins [149]), but it is included as a possible housekeeping function due to its high similarity to other insect enzymes [149] and because these enzymes normally need an associated reductase driven by NADPH+, which is normally only found intracellularly. Members of the CYP4 family can be found in peroxisomes, where they can be associated to arachidonic acid or eicosanoid reactions [150]. Of interest, AET-6749 is similar to a 40-kDa farnesylated protein associated with peroxisomes[151], indicating the presence of this organelle in AEdes SG and the possible reason for the signal peptide that may be needed for directing this enzyme to the peroxisome.

Proteasome and lysosomal machinery
Seventeen proteins (16 novel) were associated with the proteasome machinery, including several proteasome subunits and ubiquitin-related enzymes. Two previously described lysosomal enzymes are also listed in Additional File 2.

Cell metabolism
Forty-three proteins associated with nt, aa, carbohydrate, lipid, and heme metabolism or transport are described. AET-12468 is similar to enzymes annotated as kynurenine formamidase [152] and has a KOG motif indicative of this enzyme [153]; 9 transcripts were found among the 15,625 salivary EST but only 6 in the 217,296 nonsalivary EST, indicating this enzyme is overexpressed in the SG of AEdes. Kynurenine formamidase is a key enzyme in the degradation of tryptophan, producing L-kynurenine from Nformyl-kynurenine, the product of the action of L-tryptophan:oxygen 2,3-oxidoreductase on tryptophan, and a precursor to xanthurenic acid, which has been described in the SG of An. stephensi [154]. Xanthurenic acid has also been reported as the mosquito-derived gametocyte exflagellation factor of Plasmodium [155,156]. The presence of xanthurenic acid in AEdes saliva remains to be demonstrated, although a recent report indicates that AEdes mosquitoes deficient in the production of xanthurenic acid sustain normal P. gallinaceum development [157].

Energy metabolism
Fifty-four enzymes (51 novel) are presented as involved in energy metabolism. Most of these are mitochondrial con- The 34-kDa gene region in supercontig1.92 Figure 9 The 34-kDa gene region in supercontig1.92.
stituents, a few of which are overrepresented in the salivary libraries compared with the other libraries, perhaps due to the larger-than average-salivary metabolism associated with protein synthesis and secretion. Evidence for expression of the alpha and beta subunits of the F0F1-type ATP synthase were found by MS/MS data obtained from bands labeled F0F1α and F0F1β on the 2D gel ( Figure 4) indicating their abundant expression.
Cytoskeletal, adhesion, and extracellular matrix proteins Fifteen proteins (14 are novel to AEdes) are associated with cytoskeletal, intercellular adhesion, or extracellular matrix functions, including actins, dynactin, tubulins and annexins, and the basal lamina protein named as SGS1, which was found to be a SG receptor for P. gallinaceum sporozoites [158]. Notably, this protein family has homologues only in An. gambiae, where it was abundantly expressed in the SG of adult females [12] and in bacteria, the most closely related protein outside Anopheles being from the Wolbachia [12,158]. Four such large proteins (~200 kDa) were described in Anopheles, all intronless and contained in a tandem repeat on chromosome arm 3R, while six have been identified in AEdes, also intronless [159], and consistent with their horizontal acquisition from a Wolbachia bacteria. For more details on this protein family, see reference [158].
Probably housekeeping, function unknown Fifty-nine proteins are described (all novel to AEdes) that are conserved with other organisms, thus characterizing the large group of 'conserved hypothetical' proteins [160] or are just hypothetical proteins with no similarities to other known proteins (five cases only). Two of the conserved hypothetical proteins are clearly membrane proteins of unknown function. Several members of this group are significantly overexpressed in the SG when EST's in the sialotranscriptome are compared with the remaining transcripts.

Conclusion
Using high-throughput transcriptome analysis, we significantly expanded the AE. aegypti SG transcript repertoire. A total of 614 transcripts was identified, 573 of which are new, and mostly full length. A subset of 136 transcripts was identified as possibly SG specific, 97 of which are novel. Analysis of tissue-specific transcription of selected genes revealed at least 31 genes whose expression is specific or enriched in female SG, whereas 24 additional genes were expressed in female SG and in males but not in other female tissues. Most of the 55 proteins coded by these transcripts have no known function and represent high-priority candidates for expression and functional analysis as antihemostatic or antimicrobial agents. This catalogue makes AE. aegypti the mosquito vector for which the most complete salivary transcriptome is available. We hope that this updated catalogue will help our continuing effort of understanding the evolution of blood sucking in vector arthropods and the discovery of novel pharmacologically active compounds.
An unexpected finding of this work was the occurrence of four protein families specific to SG that were probably a product of horizontal transfer from prokaryotic organisms to mosquitoes. Previously, the SGS family was shown to localize specifically in the basal surface of SG cells and may function as a Plasmodium receptor [158].
Here we identify three new families of salivary and possibly secreted proteins (62,56, and 34 kD) characterized by having uniexonic genes and PSI-BLAST retrieval of only salivary proteins of hematophagous Diptera and bacterial proteins. Although horizontal gene transfer is common in prokaryotic organisms, it is a relatively rare finding in eukaryotes [161]. To the extent that these genes are really of bacterial origin, it may emphasize the unusual paths of SG gene evolution in the quest of hematophagous animals to obtain their 'perfect' potion that allows disarming of the complex host pathways of inflammation and hemostasis that would otherwise disrupt blood feeding.

Mosquitoes
Two laboratory colonies were used in this work, one at Dr. Ribeiro To amplify the cDNA using a PCR reaction, 4 μl of the phage sample was used as a template. The primers were sequences from the λ TriplEx2 vector and named pTEx2 5 seq (5' -TCCGAGATCTGGACGAGC-3' ) and pTEx2 3LD (5' -atacgactcactatagggcgaa ttggc-3' ), positioned at the 5' end and the 3' end of the cDNA insert, respectively.  Figure 4.

Protein identification by mass spectrometry
Protein identification of 2Dgel-separated proteins was performed on reduced and alkylated trypsin-digested samples prepared by standard mass spectrometry protocols. Tryptic digests were analyzed by coupling the Nanomate (Advion BioSciences) -an automated chip-based nano-electrospray interface source -to a quadrupole time-of-flight mass spectrometer, QStarXL MS/MS System (Applied Biosystems/Sciex). Computer-controlled, datadependent automated switching to MS/MS provided peptide sequence information. AnalystQS software (Applied Biosystems/Sciex) was used for data acquisition. Data processing and databank searching were performed with Mascot software (Matrix Science). The NR protein database from the NCBI, National Library of Medicine, NIH, was used for the search analysis, as was a protein database generated during the course of this work.

Bioinformatic tools and procedures
EST were trimmed of primer and vector sequences, clusterized, and compared with other databases as described before [102]. The BLAST tool [162], CAP3 assembler [163], ClustalW [164], and Treeview software [165] were used to compare, assemble, and align sequences and to visualize alignments. Phylogenetic analysis and statistical neighbor-joining bootstrap tests of the phylogenies were also done with the Mega3 package [166]. For functional annotation of the transcripts we used the tool blastx [107] to compare the nt sequences with the NCBI NR protein database of the NCBI and to the Gene Ontology (GO) database [167]. The tool rpsblast [107] was used to search for conserved protein domains in the Pfam [168], Smart [169], Kog [170], and conserved domains (CDD) databases [171]. We have also compared the transcripts with other subsets of mitochondrial and rRNA nt sequences downloaded from NCBI and to several organism proteomes downloaded from NCBI (yeast), Flybase (D. melanogaster), or ENSEMBL (An. gambiae). Segments of the three-frame translations of the EST (as the libraries were unidirectional, we did not use six-frame translations) starting with a methionine in the first 100 predicted aaor the predicted protein translation, in the case of complete coding sequences -were submitted to the SignalP server [172] to help identify translation products that could be secreted. O-glycosylation sites on the proteins were predicted with the program NetOGlyc [173]. Functional annotation of the transcripts was based on all the comparisons above. Following inspection of all results, transcripts were classified as either (S)ecretory, (H)ousekeeping, or of (U)nknown function, with further subdivisions based on function and/or protein families. To map the EST and contigs in the genome, blastn was used [107].
To speed the program, each genomic fasta file was broken into 30-kb fragments with 5 kb from previous sequence. For visualization of EST on the AE. aegypti genome, we used the Artemis tool [174] after transforming the blastn output to a file compatible to Artemis using a program written in Visual Basic.
To compare the EST frequency in AE. aegypti salivary cDNA libraries with EST frequency in other libraries whose mRNA derive from other sources (downloaded from the NCBI EST database DBEST), all available EST from AE. aegypti plus the EST set from a EST hemocyte library from DrBruce Christensen's laboratory [175] plus our own salivary EST set were pooled to obtain a total of 232,921 EST; these were assembled as described above to create a searchable annotated database of 28,458 contigs and singletons, which is available for browsing at Anobase [10]. The combined EST database thus derives from 29 different EST libraries, 2 of which are from SG of adult female mosquitoes (4,040 from Ribeiro/Wikel laboratories, and 11,585 from Dr. Sergio Verjovski's laboratory); the remainder are from different organs or whole organisms at different developmental stages, or from adult mosquitoes infected or not with different pathogens. Details of these libraries are available at the EST dataset website [10]. From each of these 28,458 contigs, we determined the EST contribution from each of the 29 libraries to the final assembled contigs, thus obtaining for each contig the total salivary and nonsalivary contribution. A χ 2 test was applied to the data set to determine whether a salivary contribution was above or below the null hypothesis of no differential library contribution when the expected EST frequency was above 5, as indicated for the correct use of the test. When the Pvalue was below 0.05, we considered the deviation of equal EST distribution among salivary and remaining libraries as significant.

RT-PCR expression analysis
For RT-PCR analysis, SG were dissected from adult females 1 to 5 days after emergence and stored at -80°C. Total RNA was extracted from female glands, carcasses (i.e. adult females with SG removed), and adult males using the TRIZOL reagent (Invitrogen).
Approximately 50 ng RNAse-free DNase-treated total RNA (Invitrogen) was used for the RT-PCR amplification by the SuperScript one-step RT-PCR system (Invitrogen) according to manufacturer's instructions. Typically, reverse transcription (50°C, 30 min) and heat inactivation of the reverse transcriptase (94°C, 2 min) were followed by 30 PCR cycles: 30s at 94°C, 30s at 55°C, 1 min. at 72°C; 25 cycles were used for the amplification of the ribosomal protein S5 mRNA (rpS5) to keep the reaction below saturation levels and to allow reliable normalization. For some clones (gi|94468620, gi|94468350, gi|94468634, and gi|42632615), 35 cycles of amplification were needed to obtain detectable bands. The oligonucleotide primers used for rpS5 amplification were: rpS5-F, 5' -ATTA-CATCGCCGTCAAGG AG-3' , and rpS5-R, 5' -TCATC ATCAGCGAGTTGGTC-3'. The sequence of the other oligonucleotide primers is available as Supplemental Material. Amplification reactions were analyzed on 1.2% agarose gels. Each sample was analyzed by RT-PCR two to three times using independent batches of total RNA.