Figure 1

Evolutionary relationship of platypus TERT. (a) Comparison of the protein domains and motifs in the platypus TERT protein (Oan) with seven TERT proteins of selected vertebrates: Hsa - human (Homo sapiens), Mmu - mouse (Mus musculus), Mdo - short-tailed opossum (Monodelphis domestica), Gga - domestic chicken (Gallus gallus), Aca - green anole (Anolis carolinensis), Xle - African clawed toad (Xenopus laevis), Tru - pufferfish (Takifugu rubripes). Different colors indicate the four different domains (TEN, TRBD, RT, CT), with the darker tone indicating conserved motifs within the domains. The names of the motifs are depicted under the platypus TERT schema. L1, L2, and L3 designate three linker regions of variable length and sequence. The two green filled circles show the boundaries of the regions encoded by the second TERT exon, including the putative second exon of platypus. (b) The percentage of similar amino acids at the same positions in the aligned sequences of TERT proteins of seven vertebrate species shown in panel (a) relative the platypus TERT protein. The percentages calculated relative to the length of platypus sequence are shown for separate conserved domains (TEN, TRBD, RT, and CT) and the full-length protein (TERT). TRBD domain sequence excludes sequences of linkers L2, L3. (c) Cumulative length of the three linker regions (L1, L2, L3) in the TERT proteins of different species is shown as percentage of the length of these regions in platypus TERT. The lengths were calculated based on the alignment of the TERT proteins of different species shown in Figure S3 and on the definition of the three linker regions shown in Figure 1a and Figure S2. The graph includes TERT proteins shown in panel (a) and following additional proteins: Ptr - chimp (Pan troglodytes), Mml - macaque rhesus (Macaca mulatta), Clu - dog (Canis lupus), Bta - cow (Bos taurus), Laf - African elephant (Loxodonta africana), Rno - rat (Rattus norvegicus), Mau - hamster (Mesocricetus auratus), Meu - wallaby (Macropus eugenii), Cja - Japanese quail (Coturnix japonica), Cmo - Muscovy duck (Cairina moschata), Tgu - zebra finch (Taeniopygia guttata), Cmi - elephant shark (Callorhinchus milii), Dre - zebrafish (Danio rerio), Nfu - killifish (Nothobranchius furzeri), Ola - medaka (Oryzias latipes), Ome - medaka (Oryzias melastigma), Eco - grouper (Epinephelus coioides), SpuL and SpuS - long and short form TERT of sea urchin (Strongylocentrotus purpuratus), Hro - leach (Helobdella robusta), Dpu - water flee (Daphnia pulex), and Hma - hydra (Hydra magnipapillata). Insect, nematode, and urochordate TERTs were not included because these proteins do not contain all four basal structural domains of the vertebrate TERT protein [38, 57]. (d) Phylogenetic tree of vertebrate TERT proteins constructed by the Bayesian inference method. The construction is based on the alignment shown in the Additional file 5: Figure S3. For the abbreviation of protein species origin see the legend to panels (a) and (c). All these proteins were presumably full-length except the chimp (98% complete), opossum (99.5% complete), wallaby (97% complete), and elephant shark (approximately 80% complete). Sea urchin SpuL TERT was used to determine the root of the tree (indicated by the arrow, actual branch with SpuL not shown). Numbers shown at the corresponding branches are clade credibility values. Because most of the branches had clade credibility equal to 1.00, only those with the value <1.00 are shown. The long and medium linkers are indicated by squares by the abbreviated species names. The black squares indicate TERT proteins with long linkers (the L1, L2 and L3 linkers reaching 100%-160% of the length of platypus linkers). A TERT protein with the linkers of medium length (60%-99% of the platypus linkers) is marked by gray square.