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Table 2 LTR retroelements discovered in the genome of Silurana tropicalis (SIL-G) and different transcriptomes of S. tropicalis (SIL-T: adult tissues; SIL-D: developmental stages), Cyclorana alboguttata (CYC-T: adult individuals), and Pelophylax lessonae (PEL-T: adult tissues) with remarks on the occurrence and distribution of these elements among animals, plants, and fungi

From: LTR retroelements are intrinsic components of transcriptional networks in frogs

Family Type Occurrence/remarks Ref. Genome Transcriptome
SIL-G SIL-T SIL-D CYC-T PEL-T
Bel/Pao Kobel first detected in the genome of the hemichordate Saccoglossus kowalevskii; present in protostomes and deuterostomes [32]
Only known from animal genomes; relatively few elements are reported across diverse animal phyla
  Hydra3.1 described from the genome of Hydra magnipapillata; also present in cnidarian and protostome genomes [42]     
Ty1/Copia Hydra1.1 includes two elements that have described from the invertebrate Hydra magnipapillata and the zebrafish Danio rerio [32]  
Widespread in eukaryotic genomes; two main sub-clades can be distinguished
  Mtanga so far only known from the genome of the mosquito Anopheles gambiae [43]    
  Zeco restricted to crustaceans, urochordates, and fish [44]     
Ty3/Gypsy Amn-san belongs to the vertebrate lineage of chromoviruses, active in fish, amphibians, and reptiles [32]
The largest family of LTR REs; widespread among the genomes of plants, animals, and fungi
  Cer first described from nematodes [45]    
  CsRN1 characterized from the genome of the trematode Clonorchis sinensis [46]      
  Gmr circulate within the genomes of deuterostomes; characterized by Ty1/Copia pol-domain organization [47, 48]
  Mag widely spread through animal genomes including vertebrates [49, 50]
Retroviridae MuERV poorly known outside mammals (belongs to class 3 of retroviruses) [51, 52]    
Exclusively found in vertebrate genomes; characterized by the presence of a gene encoding an envelope protein
  SnRV described from the snakehead fish (Ophicephalus striatus); belongs to class 1 of retroviruses [53]  
  XEN1 described from Xenopus laevis; belongs to class 1 of retroviruses [54]