Abstract
Amphibians evolved in the Devonian period about 400 Mya and represent a transition step in tetrapod evolution. Among amphibians, high-throughput sequencing data are very limited for Caudata, due to their largest genome sizes among terrestrial vertebrates. In this paper we present the transcriptome from the fire bellied newt Cynops orientalis. Data here presented display a high level of completeness, comparable to the fully sequenced genomes available from other amphibians. Moreover, this work focused on genes involved in gametogenesis and sexual development. Surprisingly, the gsdf gene was identified for the first time in a tetrapod species, so far known only from bony fish and basal sarcopterygians. Our analysis failed to isolate fgf24 and foxl3, supporting the possible loss of both genes in the common ancestor of Rhipidistians. In Cynops, the expression analysis of genes described to be sex-related in vertebrates singled out an expected functional role for some genes, while others displayed an unforeseen behavior, confirming the high variability of the sex-related pathway in vertebrates.
Highlights
Amphibians represent a group of vertebrates containing over 7,100 species worldwide[1]
Our analyses demonstrated a high level of completeness of the Cynops orientalis transcriptome, comparable to the in-silico transcriptomes of the fully sequenced genomes available for some amphibians
The mRNA collection obtained for the Chinese fire-bellied newt is a valid alternative molecular resource useful for gene expression studies, comparative transcriptomics and large-scale evolutionary analyses
Summary
Amphibians represent a group of vertebrates containing over 7,100 species worldwide[1]. The genomes of newts contain a large proportion of repetitive sequence and are the largest ones among terrestrial vertebrates[4] These factors currently represent a significant challenge for whole genome assembly[5], in particular due to the high computational resources required for handling the large amount of input sequencing data and the technical limitations of most assembly algorithms, optimized for genomes with a size comparable with human or smaller. Data on the expression and function of genes participating in sexual development and gametogenesis in urodeles and in general in amphibians are very limited[11,12,13,14,15,16,17,18] The investigation of these processes in this taxonomic group is extremely interesting for the variety of mechanisms involved in sexual development present in Anura and Caudata and for their phylogenetic position. Our data represent a useful tool for future studies involving gene expression experiments, comparative transcriptomics, genomics, and metabolomics in amphibians
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