The vitellogenin genes in Cynops orientalis: New insights on the evolution of the vtg gene family in amphibians

The vitellogenins (Vtgs) are glycolipophosphoproteins that play a key role in constituting nutritional reserves for embryo development in nonmammalian vertebrates. However, additional functional roles have been evidenced. These vtg genes are present in multiple copies, different in number and sequences in various vertebrate lineages. The comprehension of the vtg gene family evolutionary history remains a matter of intense interrogation for this field of research. In tetrapods, information about vtg genes are limited to few taxa. Up to date concerning amphibians, detailed studies have been conducted only in Anura. Therefore, in this study, to further increase knowledge about vtg genes in Amphibia class, the urodele Cynops orientalis (Amphibia: Caudata) was analyzed and four complete vtg sequences were obtained. Moreover, genomic data available for the caecilians Microcaecilia unicolor and Rhinatrema bivittatum (Amphibia: Gymnophiona) were also included. In these amphibians, our findings evidenced the presence of a vtgI sequence ortholog to that of tetrapods, absent in Anura. Moreover, microsyntenic, phylogenetic, and gene conversion analyses allowed postulating two hypotheses to explain the complex evolutionary history of this gene family.