A Comparative View on Sex Differentiation and Gametogenesis Genes in Lungfish and Coelacanths

Abstract

Gonadal sex differentiation and reproduction are the keys to the perpetuation of favorable gene combinations and positively selected traits. In vertebrates, several gonad development features that differentiate tetrapods and fishes are likely to be, at least in part, related to the water-to-land transition. The collection of information from basal sarcopterygians, coelacanths, and lungfishes, is crucial to improve our understanding of the molecular evolution of pathways involved in reproductive functions, since these organisms are generally regarded as “living fossils” and as the direct ancestors of tetrapods. Here, we report for the first time the characterization of >50 genes related to sex differentiation and gametogenesis in Latimeria menadoensis and Protopterus annectens. Although the expression profiles of most genes is consistent with the intermediate position of basal sarcopterygians between actinopterygian fish and tetrapods, their phylogenetic placement and presence/absence patterns often reveal a closer affinity to the tetrapod orthologs. On the other hand, particular genes, for example, the male gonad factor gsdf (Gonadal Soma-Derived Factor), provide examples of ancestral traits shared with actinopterygians, which disappeared in the tetrapod lineage.

The transcriptome of the newt Cynops orientalis provides new insights into evolution and function of sexual gene networks in sarcopterygians

“…5c). The sexual dimorphic expression of srd5a1 and srd5a3 in C. orientalis gonads is in agreement with previous reports from lungfish 53 , frogs 78 , rat 79 , human 80,81 , and teleosts 78 . The expression in ovaries of srd5a1 and srd5a3 implicates the potential production of DHT whose role in amphibian gonads still need to be clarified.…”

“…4). Moreover, the same expression pattern that we find in the Chinese fire-bellied newt has been reported for other vertebrate species such as lungfish and teleosts 53 . The lack of identification of an orthologous amhr2 sequence in Cynops is likely attributable to absence of transcripts and not a gene loss event since this gene has been found in other amphibians 58,59 .…”

“…The expression analysis revealed a male biased sexually dimorphic pattern (Fig. 5a), although with values lower than those identified in basal sarcopterygian fish and teleosts 53 . www.nature.com/scientificreports www.nature.com/scientificreports/ Desert hedgehog (dhh) is a member of the Hedgehog gene family, which in vertebrates includes two other homologues, sonic hedgehog (shh) and indian hedgehog (ihh) 64 .…”

“…The set of genes involved in sex differentiation and gametogenesis analyzed previously in basal sarcopterygians 53 was investigated also in C. orientalis to increase knowledge in early tetrapods. This analysis performed on gonad transcriptomes allowed to retrieve 38 transcripts annotated from genes involved in sexual development (Table 1), which show complete CDSs except for 6 transcripts (Supplementary Table S5).…”

“…Moreover, in some teleosts it has a role as male sex initiator 61 or as master sex determining gene 60,62 . We have previously reported the presence of an orthologous sequence in the cartilaginous fish Callorhinchus milii and in the two basal sarcopterygian fish, Latimeria menadoensis and Protopterus annectens 53,63 . The analysis of C. orientalis transcriptome identified a bona fide gsdf sequence ( Supplementary Fig.…”