Abstract
Genes involved in sex determination and differentiation have been identified in mice, humans, chickens, reptiles, amphibians and teleost fishes. However, little is known of their functional conservation, and it is unclear whether there is a common set of genes shared by all vertebrates. Coelacanths, basal Sarcopterygians and unique “living fossils”, could help establish an inventory of the ancestral genes involved in these important developmental processes and provide insights into their components. In this study 33 genes from the genome of Latimeria chalumnae and from the liver and testis transcriptomes of Latimeria menadoensis, implicated in sex determination and differentiation, were identified and characterized and their expression levels measured.Interesting findings were obtained for GSDF, previously identified only in teleosts and now characterized for the first time in the sarcopterygian lineage; FGF9, which is not found in teleosts; and DMRT1, whose expression in adult gonads has recently been related to maintenance of sexual identity. The gene repertoire and testis-specific gene expression documented in coelacanths demonstrate a greater similarity to modern fishes and point to unexpected changes in the gene regulatory network governing sexual development.
Highlights
Two major processes take place in sexual development: sex determination and sex differentiation
Gene ontology (GO) analyses of ‘sex determination’ and ‘sex differentiation’ term annotations of the L. menadoensis transcriptome were conducted and the results compared to selected vertebrate genomes (Tables S1 and S2); 25 contigs were identified as orthologues of a GO0007530 annotation, and 297 contigs were orthologues of the GO0007544 annotation
CDSs were retrieved from the L. chalumnae genome and the L. menadoensis testis and liver transcriptomes (Tables 1 and 2) and their expression levels assessed
Summary
Two major processes take place in sexual development: sex determination and sex differentiation. The former process determines whether the bipotential primordium will develop into a testis or an ovary; the latter takes place after sex determination and involves the actual development of testes or ovaries from the undifferentiated gonad [1]. It has emerged that sex-specific mechanisms, which are critical to maintaining the male or female identity of the testis and ovary, operate in adult mammalian gonads [4,5,6]. In vertebrates—with the possible exception of birds [7]—such secondary sexual traits are generally believed to be instructed exclusively by the developing testis or ovary through sex steroids, whereas in invertebrates each somatic cell seems to have an inherent sexual identity [8]. Sex steroids and the proteins involved in their metabolism and binding play an earlier role in the sex differentiation process of fish, amphibians, reptiles, birds, and marsupials [9,10,11,12,13,14,15,16,17,18,19,20]
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