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.

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Populations of Zootoca vivipara appear karyologically well differentiated by heterochromatin distribution both in autosomes and sex-chromosomes; allopatric oviparous populations possess few elements with centromeric heterochromatin and W acrocentric sex-chromosomes with heterochromatin only on the centromere; Alpine, as well as central-western European viviparous populations possess conspicuous centromeric bands of heterochromatin on all of the chromosome pairs and a metacentric W chromosome with paracentromeric and telomeric heterochromatin bands; viviparous populations, living east and possibly north of the Carpathian Mountains, have many elements with interstitial and telomeric heterochromatin and an acrocentric W chromosome with telomeric and subtelomeric heterochroma. These data suggest an origin and evolution of sex-chromosomes in this species, that, interestingly, parallels the recent hypothesis (Heulin et al., 1993) on the rise and evolution of viviparity and speciation in Zootoca.

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