A Duplicated, Truncated Gene Is Involved in Male Sex Determination in an Old World Silverside.

A master sex-determining gene, the Y chromosome-linked anti-Müllerian hormone () gene, has been described in two New World atheriniform species but little is known on the distribution, evolution, and function(s) of this gene in other Atheriniformes. Interestingly, has been found to coexist with temperature-dependent sex determination (TSD), providing a unique opportunity to explore the interplay between genotypic and environmental sex determination. In this study, the search for an homolog was extended to an Old World atheriniform, the cobaltcap silverside (Atherinidae). The full sequences, including the coding and noncoding regions, of the autosomal () and a putative were obtained. The deduced Amha and Amhy proteins comprised 511 and 340 amino acids (aa), respectively. PCR analysis with genomic DNA from wild adults and from laboratory-reared juveniles revealed a high, but not complete association of ∼95% between and maleness. The spatiotemporal expression of and during gonadal sex differentiation was analyzed by qRT-PCR and hybridization (ISH). transcription (in -positive larvae) started before and peaked during histological differentiation of the gonads whereas was negligible during the same period in both genotypes. These results demonstrate that the , although with some structural differences in relation to the of some New World atheriniforms, is strongly associated with maleness and probably important for testicular development in this Old World atheriniform. Thus, is a candidate sex determination gene in cobaltcap silverside and it will be key to scrutinize the mechanism of sex determination in this species.