Vertebrate sex-determining genes play musical chairs

Abstract

Sexual reproduction is one of the most highly conserved processes in evolution. However, the genetic and cellular mechanisms making the decision of whether the undifferentiated gonad of animal embryos develops either towards male or female are manifold and quite diverse. In vertebrates, sex-determining mechanisms range from environmental to simple or complex genetic mechanisms and different mechanisms have evolved repeatedly and independently. In species with simple genetic sex-determination, master sex-determining genes lying on sex chromosomes drive the gonadal differentiation process by switching on a developmental program, which ultimately leads to testicular or ovarian differentiation. So far, very few sex-determining genes have been identified in vertebrates and apart from mammals and birds, these genes are apparently not conserved over a larger number of related orders, families, genera, or even species. To fill this knowledge gap and to better explore genetic sex-determination, we propose a strategy (RAD-Sex) that makes use of next-generation sequencing technology to identify genetic markers that define sex-specific segments of the male or female genome.

Keywords: Déterminisme du sexe; Evolution; Fish; Next-generation sequencing; Poissons; Sex-determination; Séquençage nouvelle génération; Vertebrates; Vertébrés; Évolution.

Fig. 1

Vertebrate sex-determining genes play musical chairs. Evolution and diversity of sex-determining genes in vertebrates (see text for details). Species or groups of species with an already known or highly suspected sex-determining gene are shown in black boxes. Blue triangles represent master sex-determining genes with a certain degree of evolutionary conservation. Red triangles represent group of species with a high turnover of sex-determining genes. The red star shows the position of the teleost-specific whole-genome duplication.

Fig. 2

Distribution of Restriction Associated DNA-tag (RAD-tag) markers along the 24 chromosomes of the medaka sequenced genome. The significantly sex-biased markers identified mid LG1 (chromosome Y) as the location of the sex-determining locus. Markers retained in this analysis have been scored in at least 25 individuals within the population.