Chromosomal Rearrangements during Turtle Evolution Altered the Synteny of Genes Involved in Vertebrate Sex Determination

Sex-determining mechanisms (SDMs) set an individual's sexual fate by its genotype (genotypic sex determination, GSD) or environmental factors like temperature (temperature- dependent sex determination, TSD), as in turtles where the GSD “trigger” remains unknown. SDMs co-evolve with turtle chromosome number, perhaps because fusions/fissions alter the relative position/regulation of sexual development genes. Here, we map 10 such genes via FISH onto metaphase chromosomes in 6 TSD and 6 GSD turtles for the first time. Results unco vered intrachromosomal rearrangements involving 3 genes across SDMs (Dax1,Fhl2, andFgf9) and a chromosomal fusion linking 2 genes (Sf1andRspo1) in 1 chromosome in a TSD turtle (Pelomedusa subrufa) that locate to 2 chromosomes in all others. Notably,Sf1and its repressorFoxl2map toApalone spinifera's ZW chromosomes but to a macro- (Foxl2) and a microautosome (Sf1) in other turtles potentially inducing SDM evolution. However, our phylogenetically informed analysis refutesFoxl2(but notSf1) asApalone's master sex-determining gene.The absence of common TSD-specific or GSD-specific rearrangements underscores the independent evolutionary trajectories of turtle SDMs. Further comparative analyses using more genes from the sexual development network are warranted to inform genome evolution and its contribution to enigmatic turnovers of vertebrate sex determination.Cytogenet Genome Res
Source: Cytogenetic and Genome Research - Category: Genetics & Stem Cells Source Type: research