The Tgf-β family member Gdf6Y determines the male sex inNothobranchius furzeriby suppressing oogenesis-inducing genes

Abstract

ABSTRACTThe short-lived African killifishNothobranchius furzerilives in seasonal freshwater ponds and has evolved remarkable traits to survive in this limited environment. One of those traits is a genetic XX/XY sex-determination system, which ensures an equal distribution of both sexes. Comparisons of female and male genomic sequences identified the Y-chromosomal copy of the TGF-β family membergdf6as the candidate male sex-determining (SD) gene, which was namedgdf6Yin contrast to the X-chromosomal allelegdf6X. CRISPR/Cas9-mediated inactivation ofgdf6YinN. furzeriled to a complete male-to-female sex reversal in XY animals. The homozygous inactivation ofgdf6Xon the other hand led to a detrimental phenotype post-hatching. This phenotype was compensated bygdf6Y, revealing that the latter became the SD gene while retaining at least some of its originalgdf6function.Gdf6Yis expressed in testicular somatic cells already prior to hatching, where it represses the germ cell-intrinsic feminizing genefoxl2l. We have identified components of the TGF-β signaling pathway, especially the inhibitor of DNA binding genesid1/2/3, and the mRNA decay activatorzfp36l2, as Gdf6Y targets. We conclude that Gdf6Y exerts its function as the male sex-determining gene by suppressing female-specific genes in the developing gonad of maleN. furzeri.