A Tandem Duplicate of Anti-Müllerian Hormone with a Missense SNP on the Y Chromosome Is Essential for Male Sex Determination in Nile Tilapia,Oreochromis niloticus

Variation in the tgf-β signaling pathway is emerging as an important mechanism by which gonadal sex determination is controlled in teleosts. here we show that amhy,a y-specific duplicate of the anti-müllerian hormone (amh) gene,induces male sex determination in nile tilapia. amhy is a tandem duplicate located immediately downstream of amhδ-y on the y chromosome. the coding sequence of amhy was identical to the x-linked amh (amh) except a missense snp (c/t) which changes an amino acid (ser/leu92) in the n-terminal region. amhy lacks 5608 bp of promoter sequence that is found in the x-linked amh homolog. the amhδ-y contains several insertions and deletions in the promoter region,and even a 5 bp insertion in exonvi that results in a premature stop codon and thus a truncated protein product lacking the tgf-β binding domain. both amhy and amhδ-y expression is restricted to xy gonads from 5 days after hatching (dah) onwards. crispr/cas9 knockout of amhy in xy fish resulted in male to female sex reversal,while mutation of amhδ-y alone could not. in contrast,overexpression of amhy in xx fish,using a fosmid transgene that carries the amhy/amhδ-y haplotype or a vector containing amhy orf under the control of cmv promoter,resulted in female to male sex reversal,while overexpression of amhδ-y alone in xx fish could not. knockout of the anti-müllerian hormone receptor type ii (amhrii) in xy fish also resulted in 100% complete male to female sex reversal. taken together,these results strongly suggest that the duplicated amhy with a missense snp is the candidate sex determining gene and amhy/amhrii signal is essential for male sex determination in nile tilapia. these findings highlight the conserved roles of tgf-β signaling pathway in fish sex determination. © 2015 li et al.