A duplicated <i>amh</i> is the master sex-determining gene for <i>Sebastes</i> rockfish in the Northwest Pacific

Abstract

Teleost fish are the most diverse group of vertebrates and provide opportunities to study the evolution of sex determination (SD) systems. Using genomic and functional analyses, we identified a male-specific duplication of <i>anti-Müllerian hormone</i> (<i>amh</i>) gene as the male master sex-determining (MSD) gene in <i>Sebastes schlegelii</i>. By resequencing 10 males and 10 females, we characterized a 5 kb-long fragment in HiC_Scaffold_12 as a male-specific region, which contained an <i>amh</i> gene (named <i>amhy</i>). We then demonstrated that <i>amhy</i> is a duplication of autosomal <i>amh</i> that was later translocated to the ancestral Y chromosome. <i>amha</i> and <i>amhy</i> shared high-nucleotide identity with the most significant difference being two insertions in intron 4 of <i>amhy</i>. Furthermore, <i>amhy</i> overexpression triggered female-to-male sex reversal in <i>S. schlegelii</i>, displaying its fundamental role in driving testis differentiation. We developed a PCR assay which successfully identified sexes in two species of northwest Pacific rockfish related to <i>S. schlegelii</i>. However, the PCR assay failed to distinguish the sexes in a separate clade of northeast Pacific rockfish. Our study provides new examples of <i>amh</i> as the MSD in fish and sheds light on the convergent evolution of <i>amh</i> duplication as the driving force of sex determination in different fish taxa.