Transcriptional Ontogeny Platform of Sex Determination/Sex Differentiation Genes in Almaco Jack Larvae

Abstract

AbstractThe fish sex determination/sex differentiation (SD) system is still intriguing in many species, such as Seriola fish. Marine amberjacks have a conserved ZW/ZZ SD system. We aimed to identify how early SD genes were expressed in larval Almaco Jack Seriola rivoliana by RNA sequencing and to determine whether there was an early developmental differential expression up to the onset of exogenous feeding. Transcriptome analysis identified sox5 and sox7 (female) and sox3 and sox8 (male) genes; all of the known female SD genes, including hsd17b1 (master sex gene in Seriola), foxl2, and cyp19a, plus genes involved in female sexual development and maintenance, estrogen signaling, and osteoclast proliferation; and all of the known male SD genes, including dmrt1, nr5a1, gsdf, amhy, and amhr2. The expression of most SD genes occurred on each day during larval development. However, most of them showed low abundance levels and null differential expression except for the downregulation of the sox and foxl2 genes, which might have served an unknown function or were maternally derived rather than autonomously downregulated. We suggest that the concomitant expression of female and male SD genes in early larval stages is a biological transcriptional ontogeny sex platform that ensures posterior sex‐specific expression and sex differentiation. A single missense single‐nucleotide polymorphism (SNP) near the catalytic center of hsd17b1 has been suggested to differentiate phenotypic sex in Seriola by an endocrine regulation on estradiol synthesis. In that case, the ontogeny sex platform would be directed by the SNP but still critical to differentiate gonads.