Sexual plasticity is affected by sex chromosome karyotype and copy number of sex determiner in tilapia

Abstract

Teleost fish exhibit remarkable plasticity of sexual differentiation as sex reversal can be induced by exogenous steroid hormones. To date, little is known about whether the sex chromosome karyotype and copy number of sex determiners affects sex reversal in fish. The Nile tilapia (XX/XY system with amhy as sex determiner) and blue tilapia (ZZ/ZW system) are two closely cichlids widely used for aquaculture. In this study, we measured the sex reversal rates of XY, YY-amhy+/+, YY-amhy+/−, ZX and ZZ tilapia by 17β-estradiol (E2) treatment, ZW and WW tilapia by aromatase inhibitor (letrozole) treatment and aimed to promote sex reversal of YY fish through blockage of androgen synthesis and administration of E2. Statistically, E2 treatment resulted in lower sex reversal rate in YY and ZZ fish compared with XY and ZX fish, respectively. In addition, letrozole treatment led to lower sex reversal rate in WW fish compared with ZW fish. Importantly, E2 treatment of YY fish with mutation of one copy of amhy resulted in similar sex reversal rate compared with XY fish. These results implied that the two homogametic sex chromosomes in YY and ZZ fish antagonized the E2 induced sex reversal due to the up-regulation of the male pathway genes, and in WW fish antagonized the effects of the letrozole induced sex reversal. Simultaneous treatment of E2 and trilostane, an inhibitor of 3β-hydroxysteroid dehydrogenase, promoted sex reversal of YY fish. Taken together, our results demonstrate that sexual plasticity is associated with the sex chromosome karyotype and copy number of the sex determiner in tilapia. The production of YY neofemale tilapia allowed establishment of a YY maintenance line and large scale breeding of XY genetically male tilapia in aquaculture.