The sensitive period for male-to-female sex reversal begins at the embryonic stage in the Nile tilapia and is associated with the sexual genotype

Abstract

SUMMARYIn this study, we sought to determine the mechanism of early sex reversal in a teleost by applying 4 hr feminization treatments to XY (17a-ethynylestradiol 2000 mg L À1 ) and YY (6500 mg L À1 ) Nile tilapia embryos on the first day post-fertilization (dpf). We then searched for changes in the expression profiles of some sex-differentiating genes in the brain (cyp19a1b, foxl2, and amh) and in sex steroids (testosterone, 17b-estradiol, and 11-ketotestosterone) concentrations during embryogenesis and gonad differentiation. No sex reversal was observed in YY individuals, whereas sexreversal rates in XY progeny ranged from 0À60%. These results, together with the clearance profile of 17a-ethynylestradiol, confirmed the existence of an early sensitive period for sex determination that encompasses embryonic and larval development and is active prior to any sign of gonad differentiation. Estrogen treatment induced elevated expression of cyp19a1b and higher testosterone and 17b-estradiol concentrations at 4 dpf in both XY and YY individuals. foxl2 and amh were repressed at 4 dpf and their expression levels were not different between treated and control groups at 14 dpf, suggesting that foxl2 did not control cyp19a1b in the brains of tilapia embryos. Increased cyp19a1b expression in treated embryos could reflect early brain sexualization, although this difference alone cannot account for the observed sex reversal as the treatment was ineffective in YY individuals. The differential sensitivity of XY and YY genotypes to embryonic induced-feminization suggests that a sex determinant on the sex chromosomes, such as a Y repressor or an X activator, may influence sex reversal during the first steps of tilapia embryogenesis.

The Reversible Sex of Gonochoristic Fish: Insights and Consequences

“…Accumulation of hormones in the egg or vitellus could be delaying the effect on the embryo. However, this hypothesis does not explain the increase in male percentage when precocious high temperatures were applied [Gennotte et al, 2014]. Moreover, similar EE2 bio-concentrations were obtained with a single immersion treatment at 10 dpf resulting in lower female proportions.…”

“…Although similar androgen 11KT (11 ketotestosterone) treatment or treatment with an aromatase inhibitor resulted in only 10% masculinization [Gennotte et al, 2015]. Uptake and clearance rates showed that EE2 levels in the eggs dropped at 4 dpf, but the whole body levels were still elevated at 10 dpf [Gennotte et al, 2014]. Accumulation of hormones in the egg or vitellus could be delaying the effect on the embryo.…”

“…A precocious sensitive period for sex reversal might also exist in tilapia monosex embryos, since the proportion of females or males increased (20-25%) with 17MT or EE2 immersion treatments of <12 h on XX or XY eggs [Rougeot et al, 2008a, b;Gennotte et al, 2014]. Although similar androgen 11KT (11 ketotestosterone) treatment or treatment with an aromatase inhibitor resulted in only 10% masculinization [Gennotte et al, 2015].…”

Simultaneous exposure to estrogen and androgen resulted in feminization and endocrine disruption

“…Genetic males can be reversed to phenotypic females with estrogens if the treatment is applied before sex differentiation in vertebrates including marsupials (Coveney et al 2001), birds (Scheib 1983), reptiles (Merchant-Larios et al 1997), and teleosts (Kobayashi et al 2003, Baron et al 2004, Gennotte et al 2014. In species with natural sex reversal, increase of serum E 2 levels always associated with male to female sex reversal in protandrous fish (Guiguen et al 1993).…”

“…However, the expression levels of the de novo DNA methyltransferases genes dnmt4, dnmt6 and dnmt8 were down-regulated in MTCE 2 -XY gonad compared with the Ctrl-XY and they displayed no significant change in the MTCE 2 -XX gonad compared withhas been no report showing the successful sex reversal of a testis into an ovary in teleosts. In fact, high doses of E 2 treatment are needed to induce complete male to female sex reversal in rainbow trout, tilapia and other teleosts (Krisfalusi & Nagler 2000, Bhandari et al 2005, Gennotte et al 2014. This might be explained by the following two possible reasons: i) though the ovarian differentiation occurs earlier than testicular differentiation, the male determining gene, such as amhy in tilapia, expresses even earlier than the female pathway genes (Eshel et al 2014, Li et al 2015a, and therefore high doses of E 2 are needed to antagonize the male pathway genes, which is further supported by the differential sensitivity of XY and YY genotypes to embryonic induced-feminization (Gennotte et al 2014); and ii) almost all steroidogenic enzyme genes are expressed in XX gonads but not in XY gonads at 5 dah (Tao et al 2013), and therefore high doses of E 2 are needed to induce those genes, especially cyp19a1a, expression for ovarian differentiation.…”