Low concentrations of dihydrotestosterone induce female‐to‐male sex reversal in the frog Pelophylax nigromaculatus

Abstract

Previous studies have demonstrated that some amphibian species can be sex-reversed by high concentrations of androgens. Little attention has focused on the effects of androgenic endocrine-disrupting chemicals (EDCs) on amphibians. The present study aimed to investigate the effects of lower concentrations of the androgenic EDC 5α-dihydrotestosterone (DHT) on gonadal differentiation and development in Pelophylax nigromaculatus, a true frog distributed widely in East Asia. Tadpoles at Gosner stage 24/25 were exposed to nominal concentrations of 40 ng/L, 400 ng/L, and 4000 ng/L DHT to complete metamorphosis. In all DHT treatment groups, males and ambiguous sexes were identified based on gonadal morphology, whereas no females were found; thus, all treatment groups exhibited male-skewed ratios compared with the control group. Gonadal histological examination revealed that ambiguous sexes displayed overall testicular structure with certain ovarian characteristics, demonstrating that DHT-induced sex-ambiguous gonads were incomplete ovary-to-testis reversals (IOTTRs). The expression levels of some ovary-biased genes in the IOTTRs were significantly higher than in the control testes but lower than in the control ovaries. These results show that low concentrations of DHT induced complete or incomplete female-to-male sex reversal in P. nigromaculatus, and incomplete sex reversal retained certain ovarian characteristics not only at gonadal morphological and histological levels but also at the molecular level. They present study highlights potential risks of DHT and other androgenic EDCs for P. nigromaculatus.

Blockage of androgen and administration of estrogen induce transdifferentiation of testis into ovary

“…DHT increased the levels of 11-KT and decreased the E2/11-KT ratio in both sexes in rainbow fish (Bhatia & Kumar 2016). In amphibians, female-tomale sex reversal was induced by high concentration of testosterone and DHT (Okada et al 2008, Phuge & Gramapurohit 2014, Xu et al 2015. In the present study, female-to-male PSR was successfully induced by treatment of XX tilapia from 0 to 30 dah with A4, testosterone and DHT alone.…”

Sex Reversal in Amphibians

“…Similarly, a dimorphic expression of cyp19 was observed in H. retardatus in which it occurred 15 days after hatching, i.e., prior to the morphological differentiation of the gonads [Sakata et al, 2005[Sakata et al, , 2006. Such a dimorphic expression of aromatase has also been reported in several anuran species, including G. rugosa, X. laevis, and P. nigromaculatus [Kato et al, 2004;Sakata et al, 2006;Maruo et al, 2008;Mawaribuchi et al, 2014;Xu et al, 2015], and was used to predict the phenotypic sex in L. sylvaticus and S. tropicalis [NavarroMartín et al, 2012]. In X. laevis , the dimorphic expression of cyp19A1 occurred just after sex determination in several masses of cells, each surrounded by a basement membrane, that were aligned along the anteroposterior axis [Mawaribuchi et al, 2014].…”

Tetrabromoethylcyclohexane affects gonadal differentiation and development in the frog Pelophylax nigromaculatus

“…The sex of each froglet was roughly identified by examining gross gonadal morphology under a dissecting microscope. According to our previous studies (Li et al, 2015;Xu et al, 2015), a normal testis is a smooth, pear-shaped organ and without visible metamere, while a typical ovary is composed of 7-8 ovary lobes separated by metameres and is obviously longer and wider than a testis. The individual with typical testes was identified as a male, whereas the individual with typical ovaries was identified as a female.…”

“…If so, TBECH could disrupt a variety of biological processes involving androgen, especially gonadal differentiation and development. It is well known that some vertebrate species, such as fish and amphibians, can be sex-reversed by environmental androgens (Scholz and Kluver, 2009;Svensson et al, 2016;Xu et al, 2015). Thus, TBECH may be able to induce gonadal masculinization in the species whose gonadal differentiation is sensitive to environmental androgens.…”

“…Shirane (1986) reported that 50 μg/L testosterone resulted in female-to-male reversal of all P. nigromaculatus. Our recent studies found that even at low concentrations, both 17β-trenbolone and 5α-dihydrotestosterone (DHT) induced complete or incomplete female-to-male reversal of almost all P. nigromaculatus (Li et al, 2015;Xu et al, 2015). Given the sensitivity of gonadal differentiation to androgenic chemicals, we have proposed that P. nigromaculatus can be used as a model species for studying the effects of androgenic chemicals on gonadal differentiation and development in amphibians.…”