The zebrafish is established as an important model system for studying development and disease, and characterisation of the developmental and functional roles of steroids is crucial for its effective employment in this remit. Whilst oestrogens are known to be essential for female development in zebrafish, the roles of androgens in the development, maintenance and function of the male reproductive system remain unclear.
In order to investigate these processes, we have developed novel zebrafish lines carrying deletions in the gene cyp11c1, the zebrafish homologue of CYP11B1 (11ß-hydroxylase). As in mammals, 11ß-hydroxylase is crucial for production of cortisol, however, in zebrafish this enzyme also plays a crucial role in androgen biosynthesis. Zebrafish larvae deficient in glucocorticoid signalling exhibit an impaired visual background adaption they are unable to rapidly adjust pigmentation in response to changes in light conditions. Cyp11c1 mutant zebrafish larvae exhibit impaired visual background adaptation, as well as reduced expression of glucocorticoid responsive genes fkbp5 and pck1, indicating successful disruption of steroidogenesis in our mutant lines.
Adult cyp11c1 mutant zebrafish may possess either testes or ovaries, this is in agreement with our previous studies which have shown that androgens are dispensable, or only required at very low concentrations, for testes differentiation in this species. Male cyp11c1 mutant zebrafish exhibit primarily female secondary sex characteristics and are infertile when crossed with a wild-type female. Analysis of mating behaviour has revealed that cyp11c1 mutant male zebrafish exhibit decreased stereotypic breeding behaviours when crossed with a wild-type female, compared to wild-type siblings. This indicates that androgens may be important regulators of sexual behaviour in zebrafish.
Histological examination of the testes of cyp11c1 mutant zebrafish revealed a disorganised structure with smaller and less defined seminiferous tubules. Although all stages of spermatogenesis were represented in the testes of cyp11c1 mutant zebrafish, the number of mature spermatozoa appeared to be reduced whereas earlier generations appeared to be more abundant than in wild-type siblings. Further histological investigation of the reproductive tract revealed a severely hypoplastic spermatic duct in cyp11c1 mutant zebrafish. Semen release was severely impaired in cyp11c1 mutant zebrafish, probably as a result of spermatic duct malformation. In addition, semen collected from cyp11c1 mutants contained significantly fewer sperm that wild-type siblings.
Cyp11c1 mutant zebrafish appear to be more androgen deficient than previously described lines, and represent an exciting opportunity to gain further insight into the roles of androgens in male reproductive development, function and behaviour.
19 - 21 Sep 2019
European Society for Paediatric Endocrinology