The roles of steroids in zebrafish sex differentiation, gonadal development and function of the adult gonad are poorly understood. Herein, we have employed a ferredoxin 1b (fdx1b) mutant zebrafish to explore such processes. Fdx1b is an essential electron-providing cofactor to mitochondrial steroidogenic enzymes, which are crucial for glucocorticoid and androgen production in vertebrates. Fdx1b-/- zebrafish mutants develop into viable adults, in which concentrations of androgens and the glucocorticoid, cortisol, are significantly reduced. Adult fdx1b-/- mutant zebrafish display predominantly female secondary sex characteristics but may possess either ovaries or testes, confirming that androgen signaling is dispensable for testicular differentiation in this species, as previously demonstrated in androgen receptor mutant zebrafish. Adult male fdx1b-/- mutant zebrafish do not exhibit characteristic breeding behaviors, and sperm production is reduced, resulting in infertility in standard breeding scenarios. However, eggs collected from wild-type females can be fertilized by the sperm of fdx1b-/- mutant males by IVF. The testes of fdx1b-/- mutant males are disorganized and lack defined seminiferous tubule structure. Expression of several pro-male and spermatogenic genes is decreased in the testes of fdx1b-/- mutant males, including pro-male transcription factor SRY-box 9a (sox9a) and spermatogenic genes insulin-like growth factor 3 (igf3) and insulin-like 3 (insl3). This study establishes an androgen- and cortisol-deficient fdx1b zebrafish mutant as a model for understanding the impacts of steroid deficiency on sex development and reproductive function. This model will be particularly useful for further investigation of the roles of steroids in spermatogenesis, gonadal development and regulation of reproductive behavior, thus enabling further elucidation of the physiological consequences of endocrine disruption in vertebrates.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)