Developmental Delay and Male-Biased Sex Ratio in Knockout Zebrafish.

The estrogen receptor signaling pathway plays an important role in vertebrate embryonic development and sexual differentiation. There are four major estrogen receptors in zebrafish: , , and . However, the specific role of different estrogen receptors in zebrafish is not clear. To investigate the role of in zebrafish development and reproduction, this study utilized TALENs technology to generate an knockout homozygous zebrafish line. The number of eggs laid by knockout female zebrafish did not differ significantly from that of wild zebrafish. The embryonic development process of wild-type and knockout zebrafish was observed, revealing a significant developmental delay in the knockout zebrafish. Additionally, mortality rates were significantly higher in knockout zebrafish than in their wild-type counterparts at 24 hpf. The reciprocal cross experiment between knockout zebrafish and wild-type zebrafish revealed that the absence of resulted in a decline in the quality of zebrafish oocytes, while having no impact on sperm cells. The knockout of also led to an abnormal sex ratio in the adult zebrafish population, with a female-to-male ratio of approximately 1:7. The quantitative PCR (qPCR) and in situ hybridization results demonstrated a significant downregulation of expression in knockout embryos compared to wild-type embryos throughout development (at 2 dpf, 3 dpf and 4 dpf). Additionally, the estrogen-mediated induction expression of was attenuated, while the estradiol-induced upregulated expression of was disrupted. These results suggest that is involved in regulating zebrafish oocyte development and sex differentiation.