Gonadotropins regulate ovarian germ cell mitosis/meiosis decision in the embryonic chicken.

Gonadotropins are required for gametogenesis but in embryonic gonads this mechanism is not well understood. Here we use chicken embryos to investigate the mechanism that gonadotropins regulate the ovarian germ cell mitosis/meiosis decision. Treatment with follicle-stimulating hormone (FSH) delayed germ cell meiosis entry and promoted their proliferation. This action was blocked by an aromatase inhibitor. Treatment with luteinizing hormone (LH) accelerated germ cell meiosis entry and promoted transcription of 3βHSDII to increase progesterone (P4) production. In the cultured ovaries, P4 triggered meiotic initiation in germ cells. MiR181a, which acts to downregulate the NR6A1 transcript to inhibit the meiotic initiation, was upregulated by FSH and downregulated by LH. Collectively, gonadotropins regulate germ cells mitosis and meiotic initiation through steroid hormones and a miR181a-mediated pathway. In particularly, FSH delays germ cell meiosis entry and promotes cell proliferation via estrogen while LH accelerates the meiotic initiation via elevated P4 production.