Initiation of meiosis from human iPSCs under defined conditions through identification of regulatory factors.

Meiotic failure is a major cause of infertility, but the lack of an in vitro model of human meiosis is a barrier to understanding its mechanism. Here, we establish a method to initiate meiosis directly from male or female human-induced pluripotent stem cells (iPSCs). DNMT1 inhibition, retinoid signaling activation, and overexpression of regulatory factors (antiapoptotic BCL2 and promeiotic HOXB5, BOLL, or MEIOC) rapidly activates meiosis over a 15-day protocol. Our protocol bypasses the primordial germ cell stage and directly generates cells expressing genes similar to meiotic oogonia, including oogonia markers, all synaptonemal complex components, and meiotic recombination machinery. DNMT1 inhibition rapidly erases DNA methylation, including at imprinting control regions and promoters of meiotic genes. Microscopy shows key aspects of meiosis, including chromosome axis formation and synapsis in live human cells. Our model of human meiosis provides opportunities for studying this critical reproductive process under chemically defined conditions in vitro.