Zinc maintains prophase I arrest in mouse oocytes through regulation of the MOS-MAPK pathway

Meiosis in mammalian females is marked by two arrest points, at prophase I and metaphase II, which must be tightly regulated in order to produce a haploid gamete at the time of fertilization. The transition metal zinc has emerged as a necessary and dynamic regulator of the establishment, maintenance, and exit from metaphase II arrest, but the roles of zinc during prophase I arrest are largely unknown. In this study, we investigate the mechanisms of zinc regulation during the first meiotic arrest. Disrupting zinc availability in the prophase I arrested oocyte by treatment with the heavy metal chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine (TPEN) causes meiotic resumption even in the presence of pharmacological inhibitors of meiosis. We further show that the MOS-MAPK pathway mediates zinc-dependent prophase I arrest, as the pathway prematurely activates during TPEN-induced meiotic resumption. Conversely, inhibition of the MOS-MAPK pathway maintains prophase I arrest. While prolonged zinc insufficiency ultimately results in telophase I arrest, early and transient exposure of oocytes to TPEN is sufficient to induce meiotic resumption and bypass the telophase I block, allowing the formation of developmentally competent eggs upon parthenogenetic activation. These results establish zinc as a crucial regulator of meiosis throughout the entirety of oocyte maturation, including the maintenance of and release from the first and second meiotic arrest points.