Arresting Meiosis In mammals, meiotic maturation of oocytes must be coordinated precisely with ovulation to produce a developmentally competent egg at the right time for fertilization. How is coordination achieved? Follicular granulosa cells prevent precocious resumption of meiosis in oocytes, maintaining meiotic arrest until the pre-ovulatory hormone surge. Granulosa cells produce cyclic guanosine monophosphate, which is delivered to oocytes and arrests meiotic progression by inhibiting oocyte cyclic adenosine monophosphate degradation. How cGMP production is regulated is unclear. Now, Zhang et al. (p. 366 ) report that NPPC (natriuretic peptide precursor type C), produced by mural granulosa cells, and its receptor NPR2, a guanylyl cyclase expressed by cumulus cells, together promote cGMP production by cumulus cells and are thus essential for maintaining meiotic arrest in mouse oocytes.