Mouse oocytes restore antral stage partial mechanical denudation in vitro

Abstract

In vitro oocyte culture might be the sole option for fertility preservation in some patients. This relies on constant oocyte-somatic bidirectional communication, and its precocious disruption alters oocyte competence. In non-hCG-triggered human in vitro maturation (IVM), retrieval of cumulus-oocyte-complexes (COCs) by needle aspiration from the targeted small follicles (2-8 mm) leads to the collection of some partially denuded (PD) COCs with poor developmental competence. Hypothetically, re-establishing connectivity in these COCs could rescue oocyte quality. To test this, we used a well-characterized mouse preantral follicle culture system. On day 8, at antral stage, in part of the follicles the oocytes were mechanically denuded while in other follicles in vitro grown oocytes were replaced with age matched fully stripped in vivo grown ones. The denuded oocytes were cultured on top of the somatic compartment until day 12, when oocyte-somatic reconnection was assessed. Furthermore, to better mimic the current biphasic IVM set-up, fully surrounded (FS) COCs were collected from 19-21 days-old unprimed mice. Following partial mechanical denudation, COCs were cultured under meiotic inhibition for 2-4 days, to test oocyte-CCs reconnection. Meiotic and developmental competence endpoints were compared between reconnected and FS cultured COCs. We concluded that (i) in vivo and in vitro grown antral oocytes reconnect with in vitro grown somatic companions; (ii) PD-COCs restore the FS morphology in culture, under meiotic inhibition; (iii) oocyte quality from reconnected and intact cultured COCs is comparable. These observations encourage translational work to rescue partially denuded oocytes in human IVM.