IVM of mouse fully grown germinal vesicle oocytes upon a feeder layer of selected cumulus cells enhances their developmental competence

Abstract

In the ovary, acquisition of oocyte developmental competence depends on a bidirectional exchange between the gamete and its companion cumulus cells (CCs). In this study we investigated the contribution of CCs surrounding oocytes of known developmental competence or incompetence to the acquisition of oocyte developmental competence. To this end, feeder layers of CCs (FL-CCs) were prepared using CCs isolated either from: (1) developmentally competent mouse oocytes whose nucleolus was surrounded by a chromatin ring (FL-SN-CCs); or (2) developmentally incompetent mouse oocytes whose nucleolus was not surrounded by a chromatin ring (FL-NSN-CCs). Denuded, fully grown oocytes (DOs) were matured to the MII stage on either FL-SN-CCs or FL-NSN-CCs, inseminated with spermatozoa and cultured throughout preimplantation development. FL-SN-CCs significantly improved the acquisition of oocyte developmental competence, with a blastocyst development rate equal to that for maturation of intact cumulus–oocyte–complexes. In contrast, DOs matured on FL-NSN-CCs or in the absence of CCs exhibited developmental failure, with embryos arresting at either the 4-cell or morula stage. These results set a culture platform to further improve the protocols for the maturation of DOs and to unravel the molecules involved in the cross-talk between the gamete and its companion CCs during the germinal vesicle to MII transition.

In Vitro Maturation of Fully Grown Mouse Antral Follicles in the Presence of 1 nM 2-Hydroxyestradiol Improves Oocytes’ Developmental Competence

“…To this end, we employed a number of known cytological quality markers of the meiotic division to compare MI or MII oocytes matured in vitro, either in the absence or in the presence of 1 nM 2-OHE 2 , and those obtained by ovulation. Specifically, we analysed (i) the PB-I volume [6,[34][35][36][37][38][39][40][41][42][43] and its position in respect to the oocyte's spindle [44]; (ii) the presence and extension of the cortical F-actin cap [45][46][47]; (iii) the meiotic spindle shape and area [48][49][50][51] and (iv) the microtubule organisation centre (MTOC) localisation [8,48,52].…”

“…The importance to preserve the communication between oocyte and surrounding granulosa cells becomes evident when cumulus-oocyte complexes (COCs) are isolated from fully grown antral follicles and in vitro cultured [ 3 , 4 ]. In the mouse, the efficiency of COCs in vitro maturation (IVM) varies depending on both strain (i.e., outbred or inbred) [ 5 ] and culture conditions [ 6 , 7 ], although the meiotic and developmental competence of metaphase II (MII) oocytes obtained in vitro remains lower compared with that of ovulated MII oocytes [ 8 , 9 ].…”

Comprehensive analysis of nonsurrounded nucleolus and surrounded nucleolus oocytes on chromatin accessibility using ATAC‐seq

“…The NSN oocytes, as immature GV oocytes, also enter GVBD at almost the same time as SN, hence they are lacking an extent of time during which NSN would have converted to SN in vivo, and this deficit of time results in fewer transcripts accumulated. The poor developmental ability of NSN oocytes is manifested as reduced polar body extrusion and low zygote development rates (Cavalera, Simovic, et al, 2019; Cavalera, Zanoni, et al, 2019), and the fertilized embryos of NSN oocytes often stop developing at the two‐cell stage (Chen et al, 2017). RNA sequencing (RNA‐seq) data of GV oocytes has indicated that SN oocytes possess more transcripts than NSN oocytes (Ma et al, 2013), which is essential for oocyte development, fertilization, and zygote development.…”