Differential response of cumulus cell-enclosed and denuded mouse oocytes in a meiotic induction model system

Abstract

In this study we have examined the effects of denuded oocyte coculture with dissociated cumulus cells (CC) or intact oocyte-CC complexes on meiotic resumption. When denuded oocytes (DO) or cumulus cell-enclosed oocytes (CEO) were cultured in 40-microl drops of medium under oil, and held in meiotic arrest with 4 mM hypoxanthine plus 25 microM dbcAMP, they underwent germinal vesicle breakdown (GVB) at similar frequencies (34%-35%). Coculture of DO with complexes or dissociated CCs stimulated maturation (50% and 61% GVB, respectively), with no effect of DO on maturation of cocultured CEO (32% GVB). This coculture effect was increased with the number of CCs added to the culture drop. When either glucose or glutamine was eliminated from the medium, no meiotic induction resulted from cocultured CCs. When CEO were cultured alone in microdrops, increasing their number from 10 to 50 significantly lowered the percentage resuming maturation, an effect also reduced by removing glucose and/or glutamine from the medium. This effect was not observed with DO. When inhibitory medium was conditioned overnight with complexes, subsequent culture with DO led to higher maturation percentages than culture in unconditioned medium; however, when CEO were cultured in conditioned medium, there was either no effect or increased inhibition of maturation. Assay of glucose and pyruvate in spent medium showed that DO cultured alone consumed glucose and pyruvate, but under CC coculture conditions more glucose was consumed and significant amounts of pyruvate accumulated in the medium, changes that led to an increase in the maturation of DO. Further experiments showed that DO were more sensitive than CEO to the meiosis-inducing effect of pyruvate. These results demonstrate different responsiveness of DO and CEO to coculture conditions and question the physiological relevance of denuded oocyte/CC coculture to study meiotic induction.

Autologous mature follicular fluid: its role in in vitro maturation of human cumulus-removed oocytes

“…Therefore the existence of cumulus cells has a positive impact on the maturation and subsequent development of oocytes. This observation is confirmed by studies in other mammals (9)(10)(11)(12)(13).…”

“…First, co-culture of immature oocytes with GCs may alter the chemical composition of IVM medium by altering the concentration of metabolites, removing undesirable factors or detoxifying the IVM medium (12,36). Second, the added GCs may contribute maturation-related factors or signals that directly affect the IVM of oocytes (9,(11)(12)(13)21). Thus, IVM co-culture with GCs, especially IVM co-culture with autologous ones, was raised specifically to assist the IVM of human oocytes.…”

The value of second polar body detection 4 hours after insemination and early rescue ICSI in preventing complete fertilisation failure in patients with borderline semen

“…Cumulus cell removal could also cause significant metabolic changes to the oocytes, which further affects the oocyte maturation and fertilisation process. As reported by Downs et al (2006), denuded oocytes cultured alone consumed glucose and pyruvate, but with cumulus cells attached more glucose was consumed and significant amounts of pyruvate were accumulated in the medium, leading to an increase in the maturation of denuded oocytes. However, most of these in vitro-matured oocytes are cytoplasmically immature and appear to undergo higher sperm penetration of the zona consistent with their failure to undergo complete cortical granule loss (Van Blerkom et al 1994).…”

The impact of obesity on egg quality

“…In contrast to the low PFK activity in oocytes [75], the cumulus cells also have high PFK activity [77]. Oocyte maturation cannot occur without either cumulus cells or pyruvate provided in the media [30,78] and glucose alone will not support maturation of denuded oocytes without the addition of cumulus cells [29]. Therefore it is important to consider the cumulus cells when addressing oocyte metabolism.…”