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Differential response of cumulus cell‐enclosed and denuded mouse oocytes in a meiotic induction model system
Author(s) -
Downs Stephen M.,
Gilles Ryan,
VanDerhoef Christopher,
Humpherson Peter G.,
Leese Henry J.
Publication year - 2006
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.20416
Subject(s) - oocyte , germinal vesicle , biology , hypoxanthine , glutamine , andrology , blastocyst , cumulus oophorus , endocrinology , microbiology and biotechnology , biochemistry , embryo , embryogenesis , amino acid , enzyme , medicine
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‐µl drops of medium under oil, and held in meiotic arrest with 4 mM hypoxanthine plus 25 µM 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. Mol. Reprod. Dev. © 2005 Wiley‐Liss, Inc.