The role of oocyte maturation inhibitor in follicular regulation of oocyte maturation

Abstract

Pincus & Enzmann suggested that meiotic maturation in mammals is held in abeyance by a follicular factor. Recently, OMI from porcine follicular fluid and granulosa cells was partly purified and characterized. However, OMI is only one of the factors involved in the control of the meiotic process. Other factors, such as oocyte-cumulus cell communication, cyclic AMP and steroids are probably involved in controlling meiosis. Some of the putative mechanisms involved in the control of meiosis are depicted. Meiosis is prevented in antral follicles by OMI produced by granulosa cells. The inhibitory action of OMI is apparently exerted through the mediation of cumulus cells and the signal conveyed through cumulus cell-oocyte gap junctions. It is not known whether cAMP or OMI are transferred to the oocyte as the inhibitory signal. LH induces the resumption of meiosis, possibly through the mediation of mural granulosa and cumulus cells. The mode of action of LH in inducing meiosis remains to be elucidated: LH may act either by eliminating the inhibitory signal, by blocking its transfer via the cumulus cell-oocyte junctions or by terminating OMI production. Alternatively, LH may generate a yet unspecified positive signal. More studies are needed to understand the intricate mechanism involved in the control of meiotic maturation. Purification of OMI to homogeneity is required for assessing the precise physiological role of this factor in the meiotic process.