Function of the Cumulus Oophorus Before and During Mammalian Fertilization

Abstract

Fertilization encompasses a series of different steps which have to be performed in a well-orchestrated way to create a new individual. They include sperm capacitation, sperm binding and penetration of the zona pellucida, traversing the perivitelline space, binding and fusion with the oolemma, activation of the oocyte and decondensation of the sperm head to form the male pronucleus. In most mammalian species, cumulus cells surround the oocyte at the time of fertilization. Removal of the cumulus oophorus at this point of time often leads to a drop in fertilization rates. It is not yet known how cumulus cells interact with the oocyte or with spermatozoa to promote fertilization. There are different possibilities: 1 cumulus cells cause mechanical entrapment of spermatozoa and guide hyperactivated spermatozoa towards the oocyte, while preventing abnormal spermatozoa to enter the cumulus matrix; 2 cumulus cells create a micro-environment for the spermatozoa which favours their capacitation and penetration into the oocyte; 3 cumulus cells prevent changes in the oocyte which are unfavourable for normal fertilization; these changes can be located in the zona pellucida or in the cytoplasm. In this review, studies in several species are listed to prove the importance of these three cumulus cell functions and the current lines of research are highlighted. Moreover, different ways to improve in vitro fertilization of bovine cumulus-denuded oocytes are discussed.

Influence of Insulin-Like Growth Factor-I on Maturation and Fertilization Rate of Immature Oocyte and Embryo Development in NMRI Mouse with TCM199 and α -MEM Medium

“…As well as cumulus cells change the oocyte cytoplasm and zona pellucida to increase normal fertilization rate [19].…”

Cytoplasmic and nuclear maturation of oocytes in mammals – living in the shadow of cells developmental capability

“…The corona radiata cells form a unique micro-environment for the proper development of the oocyte. These cells, by numerous gap-junctions, and by auto-and paracrine interactions communicate with each other, oocytes and granular cells of the follicle [31], [32]. Low molecular weight nutrients, nucleotides, amino acids and energy compounds, necessary for oocyte's growth phase, are also supplied through the gap-junctions.…”

Cryopreservation of Sheep Produced Embryos – Current and Future Perspectives

“…Cumulus cells are important to IVM success and subsequent fertilization. These cells and their physical contact with the oocyte are of primordial importance not only for the resumption and progression of nuclear maturation but also for cytoplasmic maturation [129][130][131].…”