The secretion and metabolism of cumulus cells support fertilization in the bovine model

The cumulus oophorus is a structure that surrounds the mammalian egg and plays a key role in fertilization. However, very little is known with regards to how secretions from the cumulus cells can specifically promote fertilization. We hypothesized that secretions from bovine cumulus cells, and the reduction of oxygen stress by metabolic change, would enhance the fertilization capacity of sperm during in vitro fertilization (IVF) procedures. To prove our hypothesis, sperm were pre-incubated in chemically defined capacitation media containing methyl-beta-cyclodextrin and used to inseminate cumulus cell oocyte complexes, or denuded oocytes, with some components. While sperm capacitation was induced in capacitation media, fertilization was impeded by the removal of cumulus cells from cumulus cell oocyte complexes. Secretions from cumulus cells promoted the formation of two pronuclei via a filter and the fertilization of denuded oocytes was dramatically enhanced with hyaluronate, low oxygen concentration, or progesterone in fertilization media (P