Glucose participates in sperm-oocyte fusion in the mouse

Glucose metabolism is necessary for successful fertilization in the mouse, but the precise step of this process that requires glucose has not been determined. In this study we have investigated the involvement of glucose in the gamete binding and fusion process. The relationship between the metabolism of this carbohydrate in the oocyte and this particular step of fertilization has also been studied. A binding and fusion assay was performed by inseminating zona-free oocytes with capacitated sperm. Sperm binding and the fusion reaction were assessed by counting the sperm bound to the oolemma and the sperm heads decondensed in the ooplasm, respectively. To determine the importance of glucose metabolism, nonmetabolized glucose analogues (L-glucose, 2-deoxyglucose, 3-O-methylglucose) were used instead of glucose. The binding/fusion assay was also performed in the presence of glucose uptake inhibitors (cytochalasin B, phloretin, phlorizin). We have obtained evidence that glucose was specifically required for sperm penetration into zona-free oocytes (gamete fusion) but not for sperm binding to the oolemma. The metabolism of this carbohydrate appears to be essential, since nonmetabolized glucose analogues were unable to support this process. Although glucose metabolism was detectable in the oocyte, it did not appear to be related to the gamete fusion function. We hypothesize that the male gamete, which utilizes glucose as an energy substrate for various functions, may have a specific need to metabolize this hexose during fusion and incorporation within the oocyte.