Characterization of glycolysis and pentose phosphate pathway activity during sperm entry into the mouse oocyte

Studying the events that occur during gamete fusion and sperm decondensatio n in the oocyte remains difficult because sperm-oocyte fusion and subsequen t sperm decondensation represent a short part of the fertilization process, and their exact timing is difficult to determine. There is therefore a nee d for greater understanding of the events that occur during this period.. T he main purpose of this study was to examine the metabolic aspects of this time frame by characterizing glucose metabolism (glycolytic and pentose pho sphate pathway [PPP] activities) during sperm fusion and decondensation int o zona-free oocytes in mice. The metabolism of glucose through both glycoly sis and the PPP was measured in ovulated MII oocytes, free of cumulus cells , and the levels of glucose metabolized were found to be low. Upon sperm en try, both glycolytic and; PPP activity increased substantially. To determin e whether this elevation in glucose metabolism was part of the activation p rocess, the metabolism of parthenogenetically activated oocytes was measure d, and no increase in metabolism was observed. The characterization of gluc ose metabolism during sperm fusion and decondensation into the oocyte, and comparison to parthenogenetically activated oocytes, showed that the fertil izing sperm is responsible for an increase in both glycolytic and PPP activ ity during fusion and/or decondensation, The significance of this observati on during the fertilization process and for the developing embryo is as yet unclear and warrants further investigation.