Protein Kinase C Activity in Mouse Eggs Regulates Gamete Membrane Interaction
Every mammalian life develops from one cell after fertilization of an egg by the sperm. The molecular pathways governing this event are still poorly understood. Numerous reports indicate that mammalian eggs highly express various protein kinase C (PKC) isoforms. Accordingly, we hypothesize that PKC activity in the egg plays an important role during egg-sperm membrane binding and fusion. In this study, we tested our hypothesis in mouse gametes using two types of PKC inhibitors (calphostin c and staurosporine) and the typical PKC activator, phorbol ester 12-tetradecanoylphorbol-13 acetate (PMA). After treatment with the individual drug, eggs were inseminated with sperm. The sperm binding number (SB) and fusion rate (FR) were scored using light and fluorescence microscopy. By applying the Student’s t-test, we confirmed that the FR and SB were significantly decreased after PKC activator or inhibitors treatments. All treatment groups, 1 μM calphostin c, 1 μM staurosporine, or 1 nM PMA showed the significant reduction of FR and SB. Further analysis indicated that the inhibition effects of calphostin c and PMA were dose- and time- dependent. Moreover, under scanning electron microscopy (SEM), we observed that the number and shape of microvilli on the PMA-treated eggs, but not on the calphostin c-treated eggs, was severely changed. Taken together, these results suggest that egg PKC activity plays an important role in the signaling regulation of sperm-egg membrane binding and fusion during fertilization.