Expression and function of the c-kit proto-oncogene protein in mouse sperm

The presence and role of the c-kit protein were examined in mature sperm of the mouse. Monoclonal antibodies (mAbs) against the c-kit protein were used to perform immunohistochemical staining, electron microscopy studies, and Western blot analysis. The acrosomal region of both fixed and unfixed noncapacitated sperm stained with the antibodies. No acrosomal staining was noted in acrosome-reacted (AR) sperm. Electron microscopy studies demonstrated immunogold label on the plasma membrane of the acrosome and confirmed the lack of binding following the acrosome reaction. Proteins corresponding to 33 kDa, 48 kDa, and 150 kDa were detected by the antibodies utilizing Western blot analysis. The 48-kDa and 150-kDa proteins were released into the media during sperm capacitation, and release from the acrosome was dependent upon the acrosome reaction. The mAbs significantly inhibited the acrosome reaction and increased sperm agglutination. Monoclonal antibody ACK1 significantly inhibited the motility of the sperm, whereas mAbs ACK2 and NCL-ckit did not. These results suggest that c-kit-related proteins are present in mature sperm and may play a role in capacitation and/or the acrosome reaction.