EXPRESSION AND FUNCTION OF THE C-KIT PROTOONCOGENE PROTEIN IN MOUSE SPERM

The presence and role of the c-kit protein were examined in mature spe rm of the mouse. Monoclonal antibodies (mAbs) against the c-kit protei n were used to perform immunohistochemical staining, electron microsco py studies, and Western blot analysis. The acrosomal region of both fi xed and unfixed noncapacitated sperm stained with the antibodies. No a crosomal staining was noted in acrosome-reacted (AR) sperm. Electron m icroscopy studies demonstrated immunogold label on the plasma membrane of the acrosome and confirmed the lack of binding following the acros ome reaction. Proteins corresponding to 33 kDa, 48 kDa, and 150 kDa we re detected by the antibodies utilizing Western blot analysis. The 48- kDa and 150-kDa proteins were released into the media during sperm cap acitation, and release from the acrosome was dependent upon the acroso me reaction. The mAbs significantly inhibited the acrosome reaction an d increased sperm agglutination. Monoclonal antibody ACK(1) significan tly inhibited the motility of the sperm, whereas mAbs ACK(2) and NCL-c kit did not. These results suggest that c-kit-related proteins are pre sent in mature sperm and may play a role in capacitation and/or the ac rosome reaction.