ACROSOME BIOGENESIS IN THE HAMSTER - ULTRASTRUCTURALLY DISTINCT MATRIX REGIONS ARE ASSEMBLED FROM A COMMON PRECURSOR POLYPEPTIDE

The hamster sperm acrosome contains a stable matrix complex that binds specific hydrolases and appears to regulate their release during the acrosome reaction. This complex comprises two contiguous but ultrastru cturally distinct regions that are segregated to specific sites within the acrosome. In this study, we define the temporal expression, proce ssing, and localization of major matrix proteins of 29 kDa (AM29) and 22 kDa (AM22) during spermiogenesis and post-testicular sperm maturati on in the epididymis. Peptide mapping, N-terminal microsequence analys is, immunoblotting, and immunocytochemistry were used to demonstrate t hat AM29 and AM22 of mature spermatozoa are structurally related and a ppear to arise from a common 40-kDa precursor protein expressed in rou nd spermatids. A monoclonal antibody that recognized only the mature f orms of the matrix proteins and a polyclonal antibody that recognized both the precursor and fully processed matrix proteins were prepared a nd used to demonstrate that the precursor protein is present in the ac rosome of round spermatids and that it undergoes size processing durin g the terminal stages of spermiogenesis so that the mature matrix poly peptides are evident in epididymal spermatozoa. Finally, using light a nd electron microscopic immunocytochemistry, we demonstrated that the matrix polypeptides are excluded from the equatorial segment and are l ocalized to both structurally distinct matrix domains of the mature ac rosome. These data show that processing of the major proteins of the a crosomal matrix occurs in a temporally regulated fashion after their t ransport to the acrosome and that the processed products can assemble into ultrastructurally distinct matrix elements.