PARENT SESSION
PLATFORM SESSION 19: SPERM-EGG BINDING AND EGG ACTIVATION
Chair: Miller, David¹, ¹
Co-chair: Rivera, Rocio¹, ¹
Harborside E
2:00 PM-4:00 PM

(435) THE ACROSOMAL MATRIX OF GUINEA PIG AND MOUSE SPERM IS A LATTICE-LIKE STRUCTURE THAT CONTAINS THE ZONA-BINDING PROTEIN SP56.

Bush, R Thomas¹, Perkins, Aaron¹, Gerton, George², Foster, James¹, ¹ Biology Department, Ashland, VA² Center for Research on Reproduction and Women's Health, Philadelphia, PA

ABSTRACT- The mammalian sperm acrosome plays a critical, albeit incompletely understood, role in fertilization. The acrosome is a secretory vesicle and, in some mammalian species (e.g. guinea pig), it has a "dense core" acrosomal matrix (AM) that is relatively resistant to detergent extraction and can be isolated intact at low pH in the presence of serine protease inhibitors. During acrosomal exocytosis the AM is disassembled in part by proteolytic processing. To analyze the ultrastructure of the AM in guinea pig and mouse sperm we used a protease inhibitor cocktail to delay disassembly of the AM and employed several electron microscopic approaches. SEM images show that the AM in guinea pig sperm is an extensive lattice-like structure with numerous fenestrations characteristic of other cell-associated matrices. SEM images of the AM in mouse sperm show a less extensive structure with a fenestrated appearance. The AM latticework was only observed in sperm that were incubated with protease inhibitors. Since the mouse acrosomal matrix has not been well characterized at the ultrastructural level, standard TEM and immunogold EM approaches were employed to characterize the AM in mouse sperm undergoing acrosomal exocytosis in the presence of a protease inhibitor cocktail. TEM images of these sperm show acrosomal matrix material associated with the inner acrosomal membrane and with hybrid vesicles of the outer acrosomal membrane and plasma membrane. Immunogold labeling shows that the zona-binding protein sp56 is present within the acrosomal matrix material that is exposed on the sperm surface during acrosomal exocytosis. Thus, these findings suggest a role for the acrosomal matrix in sperm-zona pellucida binding during fertilization. Supported in part by a Randolph-Macon College Craigie Fellowship to JAF and HD22899 from the NIH to GLG.

KEY WORDS: fertilization, acrosome, sp56, electron microscopy