ACROSOMAL DISRUPTION IN SPERM Freeze-Fracture of Altered Membranes

"Capaci ta t ion" is a physiological event which alters sperm to permit rapid penetration through oocyte investments and fusion between gametes. Acrosomal "reaction," the physiological release of acrosomal contents, occurs after this facilitating process. In this study, acrosomal "disruption" of guinea pig and rat sperm was achieved in vitro by incubating sperm together with the follicular contents of superovulated mice. The samples contained both "reacted" and "disrupted" sperm. Thin sections of affected sperm revealed rupture and vesiculation of the plasma membrane overlying the acrosome, as well as loss of both the outer acrosomal membrane and the acrosomal content. Freeze-fracture revealed disintegration of the characteristic geometric patterns in regions of the acrosomal and plasma membranes thus disrupted and major modifications in particle distribution in the sperm tail. In the guinea pig, strands of 6-8-nm particles, usually confined to the plasma membrane of the midpiece, which overlies mitochondria, also appeared in the principal piece. Likewise, in rat sperm, bands of similarly small particles formed acute angles throughout the membrane of the principal piece. Compared with the membranes of control preparations, these membrane alterations are apparently a direct consequence of incubation with ovarian follicular contents. Various regions of mammalian sperm have highly specialized functions (1-3). These areas also reveal distinctive membrane differentiations in freezefracture; this is true of sperm in the rat, rabbit, bull, water buffalo, monkey, and man (4-11). It is particularly true in the case of guinea pig sperm, one of' the most elaborately differentiated in the species studied (12). Portions of the plasma membrane of the guinea pig sperm head display a discoid "quilt" of elevations and depressions. That part overlying the equatorial segment of the acrosome has a serrated appearance, while islands of particles in rectilinear array inhabit limited portions of the membrane overlying the postacrosomal dense lamina. Also, large areas of the acrosomal membrane exhibit a cobblestone array of particles. The nuclear envelope composing the anterior limit of the implantation fossa contains unusually large particles. In the tail, the plasma membrane of the midpiece has sheaths made up of small particle strands over the mitochondria. Beyond the roughened anulus, the plasma membrane of the principal piece has a linear "zipper" of large particles opposite fiber 1. In the rat, the particle arrays are similar but less elaborate. The implications of these focal variations are, first, that they participate in regional functional THE JOURNAL OF CELL BIOLOGY . VOLUME 63, 1974 p a g e s 466 479 on F ebuary 1, 2013 jcb.rress.org D ow nladed fom Published November 1, 1974