Acrosome Biogenesis in the Hamster: Ultrastructurally Distinct Matrix Regions Are Assembled from a Common Precursor Polypeptide(2)
In several mammalian species, the acrosomal contents are segregated into spatially distinct domains of differing ultrastructural appearance . In the guinea pig, specific acrosomal matrix polypeptides localized to restricted domains of the apical segment have been identified and characterized . Ibis suggests that regionally localized matrix assemblies may partition the acrosomal interior into distinct functional domains. The acrosomal contents of hamster spermatozoa also exhibit regional differences in structural appearance , and specific elements of the acrosomal matrix remain intact and associated with the hybrid membrane complex after the acrosome reaction . These acrosomal matrix elements also resist solubilization by various extraction regimens, emphasizing their structural stability. Buy Asthma Inhalers Online
We previously purified a stable acrosomal assembly from cauda epididymal hamster spermatozoa that comprises two ultrastructurally distinct acrosomal matrix domains and the detergent-insoluble membrane skeleton of the outer acrosomal membrane, and we demonstrated its ability to bind both proacrosin and N-acetylglucosaminidase . This acrosomal structure was termed the acrosomal lamina-matrix (ALM) complex. The two matrix components of the ALM adhere to different regions of the outer acrosomal membrane and are spatially restricted within the acrosome . Thus the AT M represents a stable infrastructure that may segregate hydrolases within the acrosome and regulate their release during the acrosome reaction; moreover, it may also represent a cy-toskeleton-like framework that affects the vesiculation of the outer acrosomal membrane during the acrosome reaction and that maintains the integrity of the shed acrosomal cap. The molecular mechanisms that regulate the assembly and define the precise spatial distribution of distinct matrix elements within the acrosome are poorly understood. In this study, we identify the temporal expression, the molecular relationships, and the spatial distribution of the major acrosomal matrix polypeptides in hamster spermatids and spermatozoa.