The Mammalian Oviductal Sperm Reservoir: Identification of Receptors for Bull Sperm on the Oviductal Epithelium
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In eutherian mammals, a storage reservoir is formed when sperm become trapped in the initial segment of the oviduct by binding to the epithelium lining its wall. In bull sperm, seminal vesicle secretory proteins in the bovine seminal plasma (BSP) protein family, namely PDC-109 (BSP A1/A2), BSP-A3, and BSP-30-kDa, coat the sperm head and enable sperm to bind to the oviductal epithelium. This study was undertaken to identify at least one receptor for BSP-30-kDa on the oviductal epithelium. Proteins extracted from apical plasma membranes of the oviductal epithelium were added to a column of BSP-30-kDa bound to anti-BSP-30-kDa covalently conjugated to Protein-A agarose beads. Unbound proteins were washed from the beads and proteins that bound to the column were eluted by adding EGTA, a calcium chelator, because sperm binding to the oviductal epithelium is dependent on calcium. The eluates were resolved on SDS PAGE gels, and silver staining detected two prominent bands of approximately 37 and 34 kDa. Tandem mass spectrometry identified the protein constituents of the bands as annexins (ANXA) 1, 2, and 4. Anti-annexin antibodies also labeled the cilia and apical surfaces of the epithelium in sections of bovine oviduct. Annexins belong to a multigene family of calcium-dependent, phospholipid binding proteins. Annexins are important in several biological processes such as cell adhesion, ion channel modulation, signal transduction, and regulation of membrane structure. It was concluded that annexins are primary candidates for the sperm receptors on bovine oviductal epithelium.
dissertation or thesis