Immunohistochemical localization of epididymal secretory glycoprotein EP1 in the adult male chimpanzee.

Proteins, synthesized by the epididymal epithelium, are secreted sequentially into the lumen of the ducts epididymis where they effect sperm maturation and enable functional motility and fertilizing capacity. EP1 is a major secretory glycoprotein of chimpanzee (Pan troglodytes) epididymis. The epididymal duct exhibits diverse histology (Smithwick & Young, 1997). Epithelia I-V of the efferent ducts show no characteristic anti-EP1 binding. The densest granules of anti-EP1 reaction product appear in epithelium VI adjacent to the basal lamina in the infranuclear region of the principal cells (PCs), in the cytoplasm of the apical half of the PCs, and in the perinuclear and perivacuolar cytoplasm of the basal cells. In epithelia VII-XIV of the ductus epididymis proper, anti-EP1 binding decreases distally and is localized in the cytoplasm of the PCs and basal cells, among the stereocilia of the luminal border, within various microvillar borders, and in the luminal fluid. Therefore, EP1 appears to be synthesized and secreted primarily in the caput region of the ductus epididymis and may be reabsorbed nonselectively across epithelia with apical microvilli, including the non-ciliated cells of efferent ducts, the distal corpus and cauda of the ductus epididymis, and the proximal ductus deferens.