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

Proteins, synthesized by the epididymal epithelium, are secreted sequential ly into the lumen of the ductus epididymis where they effect sperm maturati on and enable functional motility and fertilizing capacity. EP1 is a major secretory glycoprotein of chimpanzee (Pan troglodytes) epididymis, The epid idymal duct exhibits diverse histology (Smithwick & Young, 1997), Epithelia I-V of the efferent ducts show no characteristic anti-EP1 binding. The den sest 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 a nd perivacuolar cytoplasm of the basal cells. In epithelia VII-XIV of the d uctus epididymis proper, anti-EP1 binding decreases distally and is localiz ed in the cytoplasm of the PCs and basal cells, among the stereocilia of th e luminal border, within various microvillar borders, and in the luminal fl uid. Therefore, EPI 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, an d the proximal ductus deferens.