Maturation antigen of the mouse sperm flagellum: II. Origin from holocrine cells of the distal caput epididymis.

During epididymal transit, the mouse sperm flagellum acquires a surface glycoprotein (SMA4) from epididymal fluid that functions as a sperm antiagglutinin. To determine the origin of this molecule, testes and epididymides of male mice were sectioned for light microscopy and stained with wheat germ agglutinin (WGA)-peroxidase, a probe that has been used previously to examine the biology of SMA4. WGA reactivity was localized to the cytoplasm in a small population of cells in the distal caput epididymis. Testis cells and principle cells of the caput were nonreactive with WGA, while stereocilia were stained on principle cells in the corpus and cauda. The WGA-positive cells in the distal caput were identified as holocrine cells on the basis of morphology, distribution, and PAS + reaction. At high magnification, intense WGA reactivity was due to the presence of numerous apical granules in the cytoplasm. The location of the cells in distal caput coincided exactly with the region of tubule in which sperm first acquired SMA4 on their flagellae. These data suggest that holocrine cells near the junction of caput and corpus epididymis are the source of the sperm antiagglutinin SMA4.