The ductuli efferentes (DE) form a transit passage for the passage of spermatozoa from the rete testis to the epididymis. After spermiation, various epithelial secretory proteins are transferred via extracellular vesicles (EVs) to the spermatozoa for their maturation and long-term viability. The aim of the present study was to investigate the distribution, classification, and source of multivesicular bodies (MVBs) and their EVs in the epithelia of the efferentes duct in a turtle species, the soft-shelled freshwater turtle Pelodiscus sinensis by using light and transmission electron microscopy. The results showed that CD63 as a classical exosome marker was strongly immunolocalized within the apical and lateral cytoplasm of the ciliated cells (CC) and moderate to weak in the non-ciliated cells (NCC) of DE. The ultrastructure revealed that early endosome was present at the basement membrane and perinuclear cytoplasm of both CC and NCC, whereas MVBs were located over the nucleus in the cytoplasm of NCC and adjacent to the basal bodies of cilia within the CC. Many EVs, as sources of MVBs, were located within the blebs that were attached to the cilia of CC, within the apical blebs from NCC, and the lateral spaces of CC and NCC. There was ultrastructure evidence of EVs associated with spermatozoa in the lumens of DE. Collectively, the present study provides cytological evidence that the DE epithelium secreted EVs to the lumen by (1) apical blebs, (2) ciliary blebs, and (3) from the basolateral region. These EVs were associated with spermatozoa in the DE lumen of this turtle. Characterization and cellular distribution of these EVs in the DE of a turtle may provide a study model to further investigate the transferring of micromolecules via EVs to the spermatozoa.
Keywords: apical blebs; cilia; efferent duct; exosomes; extracellular vesicles; turtle.