Problem: The present study was carried out to evaluate the changes in morphology and motility of spermatozoa retrieved from different regions of the epididymis of the cynomolgus monkey. The role of the epididymis in sperm maturation is assessed by assaying protein synthesis within different regions of the epididymis and by correlating these with changes in spermatozoal membrane surface components.
Method: Spermatozoa retrieved from proximal caput (CP), midcorpus (CO), and distal cauda (CD) were assessed by morphological evaluation and computerized motion analysis. Membrane surface proteins of spermatozoa of different epididymal regions were extracted and separated on SDS-PAGE. Protein synthesis of different regions of the epididymis were assayed in vitro by [35S]-methionine incorporation.
Results: Spermatozoa obtained from different regions of the epididymis differed morphologically only in the location of the cytoplasmic droplet. Specifically, from caput to corpus to cauda, sperm steadily exhibited a more distal cytoplasmic droplet. When the motion parameters of velocity and amplitude of the lateral head were examined, CP spermatozoa were not progressively motile, and poor duration of movement was most noticeable for CO spermatozoa compared with CD spermatozoa. Membrane extracts from CP, CO, and CD epididymal monkey spermatozoa differed in only several protein bands. Three major polypeptide bands (19, 30, and 60 kD) that were absent from CP sperm were present in CO and CD sperm, with the latter showing increased intensity. Several polypeptides were lost from the sperm during epididymal transit: a 25-kD band was lost in CD sperm; and bands at 27 kD, 50-52 kD, and 90 kD were only present for CP sperm. Additionally, regional differences exist for proteins secreted by the cynomolgus monkey epididymis. Proteins (15, 25 kD) were only secreted in the CP region; a 38-kD protein increased in intensity from the CP to CD regions, whereas a 21-kD protein was absent from CD-secreted medium.
Conclusion: These preliminary findings permitted the identification of several "maturational antigens" for cynomolgus monkey spermatozoa. Further characterization of these antigens that are modified during epididymal transit is warranted to determine their significance in the acquisition of progressive motility and fertilizing ability by epididymal spermatozoa.