Extratesticular sperm maturation in the brushtail possum, Trichosurus vulpecula

The changes in distribution of protein and sugar components in, and on, the plasmalemma of the spermatozoon during epididymal transit of a marsupial, the brushtail possum, Trichosurus vulpecula, are described. Freeze-fracture studies indicate a change in organization of plasmalemma intramembranous p articles of both the head and midpiece of the tail as the spermatozoa pass from the caput to cauda epididymides. Staining with fluorescein isothiocyan ate (FITC)-lectins shows that heads of caput spermatozoa stain with Con A, WGA, RCA(120), LCA and JAC, whereas those from the cauda epididymides stain only with LCA and JAC, thus suggesting that N-acetyl-beta-D-glucosamine, a lpha-D-glucose, or beta-D-galactose may either become lost or masked during epididymal transit. A reduction of alpha-D-mannose is also suggested. Coll ectively these results show that the plasmalemma of the spermatozoon of at least this marsupial species undergoes both protein and saccharide modifica tion during transit of the epididymis. How these findings relate to sperm m aturation in preparation for sperm-egg binding has yet to be determined.