Responses of monkey epididymal sperm of different maturational status to second messengers mediating protein tyrosine phosphorylation, acrosome reaction, and motility

The maturation of various aspects of sperm function have been demonstrated in monkey and human epididymal sperm, including the ability to undergo the acrosome reaction. The present study aimed to investigate the maturational changes in non-human primate sperm in the signal transduction mechanisms le ading to the acrosome reaction involving cyclic AMP, Ca2+ influx, protein k inase C, and protein tyrosine phosphorylation. Sperm from the caput, corpus , and cauda epididymidis of cynomolgus monkeys were incubated in a complete medium for 2.5 hr, followed by 30 min stimulation with 1 mM dibutyryl cAMP and 1 mM caffeine, 50 mu M 1,2-dioctanoyl-sn glycerol (DOG), and 50 mu M C a2+-ionophore A23187. Quantitative Western blotting revealed little differe nce in tyrosine phosphorylated proteins among the caput, corpus, and cauda sperm without stimulation. Incubation with cAMP increased the amount of tyr osine phosphorylated proteins up to 10-fold in the corpus and cauda sperm, but to a lower extent in the caput sperm. Ca2+-ionophore attenuated the cAM P stimulation but had no effect on its own. Such responses in tyrosine phos phorylated proteins were in great contrast to the responses in the acrosome reaction, where A23187 was the strongest stimulant, resulting in induction of the reaction in 50 +/- 5%, 11 +/- 5%, and 8 +/- 4% cauda, corpus and ca put sperm, respectively (mean +/- sem, n = 6). DOG and cAMP in combination induced acrosome reactions in about 10% of viable cells in the cauda and co rpus but not caput sperm. Caput sperm responded to cAMP with increases in p ercentage motility without forward progression whereas cauda sperm displaye d marked kinematic changes expected of hyperactivation. Comparisons of resp onses suggest that the major tyrosine phosphorylated proteins detected are unlikely to be involved immediately in the precipitation of the acrosome re action, but more related to flagellar motion. Development of signal transdu ction pathways is part of the epididymal maturational process. (C) 1999 Wil ey-Liss, Inc.