Motility potential of macaque epididymal sperm: The role of protein phosphatase and glycogen synthase kinase-3 activities

Human and monkey ejaculated sperm contain protein phosphatase-1 (PP1), PP1 inhibitor 2 (I2), and glycogen synthase kinase-3 (GSK-3). Inhibition of eja culated human sperm protein phosphatase (PP) activity with calyculin-a (CL- A) significantly stimulates motility, implicating protein dephosphorylation in motility regulation. The present experiments were conducted to characte rize and compare PP and GSK-3 activity in monkey caput and caudal epididyma l sperm, to determine the cellular distribution of these enzymes, and to te st the thesis that epididymal sperm PP activity is inversely related to mot ility. Caput epididymal sperm populations, (8.8% motile) contained levels o f PP activity that were >3 times as high as those of caudal spermatozoa. Th is PP activity was further identified by inhibitor response profiles as PPI . In both caput and caudal sperm, the majority of this PP1 activity was loc alized in 100,000 x g soluble fractions. Western blot analysis indicated th at a portion of this difference was the result of elevated amounts of PPI i n caput compared with caudal epididymal sperm. The presence of GSK-3 activi ty was undetectable in 100,000 x g insoluble fractions of epididymal sperm, whereas both caput and caudal sperm soluble fractions contained GSK-3 acti vity, which was approximately threefold higher in caput sperm compared with caudal populations. Treatment of caput epididymal sperm from the rhesus ma caque with the PP inhibitor CL-A resulted in a significant, dose-dependent increase from 8 to 38% motile cells (without any effect on their path veloc ity). in contrast, CL-A had no significant influence on either percent moti lity or path velocity of caudal epididymal sperm. Cytosolic PP1 and GSK-3 a ctivities appear to be inversely related to the motility of monkey epididym al sperm and may have a regulatory role in the development of the potential for motility in epididymal sperm.