PARENT SESSION
SLIDE SESSION 9: SPERMATOGENESIS
Chairs: Deborah O'Brien, John Herr, Cynthia Shirley (Trainee)
Univ Ottawa-UCU Auditorium
1:30 PM-3:30 PM

SPERM PROTEIN PHOSPHATASE, PP12, IS BOUND TO ACTIN AND A HOMOLGUE OF THE YEAST PROTEIN PHOSPHATASE BINDING PROTEIN SDS22.

Huang, Zaohua¹, Jack, Shannon¹, Carr, Daniel², Bollen, Mathieu³, Vijayaraghavan, Srinivasan¹, ^{1 2 3}

ABSTRACT- We have shown that in mammalian spermatozoa, testis-specific, PP12 is the predominant serine/threonine protein phosphatase. A decrease in the catalytic activity of the enzyme is associated with motility development. Inhibition of the enzyme in vitro leads to motility initiation and stimulation in epididymal spermatozoa. Results in this report relate to the biochemical mechanisms by which PP12 is regulated in spermatozoa. We purified sperm PP12 by immuno-affinity column chromatography using antibodies against the unique carboxy terminus of PP12. Purified PP12 was found to be associated with two proteins - actin and a protein identical to the human homologue of yeast protein phosphatase (PP1) binding protein SDS-22. This microsequencing data was confirmed by Western blot analysis with actin and SDS-22 antibodies. Actin and SDS-22, immunoprecipitated from soluble sperm extracts are bound to PP12 as determined by Western blot and PP1 enzyme assays. Purified PP12 complex is inactive. We hypothesize that sperm PP12 targeting and its activity are regulated by phosphorylation of its binding proteins, actin and SDS-22. Studies are underway to identify the protein kinase(s) involved in regulating sperm PP12 activity and to determine the intrasperm localization of PP12 and its regulatory proteins. Taken together our data suggest that a novel signaling pathway consisting of an evolutionarily conserved PP12 and its binding partners is involved in the regulation of spermatozoan function.

KEY WORDS: sperm motility, protein phosphatase, actin, SDS