EPIDIDYMAL MATURATION OF THE cAMP/ PROTEIN TYROSINE PHOSPHORYLATION PATHWAYS ASSOCIATED WITH SPERM CAPACITATION

FORNES MW.; VISCONTI PE.; KOPF GS.

Montreal

Simposio; 8th International Symposium on Spermatology; 1998

International Symposium on Spermatology

Introduction: After ejaculation, mammalian sperm have not acquired fertilizing capacity. They require a finite period of residence in the female reproductive tract to undergo a maturational process known as capacitation. Previously, we demonstrated that capacitation of cauda epididymal sperm correlates with protein tyrosine phosphorylation of a subset of proteins; this phosphorylation is up-regulated by a cAMP /protein kinase A (PKA) pathway. On the other hand, sperm recovered from the caput epididymis of the mouse, do not have the ability to undergo capacitation and do not display the increase in protein tyrosine phosphorylation. In the present work we analyzed whether protein tyrosine phosphorylation could occur in mouse sperm from the caput region of the epididymis when we stimulate the cAMP pathway using the permeable cAMP analog, dibutyryl cAMP (dbcAMP) and the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX). Methods: Immunoblots of phosphotyrosine containing proteins and assays of PKA activity are as previously described. Results: In contrast to the effects observed with cauda sperm, addition of dbcAMP plus IBMX to caput sperm did not induce protein tyrosine phosphorylation, although these compounds were permeable in both caput and cauda sperm. To study the different parts of this signal transduction pathway, we measured PKA activity in caput and cauda sperm and found that there is an increase in the total PKA activity during epididymal maturation. This increase was not due to the presence of more PKA catalytic subunit in cauda vs caput sperm. The lower total PKA activity in the caput sperm in due to the presence of a PKA inhibitor, not yet characterized. This inhibitor appears to be non comparative with respect to ATP and kemptide, the synthetic substrate used in these assays. Discussion: This work shows for the first time that changes in signal transduction pathways follow epididymal maturation. Our laboratory is further pursuing the identification of the PKA inhibitor and how it interacts with PKA.