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Development of the signalling pathways associated with sperm capacitation during epididymal maturation
Author(s) -
Baker Mark A.,
Lewis Beverley,
Hetherington Louise,
Aitken R. John
Publication year - 2003
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.10255
Subject(s) - capacitation , biology , sperm , microbiology and biotechnology , signalling pathways , signal transduction , epididymis , signalling , genetics
Abstract As spermatozoa mature within the epididymis they acquire the potential for capacitation and ultimately fertilization. In biochemical terms, the former is reflected in the progressive activation of a signal transduction pathway characterized by cAMP‐mediated induction of phosphotyrosine expression on the sperm tail. In this study, we have examined the cellular mechanisms controlling this maturational event. Caput epididymal spermatozoa exhibited tyrosine phosphorylation on the sperm head that was largely unresponsive to cAMP and not significantly impaired by removal of extracellular HCO 3 − . In contrast, caudal epididymal spermatozoa exhibited low levels of phosphorylation on the sperm head, yet responded dramatically to cAMP by phosphorylating a new set of proteins on the sperm tail via mechanisms that were highly dependent on extracellular HCO 3 − . The impact of extracellular HCO 3 − depletion on caudal cells was not associated with a significant change in the redox regulation of cAMP but could be fully reversed by buffering the intracellular pH with N ‐Tris[Hydroxymethyl]methyl‐3‐amino‐propanesulfonic acid (TAPS). The pattern of tyrosine phosphorylation was also profoundly influenced by the presence or absence of added extracellular calcium. In the presence of this cation, only caudal spermatozoa could respond to increased extracellular cAMP with tyrosine phosphorylation of the sperm tail. However, in calcium‐depleted medium, this difference completely disappeared. Under these conditions, caput and caudal spermatozoa were equally competent to exhibit phosphotyrosine expression on the sperm tail in response to cAMP. These results emphasize the pivotal role played by calcium and HCO 3 − in modulating the changes in tyrosine phosphorylation observed during epididymal maturation. Mol. Reprod. Dev. 64: 446–457, 2003. © 2003 Wiley‐Liss, Inc.