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Hum. Reprod. Advance Access published online on August 26, 2008
Human Reproduction, doi:10.1093/humrep/den314
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© The Author 2008. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Src activation triggers capacitation and acrosome reaction but not motility in human spermatozoa

Gabriele Varano1, Adriana Lombardi1, Giulia Cantini1, Gianni Forti1, Elisabetta Baldi2 and Michaela Luconi1,3

1 Endocrinology Unit, Department of Clinical Physiopathology, DENOTHE Center for Research, Transfer and High Education, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy 2 Andrology Unit, Department of Clinical Physiopathology, DENOTHE Center for Research, Transfer and High Education, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy

3 Correspondence address. Tel: +39-055-4271369; Fax: +39-055-4271371; E-mail: m.luconi{at}dfc.unifi.it

BACKGROUND: Protein tyrosine phosphorylation is one of the main processes associated with sperm activation. Although this process and its targets have been well characterized, only few tyrosine kinases have been identified so far and their roles in spermatozoa are still largely unknown. In this study, we report the presence and localization of Src kinase in ejaculated human spermatozoa and investigate its role in regulating the processes underlying sperm activation.

METHODS AND RESULTS: Specific anti-Src antibodies, against different epitopes of the protein, identified a single band of ~70 kDa relating to a protein which is mainly localized in the post-acrosomal region of the head, neck and midpiece. By immunoprecipitation and immunofluorescence techniques performed with antibodies against Src phosphorylated at Tyr416, which identifies the active kinase, we showed an increased phosphorylation during sperm capacitation. Blocking Src activity with SU6656 resulted in a significant reduction in the protein tyrosine phosphorylation. Moreover, this inhibitor also blocked the progesterone-induced acrosome reaction and interfered with the calcium response to progesterone evaluated in fura-2-loaded spermatozoa. No effect on sperm motility and hyperactivation resulted from incubation with SU6656.

CONCLUSIONS: We identified a novel Src isoform in human spermatozoa, which appears to be involved in regulating sperm capacitation, calcium fluxes, tyrosine phosphorylation and acrosome reaction.

Key words: tyrosine kinase/sperm/capacitation/acrosome reaction/Src

Submitted on February 21, 2008; resubmitted on July 15, 2008; accepted on July 21, 2008.


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