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First published online 3 June 2008
doi: 10.1242/jcs.030379

Journal of Cell Science 121, 2130-2135 (2008)
Published by The Company of Biologists 2008
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Short Report

Dynamic resolution of acrosomal exocytosis in human sperm

Claire V. Harper1,*, Joanne A. Cummerson2, Michael R. H. White1, Stephen J. Publicover3 and Peter M. Johnson2

1 Centre for Cell Imaging, School of Biological Sciences, Biosciences Building, Crown Street, University of Liverpool, L69 7ZB, UK
2 Division of Immunology, School of Infection and Host Defence, Duncan Building, Daulby Street, University of Liverpool, L69 3GA, UK
3 School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK

* Author for correspondence (e-mail: claire.harper{at}liv.ac.uk)

Accepted 22 April 2008

Summary

An essential step in mammalian fertilisation is the sperm acrosome reaction (AR) – exocytosis of a single large vesicle (the acrosome) that surrounds the nucleus at the apical sperm head. The acrosomal and plasma membranes fuse, resulting in both the release of factors that might facilitate penetration of the zona pellucida (which invests the egg) and the externalisation of membrane components required for gamete fusion. Exocytosis in somatic cells is a rapid process – typically complete within milliseconds – yet acrosomal enzymes are required throughout zona penetration – a period of minutes. Here, we present the first studies of this crucial and complex event occurring in real-time in individual live sperm using time-lapse fluorescence microscopy. Simultaneous imaging of separate probes for acrosomal content and inner acrosomal membrane show that rapid membrane fusion, initiated at the cell apex, is followed by exceptionally slow dispersal of acrosomal content (up to 12 minutes). Cells that lose their acrosome prematurely (spontaneous AR), compromising their ability to penetrate the egg vestments, are those that are already subject to a loss of motility and viability. Cells undergoing stimulus-induced AR (progesterone or A23187) remain viable, with a proportion remaining motile (progesterone). These findings suggest that the AR is a highly adapted form of exocytosis.

Key words: Acrosome, Exocytosis, Human, Sperm


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The acrosome reaction in real time

JCS 2008 121: 1301. [Full Text]  





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