Dynamic resolution of acrosomal exocytosis in human sperm

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 penetrat...

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Bibliographic Details
Published inJournal of cell science Vol. 121; no. 13; pp. 2130 - 2135
Main Authors Harper, Claire V, Cummerson, Joanne A, White, Michael R.H, Publicover, Stephen J, Johnson, Peter M
Format Journal Article
LanguageEnglish
Published England The Company of Biologists Limited 01.07.2008
Subjects
Acrosome - physiology
Acrosome Reaction
Animals
Exocytosis
Female
Humans
Kinetics
Male
Membrane Fusion
Microscopy, Fluorescence
Sperm Capacitation
Sperm-Ovum Interactions
Spermatozoa - physiology
Spermatozoa - ultrastructure
Zona Pellucida - physiology
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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.
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ISSN:0021-9533
1477-9137
DOI:10.1242/jcs.030379