Calmodulin, gametes and fertilisation.
The role of calmodulin in fertilisation events was examined in a zona-free mouse system by using a selective calmodulin inhibitor, calmidazolium (1 microM). The effects of this antagonist were studied either on the ooplasmic calcium oscillations induced by fertilisation by using the Ca2+ indicator, fluo-3/AM, or on pronucleus formation 4 h later by using the nucleic acid stain, Syto-15. When the calmidazolium treatment was applied to one or the other gamete before insemination, the fertilisation process was affected only when spermatozoa were treated: most of the oocytes were partially fertilised as demonstrated by the profile of Ca2+ oscillations and the presence of polar bodies with no typical male and female pronuclei. When the treatment was applied during insemination, more than half the oocytes were unfertilised and only a few were partially fertilised. These results demonstrate that: (1) the calmodulin-dependent events taking place in spermatozoa before insemination appear essential at least for regular Ca2+ oscillations and for pronucleus formation; (2) the inhibition of calmodulin by calmidazolium applied to metaphase II oocytes before insemination has no major impact on their fertilising ability; and (3) at the time of gamete fusion calmodulin, either from the oocyte or from the spermatozoon, is essential for fertilisation to occur.
INSERM Unité 355, Clamart, France. anne.marie.courtot@inserm.ipsc.u-psud.fr
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Courtot
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Pesty
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Lefèvre
D020101:Acrosome Reaction / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology*; D002467:Cell Nucleus / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005307:Fertilization in Vitro; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D018613:Microscopy, Confocal; D009865:Oocytes / Q000502:physiology*; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*
D002147:Calmodulin; D004791:Enzyme Inhibitors; D007093:Imidazoles; C031938:calmidazolium; D002118:Calcium