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BHloveBGL
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2Â¥2013-11-03 00:29:21
бÑôÁõ·ã
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3Â¥2013-11-03 10:02:28
chaizhaoyang
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4Â¥2013-11-03 18:54:43
chaizhaoyang
Ìú³æ (³õÈëÎÄ̳)
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It was then crucial to assess whether gamete fusion takes place in conditions where the sperm stays in periphery of the egg cell, which nevertheless undergoes activation-like events. Occasionally, experiments in which no Ca2+ influx was detected, but in which there was a [Ca2+]Cyt elevation, showed that the sperm, which was not previously loaded with the fluorescent dye Fluo-3 (see Methods), was transiently labelled, probably by diffusion of dye from the egg cell. To test whether membrane fusion does take place in presence of 10 ¦ÌM GdCl3, a sperm cell was adhered to an egg cell with an R18-labelled membrane8. When R18 did not diffuse from the egg cell to the sperm, then no cell wall could be detected 3 h after gamete adhesion (n = 6). When, however, R18 diffused from the egg cell to the sperm, still visible in the periphery, then a cell wall would be detected around the egg cell (n = 3, Fig. 3). Although these experiments were done in parallel, without direct confirmation of fluxes and [Ca2+]Cyt, they strongly suggest that in the presence of 10 ¦ÌM GdCl3, although sperm incorporation is inhibited along with the onset of a global Ca2+ influx, cytosolic and membrane continuity between gametes may be established. In some cases this seems sufficient to trigger a rise in [Ca2+]Cyt and egg activation. It thus seems that although an increase in [Ca2+]Cyt is necessary and sufficient for activation, a global Ca2+ influx is not. The Ca2+ influx may, however, be associated with sperm incorporation and subsequent karyogamy. As the Ca2+-vibrating probe allows precise spatial analysis of Ca2+ fluxes, we made a careful scan of the membrane on adhered gametes in the presence of 10 ¦ÌM GdCl3. Ca2+ fluxes were recorded at different positions of the probe relative to the sperm.When a cell wall was detected (but sperm incorporation was inhibited), a global Ca2+ influx was not recorded but a localized Ca2+ influx of about 1.0 pmol cm¨C2 s¨C1 was detected close to the sperm, in a region that did not exceed 5 ¦Ìm diameter around the sperm position (n = 2; Fig. 4). Consequently, in the presence of 10 ¦ÌM GdCl3, a localized Ca2+ influx seems to persist close to the fusion site, which, in the absence of Gd3+ becomes the focal point for the spread of the Ca2+ influx wavefront5. Two mechanisms, differing in their Gd3+ sensitivity and their localization, could thus be involved in the entry of Ca2+ after gamete fusion. |
5Â¥2013-11-03 19:11:47













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