Spatiotemporal dynamics of the [Ca2+]i rise induced by microinjection of sperm extract into mouse eggs: preferential induction of a Ca2+ wave from the cortex mediated by the inositol 1,4,5-trisphosphate receptor.
Hamster sperm extract (SE) possessing Ca2+ oscillation-inducing activity was microinjected into the peripheral or central region of mouse eggs, and the first increase in intracellular Ca2+ concentration ([Ca2+]i), together with the spread of fluorescence-labeled SE in the ooplasm, was investigated by imaging with confocal microscopy. Injection into the periphery always induced a Ca2+ wave that started from the injection site after a delay of 5 to 30 s depending on the concentration of SE. The diluted SE caused a wave of two-step [Ca2+]i rises, which was always observed at fertilization. Injection into the center could induce a radial Ca2+ wave with relatively high dose of SE, but lower dose of SE caused a [Ca2+]i rise after a longer delay which was initiated synchronously over the ooplasm or was preceded in a peripheral area. Injection of diluted SE remarkably prolonged the delay time and reduced the rate of [Ca2+]i rise. The critical concentration of SE needed to induce [Ca2+]i rise was significantly lower in the periphery. These results indicate that the sensitivity to SE is higher in the cortex. SE-induced [Ca2+]i rises were blocked by an antibody against the type 1 inositol 1,4,5-trisphosphate receptor (InsP3R). The cortex was substantially more sensitive to injected InsP3 induction of Ca2+ release than the center. It is suggested that the cortex of mouse eggs may involve a functionally specialized organization of InsP3Rs and Ca2+ pools in which a cytosolic sperm factor(s) could act upon sperm-egg fusion to cause Ca2+ release, leading to the Ca2+ wave at fertilization.
Oda
S
S
Department of Physiology, Tokyo Women's Medical University School of Medicine, Shinjuku-ku, Tokyo, 162-8666, Japan. odasho@research.twmc.ac.jp
Deguchi
R
R
Mohri
T
T
Shikano
T
T
Nakanishi
S
S
Miyazaki
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000276:immunology / Q000378:metabolism*; D020013:Calcium Signaling; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D005260:Female; D005306:Fertilization / Q000502:physiology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence; D010063:Ovum / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000276:immunology / Q000378:metabolism*; D013094:Spermatozoa / Q000378:metabolism*; D013997:Time Factors
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D018160:Receptors, Cytoplasmic and Nuclear; C118500:inositol 3,4,5-trisphosphate; D002118:Calcium