Spatiotemporal analysis of [Ca2+]i rises in mouse eggs after intracytoplasmic sperm injection (ICSI).
Intracytoplasmic sperm injection (ICSI) into mammalian eggs induces repetitive rises in intracellular Ca2+ concentration ([Ca2+]i) which are the pivotal signal in fertilization. Spatiotemporal aspects of [Ca2+]i rises following ICSI into the periphery of mouse eggs were investigated with high-speed confocal microscopy. The first Ca2+ response was generated 25-30 min after ICSI, when [Ca2+]i increased slowly and reached a certain level. The [Ca2+]i rise occurred synchronously over the ooplasm, attained the peak in 40-70 s, and lasted for 5-7 min. Succeeding Ca2+ responses occurred at intervals of 20-30 min, associated with the faster rate of [Ca2+]i rise and the shorter duration as Ca2+ oscillations progressed. The [Ca2+]i rises took the form of a wave that started from an arbitrary cortical region, but not from the vicinity of the injected sperm head. The Ca2+ wave became more pronounced and propagated across the egg faster in the later Ca2+ responses. An artifactual [Ca2+]i rise was inevitably produced during the ICSI procedure. The larger artifact affected the subsequent first Ca2+ response, resulting in the faster [Ca2+]i rise (time to peak, 10-20 s), slight spatial heterogeneity of [Ca2+]i rise in the ooplasm (but not a wave) and the shorter duration (3-4 min). The artifact slightly affected the amplitude of the second Ca2+ response, but little affected the later Ca2+ responses. It is suggested that the factor(s) that leaked out of the injected spermatozoon diffuses to a wide area and sensitizes Ca2+ channels of the endoplasmic reticulum to induce Ca2+ release synchronously over the ooplasm. The enhanced sensitization leads to propagating Ca2+ release initiated from the cortex that is more sensitive to the sperm factor.
Sato
M S
MS
Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Japan. mnsato@nips.ac.jp
Yoshitomo
M
M
Mohri
T
T
Miyazaki
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D008815:Mice, Inbred Strains; D009865:Oocytes / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D020554:Sperm Injections, Intracytoplasmic
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D002118:Calcium