Repetitive sperm-induced Ca2+ transients in mouse oocytes are cell cycle dependent.
Mature mouse oocytes are arrested at metaphase of the second meiotic division. Completion of meiosis and a block to polyspermy is caused by a series of repetitive Ca2+ transients triggered by the sperm at fertilization. These Ca2+ transients have been widely reported to last for a number of hours but when, or why, they cease is not known. Here we show that Ca2+ transients cease during entry into interphase, at the time when pronuclei are forming. In fertilized oocytes arrested at metaphase using colcemid, Ca2+ transients continued for as long as measurements were made, up to 18 hours after fertilization. Therefore sperm is able to induce Ca2+ transients during metaphase but not during interphase. In addition metaphase II oocytes, but not pronuclear stage 1-cell embryos showed highly repetitive Ca2+ oscillations in response to microinjection of inositol trisphosphate. This was explored further by treating in vitro maturing oocytes at metaphase I for 4-5 hours with cycloheximide, which induced nuclear progression to interphase (nucleus formation) and subsequent re-entry to metaphase (nuclear envelope breakdown). Fertilization of cycloheximide-treated oocytes revealed that continuous Ca2+ oscillations in response to sperm were observed after nuclear envelope breakdown but not during interphase. However interphase oocytes were able to generate Ca2+ transients in response to thimerosal. This data suggests that the ability of the sperm to trigger repetitive Ca2+ transients in oocytes is modulated in a cell cycle-dependent manner.
Jones
K T
KT
Medical Research Council Experimental Embryology and Teratology Unit, St. George's Hospital Medical School, London, UK.
Carroll
J
J
Merriman
J A
JA
Whittingham
D G
DG
Kono
T
T
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D005307:Fertilization in Vitro; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D017136:Ion Transport; D008297:Male; D008677:Metaphase; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D009865:Oocytes / Q000378:metabolism*; D013094:Spermatozoa / Q000502:physiology
D015544:Inositol 1,4,5-Trisphosphate; D003513:Cycloheximide; D002118:Calcium