Calcium signals for egg activation in mammals.
A dramatic increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) occurs in eggs at fertilization common to all animal species examined to date, and this serves as a pivotal signal for egg activation characterized by resumption of meiotic cell division and formation of the pronuclei. In mammalian eggs, repetitive [Ca(2+)](i) rises (Ca(2+) oscillations) each of which accompanies a propagating wave across the egg occur due to release of Ca(2+) from the endoplasmic reticulum mainly through type 1 inositol 1,4,5-trisphosphate (IP(3)) receptor. Ca(2+) oscillations are induced by a cytosolic sperm factor driven into the egg cytoplasm upon sperm-egg fusion. A current strong candidate of the sperm factor is a novel sperm-specific isozyme of phospholipase C (IP(3)-producing enzyme), PLCzeta. Recent extensive research has reveled characteristics of PLCzeta such as the Ca(2+) oscillation-inducing activity after injection of PLCzeta-encoding RNA or recombinant PLCzeta into mouse eggs, extremely high Ca(2+)-sensitivity of the enzymatic activity in vitro, and nuclear translocation ability possibly related to cell-cycle-dependent regulation of Ca(2+) oscillations. [Ca(2+)](i) rises cause successive activation of calmodulin-dependent kinase II and E3 ubiquitin ligase, lead to proteolysis of ubiquitinated cyclin B1 and inactivation of metaphase-promoting factor (Cdk1/cyclin B1 complex), and result in the release of eggs from meiotic arrest.
Miyazaki
Shunichi
S
Department of Physiology, Tokyo Women's Medical University School of Medicine, Japan. shunm@research.twmu.ac.jp
Ito
Masahiko
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D005260:Female; D005306:Fertilization; D008297:Male; D008954:Models, Biological; D010063:Ovum / Q000378:metabolism*; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000378:metabolism
D002118:Calcium