Egg activation: Upstream of the fertilization calcium signal

Abstract

Interaction of sperm and egg at fertilization induces well-coordinated molecular events including specific recognition between species, adhesion and fusion, that lead to the formation of a zygote, a totipotent cell that develops into a new individual. A calcium signal, common to a great number of species, from marine invertebrates to mammals, is essential to activate the metabolism of the unfertilized oocyte. However, how fertilization triggers this calcium signal and initiates development of the early embryo is far from understood. The signaling pathways activated in eggs may be similar to those described in somatic cells, since changes in intracellular free calcium and in mitosis activating protein (MAP) kinase activity occur in both systems after activation. Several hypotheses are currently proposed, implying a spermatic ligand binding to a specific receptor expressed at the egg surface, or where the fused sperm either allows the transit of external calcium into the egg or injects one (or several) activating factor(s). It is still not known which of these ideas is true. We concentrate in this review on the possible signaling pathways involving IP3 (inositol trisphosphate), since its production is involved in most species to generate the fertilization calcium wave.

An insufficient increase of cytosolic free calcium level results postovulatory aging-induced abortive spontaneous egg activation in rat

“…An increase of cytosolic free Ca 2+ (due to burst from internal stores) induces EA during fertilization [5,38,39]. Further, CI increases cytosolic free Ca 2+ level [35] and induces EA in several mammalian species [11,14,16,32,[40][41][42].…”

“…The fertilizing spermatozoa increases cytosolic free calcium (Ca 2+ ) level and induces egg activation (EA), which is morphologically characterized by an exit from M-II arrest, extrusion of second polar body (PB-II), cortical granules exocytosis and pronuclei formation [1,2]. The inositol 1,4,5-triphosphate-sensitive stores are the primary source for an increase of cytosolic free Ca 2+ level during EA [3][4][5]. Calcium ionophore A23187 (CI) increases cytosolic free Ca 2+ level and induces EA in vitro [6][7][8][9].…”

Flipping the switch: How a sperm activates the egg at fertilization

“…In vertebrates for example, G proteins can directly stimulate SFK activity (Hall et al, 1999;Ma et al, 2000;Luttrell and Lefkowitz, 2002), and, in turn, SFKs can modulate the activity of G proteins by tyrosine phosphorylation (Bushman et al, 1990;Luttrell et al, 1992). An increase in tyrosine kinase activity has been reported following fertilization in sea urchins (Ciapa and Epel, 1991;Ciapa and Chiri, 2000) and, recently, the first sea urchin upstream activating Src family kinase, named SFK1, was reported (Giusti et al, 2003).…”

Efeito de bloqueadores de canais de íons cálcio sobre espermatozóides e oócitos de hamsters fecundados in vivo e in vitro

“…A variação da concentração de cálcio intracelular induz o aumento de forma periódica (ondas) após a fertilização em oócitos de mamíferos como camundongos, hamsters e coelhos (SHIINA et al, 1993). (ALBERTS et al, 2002;BOOTMAN et al, 2001;CIAPA;CHIRI, 2000;MIYAZAKI, 1990;MIYAZAKI et al, 1993;WASSARMAN;ALBERTINI, 1994;WHITE;YUE, 1996).…”

“…Receptores de rianodina em alguns mamíferos (camundongos, bovinos e humanos) podem também estar presentes na membrana do retículo endoplasmático para a liberação de cálcio (CIAPA; CHIRI, 2000;KLINE, 2000).…”