Mehlmann L M, Carpenter G, Rhee S G, Jaffe L A
Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut, 06032, USA.
Dev Biol. 1998 Nov 1;203(1):221-32. doi: 10.1006/dbio.1998.9051.
The initiation of Ca2+ release at fertilization of mammalian eggs requires inositol trisphosphate (Miyazaki et al., 1992, Science 257, 251-255), indicating that an enzyme of the phospholipase C family is probably activated. Because Ca2+ release at fertilization in echinoderm eggs is initiated by SH2 domain-mediated activation of phospholipase Cgamma (Carroll et al., 1997, J. Cell Biol. 138, 1303-1311), we examined the possible role of PLCgamma in initiating Ca2+ release at fertilization in mouse eggs. Both PLCgamma isoforms, PLCgamma1 and PLCgamma2, are present in mouse eggs and sperm, and stimulation of these enzymes in the egg by way of an exogenously expressed PDGF receptor causes Ca2+ release. Recombinant SH2 domains of PLCgamma1 and PLCgamma2 inhibit PLCgamma1 and PLCgamma2 activation by the PDGF receptor, completely preventing Ca2+ release in response to PDGF when injected at an approximately 20- to 40-fold excess over the concentrations of endogenous proteins. However, even at an approximately 100- to 400-fold excess over endogenous protein levels, PLCgamma1 and PLCgamma2 SH2 domains do not inhibit Ca2+ release at fertilization. These findings indicate that Ca2+ release at fertilization of mouse eggs does not require SH2-domain-mediated activation of PLCgamma. However, activation of PLCgamma in the egg by an alternative pathway, or introduction of activated PLCgamma from the sperm, may be important.
哺乳动物卵子受精时Ca2+释放的起始需要肌醇三磷酸（宫崎等人，1992年，《科学》257卷，251 - 255页），这表明磷脂酶C家族的一种酶可能被激活。由于棘皮动物卵子受精时Ca2+释放是由SH2结构域介导的磷脂酶Cγ激活引发的（卡罗尔等人，1997年，《细胞生物学杂志》138卷，1303 - 1311页），我们研究了PLCγ在小鼠卵子受精时引发Ca2+释放中的可能作用。PLCγ的两种同工型，PLCγ1和PLCγ2，都存在于小鼠卵子和精子中，通过外源性表达的血小板衍生生长因子（PDGF）受体刺激卵子中的这些酶会导致Ca2+释放。PLCγ1和PLCγ2的重组SH2结构域抑制PDGF受体对PLCγ1和PLCγ2的激活，当以比内源性蛋白质浓度高约20至40倍的量注射时，能完全阻止对PDGF的Ca2+释放反应。然而，即使以比内源性蛋白质水平高约100至400倍的量，PLCγ1和PLCγ2的SH2结构域也不会抑制受精时的Ca2+释放。这些发现表明小鼠卵子受精时的Ca2+释放不需要SH2结构域介导的PLCγ激活。然而，通过替代途径激活卵子中的PLCγ，或从精子中引入活化的PLCγ，可能很重要。
