Williams C J, Mehlmann L M, Jaffe L A, Kopf G S, Schultz R M
Center for Research on Reproduction and Women's Health, University of Pennsylvania Health System, University of Pennsylvania, Philadelphia 19104, USA.
Dev Biol. 1998 Jun 1;198(1):116-27.
Embryonic development is initiated after the fertilizing sperm contacts the egg and triggers a process termed "egg activation," resulting in calcium release, cortical granule exocytosis, recruitment of maternal mRNAs, and cell cycle resumption. Heterotrimeric guanine nucleotide-binding proteins (G proteins) may be involved in mouse egg activation since inhibition of G protein beta gamma subunits partially inhibits sperm-induced cell cycle resumption. In addition, specific events of egg activation can be initiated in the absence of sperm by acetylcholine stimulation of mouse eggs overexpressing the human m1 muscarinic receptor, a G protein-coupled receptor. In somatic cell, G proteins in the Gq family couple ligand stimulation of the m1 muscarinic receptor to activation of phospholipase C, resulting in the production of inositol 1,4,5-trisphosphate (IP3) and IP3-mediated release of intracellular calcium. Since IP3-mediated calcium release is involved in egg activation at fertilization, we have examined the role of Gq family G proteins in both sperm-independent (muscarinic receptor-mediated) and sperm-induced egg activation using a function-blocking antibody raised against the common C-terminal region of Gq and G11 proteins. We show that this antibody effectively inhibits Gq family G proteins in mouse eggs by demonstrating that the antibody inhibits egg activation in response to stimulation of the m1 muscarinic receptor. This same antibody, however, does not inhibit sperm-induced egg activation events. These results indicate that although activation of Gq family G proteins can result in egg activation in the mouse, it is unlikely that these proteins are used by the sperm to initiate egg activation at fertilization.
胚胎发育在受精精子与卵子接触并触发一个称为“卵子激活”的过程后启动，导致钙释放、皮质颗粒胞吐、母体mRNA募集和细胞周期恢复。异源三聚体鸟嘌呤核苷酸结合蛋白（G蛋白）可能参与小鼠卵子激活，因为抑制G蛋白βγ亚基可部分抑制精子诱导的细胞周期恢复。此外，通过对过表达人m1毒蕈碱受体（一种G蛋白偶联受体）的小鼠卵子进行乙酰胆碱刺激，可在无精子的情况下启动卵子激活的特定事件。在体细胞中，Gq家族的G蛋白将m1毒蕈碱受体的配体刺激与磷脂酶C的激活偶联起来，导致肌醇1,4,5-三磷酸（IP3）的产生以及IP3介导的细胞内钙释放。由于IP3介导的钙释放参与受精时的卵子激活，我们使用针对Gq和G11蛋白共同C末端区域产生的功能阻断抗体，研究了Gq家族G蛋白在非精子依赖（毒蕈碱受体介导）和精子诱导的卵子激活中的作用。我们通过证明该抗体抑制对m1毒蕈碱受体刺激产生的卵子激活，表明该抗体有效抑制小鼠卵子中的Gq家族G蛋白。然而，同一抗体并不抑制精子诱导的卵子激活事件。这些结果表明，尽管Gq家族G蛋白的激活可导致小鼠卵子激活，但这些蛋白不太可能被精子用于在受精时启动卵子激活。
