Guttridge K L, Smith L D, Miledi R
Department of Psychobiology and Developmental, University of California, Irvine 92717-4550.
Proc Natl Acad Sci U S A. 1995 Feb 28;92(5):1297-301. doi: 10.1073/pnas.92.5.1297.
We cloned the Xenopus laevis form of Gq alpha subunit to study its effects on oocyte maturation. Injection of Xenopus Gq alpha mRNA into stage 6 oocytes activated the phospholipase C/phosphatidylinositol pathway. The oocyte membrane became permeable to calcium ions and was able to generate transient inward currents (T(in)), due to the opening of Ca(2+)-dependent Cl- channels. The T(in) amplitude developed over several hours and disappeared by 24 hr. Diacylglycerol levels were found to parallel the appearance and disappearance of the T(in). The concurrent decline of T(in) values and diacylglycerol was not due to a failure in the synthesis of Gq alpha protein, which was produced continuously for > 24 hr. After Xenopus Gq alpha mRNA injection, germinal vesicle breakdown (GVBD) was variable (0-100%) in stage 6 oocytes, whereas none of the stage 4 oocytes underwent GVBD. In contrast, stage 6 oocytes injected with mRNA encoding the Go alpha G protein consistently underwent GVBD but did not acquire T(in). Our results show that activation of phospholipase C is not an absolute requisite for the induction of maturation, although in oocytes of some frogs phospholipase C activation can trigger a pathway to GVBD.
我们克隆了非洲爪蟾Gqα亚基的形式，以研究其对卵母细胞成熟的影响。将非洲爪蟾Gqα mRNA注射到6期卵母细胞中可激活磷脂酶C/磷脂酰肌醇途径。由于Ca(2+)依赖性Cl-通道的开放，卵母细胞膜对钙离子变得通透，并能够产生瞬时内向电流（T(in)）。T(in)幅度在数小时内形成，并在24小时时消失。发现二酰基甘油水平与T(in)的出现和消失平行。T(in)值和二酰基甘油的同时下降并非由于Gqα蛋白合成失败，因为Gqα蛋白持续产生超过24小时。注射非洲爪蟾Gqα mRNA后，6期卵母细胞中的生发泡破裂（GVBD）是可变的（0-100%），而4期卵母细胞均未发生GVBD。相反，注射编码Goα G蛋白的mRNA的6期卵母细胞始终发生GVBD，但未获得T(in)。我们的结果表明，磷脂酶C的激活不是诱导成熟的绝对必要条件，尽管在某些青蛙的卵母细胞中，磷脂酶C的激活可以触发一条通向GVBD的途径。
