Xenopus Gqα subunit activates the phosphatidylinositol pathway in Xenopus oocytes but does not consistently induce oocyte maturation

Abstract

We cloned the Xenopus laevis form of Gqα subunit to study its effects on oocyte maturation. Injection of Xenopus Gqα 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 (Tin), due to the opening of Ca2+-dependent Cl- channels. The Tin amplitude developed over several hours and disappeared by 24 hr. Diacylglycerol levels were found to parallel the appearance and disappearance of the Tin. The concurrent decline of Tin values and diacylglycerol was not due to a failure in the synthesis of Gqα protein, which was produced continuously for >24 hr. After Xenopus Gqα 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 Goα G protein consistently underwent GVBD but did not acquire Tin. 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.