sn-1,2-Diacylglycerol levels increase in progesterone-stimulatedXenopus laevis oocytes

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Abstract
Full-grown Xenopus laevis oocytes resume meiosis from prophase arrest in response to progesterone stimulation. Recent studies have shown that the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), a very potent activator of protein kinase C, can also induce the resumption of meiosis in amphibian oocytes. We have investigated the possibility that sn-1,2-diacylglycerol (DAG), the intracellular activator of protein kinase C, may be involved in the pathway normally used by progesterone. We have found that full-grown oocytes arrested in meiotic prophase contain 48 ± 5 pmoles DAG/oocyte. This level increases within the first 5 minutes following the addition of progesterone and reaches a maximum of 75 ± 10 pmoles following 60 minutes of steroid stimulation. Progesterone induces the up-regulation of a Na+ /H+ antiport in the plasma membrane of the oocyte causing an increase in pHi following 60 minutes of steroid stimulation. We have found that the addition of 200 μM DAG (1,2-dioctanoylglycerol, diC8) to the culture medium can cause a partial up-regulation of this Na+ /H+ pump in the absence of hormonal stimulation. These results suggest that DAG and protein kinase C may be involved in regulating certain aspects of meiotic maturation in progesterone-stimulated Xenopus oocytes.