Oogenesis and oocyte isolation.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
R L Varnold
Publications and source records attributed to R L Varnold.
Microinjected GTP-gamma-S inhibits progesterone-induced maturation of Xenopus oocytes.
GTP-gamma-S inhibits progesterone-induced maturation of Xenopus laevis oocytes and induces a rise in their cAMP levels. GTP-gamma-S does not inhibit MPF-induced maturation. Although GTP-gamma-S prevents the progesterone-induced increases in protein synthesis and phosphorylation, it has no effect on the basal rates of either. GTP-gamma-S also prevents the initial DAG drop induced by progesterone. GDP-beta-S effects are ambiguous, but it seems not to affect progesterone-induced maturation. These results suggest that although G-proteins are associated with the pathways affected by progesterone, the effects of progesterone are not mediated by a typical receptor/G-protein/effector interaction.
Animals↗
Protein kinase C and progesterone-induced maturation in Xenopus oocytes.
Though progesterone-induced maturation has been studied extensively in Xenopus oocytes, the mechanism whereby the prophase block arrest is released is not well understood. The current hypothesis suggests that a reduction in cAMP and subsequent inactivation of cAMP-dependent protein kinase is responsible for reentry into the cell cycle. However, several lines of evidence indicate that maturation can be induced without a concomitant reduction in cAMP. We show that the mass of diacylglycerol in whole oocytes and plasma membranes decreases 29% and 10% respectively, within the first 15 sec after the addition of progesterone. Diacylglycerol in plasma membranes further decreased 59% by 5 min. We also show that the protein kinase C inhibitors sphingosine and staurosporine can induce oocyte maturation. In addition, the synthetic diglyceride, DiC8, and microinjected PKC can inhibit or delay progesterone-induced maturation. These results together suggest that a transient decrease in protein kinase C activity may regulate entry into the cell cycle. The mechanism whereby DAG is decreased in response to progesterone is unclear. Initial studies show that progesterone leads to a decrease in IP3 suggesting that progesterone may act by reducing the hydrolysis of PIP2. On the other hand, progesterone caused a decrease in the amount of [3H]arachidonate labelling in DAG during the same time suggesting that progesterone may stimulate lipase activity. The relationship between postulated changes in the PKC pathway and those hypothesized for the PKA pathway are discussed.
Alkaloids↗
Decreased NADH-oxidoreductase activities as an early response in rat liver to the carcinogen 2-acetylaminofluorene.
Reduced nicotinamide adenine dinucleotide (NADH):ferricyanide reductase and DT-diaphorase specific activity in total homogenates of rat liver are markedly decreased as a very early biochemical event of hepatocarcinogenesis induced by the carcinogen 2-acetylaminofluorene (AAF). A 50 to 75% decrease in NADH:ferricyanide reductase was observed after 1 day of AAF (0.025% in the diet) feeding and persisted throughout a 7-week continuum of AAF administration. Carcinogen added directly to cell extracts had no effect. Similar results were obtained with single injections of either AAF or diethylnitrosamine. Xanthine dehydrogenase was also reduced in liver following AAF administration to nearly the same extent as NADH:ferricyanide reductase and DT-diaphorase. Total NADH-cytochrome c reductase and mitochondrial activity as estimated from succinic dehydrogenase were not affected by carcinogen administration relative to basal dietary controls. The reduced nicotinamide adenine dinucleotide phosphate:cytochrome c reductase that functions in drug detoxification was elevated. With livers of animals fed 4-acetamidophenol, a hepatotoxin chemically related to AAF, small decreases were noted in NADH:ferricyanide reductase, but not in xanthine dehydrogenase nor in DT-diaphorase. Initial lowering of these activities in the livers of the carcinogen-treated animals is preceded by or concomitant with a reduction in the levels of extramitochondrial pyridine nucleotides known from other studies to result from DNA damage.
2-Acetylaminofluorene↗
Phosphorylation of membrane-located proteins of soybean in vitro and response to auxin.
Isolated membranes of soybean incorporate (32)P from gamma-[(32)P]ATP in vitro. The incorporation was rapid and did not require added calcium. When displayed on 10% sodium dodecyl sulfate-polyacrylamide gels, several protein bands were revealed. An apparent auxin (2,4-dichlorophenoxyacetic acid) stimulation of (32)P incorporation into material from membrane vesicles insoluble in trichloroacetic acid-perchloric acid may be reflected partly in enhanced incorporation into protein bands with apparent molecular weights of 45,000 and 50,000. Additionally, a low molecular weight component was sometimes observed where incorporation was stimulated 2- to 3-fold by auxin. However, protein-bound radioactivity represented only a small fraction of the total radioactivity of the acid-insoluble material. Other labeled constituents, not retained on the gels, may contribute to the apparent, rapid (10 s or less) auxin response of the isolated membranes. Stimulation of incorporation into the low molecular weight component was given by diglyceride plus calcium, constituents known to augment protein kinase activities in other systems.
Journal Article↗
Changes in protein kinase activities during 2-acetylaminofluorene-induced hepatocarcinogenesis in the rat.
Livers of rats fed the carcinogen 2-acetylaminofluorene (AAF) at a concentration of 0.025% were analyzed for protein kinase activities with [gamma 32P]ATP as substrate and either endogenous or exogenous (casein or histone) protein acceptors both in the presence or absence of cyclic nucleotides. Total protein kinase activity of the nuclear fraction, with exogenous histone or casein as substrate, was elevated during the first week of carcinogen administration. Total cytoplasmic kinase activities exhibited a pattern of activity change with maxima at about 25 and 42-49 days after the onset of carcinogen administration. Cyclic AMP levels rose steadily to approximately a 4-fold elevation by day 49 in livers of animals receiving carcinogen with the increase beginning prior to the development of externally visible nodular hyperplastic lesions. The findings demonstrate consistent and reproducible patterns of change in protein kinase activities that accompany AAF-induced hepatocarcinogenesis in the rat and provides the basis for a more detailed investigation of specific kinases.
2-Acetylaminofluorene↗