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J Gautier

Publications and source records attributed to J Gautier.

At least 19 recordsLinked to original sources
PubMed1992

A cdc2-related kinase oscillates in the cell cycle independently of cyclins G2/M and cdc2.

The Eg1 gene in Xenopus laevis is related in sequence to the cdc2+ gene. We show here that the Eg1 gene product (cdk2) possesses histone H1 protein kinase activity and binds to PSTAIR antibodies as well as to Sepharose beads linked to the 13-kDa product of the suc 1 gene (p13suc1). Eg1 protein kinase is active only in an Mr approximately 200,000 complex with other proteins but is not associated with any of the three known Xenopus mitotic cyclins or with any newly synthesized protein in egg extracts that exhibit cell cycle oscillations in vitro. The protein kinase activity of Eg1 oscillates in the mitotic cell cycle, being high in M-phase and low in interphase. Hyperactivation of cdc2 kinase by the addition of cyclin A has no effect on the activity or oscillatory behavior of Eg1. Inhibition of cdc2 kinase activation by emetine or RNase treatment of oscillating extracts does not inhibit the activation of Eg1 but does block deactivation normally seen during exit from mitosis. These results indicate that Eg1 is regulated by a cell cycle clock independently of cyclin and cdc2 kinase.

Amino Acid Sequence↗
PubMed1991

cdc25 is a specific tyrosine phosphatase that directly activates p34cdc2.

cdc25 controls the activity of the cyclin-p34cdc2 complex by regulating the state of tyrosine phosphorylation of p34cdc2. Drosophila cdc25 protein from two different expression systems activates inactive cyclin-p34cdc2 and induces M phase in Xenopus oocytes and egg extracts. We find that the cdc25 sequence shows weak but significant homology to a phylogenetically diverse group of protein tyrosine phosphatases. cdc25 itself is a very specific protein tyrosine phosphatase. Bacterially expressed cdc25 directly dephosphorylates bacterially expressed p34cdc2 on Tyr-15 in a minimal system devoid of eukaryotic cell components, but does not dephosphorylate other tyrosine-phosphorylated proteins at appreciable rates. In addition, mutations in the putative catalytic site abolish the in vivo activity of cdc25 and its phosphatase activity in vitro. Therefore, cdc25 is a specific protein phosphatase that dephosphorylates tyrosine and possibly threonine residues on p34cdc2 and regulates MPF activation.

Amino Acid Sequence↗
PubMed1991

Cyclin B in Xenopus oocytes: implications for the mechanism of pre-MPF activation.

Using a polyclonal antibody raised against B2 cyclin from Xenopus laevis, we show that prophase-arrested Xenopus oocytes contain a stockpile of cyclin B2 protein. During progesterone-induced maturation, an increase in the synthesis of cyclin B2 is observed, although Western blotting experiments show that this new synthesis does not significantly increase the mass of cyclin over the maternal stockpile. In the oocyte cyclin B2 is already present in two forms which differ in the extent of phosphorylation, but the phosphorylated form becomes predominant as oocytes progress towards germinal vesicle breakdown (GVBD), coincident with cdc2 protein kinase activation. These two events do not depend upon formation of a new complex between cyclin and cdc2 protein kinase, since these two proteins are already found associated in resting oocytes, prior to activation of the kinase.

Animals↗
PubMed1990

The cyclin B2 component of MPF is a substrate for the c-mos(xe) proto-oncogene product.

Previous studies from this laboratory have shown that purified MPF from Xenopus eggs contains cyclin B2 complexed with cdc2 kinase. The activation of MPF during oocyte maturation is known to require expression of the c-mos(xe) proto-oncogene. We show here that immunoprecipitates of either v-mos from Moloney murine sarcoma virus-transformed NIH 3T3 cells or c-mos from Xenopus eggs phosphorylate cyclin B2 in vitro. Phosphopeptide analysis reveals a pattern similar to that observed with cdc2 kinase. Moreover, ablation of c-mos(xe) from oocytes by antisense oligonucleotide injection reduces the rate of cyclin B2 phosphorylation in oocyte extracts by 40%. These results suggest that the mechanism of activation of MPF by c-mos(xe) involves phosphorylation of the cyclin component.

Animals↗
PubMed1990

Cyclin is a component of maturation-promoting factor from Xenopus.

Highly purified maturation-promoting factor (MPF) from Xenopus eggs contains both cyclin B1 and cyclin B2 as shown by Western blotting and immunoprecipitation using Xenopus anti-B-type cyclin antibodies. Immunoprecipitates with these antibodies display the histone H1 kinase activity characteristic of MPF, for which exogenously added B1 and B2 cyclins are both substrates. Protein kinase activity against cyclin oscillates in maturing oocytes and activated eggs with the same kinetics as p34cdc2 kinase activity. These data indicate that B-type cyclin is the other component of MPF besides p34cdc2.

Adenosine Triphosphate↗
PubMed1989

Dephosphorylation and activation of Xenopus p34cdc2 protein kinase during the cell cycle.

Genetic studies in the fission yeast Schizosaccharomyces pombe have established that a critical element required for the G2----M-phase transition in the cell cycle is encoded by the cdc2+ gene. The product of this gene is a serine/threonine protein kinase, designated p34cdc, that is highly conserved functionally from yeast to man2 and has a relative molecular mass of 34,000 (34 K). Purified maturation-promoting factor (MPF) is a complex of p34cdc2 and a 45K substrate that appears in late G2 phase and is sufficient to drive cells into mitosis. This factor has been identified in all eukaryotic cells, and in vitro histone H1 is the preferred substrate for phosphorylation. The increase in the activity of H1 kinase in M-phase is associated with a large increase in total cell protein phosphorylation which is believed to be a consequence of MPF activation. We show here that the H1 kinase activity of p34cdc2 oscillates during the cell cycle in Xenopus, and maximal activity correlates with the dephosphorylated state of p34cdc2. Direct inactivation of MPF in vitro is accompanied by phosphorylation of p34cdc2 and reduction of its protein kinase activity.

Animals↗
PubMed1989

Mammalian growth-associated H1 histone kinase: a homolog of cdc2+/CDC28 protein kinases controlling mitotic entry in yeast and frog cells.

Mammalian growth-associated H1 histone kinase, an enzyme whose activity is sharply elevated at mitosis, is similar to cdc2+ protein kinase from Schizosaccharomyces pombe and CDC28 protein kinase from Saccharomyces cerevisiae with respect to immunoreactivity, molecular size, and specificity for phosphorylation sites in H1 histone. Phosphorylation of specific growth-associated sites in H1 histone is catalyzed by yeast cdc2+/CDC28 kinase, as shown by the in vitro thermal lability of this activity in extracts prepared from temperature-sensitive mutants. In addition, highly purified Xenopus maturation-promoting factor catalyzes phosphorylation of the same sites in H1 as do the mammalian and yeast kinases. The data indicate that growth-associated H1 kinase is encoded by a mammalian homolog of cdc2+/CDC28 protein kinase, which controls entry into mitosis in yeast and frog cells. Since H1 histone is known to be an in vivo substrate of the mammalian kinase, this suggests that phosphorylation of H1 histone or an H1 histone counterpart is an important component of the mechanism for entry of cells into mitosis.

Animals↗
PubMed1989

Maturation-promoting factor and the regulation of the cell cycle.

Maturation-promoting factor (MPF) is a cell cycle control element able to cause metaphase when injected into amphibian oocytes or when incubated with nuclei in a cell-free system. Highly purified MPF consists of a complex between a 34K (K = 10(3) Mr) serine/threonine protein kinase, identified as a Xenopus homolog of the cdc2+ gene product, p34cdc2, and a 45K substrate, identified as a Xenopus B-type cyclin. p34cdc2 is also present in purified preparations of chromatin-derived growth-associated histone H1 kinase from Novikoff hepatoma cells. p34cdc2 is active when dephosphorylated and inactive when phosphorylated during oocyte meiotic cell cycles and in mitotic cell cycles following egg activation. Analysis of the substrate specificity of p34cdc2 indicates a consensus sequence for phosphorylation of (K/R)S/TP(X)K/R. Among substrates identified with this consensus are histone H1 and the pp60c-src proto-oncogene, which is known to be activated and phophorylated in mitosis. MPF injection into oocytes activates ribosomal protein S6 kinase II, which is also a lamin kinase. The mechanism of activation is indirect, possibly involving the c-src proto-oncogene. Continued analysis of regulation of MPF activation/inactivation and characterization of substrates for phosphorylation will have important implications for cell cycle and cell growth control.

Animals↗
PubMed1988

Purified maturation-promoting factor contains the product of a Xenopus homolog of the fission yeast cell cycle control gene cdc2+.

In the fission yeast S. pombe, the Mr = 34 kd product of the cdc2+ gene (p34cdc2) is a protein kinase that controls entry into mitosis. In Xenopus oocytes and other cells, maturation-promoting factor (MPF) appears in late G2 phase and is able to cause entry into mitosis. Purified MPF consists of two major proteins of Mr approximately equal to 32 kd and 45 kd and expresses protein kinase activity. We report here that antibodies to S. pombe p34cdc2 are able to immunoblot and immunoprecipitate the approximately equal to 32 kd component of MPF from Xenopus eggs. The Mr approximately equal to 32 kd and 45 kd proteins exist as a complex that expresses protein kinase activity. These findings indicate that a Xenopus p34cdc2 homolog is present in purified MPF and suggest that p34cdc2 is a component of the control mechanism initiating mitosis generally in eukaryotic cells.

Animals↗
PubMed1988

Differential cytolocalization of prosomes in axolotl during oogenesis and meiotic maturation.

The prosomes, a novel type of small RNA-protein complex previously characterized in avian and mammalian cells, were isolated from axolotl (Ambystoma mexicanum) oocytes and identified by sedimentation analysis and protein composition. The prosomal nature of these particles was further ascertained by immunoblot analysis with anti-duck prosome monoclonal antibodies. By in vitro [35S]methionine labelling, de novo synthesis of prosomal proteins could be detected neither during oogenesis nor meiotic maturation. The results obtained by both indirect immunofluorescence and immunoblot analyses demonstrated a dramatic change in the localization of prosomal antigens during oocyte development. They were initially detected in the oocyte cytoplasm, during oocyte growth. At the end of vitellogenesis (stages V-VI), they entered the nucleus (germinal vesicle) and were accumulated there to the highest concentration. During oocyte maturation, after nuclear envelope breakdown, prosomal antigens were found to be localized again in the cytoplasm, until fertilization. No specific localization of prosomal antigens in mature oocytes, unfertilized and fertilized eggs was observed within the oocyte cytoplasm in relation to the cytoplasmic rearrangements leading to grey crescent formation.

Ambystoma mexicanum↗
PubMed1986

Changes in patterns of protein synthesis in axolotl oocytes during progesterone-induced maturation.

Patterns of protein phosphorylation and synthesis during axolotl (Ambystoma mexicanum) oocyte maturation were studied by incorporation of [32P]orthophosphate and [35S]methionine into polypeptides, followed by two-dimensional gel electrophoresis. Various alterations were observed after progesterone treatment: de novo appearance of [35S]methionine-labelled polypeptides, a quantitative increase in previously synthesized proteins and a quantitative decrease in or disappearance of other previously synthesized proteins. Changes in 32P- and 35S-labelling were observed very early during maturation. Neither prior oocyte enucleation nor alpha-amanitin treatment had a significant effect on these changes. Stimulation with MPF provided the same final protein pattern as PG treatment. However, cholera toxin inhibited all the changes seen during maturation. Comparisons between the patterns of [35S]methionine- and [32P]phosphate-labelling provide further information on the biochemical events that take place during oocyte maturation.

Ambystoma mexicanum↗
PubMed1985

A three-step scheme for gray crescent formation in the rotated axolotl oocyte.

It has been shown that various inhibitors of protein synthesis can elicit the precocious appearance of a gray crescent (GC) in in vitro maturing, nonactivated Ambystoma mexicanum oocytes. However, evidence has now been obtained that these treatments fail to induce GC formation when the oocytes are enucleated before initiation of maturation. The ability to form a GC is reestablished in enucleated oocytes by the injection of nucleoplasm from a normal oocyte, either before or after the injection of the inhibitor. In the latter case, the GC appears very rapidly, even though protein synthesis is at about 1/10th that of the control enucleated oocyte, after treatment with diphtheria toxin (final concentration 10(-8) M) as an inhibitor. One or several nuclear factors, in conjunction with inhibition of protein synthesis, are therefore essential for early symmetrization. The corrective nuclear factor is already present in the germinal vesicle of young oocytes, at the very beginning of vitellogenesis. It is not species specific, since enucleated axolotl oocytes can be symmetrized with Pleurodeles or even Xenopus oocyte nucleoplasm. Moreover, it has been shown that the nuclear-cytoplasmic interaction is possible only when cytoplasmic maturation has been proceeding for at least 10 hr after exposure to progesterone (at 18 degrees C). A three-step process as a prerequisite of GC formation in the oocyte is proposed: Cytoplasmic maturation must proceed till a reactive state is attained, allowing interactions with nuclear factors; Nuclear factor(s) interact(s) with matured cytoplasm; Inhibition of protein synthesis triggers GC formation. Sequence of steps 2 and 3 can be experimentally inverted but must always be preceded by step 1. Since a sharp reduction in amino acid incorporation has also been found in normally fertilized eggs just prior to GC formation, it is suggested that the scheme described above could be also applicable to normal symmetrization in this model system.

Ambystoma↗
PubMed1983

Plasma protein patterns in captive American kestrels.

Plasma proteins of the American kestrel (Falco sparverius) were analyzed by polyacrylamide disc electrophoresis for 3 different groups of birds: laying and non-laying females, and males. The electrophoretic patterns were homogeneous for each group and showed differences in the mobility of some proteins among the 3 groups. There was no significant difference among the 3 groups in the amount of proteins and in the standard parameter of albumin to globulin ratio.

Animals↗
PubMed1978

Deanol, lithium and placebo in the treatment of tardive dyskinesia. A double-blind crossover study.

A double-blind crossover study on the effects of deanol and lithium carbonate was conducted on a sample of 29 chronic schizophrenic patients with tardive dyskinesia. In addition to his usual treatment with different neuroleptics, each patient received during an 8-week period either deanol, lithium carbonate or placebo. A 4-week wash-out period was inserted between each of the 8-week periods of experimental treatment of the tardive dyskinesia. The administration of either deanol, lithium carbonate or placebo added to the neuroleptic treatment did not produce a statistically significant improvement of tardive dyskinesia in our patient population as a whole. Favorable and unfavorable responses are discussed.

Adult↗
PubMed1978

Pharmacokinetic interaction between amitriptyline and neuroleptics.

The influence of amitriptyline on the plasma level of various neuroleptics was studied in 25 chronic schizophrenic patients. The study lasted 20 weeks. Patients were kept first 4 weeks on their former neuroleptic medication, with amitriptyline added for 12 subsequent weeks, and withdrawn during the last 4 weeks when only the neuroleptic medication was continued unchanged. The plasma level of neuroleptics was assayed by gas-liquid chromatography, once weekly throughout the study. The amitriptyline plasma level was also evaluated once weekly during the 12 weeks of its administration. The mean neuroleptic plasma values for each 4-week period were pooled together in three groups: aliphatic, piperdine and piperazine phenothiazine derivatives. Amitriptyline provoked some increase of the plasma level of all phenothiazine derivatives. This augmentation was significant only transitorily, however. The putative mechanisms of this neuroleptic tricyclic antidepressant interaction are discussed.

Adult↗
PubMed1977

Influence of the antiparkinsonian drugs on the plasma level of neuroleptics.

The interaction between various neuroleptics and antiparkinsonian drugs was analyzed by measuring the neuroleptic plasma level before and after withdrawal of antiparkinsonian drugs. The population completing the study consisted of 32 chronic schizophrenics treated with chlorpromazine (8), levomepromazine (14), thioridazine (6), or haloperidol (4). Twenty-five were also receiving benztropine; 4, trihexyphenidyl; and 3, procyclidine. During the first 4 weeks patients remained on neuroleptics and antiparkinsonians, the latter being withdrawn during the 5th week, and the neuroleptics alone being administered during 16 following weeks. The plasma level of neuroleptics was assayed by gas liquid chromatography, once weekly in the morning at two different times. The analysis of variance showed a significant difference in neuroleptic plasma level when patients took neuroleptics only versus the period they had received neuroleptics and antiparkinsonians. The multiple comparison based on Studentized range Q0-05 revealed a significant progressive increase of neuroleptic plasma level during 12 weeks after withdrawal of antiparkinsonian drugs after which a plateau was reached. The hypothetical mechanisms of action of antiparkinsonians on neuroleptic plasma level are discussed.

Adult↗