PubMed Health⌕ Search

Biomedical subjects

J Brachet

Publications and source records attributed to J Brachet.

At least 19 recordsLinked to original sources
PubMed1988

Injection of an antibody against a p21 c-Ha-ras protein inhibits cleavage in axolotl eggs.

The presence of a ras protein was demonstrated in cleaving axolotl eggs by selective immunoprecipitation with a polyclonal antibody against a peptide encoded by the c-Ha-ras oncogene, cellular homolog of the v-Ha-ras oncogene of Harvey rat sarcoma virus. Injection of this antibody into axolotl oocytes subjected to progesterone treatment does not prevent meiotic maturation. Injection of the same antibody into a blastomere of axolotl eggs at the 2- or 4-cell stage causes cleavage arrest in the descendants of the injected blastomere. Cytological observations of the injected eggs show, in the arrested blastomeres, enlarged nuclei always surrounded by an intact nuclear envelope and containing uncondensed chromatin. The possible role of ras protein in meiosis and mitosis is discussed.

Ambystoma↗
PubMed1978

Cytochemical study of human lymphocytes stimulated by PHA in function of donor age.

The 3H-AM binding reflects the structural changes involved in the cellular differentiation. This parameter was studied during blastic transformation of human lymphocytes, in relation to the age of the donor. Although they are individual variations, the 3H-AM binding is higher in the young group than in the aged subjects, as well as the blast transformation score. These results indicate that the weak lymphocyte response to the mitogen lectine (PHA) stimulation could be related to some age-induced structural alterations of the chromatin, resulting in an irreversible blockage in G1, at least in some of the T lymphocytes.

Adult↗
PubMed1978

The hormonal induction of maturation in amphibian oocytes.

The maturation of the amphibian oocyte has been analyzed. Progesterone as well as organomercurials, lanthanum chloride and propranolol rapidly induce maturation. These chemicals are active only is applied on the cell surface. The mechanism seems to be an induction of the migration of Ca2+ from the cell membrane to the cytoplasm. K + may also play a role. Progesterone induced maturation involves synthesis of histone and histone kinase as well as several biologically active but chemically unidentified factors. cAMP does not seem to be directly involved, whereas protein phosphorylation is so.

Amphibians↗
PubMed1977

[The effects of diverse agents (Ca++ and K++ ionophores, organomercurials, dithiols, colchicine, and cytochalasin B) on the maturation and differentiation without cleavage in Chaetopterus eggs].

Induction of maturation in Chaetopterus oocytes requires the presence of Ca++ ions in the medium, but differentiation without cleavage can proceed in the absence of this cation. The Ca++ ionophore A 23187 induces both maturation and the cortical reaction provided that Ca++ ions are present in the medium differentiation without cleavage may follow. Valinomycin slowly induces germinal vesicle breakdown, which is followed by a sharp segregation between hyaloplasm and yolk. PHMPS, but not DTT, induces maturation. Differentiation without cleavage is more sensitive to colchicin than to cytochalasin B.

Animals↗
PubMed1977

Ionic requirements for induction of maturation (meiosis) in full-grown and medium-sized Xenopus laevis oocytes.

There is already good evidence that calcium ions are involved in the induction of maturation in full-grown amphibian oocytes; we show here that other cations (K+, Mg2+) also play a role in this process. Full-grown (1.3 mm in diameter) and medium-sized (0.8-1.0 mm in diameter) oocytes were compared in the present study. It was found that, provided the medium is K+-free, valinomycin induces maturation in full-grown, but not in medium-sized, oocytes. Increasing the CaCl2 (20 mM) or the MgSO4 (40 mM) content of the medium induces maturation in full-grown, but not in medium-sized, oocytes; however, the latter undergo germinal vesicle breakdown after treatment with either progesterone or ionophore A23187 if there is an excess of Ca2+ or Mg2+ in the medium. Maturation is possible in a Na+-free medium, but amiloride inhibits germinal vesicle breakdown when NaCl is present in the medium. It is concluded that maturation is controlled by changes in the balance between the various ions rather than by Ca2+ alone.

Amiloride↗
PubMed1976

[Induction of maturation (meiosis) in small oocytes of Xenopus. A cytological study].

Injection of endoplasm from large Xenopus oocytes which have undergone maturation into small (0.6-0.8 mm diameter) oocytes induces germinal vesicle (GV) breakdown. This process has been cytologically studied. Injection of cytoplasm from such small oocytes into large oocytes (1.0-1.2 mm diameter) is followed by the formation of a large spindle bearing many chromosomes at the site of injection.

Animals↗
PubMed1976

Induction of maturation (meiosis) in small Xenopus laevis oocytes by injection of maturation promoting factor.

Treatment of small-(stage III) or medium-sized (stage IV) Xenopus laevis oocytes with progesterone, human chorionic gonadotropin, or para-hydroxymercuriphenylsulfonate does not induce maturation. Only the full-grown oocytes (stage VI) undergo maturation when treated with either one of these three substances. In contrast, injection of maturation promoting factor into oocytes of stages III-VI invariably leads to chromosome condensation and germinal vesicle breakdown. No maturation spindle is found in oocytes smaller than 0.9 nm in diameter, and the nuclear sap does not mix with the cytoplasm in the smallest (0.45-0.55 mm in diameter) oocytes. In oocytes of 0.9 mm, maturation is identical to that of full-grown oocytes, except that the maturation spindle does not reach the cortex of the oocyte. Progesterone increases protein synthesis in medium-sized (0.8 mm in diameter) oocytes without inducing meiosis. It has little or no effect on protein synthesis in smaller oocytes.

Animals↗
PubMed1975

[Meiosis: role of a histone kinase in the condensation of ovarian oocyte chromosomes of Xenopus laevis and Ambystoma mexicanum].

By injecting heterologous histone-kinase preparations into ovarian Axolotl oocytes, it has been possible to speed up the progesterone-induced process of chromosome condensation. Moreover, in some instances, this condensation and even complete maturation have been obtained after injection of protein kinase alone, thus in the absence of hormone stimulation. Two different histone kinase preparations have been used: one was prepared from ascites cell chromatin and the other from in vitro ovulated Xenopus oocytes.

Ambystoma↗
PubMed1975

Studies on maturation in Xenopus laevis oocytes. III. Energy production and requirements for protein synthesis.

The following results were obtained: 1) The oxygen comsumption of progesterone-stimulated X. laevis oocytes increases at the time of germinal vesicle (GV) breakdown. 2) Continous treatment with 1 mM KCN, 1 mM and 0.1 mM DNP completely inhibits GV breakdown. 3) Pretreatment experiments with KCN, DNP and cycloheximide show that binding of progesterone to the plasma membrane and the specific hormone receptor requires neither energy, nor protein synthesis. 4) 1 h pulses of DNP (1mM) or cycloheximide (50 mug/ml) were applied, at various time intervals after progesterone treatment: early pulses strongly delay, but do not prevent GV breakdown; late pulses just before GV breakdown induce a number of cytological abnormalities, which ultimately lead to cytolysis. The significance of these results is discussed and the hypothesis that synthesis of the maturation producing factor (MPF) requires both energy and protein synthesis is proposed.

Animals↗