Search PubMed⌕ 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↗
PubMed1982

Studies on differentiation without cleavage in Chaetopterus. Requirement for a definite number of DNA replication cycles shown by aphidicolin pulses.

Aphidicolin, a powerful inhibitor of nuclear DNA replication, has been used to establish the level of polyploidisation required for the realization of the late morphogenetic events (segregation, pseudogastrulation and ciliation) of differentiation without cleavage in Chaetopterus-activated eggs. A parallel has been drawn between cytophotometric estimations of the DNA content and cytoplasmic differentiation in eggs treated with aphidicolin under different experimental conditions: either pulses with aphidicolin were followed by culture in sea water or the eggs were treated with aphidicolin after development had taken place in sea water for various lengths of time. The results suggest that a 'quantal' monasterial cycle might take place 3 h after activation, corresponding presumably to the fourth or fifth replication cycle. Moreover, early DNA replication seems to be more important for morphogenesis than late DNA replication.

Animals↗
PubMed1981

Studies on differentiation without cleavage in Chaetopterus: effects of inhibition of DNA synthesis with aphidicolin.

The effects of aphidicolin - a powerful inhibitor of DNA polymerase alpha and of DNA replication - on normal development and on differentiation without cleavage of Chaetopterus eggs have been studied with cytological, cytochemical, and biochemical methods. The experiments show that the initial period of pseudocleavage can take place in the absence of nuclear DNA synthesis, but further development (segregation, hatching, ciliation) requires DNA synthesis. However ciliated unicellular larvae can be obtained under conditions where the DNA content of the embryos in only 40% of the controls. In fertilized eggs, aphidicolin immediately stops cleavage. The significance of these results is discussed.

Animals↗
PubMed1980

Studies on differentiation without cleavage in Chaetopterus variopedatus: requirements for nucleic acid and protein synthesis.

Activation of unfertilized Chaetopterus eggs by treatment with an excess of KCl may lead to the production of unicellular ciliated larvae (Lillie's differentiation without cleavage). The effects of a number of inhibitors of protein (puromycin, cycloheximide, emetin), RNA (actinomycin D), and DNA (hydroxyurea) synthesis of differentiation without cleavage and on normal development have been studied in Chaetopterus. Incorporation of radioactive leucine, uridine, and thymine has been followed by biochemical methods and by autoradiography. The DNA content of the large polyploid nucleus has been estimated by cytophotometry. The initial pseudocleavage period of differentiation without cleavage is characterized by a burst in DNA and protein synthesis; the inhibitors have little or no effect on this burst and on pseudocleavage itself. Protein and DNA synthesis levels off during the following phase (segregation), but the inhibitors become more effective. RNA synthesis is almost linear for 20 h. These results are compared with those obtained on eggs from other species.

Animals↗
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↗