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.

Bioluminescent assay of ATPase activity in embryonic material using firefly luciferase.

The continuous bioluminescent assay of ATP has been adapted to the study of Mg2+-dependent ATPases, including the (Na+; K+) pump, in amphibian tissues. A discrete bioluminescent assay procedure for ATPase has also been developed. Components of the firefly luciferase assay reagent modify the observed ATPase activity but this can be circumvented by performing discrete instead of continuous measurements of enzyme activity.

Cytological Effects of Heat-Shocks on Xenopus Oocytes and Eggs: (cytasters/spindles/furrows/nucleoli).

Heat-shocks (80 min at 34°c) induce the appearance of aster-like fibrous structures (cytasters) in maturing Xenopus oocytes. Cytaster formation is suppressed by treatments with colchicine or nocodazole of heat-shocked maturing oocytes. Heat-shocks destroy the meiotic spindle, but have no effect on cytasters induced by D O treatment.

Heat-shock response in Xenopus oocytes during meiotic maturation and activation.

After a 60 min heat-shock at 36 degrees C, Xenopus oocytes are still able to accomplish a complete meiotic maturation in response to a progesterone treatment. The 36 degrees C heat-shock applied to maturing oocytes strongly enhances the synthesis of a single heat-shock protein of approx. 70 000 molecular weight (hsp70); after activation with the Ca2+-ionophore A 23187, matured oocytes still display the ability to synthesize hsp70 and to survive a heat-shock.

[Phosphorylation of the ribosomal protein S6 during maturation of Xenopus oocytes: identification of the phosphorylated amino acids].

The S6 protein from the small subunit of Xenopus oocytes in phosphorylated during progesterone-induced maturation. The identity of the amino acids phosphorylated in the S6 protein during this process has been established by two-dimensional electrophoresis followed by radioautography. The only phosphorylated amino acid we could detect is phosphoserine.

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.

[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.

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.

[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.

Induction of maturation (meiosis) in Xenopus laevis oocytes by three organomercurials.

Three organomercurials, p-hydroxymercuribenzoate, p-hydroxymercuriphenylsulfonate, and mersalyl, induce maturation (meiosis) in a large percentage (20-100 percent) of Xenopus laevis oocytes. Maturation takes place even when the follicle cells which surround the oocytes have been withdrawn. Organomercurial- and progesterone-induced maturations have many features in common: they do not occur when the inducer is injected into the oocytes, they require the presence of Ca++ in the medium, they are inhibited by cycloheximide but not by actinomycin D.

Characterization of yolk DNA from Xenopus laevis oocytes ovulated in vitro.

High molecular weight DNA was isolated from the yolk platelets of Xenopus laevis oocytes ovulated in vitro. Yolk DNA has the same buoyant density in CsCl gradients as mitochondrial and nuclear DNAs, and, like them, it is double-stranded. Yolk DNA behaves like nuclear DNA, and not like mitochondrial DNA, upon renaturation after denaturation.