Elyane Baltus

Biochemical studies of nucleate and anucleate fragments isolated from sea-urchin eggs: A comparison between fertilization and parthenogenetic activation

Abstract Nucleate and anucleate fragments of sea-urchin eggs as well as whole eggs were given RNA and protein precursors in the presence of puromycin and actinomycin. A comparison was made between events occurring after fertilization and after parthenogenetic activation.

Le dosage de l'acide désoxyribonucléique dans les oeufs de batraciens

Abstract 1. 1. A fluorometric method for the estimation of DNA in materials which contain very little of this nucleic acid is described. It can be used with as little as 5 amphibian eggs, which contain, altogether, about 0.5 μg of DNA. 2. 2. The synthesis of DNA in developing Pleurodeles eggs has been studied. The results are similar to those described in the literature. 3. 3. In early stages, 80 % of the total DNA can be sedimented by the ultracentrifugation of homogenates. 4. 4. The significance of these results is briefly discussed.

Ultrastructure of Xenopus laevis oocytes after injection of an extract from progesterone-treated oocytes

When the supernatant of a centrifuged homogenate from progesterone-treated oocytes is injected into Xenopus full grown oocytes, an incomplete and abnormal maturation called “pseudomaturation” occurs. The first sign of pseudomaturation is observed in the cortical region: the plasma membrane becomes lobulated and pieces of cortical cytoplasm are shed into the medium. The most remarkable ultrastructural characteristic of pseudomaturation is the hyperdevelopment of the internal membranous system, characterized in particular by the extensive growth of the endoplasmic reticulum, the maintenance of numerous annulate lamellae, unusually slow to disappear. The pores of the latter are often aligned and characteristically united by columns of partially fibrillar material. Before the breakdown of the germinal vesicle, sheets of fibrillar material appear at intervals in the cytoplasm, mainly around the nuclear membrane. The basal part of the nuclear membrane undergoes extensive folding before breakdown of the germinal vesicle occurs; the nuclear membrane usually ruptures near the apical pole. The main alteration in the nucleus is a rapid condensation of the fibrillar core of the numerous nucleoli; the fibrillar and the granular parts of the nucleoli segregate; they are often found associated with bundles of 340 A microtubules. Chromosome condensation is never observed.

Action de la ribonucléase sur les cellules du carcinome d'Ehrlich

The reduced form of ribonuclease acts on the cells ofEhrlichs carcinoma by producing important changes in the RNA content of cells: (1) First, there is an important synthesis of intracellular RNA and an accumulation of free nucleotides (from the external medium). This phenomenon accompanies the necrosis of the cells. (2) After this first stage begins a rapid degradation of intracellular RNA. Simultaneously, the respiration of cells decreases whilst protein content remains unchanged. The oxidized form of ribonuclease has no action on the cells.

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. In both cases, the maturation producing factor and the pseudomaturation inducing factor are produced. Organomercurial-treated oocytes react normally to activating stimuli; their protein synthesis increases, but uptake of amino acids is strongly inhibited. Progesterone and p-hydroxymercuriphenyl-sulfonate act synergically in inducing maturation. The main difference between the two agents is that p-hydroxymercuriphenylsulfonate must act for several hours, whereas, short contact with progesterone is sufficient to induce maturation.

Évolution de l'aldolase dans les fragments anucléés d'Acetabularia

Abstract Measurements of aldolase activity in enucleated fragments of Acetabulria mediaterranea have shown that this enzyme can be synthesized in the cytoplasm of the algae in the absence of the nucleus.

Adenylate cyclase and cyclic amp-phosphodiesterase activities during the early phase of maturation Xenopus laevis oocytes

Maturation (meiosis) is the transformation, upon hormonal stimulation, of a diploid ovarian oocyte into a haploid and fertilizable egg (review [ 11). In amphibians, in vitro maturation of oocytes dissected out of the ovary can generally be induced by a short incubation of the oocytes with progesterone. In Xenopus laevis, the process of maturation extends over 6-10 h; it involves several different steps the most important of which, from a biological viewpoint, is the appearance of the maturation promoting factor (MPF) after 4-6 h hormonal treatment [2]. An essential step in the initiation of maturation is the dephosphorylation of certain classes of proteins. This phenomenon is believed to result from the following sequence of events: an intracellular release of membrane-bound Ca2* would be instantaneously triggered by progesterone; Ca’+and calmodulin would activate a cyclic AMP (CAMP)-phosphodiesterase. A drop of CAMP content would follow; as a result, a cAMPdependent protein kinase activity would decrease with a subsequent dephosphorylation of proteins. Some of these steps are well substantiated by experimental data, whereas others are still hypothetical: it has been established that progesterone treatment induces the release of Ca2+from the membrane within 30-90 s [3]; a calmodulin-like protein has been isolated from Xenopus oocytes [4]; moreover, Ca2+-calmodulin injected into oocytes has been reported to induce their maturation [5], but it has not yet been proved that Ca’+and calmodulin activate in vivo an oocytic CAMP-phosphodiesterase. However, in [6] protein dephosphorylation is clearly indicated as an essential event for the initiation of maturation. Injec-

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. A cycloheximide treatment combined with a heat-shock induces, during the recovery period, the synthesis of two heat-shock proteins, of approx. 70 000 and 83 000 molecular weight.

Étude de la ribonucléase des nucléoles isolés a partir d'oocytes d'astéries (Asterias rubens)

Abstract Nucleoli isolated from starfish oocytes contain at least two different ribonucleases; one of them is active at pH 5.0 and the other at pH 7.4. The acid ribonuclease is activated by Triton X 100 and by dilute sulphuric acid. The alkaline ribonuclease is insensitive to the detergent and is completely inactivated by H 2 SO 4 .

Cytological Effects of Heat‐Shocks on Xenopus Oocytes and Eggs

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 D2O treatment.