Jean Brachet

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.

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 Maturation takes place even when the follicle cells which surround the oocytes have been withdrawn.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.

Cyclic nucleotides and amphibian development

Summary Addition of 3′, 5′-cyclic AMP (cAMP), N 6 , O 2 dibutyryl cyclic AMP (db-cAMP) and 3′,5′-cyclic GMP (cGMP) to fertilized amphibian eggs ( Ambystoma mexicanum, Xenopus laevis ) exerted little effect on development. Theophylline, at a high concentration (10 mM), produced strong developmental abnormalities; it had no effect at lower concentrations. The cAMP content of X. laevis and Rana temporaria eggs is high and does not change significantly during maturation, fertilization, cleavage and gastrulation. R. temporaria eggs contain as much cGMP as cAMP and their levels do not change significantly during development. The cGMP content of X. laevis oocytes is 1/10 to 1/20 that of cAMP. It increases after progesterone-induced maturation and decreases after ovulation. It remains low after fertilization and during cleavage. It increases again during neurulation.

Presence of rRNA in the heavy bodies of sea urchin eggs: An in situ hybridization study with the electron microscope

Experimental conditions have been found, in which the presence of rRNA can be demonstrated by in situ hybridization at the electron microscope level in the heavy bodies of sea urchin eggs. The specificity of hybridization has been controlled by ribonuclease digestion and by competition experiments with unlabelled rRNA.

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.

Easy Detection of the Nucleolar Organizers in Amphibian Oocytes

SUMMARYWhen amphibian oocytes (X. laevis, R. pipiens) are treated for a few minutes with the detergent SDS (0.3%) and then transfered to amphibian Ringer, the nucleolar organizers become visible, with the Feulgen reaction, as pink, central bodies. The are particularly easy to see when the Feulgen stained sections are examined under a fluorescence microscope. The possible applications of these observations for future work are discussed.