[Inhibition of the reinitiation of meiosis in Xenopus laevis oocytes by three natural antiproteases: antipain, chymostatin, and leupeptin]

Oocytes incubated for 1 hr. in saline containing 1 mg/ml of antipain, leupeptin or chymostatin do not reinstate meiosis when progesterone or ionophore A 23187 are added. On the contrary such oocytes remain able to undergo meiosis when injected with cytoplasm of maturing oocytes (MPF), with Rabbit phosphorylase kinase or with Beef protein kinase. These results demonstrate that the loss of responsiveness to progesterone or ionophore is not due to toxic effects but rather to some interference with a key event which occurs prior to MPF action.

Electrophoretic introduction of calcium ions into the cortex of Xenopus laevis oocytes triggers meiosis neinitiation

Meiosis reinitiation has been triggered via electrophoretic driving of Ca++ into the cortex of Xenopus laevis oocytes freed from functional follicle cells by collagenase treatment. Mg++ could not be substituted for Ca++. Ca++ induced maturation resembles progesterone induced maturation in so far both are inhibited by cycloheximide, give rise to amplifiable MPF in the cytoplasm of treated oocytes and allow chromosome condensation and the formation of a normal meiotic spindle.

Induction of meiosis by injection of heterologous protein kinase and phosphorylase kinase in Xenopus laevis oocytes

Meiosis reinitiation has been triggered by injection of beef heart protein kinase or rabbit phosphorylase kinase into Xenopus laevis oocytes. Successful injections are followed by germinal vesicle breakdown, chromosome condensation, formation of a normal meiotic spindle, and appearance of an amplifiable maturation promoting factor. Meiosis reinitiation does not occur when the enzymes are introduced into the oocytes simultaneously with EGTA or after pretreatment with cycloheximide. Antipain, an antiprotease which abolishes the response of oocytes to progesterone, does not suppress the meiosis reinitiation induced by injection of protein kinase or phosphorylase kinase.

Electrical properties of the starfish oocyte membranes

The electrical parameters of both vitelline and plasma membranes have been measured in Marthasterias glacialis oocytes. Voltage-current relationship was studied by an original method using a single intracellular micro-electrode. The analysis of V-I curves obtained by this method reveals rectifying properties of the plasma membrane. Bath application of 1-methyladenine, the hormone wich controls meiosis reinitiation, triggers without lag a partial depolarization of the plasma membrane, whereas the total ionic conductance undergoes typical variations.

[Early changes in the electric properties of the oocyte plasma membrane of Xenopus laevis during the reinitiation of meiosis induced by progesterone, para chloromercuribenzoate (PCMB) or the ionophore A 23187]

Progesterone, pCMB and ionophore -Mg++ triggers early and quite similar changes in the electrical properties of Xenopus laevis plasma membrane which may play a key role in the process of meiosis reinitiation.

Emericid, a new polyether antibiotic from Streptomyces hygroscopicus (DS 24 367)

Emericid is a new polyether polycyclic ionophore antibiotic excreted by Streptomyces hygroscopicus (DS 24 367). Active in vitro against Gram-positive bacteria, it is ineffective in vivo. At a 0.006-0.02% level in the diet it protects chickens and rabbits against coccidiosis.

Isolation of (-)-cryptosporiospin, a chlorinated cyclopentenone fungitoxic metabolite from Phialophora asteris f. sp. helianthi

The (-)-enantiomer of cryptosporiopsin, a chlorinated cyclopentenone fungitoxic metabolite, was isolated from Phialophora asteris f. sp. helianthi. Next to a comparable fungitoxic activity was shown by crypstosporiopsin, the product particularly inhibits growth of Sclerotinia sclerotiorum, an important pathogen on sunflower. Two further metabolites were tentatively identified as a stereoisomer of cryptosporiopsin and its dehydrated derivative.