Renée Tencer

Effects of histones and polylysine on the synthetic activity of the giant chromosomes of salivary glands of dipteran Larvae

1. 1. Exogenous histones or polylysine do not change the morphological pattern of the polytene chromosomes of Chironomus. 2. 2. Cytochemical studies show that the pattern of histone localization closely follows the distribution of DNA in the polytene chromosomes. Added histones or polylysine are accumulated in the chromosomes (as shown by fast green staining). 3. 3. Incorporation of 3H-uridine is inhibited by the addition of exogenous histones or polylysine, and the inhibition is proportional to the concentration of the added substances. High doses of these compounds impair 3H-thymidine incorporation into the chromosomes. 4. 4. Trypsin does not induce new puffs but attacks the chromosomes in such a way as to loosen the attachment of the paired chromosomes. 3H-Uridine incorporation is enhanced in trypsin treated nuclei. 5. 5. Trypsin probably attacks the chromosomal basic proteins; as a result, it approximately doubles the number of the DNA sites which can be bound by 3H-actinomycin. 6. 6. In Drosophila melanogaster, ecdysone induces the production of a large number of puffs all along the chromosomes. Addition of histones prevents the formation of the new puffs.

Transmembrane effects of lectins. I. Effects of wheat germ agglutinin and soybean agglutinin on furrow formation and cortical wound healing in Xenopus laevis eggs.

Abstract Studies on the binding of FITC-WGA and FITC-SBA to normal and cytochalasin (CB)-treated Xenopus eggs have demonstrated the presence of lectin receptors all over the egg surface; there are aggregates of receptors in the region where microvilli are numerous and microfilaments well organized. Addition of WGA or SBA to the incubation medium provokes inhibition of furrow formation provided that the lectins are added before the streak stage, or arrest of contraction when added during furrow formation. This arrest of contraction is followed by furrow regression. The lectins also affect wound healing. All these effects may be explained by an inhibition of membrane proteins movement and an alteration of the relations between the surface and the cytoskeleton.

Ribonucleotide reductase activity during amphibian development

Uniformly labeled [3H] uridine is incorporated into DNA by dissociated Pleurodeles blastulae; the label is found in cytosine and to a much lesser extent in thymine. Ribonucleotide reductase activity cannot be detected in full grown oocytes of Xenopus and Pleurodeles, but is present in unfertilized egg. The enzyme is synthesized (or activated) when maturation is induced in Xenopus oocytes by in vitro hormonal treatment. The enzymatic activity increases after fertilization and reaches a peak at the 2--4 cell stage; it decreases at the blastula, gastrula and neurula stages to the low level initially present in unfertilized eggs. The enzyme is no longer detectable in swimming tadpoles. Addition of hydroxyurea (1 mg/ml) to fertilized eggs leads to complete loss of ribonucleotide reductase activity: cycloheximide (20 mug/ml) inhibits the rise in activity characteristic of early cleavage, while actinomycin D (20 mug/ml) has no effect. The significance of these results in discussed.

Concanavalin A binding to oocytes and eggs of Xenopus laevis

Abstract Concanavalin A (ConA) binding to Xenopus oocytes was studied by fluorescent and electron microscopy. ConA binds to the vitelline layer around the oocytes and to the vitelline envelope of mature eggs. However, when oocytes are removed from the follicles with forceps, a regular hexagonal pattern of fluorescence can be seen: the fluorescence is due to the binding of ConA to the vitelline layer and the network is generated by the remaining follicle cells which allow the lectin to reach the vitelline layer only at their junctions or extremities. ConA binding sites have also been detected on the cortical granules and at the edge or the yolk platelets. On the other hand, the plasma membrane of the oocytes does not show appreciable binding of ConA neither during oogenesis nor after maturation. No information on modifications of the membrane during oogenesis or maturation or on any anisotropy at the surface of the egg could be gathered from the study of ConA binding.

Involvement of the cytoskeleton in early grey crescent formation in axolotl oocytes

SummaryMaturing axolotl oocytes which are treated with protein synthesis inhibitors or which are heat-shocked can be induced to reorganize their cytoplasm and to form an early grey crescent. The maturing axolotl oocyte has been used as a model system to study the role of the cytoskeleton in dorsoventral polarization as visualized by grey crescent formation. Results presented here provide evidence for the involvement of microtubules in the formation of the early grey crescent. Whereas inhibitors of microtubule polymerization and antibodies against tubulin both elicit early grey crescent formation, the effect of taxol shows that microtubule polymerization is required at a late stage in this event. The nucleus furnishes important factors required for early grey crescent formation and might play a role in microtubule polymerization.