L'action du dioxyde de sélénium sur des œufs d'amphibiens d'espèces résistantes

The eggs of some Amphibian species (Triturus helveticus Raz., Triturus alpestris Laur., Xenopus laevis Daud.) are more resistant to selenium dioxyde M/100 than eggs of Pleurodeles waltlii Michah. Minimal mitotic abnormalities are observed: 1. “empty” poles, 2. cupular poles, 3. escape of centrosphere, which separates from the spindle, and sometimes torsion of polar regions of the achromatic figure. Cytasters and newly formed spindles are also observed in the diastematic clear zone, which is dissociated and inefficient. These abnormalities are believed to be consequences of the progressive diminution of a dominant factor associated with the centriole. When dominance is weakened, secondary poles appear with or without relation to the spindle. The balance between fibrillogenesis and reproduction of centrioles is newly demonstrated. These mechanisms are compared with phenomena occuring during fertilization and parthenogenesis     

Decontamination of bacterial infection of monolayer cultures with a specific bacteriophage

Summary A few cell lines and primary monolayer cultures were accidentally infected by bacteria. These cultures were successfully decontaminated by means of the specific bacteriophage virus after quick identification of the responsible bacteria. This method presents a practical interest for preservation of valuable cultures. This work is supported by the Institut National de la Sante et de la Recherche Medicale (France) and the Fondation pour la Recherche Medicale (France).     

Action de dérivés du sélénium (séléniates et sélénites) comparée à celle d'acides divers (crotonique,acétique,citrique et phosphorique) sur les mitoses de segmentation

The action of seleniates and selenites on the segmentation mitoses is similar to that of SeO₂: polar dissociation with conserved dominance of the principal pole, stickiness and clumping of chromosomes. Crotonic and acetic acid dissociate more strongly the achromatic apparatus, which is resolved into divergent fibrillae, which are sinuous and irregularly fasciculated; the principal poles may be recognized, but their activity is more lessened: centrospheres are reduced to orangeophilic material. All these derivatives are acidic in the solutions. When the action of crotonic acid is interrupted, fibrillogenesis does not recover, but cellular centers start again to divide and the size of centrospheres enlarges by assemblage of dis-oriented cyanophilic material, arising from destroyed fibrillae. Reduction of fibrillogenesis by inactivation of the poles results in reactivation of fibrillogenesis in the diastema, expansion of the fibrillar ?clear zone? and its budding into numerous elements filling the animal hemisphere. Furrowing is consequently inhibited. Classification of mitotic dissociation is reviewed: equilibrated pluripolar mitoses (phenylurethane), pluripolar systems hierarchically organized (selenium dioxyde), pluripolar systems practically not hierarchically organized (crotonic and acetic acids).     

Réseaux de grains cytoplasmiques dans les cellules de l'organe de Bidder chez Bufo bufo L.

Résumé Les cellules de l'organe de Bidder, observées à l'aide du microscope électronique, contiennent dans leur cytoplasme des structures granulaires qui sont inconnues dans les ovocytes des ovaires d'Amphibiens. Ces structures sont formées de grains disposés concentriquement autour de vésicules allongées du réticulum lisse. Les grains, chacun de 140 Å, sont reliés entre eux par des fibrilles dans des plans circulaires et superposés, formant ainsi des réseaux cylindriques ou fusiformes. Ces réseaux peuvent être rassemblés et orientés pour constituer des faisceaux. Ils peuvent perdre le reticulum qui axe leur structure et fusionner, tandis que les grains s'associent étroitement et prennent l'aspect de fibres. Ils peuvent aussi être associés avec un matériel dense et amorphe, qui ressemble au ciment intermitochondrial. L'hypothèse d'une organisation de ribosomes est discutée.

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Granular networks in the cells of Bidder's organ in Bufo bufo L.

Summary The cells of the Bidder's organ, observed with the electron microscope, reveal in their cytoplasm granular structures unknown in Amphibian oocytes. These structures are formed of granules concentrically organized around lengthened vesicles of smooth reticulum. The granules, each about 140 Å, are linked to each other by fibrils in circular and superposed planes constituting cylindrical or spindle-shaped networks. These networks may be rassembled and directed in a way to constitute fasciculi. They may lose the reticulum which support their structure and blend into one another, while the granules closely associate each other and take the appearance of fibers. They may be connected with a dense and amorph material, which looks like intermitochondrial cement. The hypothesis about an organisation of ribosomes is discussed.

     

Relationship between the presence of microfilaments and the cell cycle of HeLa cells in synchronus culture]

Some cytoplasmic organelles have showed characteristic variations which are related to the different cell cycle phases, in thymidine synchonized HeLa cells in culture. In these cells, the most modified organelles were intracytoplasmic membranes (endoplasmic reticulum) and microfilament arrangements. Microfilaments were numerous under the cell membrane, but also some of them were dispersed in dense bundles. These structures were seen around the nucleus, 12-14 h after removal of excess thymidine (G1). They migrated to the periphery of the cell during S and G2. During mitosis, they were directly under superficial membrane-associated microfilaments.     

Action of glutaraldehyde and formaldehyde on segmentation mitoses : Inhibition of spindle and astral fibres, centrospheres blocked

Glutaraldehyde and formaldehyde act as antimitotic substances at lower concentrations and as fixatives at higher ones. The arrested mitosis is of the quinoline type (d-mitosis); it is characterized by the disappearance of all the spindle and astral fibres, by the immobilization of chromosomes in the equatorial region and by the blocking of centrospheres. These blocked centrospheres are devoid of astral fibres, densified, and intensely stained; they do not diminish in volume at the end of mitosis. An explanation for this phenomenon is proposed: the binding of two or several microtubule subunits by one molecule of the active substance into the storage structures would prevent the discharge of these microtubule subunits and consequently the construction of microtubules. Colchicine-like substances bind only to one microtubule subunit and consequently storage structures cannot be formed. The relation between fixative and antimitotic properties is discussed. A gradient of sensibility to antimitotic action is observed: the mitoses are more easily arrested in the animal than in the vegetative hemisphere.