Enlarged ventricles in the cerebrum of loop-tail mice

Résumé Les souris hétérozygotes appartenant à la mutation «loop-tail» (Lp) présentent une hydrocéphalie interne du télencéphale. Jusqu'ici, cette anomalie ainsi que les torsions de la queue et l'oscillation de la tête qui l'accompagnent n'avaient pas été étudiés en détail. Nous avons constaté que par suite de l'élargissement des ventricules encéphaliques, les structures cérébrales qui les entourent sont réduites, déformées ou déplacées. Ces aberrations neuro-anatomiques jettent de la lumière sur les perturbations du comportement observées chez ces mutants.     

La question des hétérochromosomes chez les Sauropsidés. I. Reptiles

Summary In contradiction to some Japanese authors (Oguma, Makino, Nakamura), we are unable to find any difference in the chromosome sets of the male and female ofLacerta vivipara (2N = 36). In a saurian, where the analysis is very easy (Chamaeleon bitaeniatus), there are, without the smallest doubt, 24 chromosomes in both sexes (20M + 4m). The evidence of a female heterogamety in turtles is by no means satisfying.     

Localization and analysis of nonpolar regions in onconase

A detailed analysis of the composition and properties of hydrophobic nuclei and microclusters has been carried out for onconase. Two main hydrophobic nuclei in the onconase structure were detected. Their composition and shape were found to be very similar to those of RNase A, in accordance with the predictions made. The nuclei in onconase are more compact, the side-chain atoms of residues included in the nuclei in onconase form more contacts with the environment than in RNase A. The hydrophobic nuclei should be considered as individual structural units along with elements of the secondary structure. Differences in composition and conformation of exposed loops between onconase and RNase A were found. The additional hydrophobic clusters attached to the nuclei in onconase might be involved in the fixation of an appropriate conformation of site(s) for manifestation of the biological activity of onconase. A comparison of amphibian representatives of the RNase A superfamily was also made. The results obtained suggest that the availability of nonpolar residues in established key positions of amino acid sequences determines the characteristic fold of homologous proteins and the structure of the active site cleft.     

Electrostatic trapping of ammonia molecules

The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydride molecules thermalized in ultra-cold buffer gas and optical trapping of caesium dimers generated from ultra-cold caesium atoms have been reported. However, these methods depend on the target molecules being paramagnetic or able to form through the association of atoms amenable to laser cooling, respectively, thus restricting the range of species that can be studied. Here we describe the slowing of an adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields and subsequent loading into an electrostatic trap. We are able to trap state-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm3 at temperatures below 0.35 K. We observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. Our findings illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems.     

Pixel switching of epitaxial Pd/YHx/CaF2 switchable mirrors

Exposure of rare-earth films to hydrogen can induce a metal-insulator transition, accompanied by pronounced optical changes. This 'switchable mirror' effect has received considerable attention from theoretical, experimental and technological points of view. Most systems use polycrystalline films, but the synthesis of yttrium-based epitaxial switchable mirrors has also been reported. The latter form an extended self-organized ridge network during initial hydrogen loading, which results in the creation of micrometre-sized triangular domains. Here we observe homogeneous and essentially independent optical switching of individual domains in epitaxial switchable mirrors during hydrogen absorption. The optical switching is accompanied by topographical changes as the domains sequentially expand and contract; the ridges block lateral hydrogen diffusion and serve as a microscopic lubricant for the domain oscillations. We observe the correlated changes in topology and optical properties using in situ atomic force and optical microscopy. Single-domain phase switching is not observed in polycrystalline films, which are optically homogeneous. The ability to generate a tunable, dense pattern of switchable pixels is of technological relevance for solid-state displays based on switchable mirrors.     

Senescence bypass screen identifies TBX2, which represses Cdkn2a (p19(ARF)) and is amplified in a subset of human breast cancers

To identify new immortalizing genes with potential roles in tumorigenesis, we performed a genetic screen aimed to bypass the rapid and tight senescence arrest of primary fibroblasts deficient for the oncogene Bmi1. We identified the T-box member TBX2 as a potent immortalizing gene that acts by downregulating Cdkn2a (p19(ARF)). TBX2 represses the Cdkn2a (p19(ARF)) promoter and attenuates E2F1, Myc or HRAS-mediated induction of Cdkn2a (p19(ARF)). We found TBX2 to be amplified in a subset of primary human breast cancers, indicating that it might contribute to breast cancer development.