Testing of rifampicin on possible genetic effects onDrosophila melanogaster and human leukocyte chromosomes in vitro

Zusammenfassung Mutagenitätsuntersuchungen von Rifampicin anDrosophila melanogas (X-chromosomale rezessive Letalmutationen) und an menschlichen Leukozytenchromosomen in vitro ergaben keine Anhaltspunkte für eine genetische Wirksamkeit dieser Substanz.

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We thank Mrs.R. Pieper for her carful technical assistance. We are also grateful to ProfessorR. Hess and Dr.J. Gelzer (Ciba-Geigy, Basel) for the supply of rifampicin.     

Some new data concerning effect of actinomycin D on early chick embryos

Zusammenfassung Actinomycin D führte beim Hühnerembryo zu einer deutlichen Hemmung der Herzentwicklung nach Inkubation im Nährmedium während der Entwicklungsstadien 3 und 3⁺. Nach Vorbehandlung der Stadien 3–7 und anschliessender Kultur in actinomycin D-freiem Medium fanden sich Fehlbildungen von Herz, ZNS und Somiten, die in ihrer Häufigkeit von den betroffenen Entwicklungsphasen abhängig sind.

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This study was supported by a grant from the Rutgers University Research Council No. 07-2189.     

A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way

Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 +/- 1.5) x 10(6) solar masses (M(*)). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.     

Chemical investigation of hassium (element 108)

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.     

Rapid renewal of auditory hair bundles

Stereocilia, also known as hair bundles, are mechanosensitive organelles of the sensory hair cells of the inner ear that can detect displacements on a nanometre scale and are supported by a rigid, dense core of actin filaments. Here we show that these actin-filament arrays are continuously remodelled by the addition of actin monomers to the stereocilium tips, and that the entire core of the stereocilium is renewed every 48 hours. This unexpected dynamic feature of stereocilia will help our understanding of how auditory sensory function develops and is maintained.     

The harlequin mouse mutation downregulates apoptosis-inducing factor

Harlequin (Hq) mutant mice have progressive degeneration of terminally differentiated cerebellar and retinal neurons. We have identified the Hq mutation as a proviral insertion in the apoptosis-inducing factor (Aif) gene, causing about an 80% reduction in AIF expression. Mutant cerebellar granule cells are susceptible to exogenous and endogenous peroxide-mediated apoptosis, but can be rescued by AIF expression. Overexpression of AIF in wild-type granule cells further decreases peroxide-mediated cell death, suggesting that AIF serves as a free radical scavenger. In agreement, dying neurons in aged Hq mutant mice show oxidative stress. In addition, neurons damaged by oxidative stress in both the cerebellum and retina of Hq mutant mice re-enter the cell cycle before undergoing apoptosis. Our results provide a genetic model of oxidative stress-mediated neurodegeneration and demonstrate a direct connection between cell cycle re-entry and oxidative stress in the ageing central nervous system.     

Active genes are tri-methylated at K4 of histone H3

Lysine methylation of histones in vivo occurs in three states: mono-, di- and tri-methyl. Histone H3 has been found to be di-methylated at lysine 4 (K4) in active euchromatic regions but not in silent heterochromatic sites. Here we show that the Saccharomyces cerevisiae Set1 protein can catalyse di- and tri-methylation of K4 and stimulate the activity of many genes. Using antibodies that discriminate between the di- and tri-methylated state of K4 we show that di-methylation occurs at both inactive and active euchromatic genes, whereas tri-methylation is present exclusively at active genes. It is therefore the presence of a tri-methylated K4 that defines an active state of gene expression. These findings establish the concept of methyl status as a determinant for gene activity and thus extend considerably the complexity of histone modifications.