The suppression of star formation by powerful active galactic nuclei

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.     

Atypical mitochondrial morphology of the intestinal absorptive cells of the germfree rat

Zusammenfassung Die Mitochondrien der Dünndarm-Epithelzellen 3 Monate alter keimfreier Ratten zeigten elektronenmikroskopisch auffallende Formunterschiede im Gegensatz zu Vergleichstieren desselben Wurfes, die mit Coecum-Inhalt gewöhnlicher Ratten kontaminiert wurden.

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This work was supported in part by Grant No. 5 POI AM05664-05 AMP and Grant No. 5-K6-GM-14,208-05 to the Albert Einstein College of Medicine by the National Institutes of Health.     

Submillimetre galaxies reside in dark matter haloes with masses greater than 3 × 10(11) solar masses

The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500?μm. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, M(min), such that log(10)[M(min)/M(⊙)] = 11.5(+0.7)(-0.2) at 350?μm, where M(⊙) is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation.     

Enhancement of tumor development in physically-stressed mice inoculated with an oncogenic virus

Riassunto L'applicazione di un parziale bendaggio nei topi produce uno stato di fisiologica tensione caratterizzata, in parte, dall'involuzione della ghiandola del timo. Topi sottoposti a una tale tensione sono più suscettibili allo sviluppo dei tumori quando vengono inoculati con un oncogenico virus.     

Memory

In this review we address the idea that conservation of epigenetic mechanisms for information storage represents a unifying model in biology, with epigenetic mechanisms being utilized for cellular memory at levels from behavioral memory to development to cellular differentiation. Epigenetic mechanisms typically involve alterations in chromatin structure, which in turn regulate gene expression. An emerging idea is that the regulation of chromatin structure through histone acetylation and DNA methylation may mediate long-lasting behavioral change in the context of learning and memory. We find this idea fascinating because similar mechanisms are used for triggering and storing long-term 'memory' at the cellular level, for example when cells differentiate. An additional intriguing aspect of the hypothesis of a role for epigenetic mechanisms in information storage is that lifelong behavioral memory storage may involve lasting changes in the physical, three-dimensional structure of DNA itself.     

Enhanced survival of germfree mice after infection with irradiated scrapie brain

Zusammenfassung Nachweis, dass nach Injektion mit-bestrahltem «Scrapie»-Hirn keimfrei aufgezogene Mäuse länger als normale überleben. Das Ausmass der Astrogliose war im allgemeinen der Schwere der klinischen Symptome proportional. Die Theorie wird gestützt, dass das hochgradig hitze-, strahlungs- und enzymbeständige Material «Scrapie»-infizierter Mäuse die Induktion eines latenten Viruses bewirkt.     

Iron pigmentation of the gut of germ-free and conventionalized guinea-pigs

Zusammenfassung Die Autoren berichten über vergleichend histologische Untersuchungen des Darmkanals zweier Meerschweinchengruppen, die unter keimfreien Bedingungen geboren und gehalten wurden. Die eine Gruppe wurde einmalig mit der Darmflora normaler Tiere infiziert. Die Konzentration von eisenhaltigem Pigment war bei den keimfreien Meerschweinchen geringer als in der infizierten Gruppe, was auf eine Rolle der Bakterien im Eisenmetabolismus hinweisen dürfte.

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Supported in part by Grant DA-49-193-61G27MD to the Albert Einstein College of Medicine by the Research and Development Command of the U.S. Army Medical Service and Grants A-5664 and K6-Gm-14,208 to the Albert Einstein College of Medicine by the National Institutes of Health.