An RNA Polymerase III-Dependent Heterochromatin Barrier at Fission Yeast Centromere 1

Heterochromatin formation involves the nucleation and spreading of structural and epigenetic features along the chromatin fiber. Chromatin barriers and associated proteins counteract the spreading of heterochromatin, thereby restricting it to specific regions of the genome. We have performed gene expression studies and chromatin immunoprecipitation on strains in which native centromere sequences have been mutated to study the mechanism by which a tRNAAlanine gene barrier (cen1 tDNAAla) blocks the spread of pericentromeric heterochromatin at the centromere of chromosome 1 (cen1) in the fission yeast, Schizosaccharomyces pombe. Within the centromere, barrier activity is a general property of tDNAs and, unlike previously characterized barriers, requires the association of both transcription factor IIIC and RNA Polymerase III. Although the cen1 tDNAAla gene is actively transcribed, barrier activity is independent of transcriptional orientation. These findings provide experimental evidence for the involvement of a fully assembled RNA polymerase III transcription complex in defining independent structural and functional domains at a eukaryotic centromere

Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular "reactive oxygen species" (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation. We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation). The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible. This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, etc...Comment: 159 pages, including 9 Figs and 2184 reference

The mechanical response of a syntactic polyurethane foam at low and high rates of strain

Quasi-static and dynamic experiments are conducted to characterise the mechanical response of a syntactic foam comprising hollow glass microballoons in a polyurethane matrix. Stress versus strain histories are measured in uniaxial tension and compression as well as in pure shear, at strain rates ranging from 10−4 to 103 s−1, via non-standard experimental techniques; quasi-static in-situ tests are conducted to visualise the deformation mechanisms in tension and compression. The material displays a pronounced sensitivity to the imposed strain rate and relatively high tensile and shear ductility at both low and high strain rates. A tension/compression asymmetry is displayed in quasi-static tests but is lost at high rates of strain

Charles Darwin’s early beetle collections: ‘Darwin’s beetle box’ and the Down House box

Charles Darwin’s enthusiasm for collecting beetles during his time as a student at the University of Cambridge is well known and ‘Darwin’s Beetle Box’ in the University Museum of Zoology, Cambridge has been claimed to be his student collection. A collection of beetles at Down House is similarly thought to be Darwin’s collection of British beetles, but is imprecisely dated. Here we compare the species present in the boxes with the annotations in his copy of Stephens’ ‘British Insects’, and other notes, correspondence and specimens. There is a very close match between these sources of information and in the curation of the two boxes, the pins used and the handwritten labels, including some written by Emma Darwin. These similarities and details of correspondence lead us to conclude that most both boxes represent the collections made by Charles Darwin in 1829-31, with the addition of one specimen provided by Alfred Russel Wallace in 1866 and two probably from Francis Darwin

Pollination biology of oilseed poppy, Papaver somniferum L

Although poppies (Papaver somniferum L.) are one of the oldest cultivated plants relatively little is known of their pollination biology. We have investigated the relative importance of wind and insects in the pollination of poppies and identified potential insect pollinators. Wind pollination was found to be negligible, insect pollination was responsible for the majority of out-crossing, and self-pollination was the dominant mode of poppy fertilisation. Honeybees and flies were identified as the main potential cross-pollinators of Tasmanian poppies. Using a transgenic poppy field trial in which approximately 50% of the pollen grains produced were transgenic, we have determined the level of pollen-mediated gene flow by scoring over 50000 seeds for the presence of a selectable marker gene. Gene flow was measured using a 10-m buffer area that surrounded the field trial. It was highest at 0.1 m with 3.26% of seeds found to be transgenic and declined over distance with 1.73% transgenic seeds at 0.5 m, 1.80% at 1 m, 0.86% at 2m, 0.34% at 5 m, 0.12% at 9 m, and 0.18% at 10 m. These results demonstrate that under Tasmanian conditions, pollen-mediated gene flow occurs at modest levels in poppies that are in close proximity to each other and is most probably mediated by honeybees and flies. © CSIRO 2005