Xist regulation and function eXplored

X chromosome inactivation (XCI) is a process in mammals that ensures equal transcript levels between males and females by genetic inactivation of one of the two X chromosomes in females. Central to XCI is the long non-coding RNA Xist, which is highly and specifically expressed from the inactive X chromosome. Xist covers the X chromosome in cis and triggers genetic silencing, but its working mechanism remains elusive. Here, we review current knowledge about Xist regulation, structure, function and conservation and speculate on possible mechanisms by which its action is restricted in cis. We also discuss dosage compensation mechanisms other than XCI and how knowledge from invertebrate species may help to provide a better understanding of the mechanisms of mammalian XCI

The Economic Analysis Of Wave Energy

The economic analysis of the production of electricity on a significant national scale from wave energy reported in ETSU's Strategic Review of the Renewable Energy Technologies showed that in 1982 it was una ttractive when compared with compet ing technol ogies , Subsequent analysis has refined our under standing of wave energy ecor, omics while confirming the findings of the Strategic Review. The Harwell electricity supply system model has been used to recalculate breakeven costs, net present values and benefit/cost rat ios in the s ame scenarios as used in the Strategic Review. Attention was focused on a 2 G1~ wave power station with an assumed annual l oad factor of 25% instal led between 2001 and 2010 with a life of 25 years. ~uch of t he analysis was carried out for this first wave ?Ower stati on but the sensitivities to the main assumptions and the economics of subsequent wave power stations ~ere considered. This mo re recent economic analysis shows that while wave energy can appear cost-effective under particularly favourable scenarios u sing optimistic assum p tions on costs a nd productivity, its overall economic prospects a re not go od. The analysis ~erely serves to strengthen the conclusion of the Strate g ic Review of the Renewable Energy Technologies that the economic prospects of wave energy are poor both in comparison with othe r renewable energ y technologies a nd with conventional thermal plant. This suggest s tha t wave powe r is only likely to be considered by a UK electricity board as som e form o f s trategic opti on which cou ld be relie d upon if other more ec onor:ii cally att ractive generation options became unavailable fo r non-economic reasons. Its deploynent would increase costs to the consumer in a ll scenarios considered

The economic analysis of wave energy

SIGLEAvailable from British Library Document Supply Centre- DSC:3816.467(DE-ETSU-L--7) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Hydrodynamic function of a biostable polyurethane flexible heart valve after six months in sheep

Survival to six months for sheep with a non-biostable polyurethane mitral heart valve prosthesis has been reported previously, however, with surface degradation and accumulation of calcified fibrin/thrombus that impaired leaflet motion and compromised hydrodynamic function. Newly available biostable polyurethanes may overcome this problem. Six adult sheep with biostable polyurethane trileaflet heart valve prostheses of documented hydrodynamic performance, implanted in the mitral position, were allowed to survive for 6 months. Explanted valves were photographed, resubmitted to hydrodynamic function testing, and studied by light and electron microscopy. Explanted valves were structurally intact and differed little in appearance from their preimplant state. Hydrodynamic testing showed no deterioration in pressure gradient or energy losses compared with pre-implant values. Biostable polyurethanes demonstrated improved blood compatibility leaving leaflets flexible and valve function unimpaired. Biostable polyurethanes may thus improve prospects for prolonged function of synthetic heart valve prostheses. </jats:p

Diverse factors are involved in maintaining X chromosome inactivation

X chromosome inactivation (XCI) is the most dramatic example of epigenetic silencing in eukaryotes. Once established, the inactivated X chromosome (Xi) remains silenced throughout subsequent cell divisions. Though the initiation of XCI has been studied extensively, the protein factors involved in Xi silencing and maintenance are largely unknown. Here we report the discovery of a diverse set of 32 proteins involved in maintenance of Xi silencing through a genome-wide RNAi screen. In addition, we describe the mechanistic roles of two proteins—origin recognition complex 2 (Orc2) and heterochromatin protein 1 (HP1α)—in Xi silencing. Immunofluorescence studies indicate that Orc2 and HP1α localize on Xi in mouse cells. Depletion of Orc2 by shRNA leads to the loss of both Orc2 and HP1α localization on Xi. Furthermore, the silencing of genes on Xi is disrupted in both Orc2- and HP1α-depleted cells. Finally, we show, using ChIP assay, that the localization of HP1α and Orc2 to the promoter regions of Xi-silenced genes is interdependent. These findings reveal a diverse set of proteins involved in Xi silencing, show how Orc2 and HP1α impact Xi silencing, and provide a basis for future studies on the maintenance of Xi silencing