RIP3 mediates the embryonic lethality of caspase-8-deficient mice

Apoptosis and necroptosis are complementary pathways controlled by common signalling adaptors, kinases and proteases; among these, caspase-8 (Casp8) is critical for death receptor-induced apoptosis. This caspase has also been implicated in non-apoptotic pathways that regulate Fas-associated via death domain (FADD)-dependent signalling and other less defined biological processes as diverse as innate immune signalling and myeloid or lymphoid differentiation patterns. Casp8 suppresses RIP3-RIP1 (also known as RIPK3-RIPK1) kinase complex-dependent necroptosis that follows death receptor activation as well as a RIP3-dependent, RIP1-independent necrotic pathway that has emerged as a host defence mechanism against murine cytomegalovirus. Disruption of Casp8 expression leads to embryonic lethality in mice between embryonic days 10.5 and 11.5 (ref. 7). Thus, Casp8 may naturally hold alternative RIP3-dependent death pathways in check in addition to promoting apoptosis. We find that RIP3 is responsible for the mid-gestational death of Casp8-deficient embryos. Remarkably, Casp8(-/-)Rip3(-/-) double mutant mice are viable and mature into fertile adults with a full immune complement of myeloid and lymphoid cell types. These mice seem immunocompetent but develop lymphadenopathy by four months of age marked by accumulation of abnormal T cells in the periphery, a phenotype reminiscent of mice with Fas-deficiency (lpr/lpr; also known as Fas). Thus, Casp8 contributes to homeostatic control in the adult immune system; however, RIP3 and Casp8 are together completely dispensable for mammalian development.     

Crystal structure of the CusBA heavy-metal efflux complex of Escherichia coli

Gram-negative bacteria, such as Escherichia coli, expel toxic chemicals through tripartite efflux pumps that span both the inner and outer membrane. The three parts are an inner membrane, substrate-binding transporter; a membrane fusion protein; and an outer-membrane-anchored channel. The fusion protein connects the transporter to the channel within the periplasmic space. A crystallographic model of this tripartite efflux complex has been unavailable because co-crystallization of the various components of the system has proven to be extremely difficult. We previously described the crystal structures of both the inner membrane transporter CusA and the membrane fusion protein CusB of the CusCBA efflux system of E. coli. Here we report the co-crystal structure of the CusBA efflux complex, showing that the transporter (or pump) CusA, which is present as a trimer, interacts with six CusB protomers and that the periplasmic domain of CusA is involved in these interactions. The six CusB molecules seem to form a continuous channel. The affinity of the CusA and CusB interaction was found to be in the micromolar range. Finally, we have predicted a three-dimensional structure for the trimeric CusC outer membrane channel and developed a model of the tripartite efflux assemblage. This CusC(3)-CusB(6)-CusA(3) model shows a 750-kilodalton efflux complex that spans the entire bacterial cell envelope and exports Cu I and Ag I ions.     

Structure and reactivity of a mononuclear non-haem iron(III)-peroxo complex

Oxygen-containing mononuclear iron species--iron(III)-peroxo, iron(III)-hydroperoxo and iron(IV)-oxo--are key intermediates in the catalytic activation of dioxygen by iron-containing metalloenzymes. It has been difficult to generate synthetic analogues of these three active iron-oxygen species in identical host complexes, which is necessary to elucidate changes to the structure of the iron centre during catalysis and the factors that control their chemical reactivities with substrates. Here we report the high-resolution crystal structure of a mononuclear non-haem side-on iron(III)-peroxo complex, [Fe(III)(TMC)(OO)](+). We also report a series of chemical reactions in which this iron(III)-peroxo complex is cleanly converted to the iron(III)-hydroperoxo complex, [Fe(III)(TMC)(OOH)](2+), via a short-lived intermediate on protonation. This iron(III)-hydroperoxo complex then cleanly converts to the ferryl complex, [Fe(IV)(TMC)(O)](2+), via homolytic O-O bond cleavage of the iron(III)-hydroperoxo species. All three of these iron species--the three most biologically relevant iron-oxygen intermediates--have been spectroscopically characterized; we note that they have been obtained using a simple macrocyclic ligand. We have performed relative reactivity studies on these three iron species which reveal that the iron(III)-hydroperoxo complex is the most reactive of the three in the deformylation of aldehydes and that it has a similar reactivity to the iron(IV)-oxo complex in C-H bond activation of alkylaromatics. These reactivity results demonstrate that iron(III)-hydroperoxo species are viable oxidants in both nucleophilic and electrophilic reactions by iron-containing enzymes.     

Science in the american south through the eyes of four natural historians, 1750–1850

A national scientific community developed in the United States following the American Revolution. The independent scientific societies, journals and other institutions that formed the basis of this community were, however, centred in the North. An analysis of the work of four leading natural historians of the Southern tidewater (two from before the Revolution and two from after it) suggests that their region participated in this development by shifting scientific ties and allegiances from Europe to the North rather than by creating national or regional scientific institutions.     

Volatility forecasting with double Markov switching GARCH models

This paper investigates inference and volatility forecasting using a Markov switching heteroscedastic model with a fat‐tailed error distribution to analyze asymmetric effects on both the conditional mean and conditional volatility of financial time series. The motivation for extending the Markov switching GARCH model, previously developed to capture mean asymmetry, is that the switching variable, assumed to be a first‐order Markov process, is unobserved. The proposed model extends this work to incorporate Markov switching in the mean and variance simultaneously. Parameter estimation and inference are performed in a Bayesian framework via a Markov chain Monte Carlo scheme. We compare competing models using Bayesian forecasting in a comparative value‐at‐risk study. The proposed methods are illustrated using both simulations and eight international stock market return series. The results generally favor the proposed double Markov switching GARCH model with an exogenous variable. Copyright © 2008 John Wiley & Sons, Ltd.     

New records and species of Tetranychidae and Tenuipalpidae (Acarina) from Utah and Idaho

Twenty-three species of spider mites (Tetranychidae) are recognized for Utah and Idaho; three of these are described as new: Bryobia neoribis, Pseudobryobia knowltoni, and Schizotetranychus agropyron. Eleven species of Tenuipalpidae are recorded.     

Laboratory fattening and dietary-fat effects on Meadow voles ( Microtus pennsylvanicus )

When removed from the field and maintained under laboratory conditions, meadow voles exhibited significant change in body composition. Voles increased body mass due primarily to large gains in lipid mass combined with small losses in fat-free mass. Lipid deposition amounts increased as dietary fat was increased, and animals demonstrated a leveling of body mass instead of continuous unregulated obesity. When dietary fat content was changed, lipid deposition or utilization responded directly. Thus, meadow voles regulate overall body mass and body composition (lipid and fat-free mass) at levels that correspond to dietary quality (fat) and abundance in the laboratory, and they deposit considerably more lipid than do animals in the field. Our experiments demonstrate that food quality has a substantial effect on the body composition of wild-caught animals maintained in the laboratory.