OPA1 processing controls mitochondrial fusion and is regulated by mRNA splicing, membrane potential, and Yme1L

OPA1, a dynamin-related guanosine triphosphatase mutated in dominant optic atrophy, is required for the fusion of mitochondria. Proteolytic cleavage by the mitochondrial processing peptidase generates long isoforms from eight messenger RNA (mRNA) splice forms, whereas further cleavages at protease sites S1 and S2 generate short forms. Using OPA1-null cells, we developed a cellular system to study how individual OPA1 splice forms function in mitochondrial fusion. Only mRNA splice forms that generate a long isoform in addition to one or more short isoforms support substantial mitochondrial fusion activity. On their own, long and short OPA1 isoforms have little activity, but, when coexpressed, they functionally complement each other. Loss of mitochondrial membrane potential destabilizes the long isoforms and enhances the cleavage of OPA1 at S1 but not S2. Cleavage at S2 is regulated by the i-AAA protease Yme1L. Our results suggest that mammalian cells have multiple pathways to control mitochondrial fusion through regulation of the spectrum of OPA1 isoforms.     

Temperature dependency of bark photosynthesis in beech (Fagus sylvatica L.) and birch (Betula pendula Roth.) trees

Temperature dependencies of stem dark respiration (R(d)) and light-driven bark photosynthesis (A(max)) of two temperate tree species (Fagus sylvatica and Betula pendula) were investigated to estimate their probable influence on stem carbon balance. Stem R(d) was found to increase exponentially with increasing temperatures, whereas A(max) levelled off or decreased at the highest temperatures chosen (35-40 degrees C). Accordingly, a linear relationship between respiratory and assimilatory metabolism was only found at moderate temperatures (10-30 degrees C) and the relationship between stem R(d) and A(max) clearly departed from linearity at chilling (5 degrees C) and at high temperatures (35-40 degrees C). As a result, the proportional internal C-refixation rate also decreased non-linearly with increasing temperature. Temperature response of photosystem II (PSII) photochemistry was also assessed. Bark photochemical yield (Delta F/F(m)') followed the same temperature pattern as bark CO(2) assimilation. Maximum quantum yield of PSII (F(v)/F(m)) decreased drastically at freezing temperatures (-5 degrees C), while from 30 to 40 degrees C only a marginal decrease in F(v)/F(m) was found. In in situ measurements during winter months, bark photosynthesis was found to be strongly reduced. Low temperature stress induced an active down-regulation of PSII efficiency as well as damage to PSII due to photoinhibition. All in all, the benefit of bark photosynthesis was negatively affected by low (<5 degrees C) as well as high temperatures (>30 degrees C). As the carbon balance of tree stems is defined by the difference between photosynthetic carbon gain and respiratory carbon loss, this might have important implications for accurate modelling of stem carbon balance.     

Murine norovirus 1 infection is associated with histopathological changes in immunocompetent hosts, but clinical disease is prevented by STAT1-dependent interferon responses

Human noroviruses are the major cause of nonbacterial epidemic gastroenteritis worldwide. However, little is known regarding their pathogenesis or the immune responses that control them because until recently there has been no small animal model or cell culture system of norovirus infection. We recently reported the discovery of the first murine norovirus, murine norovirus 1 (MNV-1), and its cultivation in macrophages and dendritic cells in vitro. We further defined interferon receptors and the STAT-1 molecule as critical in both resistance to MNV-1-induced disease in vivo and control of virus growth in vitro. To date, neither histopathological changes upon infection nor viral replication in wild-type mice has been shown. Here we extend our studies to demonstrate that MNV-1 replicates and rapidly disseminates to various tissues in immunocompetent mice and that infection is restricted by STAT1-dependent interferon responses at the levels of viral replication and virus dissemination. Infection of wild-type mice is associated with histopathological alterations in the intestine (mild inflammation) and the spleen (red pulp hypertrophy and white pulp activation); viral dissemination to the spleen, liver, lung, and lymph nodes; and low-level persistent infection in the spleen. STAT-1 inhibits viral replication in the intestine, prevents virus-induced apoptosis of intestinal cells and splenocytes, and limits viral dissemination to peripheral tissues. These findings demonstrate that murine norovirus infection of wild-type mice is associated with initial enteric seeding and subsequent extraintestinal spread, and they provide mechanistic evidence of the role of STAT-1 in controlling clinical norovirus-induced disease.     

Matrix fibronectin binds gammaretrovirus and assists in entry: new light on viral infections

A major entry route for the gammaretrovirus amphotropic murine leukemia virus (A-MLV) into NIH 3T3 fibroblasts is via caveola-dependent endocytosis. However, during the infection time, few viral particles can be observed intracellularly. Analyzing the dynamics of the A-MLV infection process by using total internal reflection fluorescence microscopy, we show that the majority of viruses are extracellular and bound to the fibronectin matrix. Moreover, the amounts of bound virus and of fibronectin correlated. Using confocal microscopy, nanoparticles targeted to fibronectin by a III1C-fibronectin fragment or anti-fibronectin antibody were detected intracellularly in NIH 3T3 cells; unconjugated nanoparticles neither bound to cells nor were detectable intracellularly. Furthermore, A-MLV colocalized intracellularly with the fibronectin-targeted nanoparticles, suggesting that they were taken up by the same cellular pathway. Both A-MLV entry and fibronectin turnover depend on caveolar endocytosis, and we found that inhibiting viral binding to the extracellular NIH 3T3 fibronectin-matrix dramatically reduced A-MLV infection, indeed, showing an active role of fibronectin in infection. We suggest that binding to the cellular fibronectin matrix provides a new mechanism by which viruses can enter cells.     

Does physical education modify the body composition?--results of a longitudinal study of pre-school children

The aim of the study is the analysis of body composition, motor development and cardiovascular parameters of preschool-children. In 2001/2002 a longitudinal study started in 17 nursery schools in Berlin. A total of 160 children out of the 264 children participated in a regular exercise programme. After 24 months of training significant differences of body composition, motor skills and cardiovascular parameters between 5 complete year old children of the intervention and the control group were observed. The results show that such an exercise programme is successful as a preventive measure to decrease the risk of obesity.     

Hepatic morphological alterations,glycogen content and cytochrome P450 activities in rats treated chronically with N<Superscript>ω</Superscript>-nitro-L-arginine methyl ester (L-NAME)

Chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension mediated partly by enhanced angiotensin-I-converting enzyme (ACE) activity. We examined the influence of L-NAME on rat liver morphology, on hepatic glycogen, cholesterol, and triglyceride content, and on the activities of the cytochrome P450 isoforms CYP1A1/2, CYP2B1/2, CYP2C11, and CYP2E1. Male Wistar rats were treated with L-NAME (20 mg/rat per day via drinking water) for 2, 4, and 8 weeks, and their livers were then removed for analysis. Enzymatic induction was produced by treating rats with phenobarbital (to induce CYP2B1/2), beta-naphthoflavone (to induce CYP1A1/2), or pyrazole (to induce CYP2E1). L-NAME significantly elevated blood pressure; this was reversed by concomitant treatment with enalapril (ACE inhibitor) or losartan (angiotensin II AT(1) receptor antagonist). L-NAME caused vascular hypertrophy in hepatic arteries, with perivascular and interstitial fibrosis involving collagen deposition. Hepatic glycogen content also significantly increased. L-NAME did not affect fasting glucose levels but significantly reduced insulin levels and increased the insulin sensitivity of rats, based on an intraperitoneal glucose tolerance test. Immunoblotting experiments indicated enhanced phosphorylation of protein kinase B and of glycogen synthase kinase 3. All these changes were reversed by concomitant treatment with enalapril or losartan. L-NAME had no effect on hepatic cholesterol or triglyceride content or on the basal or drug-induced activities and protein expression of the cytochrome P450 isoforms. Thus, the chronic inhibition of NO biosynthesis produced hepatic morphological alterations and changes in glycogen metabolism mediated by the renin-angiotensin system. The increase in hepatic glycogen content probably resulted from enhanced glycogen synthase activity following the inhibition of glycogen synthase kinase 3 by phosphorylation.     

FTIR studies of the redox partner interaction in cytochrome P450: The Pdx–P450cam couple

Recently we have developed a new approach to study protein–protein interactions using Fourier transform infrared spectroscopy in combination with titration experiments and principal component analysis (FTIR-TPCA). In the present paper we review the FTIR-TPCA results obtained for the interaction between cytochrome P450 and the redox partner protein in two P450 systems, the Pseudomonas putida P450cam (CYP101) with putidaredoxin (P450cam–Pdx), and the Bacillus megaterium P450BM-3 (CYP102) heme domain with the FMN domain (P450BMP–FMND). Both P450 systems reveal similarities in the structural changes that occur upon redox partner complex formation. These involve an increase in β-sheets and α-helix content, a decrease in the population of random coil/3₁₀-helix structure, a redistribution of turn structures within the interacting proteins and changes in the protonation states or hydrogen-bonding of amino acid carboxylic side chains. We discuss in detail the P450cam–Pdx interaction in comparison with literature data and conclusions drawn from experiments obtained by other spectroscopic techniques. The results are also interpreted in the context of a 3D structural model of the Pdx–P450cam complex.     

Why do female Lesser Spotted Eagles ( Aquila pomarina ) visit strange nests remote from their own?

There is very little confirmed information on the social organisation of breeding Lesser Spotted Eagle populations, the turnover rate of adults, and their nest-site and partner fidelity. According to established knowledge, however, breeding individuals are territorial and defend at least the immediate vicinity of the nest site against their own species. It has further been thought that females rearing young, as with the females of other raptor species, remain within a radius of only a few kilometres of their eyrie. Using GPS satellite telemetry and DNA microsatellite analysis (DNA STR typing), we were able to disprove this prevailing hypothesis. A satellite-tracked female flew over 50 km away from her eyrie (D) in at least two different directions and visited at least one other occupied eyrie (T). It was also established that at least two strange females arrived at her eyrie, which contained young, from as far away as 57 km, and probably remained there for some considerable time. The pool of alleles represented at the different loci analysed, as well as the distribution of these alleles among the individuals, excludes the possibility that these females could be sisters or even half-sisters. Visits of strange eagles at this eyrie were also confirmed by direct observation. It can therefore be assumed that males only exhibit territorial behaviour towards their own sex and not towards strange females and that females do not exhibit territorial behaviour towards other females; but all these assumptions must be confirmed by further studies. For the first time it could be proved by means of microsatellite analysis that almost all females studied used the same breeding site for 2 consecutive years. The longest established period in which both partners of a pair remained at the same breeding site was 3 consecutive years.