Senescing human cells and ageing mice accumulate DNA lesions with unrepairable double-strand breaks

Humans and animals undergo ageing, and although their primary cells undergo cellular senescence in culture, the relationship between these two processes is unclear. Here we show that gamma-H2AX foci (gamma-foci), which reveal DNA double-strand breaks (DSBs), accumulate in senescing human cell cultures and in ageing mice. They colocalize with DSB repair factors, but not significantly with telomeres. These cryptogenic gamma-foci remain after repair of radiation-induced gamma-foci, suggesting that they may represent DNA lesions with unrepairable DSBs. Thus, we conclude that accumulation of unrepairable DSBs may have a causal role in mammalian ageing.     

Mistaken Identifiers: Gene name errors can be introduced inadvertently when using Excel in bioinformatics

Background  

When processing microarray data sets, we recently noticed that some gene names were being changed inadvertently to non-gene names.     

Motion-sensitive neurones in V5/MT modulate perceived spatial position

Until recently, it was widely believed that object position and object motion were represented independently in the visual cortex. However, several studies have shown that adaptation to motion produces substantial shifts in the perceived position of subsequently viewed stationary objects. Two stages of motion adaptation have been proposed: an initial stage at the level of V1 and a secondary stage thought to be located in V5/MT. Indeed, selective adaptation can be demonstrated at each of these levels of motion analysis. What remains unknown is which of these cortical sites are involved in modulating the positional representation of subsequently viewed objects. To answer this question directly, we disrupted cortical activity by using transcranial magnetic stimulation (TMS) immediately after motion adaptation. When TMS was delivered to V5/MT after motion adaptation, the perceived offset of the test stimulus was greatly reduced. In marked contrast, TMS of V1 had no effect on the changes that normally occur in perceived position after motion adaptation. This result demonstrates that the anatomical locus at which motion and positional information interact is area V5/MT rather than V1/V2.     

Mating strategies in flowering plants: the outcrossing-selfing paradigm and beyond

Comparisons of the causes and consequences of cross- and self-fertilization have dominated research on plant mating since Darwin's seminal work on plant reproduction. Here, I provide examples of these accomplishments, but also illustrate new approaches that emphasize the role of floral design and display in pollen dispersal and fitness gain through male function. Wide variation in outcrossing rate characterizes animal-pollinated plants. In species with large floral displays, part of the selfing component of mixed mating can arise from geitonogamy and be maladaptive because of strong inbreeding depression and pollen discounting. Floral strategies that separate the benefits of floral display from the mating costs associated with geitonogamy can resolve these conflicts by reducing lost mating opportunities through male function. The results from experiments with marker genes and floral manipulations provide evidence for the function of herkogamy and dichogamy in reducing self-pollination and promoting pollen dispersal. Evidence is also presented indicating that increased selfing resulting from changes to floral design, or geitonogamy in large clones, can act as a stimulus for the evolution of dioecy. The scope of future research on mating strategies needs to be broadened to include investigations of functional links among flowers, inflorescences and plant architecture within the framework of life-history evolution.     

Origin and evolution of Japanese encephalitis virus in southeast Asia

Since it emerged in Japan in the 1870s, Japanese encephalitis has spread across Asia and has become the most important cause of epidemic encephalitis worldwide. Four genotypes of Japanese encephalitis virus (JEV) are presently recognized (representatives of genotypes I to III have been fully sequenced), but its origin is not known. We have determined the complete nucleotide and amino acid sequence of a genotype IV Indonesian isolate (JKT6468) which represents the oldest lineage, compared it with other fully sequenced genomes, and examined the geographical distribution of all known isolates. JKT6468 was the least similar, with nucleotide divergence ranging from 17.4 to 19.6% and amino acid divergence ranging from 4.7 to 6.5%. It included an unusual series of amino acids at the carboxy terminus of the core protein unlike that seen in other JEV strains. Three signature amino acids in the envelope protein (including E327 Leu-->Thr/Ser on the exposed lateral surface of the putative receptor binding domain) distinguished genotype IV strains from more recent genotypes. Analysis of all 290 JEV isolates for which sequence data are available showed that the Indonesia-Malaysia region has all genotypes of JEV circulating, whereas only more recent genotypes circulate in other areas (P < 0.0001). These results suggest that JEV originated from its ancestral virus in the Indonesia-Malaysia region and evolved there into the different genotypes which then spread across Asia. Our data, together with recent evidence on the origins of other emerging viruses, including dengue virus and Nipah virus, imply that tropical southeast Asia may be an important zone for emerging pathogens.     

The shape of the force-elbow angle relationship for maximal voluntary contractions and sub-maximal electrically induced contractions in human elbow flexors

The force-length relationship is a basic property of skeletal muscle. Knowledge of this relationship is necessary for most analyses of human movement, and in simulation models predicting movement control strategies. Studies on animal muscles have shown that force-length relationships for sub-maximal contractions are not related through a simple scaling procedure to the relationship for maximal contractions. Furthermore, potentiation might produce a shift of sub-maximal relative to maximal force-length relationships. In this study, we tested the hypothesis that human force-elbow angle relationships for sub-maximal unpotentiated contractions are shifted to larger elbow angles (i.e. larger muscle lengths) compared to the relationship for maximal voluntary contractions (MVC), and that this shift is reduced, or even abolished, for sub-maximal potentiated contractions. Force-elbow angle relationships (48-160 degrees) were obtained from healthy subjects (n=13). At each of nine tested elbow angles, the test set consisted of a single twitch (ST(pre)) and a doublet twitch (DT(pre)) stimulation of m. biceps brachii, followed by an MVC, followed by another single twitch (ST(post)) and a doublet twitch (DT(post)) stimulation. The single and doublet twitches induced sub-maximal contractions. The force-elbow angle relationships for the pre-MVC (unpotentiated) twitch contractions were shifted to larger angles compared to those obtained for MVC. The force-elbow angle relationships for the post-MVC (potentiated) twitch contractions were shifted to smaller angles compared to those obtained for the unpotentiated twitch contractions. These results support the idea that the shift to larger muscle lengths for the sub-maximal, unpotentiated force-length relationships relative to the relationship for maximal contractions may be caused by a length-dependent Ca(2+) sensitivity that may be offset, at least in part, by potentiation.     

The development of enantiostyly

Enantiostyly, the deflection of the style either to the left (left-styled) or right (right-styled) side of the floral axis, has evolved in at least ten angiosperm families. Two types of enantiostyly occur: monomorphic enantiostyly, in which individuals exhibit both stylar orientations, and dimorphic enantiostyly, in which the two stylar orientations occur on separate plants. To evaluate architectural or developmental constraints on the evolution of both forms of enantiostyly, we examined inflorescence structure and floral development among unrelated enantiostylous species. We investigated relations between the position of left- and right-styled flowers and inflorescence architecture in four monomorphic enantiostylous species, and we examined the development of enantiostyly in nine monomorphic and dimorphic enantiostylous species from five unrelated lineages. The location of left- and right-styled flowers within inflorescences ranged from highly predictable (in Solanum rostratum) to random (in Heteranthera mexicana). There were striking differences among taxa in the timing of stylar bending. In Wachendorfia paniculata, Dilatris corymbosa, and Philydrum lanuginosum, the style deflected in the bud, whereas in Heteranthera spp., Monochoria australasica, Cyanella lutea, and Solanum rostratum, stylar bending occurred at the beginning of anthesis. Comparisons of organ initiation and development indicated that asymmetries along the left-right axis were expressed very late in development, despite the early initiation of a dorsiventral asymmetry. We suggest that the evolution of dimorphic enantiostyly from monomorphic enantiostyly may be constrained by a lack of left-right positional information in the bud.     

Modified peptide antagonists of interleukin 5 exhibit extended in vivo persistence but restricted species specificity

AF18748 is disulphide-linked homodimeric peptide with 19 amino acids in each chain that antagonises the action of the eosinophil-specific cytokine, interleukin 5 (IL-5). We have generated a set of N-terminally truncated peptides derived from AF18748 and demonstrated that the first five amino acids of the peptide do not contribute to receptor binding activity. The shortened peptide blocked IL-5-dependent adhesion of eosinophils with an IC(50)of 350 pM, and had no effect on stimulation by IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), tumour necrosis factor (TNF)-alpha or fMet-Leu-Phe. The peptides were rapidly broken down in mouse plasma through cleavage of a single chain of the dimer. However, this breakdown did not correlate with loss of biological activity, indicating that the asymmetric peptide fragment retains full receptor binding capacity. The activity of AF18748 disappeared rapidly from the blood following intravenous injection into mice. Coupling of polyethylene glycol to the N-terminus of AF18748 resulted in a moderate loss in biological potency (IC(50)30 nM), but the resulting conjugate persisted in the circulation for more than 8 h after injection. Despite its high potency at the human IL-5 receptor, AF18748 was unable to antagonise the activity of IL-5 on murine B13 cells, or on canine eosinophils, indicating that the peptide is highly specific for the human IL-5 receptor.     

An improved GC/MS-based procedure for the quantitation of the isoprostane 15-F2t-IsoP in rat plasma

This article describes a procedure for the quantitation of the isoprostane 15-F_2t-IsoP (9a,11a,15S-trihydroxy-(8b)-prosta-5Z,13E-dien-1-oic acid [CAS#27415-26-5] formerly known as 8-epi-PGF_2a or 8-iso-PGF_2a, and also as iPF_2a-III). We have combined features from several earlier methods for 15-F_2t-IsoP and prostaglandins, and identified and modified those steps that may lead to poor recoveries. The resulting protocol is precise and reliable, and was validated by a blind time-course study of plasma levels in rats treated with 120 and 1200 mg CCl₄/kg body weight. Plasma levels of 15-F_2t-IsoP, as measured according to the procedure described above, are good indicators of acute oxidative stress as induced by CCl₄. The precision of the measurements allows detection of elevated plasma 15-F_2t-IsoP levels as long as 16 h after an acute exposure of 120 mg CCl₄/kg body weight, and 2 h after an exposure of 1 mg CCl₄/kg body weight. The results of this low-dose, pilot study suggest that this method has sufficient analytical precision to allow the detection of the small changes in plasma isoprostane levels, which result from chronic and/or lower-level exposures to agents causing oxidative stress.