Heat shock response and autophagy—cooperation and control

Protein quality control (proteostasis) depends on constant protein degradation and resynthesis, and is essential for proper homeostasis in systems from single cells to whole organisms. Cells possess several mechanisms and processes to maintain proteostasis. At one end of the spectrum, the heat shock proteins modulate protein folding and repair. At the other end, the proteasome and autophagy as well as other lysosome-dependent systems, function in the degradation of dysfunctional proteins. In this review, we examine how these systems interact to maintain proteostasis. Both the direct cellular data on heat shock control over autophagy and the time course of exercise-associated changes in humans support the model that heat shock response and autophagy are tightly linked. Studying the links between exercise stress and molecular control of proteostasis provides evidence that the heat shock response and autophagy coordinate and undergo sequential activation and downregulation, and that this is essential for proper proteostasis in eukaryotic systems.     

Modulating Cognition Using Transcranial Direct Current Stimulation of the Cerebellum

Numerous studies have emerged recently that demonstrate the possibility of modulating, and in some cases enhancing, cognitive processes by exciting brain regions involved in working memory and attention using transcranial electrical brain stimulation. Some researchers now believe the cerebellum supports cognition, possibly via a remote neuromodulatory effect on the prefrontal cortex. This paper describes a procedure for investigating a role for the cerebellum in cognition using transcranial direct current stimulation (tDCS), and a selection of information-processing tasks of varying task difficulty, which have previously been shown to involve working memory, attention and cerebellar functioning. One task is called the Paced Auditory Serial Addition Task (PASAT) and the other a novel variant of this task called the Paced Auditory Serial Subtraction Task (PASST). A verb generation task and its two controls (noun and verb reading) were also investigated. All five tasks were performed by three separate groups of participants, before and after the modulation of cortico-cerebellar connectivity using anodal, cathodal or sham tDCS over the right cerebellar cortex. The procedure demonstrates how performance (accuracy, verbal response latency and variability) could be selectively improved after cathodal stimulation, but only during tasks that the participants rated as difficult, and not easy. Performance was unchanged by anodal or sham stimulation. These findings demonstrate a role for the cerebellum in cognition, whereby activity in the left prefrontal cortex is likely dis-inhibited by cathodal tDCS over the right cerebellar cortex. Transcranial brain stimulation is growing in popularity in various labs and clinics. However, the after-effects of tDCS are inconsistent between individuals and not always polarity-specific, and may even be task- or load-specific, all of which requires further study. Future efforts might also be guided towards neuro-enhancement in cerebellar patients presenting with cognitive impairment once a better understanding of brain stimulation mechanisms has emerged.     

Revisiting the phylogeography and demography of European badgers (Meles meles) based on broad sampling,multiple markers and simulations

Although the phylogeography of European mammals has been extensively investigated since the 1990s, many studies were limited in terms of sampling distribution, the number of molecular markers used and the analytical techniques employed, frequently leading to incomplete postglacial recolonisation scenarios. The broad-scale genetic structure of the European badger (Meles meles) is of interest as it may result from historic restriction to glacial refugia and/or recent anthropogenic impact. However, previous studies were based mostly on samples from western Europe, making it difficult to draw robust conclusions about the location of refugia, patterns of postglacial expansion and recent demography. In the present study, continent-wide sampling and analyses with multiple markers provided evidence for two glacial refugia (Iberia and southeast Europe) that contributed to the genetic variation observed in badgers in Europe today. Approximate Bayesian computation provided support for a colonisation of Scandinavia from both Iberian and southeastern refugia. In the whole of Europe, we observed a decline in genetic diversity with increasing latitude, suggesting that the reduced diversity in the peripheral populations resulted from a postglacial expansion processes. Although MSVAR v.1.3 also provided evidence for recent genetic bottlenecks in some of these peripheral populations, the simulations performed to estimate the method''s power to correctly infer the past demography of our empirical populations suggested that the timing and severity of bottlenecks could not be established with certainty. We urge caution against trying to relate demographic declines inferred using MSVAR with particular historic or climatological events.     

Intraspecific resource partitioning by an opportunistic strategist, inland silverside Menidia beryllina

Seasonal variation in prey consumption and food resource overlap was evident in an inland water body for mature male, mature female and immature inland silverside (Menidia beryllina). During the first growth phase marked by intensive somatic growth by immature inland silverside, few adults were present in the population (28% of total catch), thus minimizing intraspecific competition for food resources between juvenile and adult inland silverside. During the second growth phase by adults, few juvenile inland silverside were present (0% of total catch) in the population, again minimizing intraspecific competition for food resources between juvenile and adult inland silverside. A divergence in food resource overlap was observed when mature male, mature female and immature inland silverside were present in the population. These population‐level demographic responses to energy acquisition are likely necessary to maximize individual growth of mature male, mature female and immature inland silverside.     

Genome sequence, structural proteins, and capsid organization of the cyanophage Syn5: a "horned" bacteriophage of marine synechococcus

Marine Synechococcus spp and marine Prochlorococcus spp are numerically dominant photoautotrophs in the open oceans and contributors to the global carbon cycle. Syn5 is a short-tailed cyanophage isolated from the Sargasso Sea on Synechococcus strain WH8109. Syn5 has been grown in WH8109 to high titer in the laboratory and purified and concentrated retaining infectivity. Genome sequencing and annotation of Syn5 revealed that the linear genome is 46,214 bp with a 237 bp terminal direct repeat. Sixty-one open reading frames (ORFs) were identified. Based on genomic organization and sequence similarity to known protein sequences within GenBank, Syn5 shares features with T7-like phages. The presence of a putative integrase suggests access to a temperate life cycle. Assignment of 11 ORFs to structural proteins found within the phage virion was confirmed by mass-spectrometry and N-terminal sequencing. Eight of these identified structural proteins exhibited amino acid sequence similarity to enteric phage proteins. The remaining three virion proteins did not resemble any known phage sequences in GenBank as of August 2006. Cryo-electron micrographs of purified Syn5 virions revealed that the capsid has a single “horn”, a novel fibrous structure protruding from the opposing end of the capsid from the tail of the virion. The tail appendage displayed an apparent 3-fold rather than 6-fold symmetry. An 18 Å resolution icosahedral reconstruction of the capsid revealed a T = 7 lattice, but with an unusual pattern of surface knobs. This phage/host system should allow detailed investigation of the physiology and biochemistry of phage propagation in marine photosynthetic bacteria.     

Activation of the galanin receptor 2 (GalR2) protects the hippocampus from neuronal damage

Expression of the neuropeptide galanin is up-regulated in many brain regions following nerve injury and in the basal forebrain of patients with Alzheimer's disease. We have previously demonstrated that galanin modulates hippocampal neuronal survival, although it was unclear which receptor subtype(s) mediates this effect. Here we report that the protective role played by galanin in hippocampal cultures is abolished in animals carrying a loss-of-function mutation in the second galanin receptor subtype (GalR2-MUT). Exogenous galanin stimulates the phosphorylation of the serine/threonine kinase Akt and extracellular signal-regulated kinase (ERK) in wild-type (WT) cultures by 435 +/- 5% and 278 +/- 2%, respectively. The glutamate-induced activation of Akt was abolished in cultures from galanin knockout animals, and was markedly attenuated in GalR2-MUT animals, compared with WT controls. In contrast, similar levels of glutamate-induced ERK activation were observed in both loss-of-function mutants, but were further increased in galanin over-expressing animals. Using specific inhibitors of either ERK or Akt confirms that a GalR2-dependent modulation in the activation of the Akt and ERK signalling pathways contributes to the protective effects of galanin. These findings imply that the rise in endogenous galanin observed either after brain injury or in various disease states is an adaptive response that reduces apoptosis by the activation of GalR2, and hence Akt and ERK.     

NO-cGMP mediated galanin expression in NGF-deprived or axotomized sensory neurons

Leukaemia inhibitory factor (LIF) and nerve growth factor (NGF) are well characterized regulators of galanin expression. However, LIF knockout mice containing the rat galanin 5' proximal promoter fragment (- 2546 to + 15 bp) driving luciferase responded to axotomy in the same way as control mice. Also, LIF had no effect on reporter gene expression in vitro, neither in the presence or absence of NGF, suggesting that other factors mediate an axotomy response from the galanin promoter. We then addressed the role of nitric oxide (NO) using NGF-deprived rat dorsal root ganglion (DRG) neuron cultures infected with viral vectors containing the above-mentioned construct, and also studied endogenous galanin expression in axotomized DRG in vivo. Blocking endogenous NO in NGF-deprived DRG cultures suppressed galanin promoter activity. Consistent with this, axotomized/NGF-deprived DRG neurons expressed high levels of neuronal NO synthase (nNOS) and galanin. Further, using pharmacological NOS blockers, or adenoviral vectors expressing dominant-negative either for nNOS or soluble guanylate cyclase in vivo and in vitro, we show that the NO-cGMP pathway induces endogenous galanin in DRG neurons. We propose that both LIF and NO, acting at different promoter regions, are important for the up-regulation of galanin, and for DRG neuron survival and regeneration after axotomy.