The role of DNA methylation in setting up chromatin structure during development

DNA methylation inhibits gene expression in animal cells, probably by affecting chromatin structure. Biochemical studies suggest that this process may be mediated by methyl-specific binding proteins that recruit enzymatic machinery capable of locally altering histone modification. To test whether DNA methylation actually has a role in the assembly of chromatin during normal development, we used cell transfection and a transgene construct genetically programmed to be either methylated or unmethylated in all cell types of the mouse. Chromatin immunoprecipitation (ChIP) analysis shows that the presence of DNA methylation brings about the deacetylation of histone H4 and methylation of Lys9 of histone H3 (H3 Lys9) and prevents methylation of Lys4 of histone H3 (H3 Lys4), thus generating a structure identical to that of methylated sequences in the genome. These results indicate that the methylation pattern established in early embryogenesis is profoundly important in setting up the structural profile of the genome.     

Functional interactions between receptors in bacterial chemotaxis

Bacterial chemotaxis is a model system for signal transduction, noted for its relative simplicity, high sensitivity, wide dynamic range and robustness. Changes in ligand concentrations are sensed by a protein assembly consisting of transmembrane receptors, a coupling protein (CheW) and a histidine kinase (CheA). In Escherichia coli, these components are organized at the cell poles in tight clusters that contain several thousand copies of each protein. Here we studied the effects of variation in the composition of clusters on the activity of the kinase and its sensitivity to attractant stimuli, monitoring responses in vivo using fluorescence resonance energy transfer. Our results indicate that assemblies of bacterial chemoreceptors work in a highly cooperative manner, mimicking the behaviour of allosteric proteins. Conditions that favour steep responses to attractants in mutants with homogeneous receptor populations also enhance the sensitivity of the response in wild-type cells. This is consistent with a number of models that assume long-range cooperative interactions between receptors as a general mechanism for signal integration and amplification.     

Coral communities are regionally enriched along an oceanic biodiversity gradient

Ecological communities are influenced by processes operating at multiple scales. Thus, a better understanding of how broad- as well as local-scale processes affect species diversity and richness is increasingly becoming a central focus in modern community ecology. Here, in a study of unprecedented geographical scope, we show significant regional and local variation in the species richness of coral assemblages across an oceanic biodiversity gradient. The gradient that we sampled extends 10,000 km eastwards from the world's richest coral biodiversity hotspot in the central Indo-Pacific. Local richness and the size of regional species pools decline significantly across 15 islands spanning the gradient. In addition, richness declines across three adjacent habitats (reef slopes, crests and flats). In each habitat, a highly consistent linear relationship between local and regional species richness indicates strong regional enrichment. Thus, even on the most diverse coral reefs in the world, local coral assemblages are profoundly affected by regional-scale processes. Understanding these historical and biogeographical influences is essential for the effective management and preservation of these endangered communities.     

Premature ageing in mice expressing defective mitochondrial DNA polymerase

Point mutations and deletions of mitochondrial DNA (mtDNA) accumulate in a variety of tissues during ageing in humans, monkeys and rodents. These mutations are unevenly distributed and can accumulate clonally in certain cells, causing a mosaic pattern of respiratory chain deficiency in tissues such as heart, skeletal muscle and brain. In terms of the ageing process, their possible causative effects have been intensely debated because of their low abundance and purely correlative connection with ageing. We have now addressed this question experimentally by creating homozygous knock-in mice that express a proof-reading-deficient version of PolgA, the nucleus-encoded catalytic subunit of mtDNA polymerase. Here we show that the knock-in mice develop an mtDNA mutator phenotype with a threefold to fivefold increase in the levels of point mutations, as well as increased amounts of deleted mtDNA. This increase in somatic mtDNA mutations is associated with reduced lifespan and premature onset of ageing-related phenotypes such as weight loss, reduced subcutaneous fat, alopecia (hair loss), kyphosis (curvature of the spine), osteoporosis, anaemia, reduced fertility and heart enlargement. Our results thus provide a causative link between mtDNA mutations and ageing phenotypes in mammals.     

Impaired PtdIns(4,5)P2 synthesis in nerve terminals produces defects in synaptic vesicle trafficking

Phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) has an important function in cell regulation both as a precursor of second messenger molecules and by means of its direct interactions with cytosolic and membrane proteins. Biochemical studies have suggested a role for PtdIns(4,5)P2 in clathrin coat dynamics, and defects in its dephosphorylation at the synapse produce an accumulation of coated endocytic intermediates. However, the involvement of PtdIns(4,5)P2 in synaptic vesicle exocytosis remains unclear. Here, we show that decreased levels of PtdIns(4,5)P2 in the brain and an impairment of its depolarization-dependent synthesis in nerve terminals lead to early postnatal lethality and synaptic defects in mice. These include decreased frequency of miniature currents, enhanced synaptic depression, a smaller readily releasable pool of vesicles, delayed endocytosis and slower recycling kinetics. Our results demonstrate a critical role for PtdIns(4,5)P2 synthesis in the regulation of multiple steps of the synaptic vesicle cycle.     

An interplanetary shock traced by planetary auroral storms from the Sun to Saturn

A relationship between solar activity and aurorae on Earth was postulated long before space probes directly detected plasma propagating outwards from the Sun. Violent solar eruption events trigger interplanetary shocks that compress Earth's magnetosphere, leading to increased energetic particle precipitation into the ionosphere and subsequent auroral storms. Monitoring shocks is now part of the 'Space Weather' forecast programme aimed at predicting solar-activity-related environmental hazards. The outer planets also experience aurorae, and here we report the discovery of a strong transient polar emission on Saturn, tentatively attributed to the passage of an interplanetary shock--and ultimately to a series of solar coronal mass ejection (CME) events. We could trace the shock-triggered events from Earth, where auroral storms were recorded, to Jupiter, where the auroral activity was strongly enhanced, and to Saturn, where it activated the unusual polar source. This establishes that shocks retain their properties and their ability to trigger planetary auroral activity throughout the Solar System. Our results also reveal differences in the planetary auroral responses on the passing shock, especially in their latitudinal and local time dependences.     

大熊猫电刺激采精及精液冷冻保存研究

对卧龙自然保护区大熊猫研究中心的９只５．５－１６．５岁的雄性大熊猫进行了１７次电刺激采精,其中３只是能进行自然交配并繁殖了后代的种公兽,比较研究了精液离心、不同稀释液和冷冻方法对大熊猫精液超低温冷冻保存后的活力、运动状态、精子和顶体形态的影响。细冷冻是１种较好的超低温冷冻精液的方法。     

Microdeletion encompassing MAPT at chromosome 17q21.3 is associated with developmental delay and learning disability

Recently, the application of array-based comparative genomic hybridization (array CGH) has improved rates of detection of chromosomal imbalances in individuals with mental retardation and dysmorphic features. Here, we describe three individuals with learning disability and a heterozygous deletion at chromosome 17q21.3, detected in each case by array CGH. FISH analysis demonstrated that the deletions occurred as de novo events in each individual and were between 500 kb and 650 kb in size. A recently described 900-kb inversion that suppresses recombination between ancestral H1 and H2 haplotypes encompasses the deletion. We show that, in each trio, the parent of origin of the deleted chromosome 17 carries at least one H2 chromosome. This region of 17q21.3 shows complex genomic architecture with well-described low-copy repeats (LCRs). The orientation of LCRs flanking the deleted segment in inversion heterozygotes is likely to facilitate the generation of this microdeletion by means of non-allelic homologous recombination.     

Progress and prospects in rat genetics: a community view

The rat is an important system for modeling human disease. Four years ago, the rich 150-year history of rat research was transformed by the sequencing of the rat genome, ushering in an era of exceptional opportunity for identifying genes and pathways underlying disease phenotypes. Genome-wide association studies in human populations have recently provided a direct approach for finding robust genetic associations in common diseases, but identifying the precise genes and their mechanisms of action remains problematic. In the context of significant progress in rat genomic resources over the past decade, we outline achievements in rat gene discovery to date, show how these findings have been translated to human disease, and document an increasing pace of discovery of new disease genes, pathways and mechanisms. Finally, we present a set of principles that justify continuing and strengthening genetic studies in the rat model, and further development of genomic infrastructure for rat research.