Disruptive coloration and background pattern matching

Effective camouflage renders a target indistinguishable from irrelevant background objects. Two interrelated but logically distinct mechanisms for this are background pattern matching (crypsis) and disruptive coloration: in the former, the animal's colours are a random sample of the background; in the latter, bold contrasting colours on the animal's periphery break up its outline. The latter has long been proposed as an explanation for some apparently conspicuous coloration in animals, and is standard textbook material. Surprisingly, only one quantitative test of the theory exists, and one experimental test of its effectiveness against non-human predators. Here we test two key predictions: that patterns on the body's outline should be particularly effective in promoting concealment and that highly contrasting colours should enhance this disruptive effect. Artificial moth-like targets were exposed to bird predation in the field, with the experimental colour patterns on the 'wings' and a dead mealworm as the edible 'body'. Survival analysis supported the predictions, indicating that disruptive coloration is an effective means of camouflage, above and beyond background pattern matching.     

Three-dimensional structure of the bacterial protein-translocation complex SecYEG

Transport and membrane integration of polypeptides is carried out by specific protein complexes in the membranes of all living cells. The Sec transport path provides an essential and ubiquitous route for protein translocation. In the bacterial cytoplasmic membrane, the channel is formed by oligomers of a heterotrimeric membrane protein complex consisting of subunits SecY, SecE and SecG. In the endoplasmic reticulum membrane, the channel is formed from the related Sec61 complex. Here we report the structure of the Escherichia coli SecYEG assembly at an in-plane resolution of 8 A. The three-dimensional map, calculated from two-dimensional SecYEG crystals, reveals a sandwich of two membranes interacting through the extensive cytoplasmic domains. Each membrane is composed of dimers of SecYEG. The monomeric complex contains 15 transmembrane helices. In the centre of the dimer we observe a 16 x 25 A cavity closed on the periplasmic side by two highly tilted transmembrane helices. This may represent the closed state of the protein-conducting channel.     

Protocadherins mediate dendritic self-avoidance in the mammalian nervous system

Dendritic arborizations of many neurons are patterned by a process called self-avoidance, in which branches arising from a single neuron repel each other. By minimizing gaps and overlaps within the arborization, self-avoidance facilitates complete coverage of a neuron’s territory by its neurites. Remarkably, some neurons that display self-avoidance interact freely with other neurons of the same subtype, implying that they discriminate self from non-self. Here we demonstrate roles for the clustered protocadherins (Pcdhs) in dendritic self-avoidance and self/non-self discrimination. The Pcdh locus encodes 58 related cadherin-like transmembrane proteins, at least some of which exhibit isoform-specific homophilic adhesion in heterologous cells and are expressed stochastically and combinatorially in single neurons. Deletion of all 22 Pcdh genes in the mouse γ-subcluster (Pcdhg genes) disrupts self-avoidance of dendrites in retinal starburst amacrine cells (SACs) and cerebellar Purkinje cells. Further genetic analysis of SACs showed that Pcdhg proteins act cell-autonomously during development, and that replacement of the 22 Pcdhg proteins with a single isoform restores self-avoidance. Moreover, expression of the same single isoform in all SACs decreases interactions among dendrites of neighbouring SACs (heteroneuronal interactions). These results suggest that homophilic Pcdhg interactions between sibling neurites (isoneuronal interactions) generate a repulsive signal that leads to self-avoidance. In this model, heteroneuronal interactions are normally permitted because dendrites seldom encounter a matched set of Pcdhg proteins unless they emanate from the same soma. In many respects, our results mirror those reported for Dscam1 (Down syndrome cell adhesion molecule) in Drosophila: this complex gene encodes thousands of recognition molecules that exhibit stochastic expression and isoform-specific interactions, and mediate both self-avoidance and self/non-self discrimination. Thus, although insect Dscam and vertebrate Pcdh proteins share no sequence homology, they seem to underlie similar strategies for endowing neurons with distinct molecular identities and patterning their arborizations.     

Prediction of central nervous system embryonal tumour outcome based on gene expression.

Embryonal tumours of the central nervous system (CNS) represent a heterogeneous group of tumours about which little is known biologically, and whose diagnosis, on the basis of morphologic appearance alone, is controversial. Medulloblastomas, for example, are the most common malignant brain tumour of childhood, but their pathogenesis is unknown, their relationship to other embryonal CNS tumours is debated, and patients' response to therapy is difficult to predict. We approached these problems by developing a classification system based on DNA microarray gene expression data derived from 99 patient samples. Here we demonstrate that medulloblastomas are molecularly distinct from other brain tumours including primitive neuroectodermal tumours (PNETs), atypical teratoid/rhabdoid tumours (AT/RTs) and malignant gliomas. Previously unrecognized evidence supporting the derivation of medulloblastomas from cerebellar granule cells through activation of the Sonic Hedgehog (SHH) pathway was also revealed. We show further that the clinical outcome of children with medulloblastomas is highly predictable on the basis of the gene expression profiles of their tumours at diagnosis.     

A membrane protein complex mediates retro-translocation from the ER lumen into the cytosol

Elimination of misfolded proteins from the endoplasmic reticulum (ER) by retro-translocation is an important physiological adaptation to ER stress. This process requires recognition of a substrate in the ER lumen and its subsequent movement through the membrane by the cytosolic p97 ATPase. Here we identify a p97-interacting membrane protein complex in the mammalian ER that links these two events. The central component of the complex, Derlin-1, is a homologue of Der1, a yeast protein whose inactivation prevents the elimination of misfolded luminal ER proteins. Derlin-1 associates with different substrates as they move through the membrane, and inactivation of Derlin-1 in C. elegans causes ER stress. Derlin-1 interacts with US11, a virally encoded ER protein that specifically targets MHC class I heavy chains for export from the ER, as well as with VIMP, a novel membrane protein that recruits the p97 ATPase and its cofactor.     

Recent temperature trends in the Antarctic

It is important to understand how temperatures across the Antarctic have changed in recent decades because of the huge amount of fresh water locked into the ice sheet and the impact that temperature changes may have on the ice volume. Doran et al. claim that there has been a net cooling of the entire continent between 1966 and 2000, particularly during summer and autumn. We argue that this result has arisen because of an inappropriate extrapolation of station data across large, data-sparse areas of the Antarctic.     

PS2消防游戏《厄运》登场

最近一段时间,消防员游戏似乎一下子受到了游戏厂商们的关注.自<18号消防员>和<樱坂消防队>后,知名游戏公司Spike在不久前又公布了一款以消防员为题材的PS2动作冒险游戏<厄运:英雄归来(HardLuck:Return of the Heroes)>,在这款游戏中,三位消防英雄将会奋不顾身的冲入火场,拯救火灾中的无数遇害者.     

Distribution of phenylalanine transaminase and phenylalanine ammonia-lyase activities in etiolated and light irradiated radish seedlings (Raphanus sativus L.).

In dark-grown Raphanus sativus seedlings the level of phenylalanine transaminase is higher in cotyledons than in root and hypocotyl. The maximum activity of phenylalanine ammonia-lyase (PAL) is found in the root. Only PAL is significantly increased by light.