Sequence variation in the outer-surface-protein genes of Borrelia burgdorferi

Borrelia burgdorferi is a spirochete pathogen transmitted among warm- blooded hosts by ixodid ticks. Frequency-dependent selection for variant outer-surface proteins might be expected to arise in this species, since rare variants are more likely to avoid immune surveillance in previously infected hosts. We sequenced the OspA and OspB genes of nine North American strains and compared them with nine strains previously described. For each gene, the mean number of synonymous substitutions per synonymous site and the mean number of nonsynonymous substitutions per nonsynonymous site show only a twofold excess of silent mutations. Synonymous rates vary widely along the OspB protein. Some regions show a significant excess of silent substitutions, while divergence in other regions is constrained by biased base composition or selection. The presence, in antigenically important regions of the protein, of significant variation among strains, as well as evidence for recombination among strains, should be considered in attempts to develop vaccines against this disease.      

产超广谱β- 内酰胺酶肺炎克雷伯菌耐药性及其基因分型分析

目的:了解新疆独山子地区肺炎克雷伯菌超广谱β-内酰胺酶(ESBLs)的发生率、作为指示剂的五种抗生素的检出情况及ESBLs主要基因型。方法:收集临床分离的148株肺炎克雷伯菌,采用双纸片协同筛选法、NCCLS推荐的表型筛选和确证试验对细菌进行ESBLs产酶株的识别;耐药基因的质粒重组、转化,聚合酶链反应(PCR)扩增阳性产物测序,通过GenBank对序确定基因型。结果:本地区肺炎克雷伯菌ESBLs的分离率达31.1%,头孢曲松(CRO)安曲南(ATM)和头孢噻肟(CTX)头孢泊肟(CPD)、头孢他定(CAZ)作为指示剂检出率分别为97.8%、95.6%、93.4%、76.0%、65.2%;本地区产ESBLs菌株耐药基因型CTX-M-22占54.3%,CTX-M-18占41.3%,TEM61.8%,52.1%的产ESBLs肺炎克雷伯菌SHV耐药基因阳性。结论:CRO、ATM和CTX对检测ESBLs阳性率较高;CTX-M-22、CTX-M-18是本地区产ESBLs菌株的主要基因型。     

Species limits and hybridization zones in Icterus cayanensis–chrysocephalus group (Aves: Icteridae)

One of the best examples of differentiation and hybridization among South American passerine birds is exhibited by Icterus cayanensis (Epaulet Oriole) and Icterus chrysocephalus (Moriche Oriole). Icterus chrysocephalus is a monotypic species restricted to northern South America. Icterus cayanensis is a polytypc species that ranges from Suriname and French Guyana to northern Argentina. Five subspecies are recognized to I. cayanensis. Hybrid zones are known between I. cayanensis and I. chrysocephalus as well as between subspecies of I. cayanenis, even though character variation has never been adequately assessed and mapped. Although molecular data support the hypothesis that I. cayanensis and I. chrysocephalus form a monophyletic group, they do not support the species limits currently recognized within this group. We analysed the geographic variation of plumage characters along the range of this group to map the geographic variation of individual plumage characters and identify the populations that have uniform phenotypic character expression and therefore represent genuine phylogenetic species. We also used molecular data to investigate the phylogenetic relationships among these species. Geographic variation of plumage characters, habitat preferences and molecular data identified four species within I. cayanensis–chrysocephalus clade: an Amazonian species group, formed by I. cayanensis and I. chrysocephalus and a Southern species group composed of I. pyrrhopterus and I. tibialis. The Amazonian species are separated by a relatively narrow hybrid zone along the Amazon valley, whereas the Southern species are separated by a hybrid zone that is larger than the ranges of the two species individually. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 583–597.     

上海城市近自然森林的重建动态

近自然森林作为城市植被恢复的重要模式,已在我国多地开展了实践,并衍生了新的造林模式。为评估不同近自然森林建设模式的群落恢复进程,本研究以上海城市裸地上重建的近自然森林为对象,通过长期监测两处分别应用原"宫胁法"与新"异龄复层落叶—常绿混交林"种植模式的近自然森林重建过程,从物种组成、垂直结构、生活型组成和目标恢复物种4个方面解析恢复动态。结果表明:两种造林模式恢复的近自然森林,随恢复进程其物种组成逐渐趋同,在十多年内已形成了落叶—常绿垂直混交结构;"异龄复层落叶—常绿混交林"造林模式可更好地促进常绿阔叶树种的恢复,尤其是常绿建群种红楠与小叶青冈。本研究证实了近自然森林恢复技术可以缩短亚热森林群落向演替后期发展的时间,以及新造林模式的有效性,为近自然森林技术的应用与实施提供了科学依据。     

Gap junction structures: Analysis of the x-ray diffraction data

Models for the spatial distribution of protein, lipid and water in gap junction structures have been constructed from the results of the analysis of X-ray diffraction data described here and the electron microscope and chemical data presented in the preceding paper (Caspar, D. L. D., D. A. Goodenough, L. Makowski, and W.C. Phillips. 1977. 74:605-628). The continuous intensity distribution on the meridian of the X-ray diffraction pattern was measured, and corrected for the effects of the partially ordered stacking and partial orientation of the junctions in the X-ray specimens. The electron density distribution in the direction perpendicular to the plane of the junction was calculated from the meridional intensity data. Determination of the interference function for the stacking of the junctions improved the accuracy of the electron density profile. The pair-correlation function, which provides information about the packing of junctions in the specimen, was calculated from the interference function. The intensities of the hexagonal lattice reflections on the equator of the X-ray pattern were used in coordination with the electron microscope data to calculate to the two-dimensional electron density projection onto the plane of the membrane. Differences in the structure of the connexons as seen in the meridional profile and equatorial projections were shown to be correlated to changes in lattice constant. The parts of the junction structure which are variable have been distinguished from the invariant parts by comparison of the X-ray data from different specimens. The combination of these results with electron microscope and chemical data provides low resolution three- dimensional representations of the structures of gap junctions.     

High rate of DNA loss in the Drosophila melanogaster and Drosophila virilis species groups

We recently proposed that patterns of evolution of non-LTR retrotransposable elements can be used to study patterns of spontaneous mutation. Transposition of non-LTR retrotransposable elements commonly results in creation of 5' truncated, "dead-on-arrival" copies. These inactive copies are effectively pseudogenes and, according to the neutral theory, their molecular evolution ought to reflect rates and patterns of spontaneous mutation. Maximum parsimony can be used to separate the evolution of active lineages of a non-LTR element from the fate of the "dead-on-arrival" insertions and to directly assess the relative frequencies of different types of spontaneous mutations. We applied this approach using a non-LTR element, Helena, in the Drosophila virilis group and have demonstrated a surprisingly high incidence of large deletions and the virtual absence of insertions. Based on these results, we suggested that Drosophila in general may exhibit a high rate of spontaneous large deletions and have hypothesized that such a high rate of DNA loss may help to explain the puzzling dearth of bona fide pseudogenes in Drosophila. We also speculated that variation in the rate of spontaneous deletion may contribute to the divergence of genome size in different taxa by affecting the amount of superfluous "junk" DNA such as, for example, pseudogenes or long introns. In this paper, we extend our analysis to the D. melanogaster subgroup, which last shared a common ancestor with the D. virilis group approximately 40 MYA. In a different region of the same transposable element, Helena, we demonstrate that inactive copies accumulate deletions in species of the D. melanogaster subgroup at a rate very similar to that of the D. virilis group. These results strongly suggest that the high rate of DNA loss is a general feature of Drosophila and not a peculiar property of a particular stretch of DNA in a particular species group.      

小鼠淋巴细胞抗原CTLA-4的胞外肽段表达及纯化

目的: 真核细胞表达小鼠淋巴细胞抗原CTLA-4胞外段肽,研究表达肽段与抗原呈递细胞B7分子结合后减轻小鼠淋巴细胞刺激后的增殖抑制,从而启动T淋巴细胞进一步增殖。方法:从小鼠脾脏淋巴细胞获得总RNA,通过逆转录PCR扩增出CTLA-4全长基因,克隆并测序。依据胞外段序列和真核表达载体pcDNA3.1序列,合成引物扩增胞外片段,两者经内切核酸酶处理、连接构建重组表达pcDNA3.1载体,重组质粒经测序验证后,采用lipofectamine 2000转染入小鼠肝癌细胞Hepa1-6,经G418筛选获得稳定表达细胞株。结果:获得小鼠CTLA-4胞外段真核表达载体和小鼠肝癌细胞Hepa1-6稳定表达转染细胞株,制备了CTLA-4胞外肽段,经His标签抗体和小鼠CTLA-4抗体Western blot检测表达蛋白带均呈阳性。结论:获得CTLA-4胞外段肽,为进一步研究该肽的作用打下基础。     

Total sleep deprivation does not significantly degrade semantic encoding

ABSTRACT

Sleep deprivation impairs performance on cognitive tasks, but it is unclear which cognitive processes it degrades. We administered a semantic matching task with variable stimulus onset asynchrony (SOA) and both speeded and self-paced trial blocks. The task was administered at the baseline and 24 hours later after 30.8 hours of total sleep deprivation (TSD) or matching well-rested control. After sleep deprivation, the 20% slowest response times (RTs) were significantly increased. However, the semantic encoding time component of the RTs remained at baseline level. Thus, the performance impairment induced by sleep deprivation on this task occurred in cognitive processes downstream of semantic encoding.