Genome-wide detection and characterization of positive selection in human populations

With the advent of dense maps of human genetic variation, it is now possible to detect positive natural selection across the human genome. Here we report an analysis of over 3 million polymorphisms from the International HapMap Project Phase 2 (HapMap2). We used 'long-range haplotype' methods, which were developed to identify alleles segregating in a population that have undergone recent selection, and we also developed new methods that are based on cross-population comparisons to discover alleles that have swept to near-fixation within a population. The analysis reveals more than 300 strong candidate regions. Focusing on the strongest 22 regions, we develop a heuristic for scrutinizing these regions to identify candidate targets of selection. In a complementary analysis, we identify 26 non-synonymous, coding, single nucleotide polymorphisms showing regional evidence of positive selection. Examination of these candidates highlights three cases in which two genes in a common biological process have apparently undergone positive selection in the same population:LARGE and DMD, both related to infection by the Lassa virus, in West Africa;SLC24A5 and SLC45A2, both involved in skin pigmentation, in Europe; and EDAR and EDA2R, both involved in development of hair follicles, in Asia.     

TPP1 is a homologue of ciliate TEBP-beta and interacts with POT1 to recruit telomerase

Telomere dysfunction may result in chromosomal abnormalities, DNA damage responses, and even cancer. Early studies in lower organisms have helped to establish the crucial role of telomerase and telomeric proteins in maintaining telomere length and protecting telomere ends. In Oxytricha nova, telomere G-overhangs are protected by the TEBP-alpha/beta heterodimer. Human telomeres contain duplex telomeric repeats with 3' single-stranded G-overhangs, and may fold into a t-loop structure that helps to shield them from being recognized as DNA breaks. Additionally, the TEBP-alpha homologue, POT1, which binds telomeric single-stranded DNA (ssDNA), associates with multiple telomeric proteins (for example, TPP1, TIN2, TRF1, TRF2 and RAP1) to form the six-protein telosome/shelterin and other subcomplexes. These telomeric protein complexes in turn interact with diverse pathways to form the telomere interactome for telomere maintenance. However, the mechanisms by which the POT1-containing telosome communicates with telomerase to regulate telomeres remain to be elucidated. Here we demonstrate that TPP1 is a putative mammalian homologue of TEBP-beta and contains a predicted amino-terminal oligonucleotide/oligosaccharide binding (OB) fold. TPP1-POT1 association enhanced POT1 affinity for telomeric ssDNA. In addition, the TPP1 OB fold, as well as POT1-TPP1 binding, seemed critical for POT1-mediated telomere-length control and telomere-end protection in human cells. Disruption of POT1-TPP1 interaction by dominant negative TPP1 expression or RNA interference (RNAi) resulted in telomere-length alteration and DNA damage responses. Furthermore, we offer evidence that TPP1 associates with the telomerase in a TPP1-OB-fold-dependent manner, providing a physical link between telomerase and the telosome/shelterin complex. Our findings highlight the critical role of TPP1 in telomere maintenance, and support a yin-yang model in which TPP1 and POT1 function as a unit to protect human telomeres, by both positively and negatively regulating telomerase access to telomere DNA.     

多毛纲(Polychaeta)动物系统学的研究进展

多毛纲动物以海洋底栖分布为主,在长期的进化过程中,产生了形形色色适应不同环境的形态特征和生活史策略.对其系统学的研究,有助于理解自然界生物多样性的保持机制及其在生物系统进化过程中所发挥的作用.从目前的研究结果来看,多毛纲动物为并系发生,但它们在环节动物系统发生树中的基部类群以及大部分并系群之间的相互关系仍有待确定.今后应该增加各类群有代表性的物种的取样数量,开展形态学特征、生活史策略以及分子遗传标记的综合研究,以期完善多毛纲动物的系统学.     

微束X射线荧光分析谱仪及其对松针中元素的分布分析

介绍了一种小型的微束X射线荧光分析谱仪,它是由导管X光透镜和能量色散X射线荧光分析谱仪组成.谱仪具有较高的空间分辨率和能量分辨率.使用本谱仪对松树针叶进行了微区分析,得出各种元素沿松针长度方向和横切面径向的分布规律.结果表明使用X光透镜的微束X射线荧光分析方法可以实现植物样品的微区分析,有助于进一步了解植物的生长与元素迁移的关系.     

平面变栅距位相光栅位移传感器的测量精度极限

提出用透射式变栅距位相光栅作位移传感器,用标量衍射理论讨论了这种传感器的测量精度与光栅的起始栅距及栅距变化系数之间的关系,同时用时域有限元差分(FDTD)算法计算了变栅距位相光栅的衍射场,计算结果表明受衍射偏振特性的影响,这种位移传感器的测量精度在理论上存在极限.     

河北省御道口牧场气候生产潜力估算

御道口牧场位于河北省围场县北部坝上地区,是河北省畜牧业生产的重要产区.根据牧场多年降水和气温等气象观测资料,同时考虑地形因素和最小面积的限制,对御道口牧场的气候生产潜力进行了估算.得出牧场的气候生产潜力在3.75～5 t·hm-2·a-1之间,牧场内适合发展人工草地的平地和缓坡(＜5°)约占总土地面积的76.5%.     

好好芭叶片RNA提取方法和cDNA干旱消减文库的构建

介绍了从好好芭成熟叶片中提取总RNA的方法;用含有SDS的裂解液裂解细胞,用DNase除去可能出现的DNA干扰,再经植物提取试剂盒纯化后,获得了高质量的完整RNA,可用于基因编码序列的克隆和基因表达的mRNA分析等精细研究,并进一步构建了好好芭干旱消减文库.     

塔里木河流域中下游典型地物光谱变化规律

由于塔里木河流域中下游距离河道在垂直向的差别,以及气候与人为因素的影响,使植被的空间分布具有异构性.典型地物光谱变化的研究为中下游生态环境的遥感监测提供了基础,实验研究表明:绿色全荣植物中,棉花由于其具有明显绿峰、水分吸收谷和近红外的高反射峰而更加容易识别,其他植物主要差别则集中在550,680,1420 nm附近的反射峰、吸收谷和1920～2500 nm之间的反射率;与绿色植被相比,枯枝的光谱在可见光部分的绿峰和红光吸收谷不明显,但在可见光部分波形有所差别,而与流沙土壤光谱相比,各波段反射率变化较大;对比不同荣枯比例的植物光谱发现,同一种植物随着荣枯配比的变化,除可见光绿峰、近红外反射峰和各水分吸收谷变化外,最明显的是在近红外1420～1820 nm之间和短波红外1920～2500 nm之间反射率随着枯枝的比例增加而明显升高;关于土壤光谱,中下游各断面占主要类型的流沙土光谱相差不大,但是盐碱土和含有一定水分的盐碱土则变化较大,而且反射率基本低于流沙土,结壳土则除在近红外和短波红外部分变化更加平缓而有所差别外,其余波段接近流沙土;同样的土壤背景下,近红外和短波红外部分反射率的差别能够在一定程度上反映覆盖度的变化.