S-phase checkpoint regulations that preserve replication and chromosome integrity upon dNTP depletion

DNA replication stress, an important source of genomic instability, arises upon different types of DNA replication perturbations, including those that stall replication fork progression. Inhibitors of the cellular pool of deoxynucleotide triphosphates (dNTPs) slow down DNA synthesis throughout the genome. Following depletion of dNTPs, the highly conserved replication checkpoint kinase pathway, also known as the S-phase checkpoint, preserves the functionality and structure of stalled DNA replication forks and prevents chromosome fragmentation. The underlying mechanisms involve pathways extrinsic to replication forks, such as those involving regulation of the ribonucleotide reductase activity, the temporal program of origin firing, and cell cycle transitions. In addition, the S-phase checkpoint modulates the function of replisome components to promote replication integrity. This review summarizes the various functions of the replication checkpoint in promoting replication fork stability and genome integrity in the face of replication stress caused by dNTP depletion.     

Can Townsend's ground squirrels survive on a diet of exotic annuals?

Southwestern Idaho desert shrub-bunchgrass rangeland is being invaded by fire-prone exotic annuals that permanently dominate the landscape following wildfires. This study was undertaken to describe diets of Townsend's ground squirrels ( Spermophilus townsendii idahoensis ) at four study sites with varying degrees of exotic annual invasion to determine if the squirrels could utilize high proportions of exotic annuals in their diets. Townsend's ground squirrels were collected in March and May of 1987 and 1988, and stomach contents were analyzed using a microhistological technique. Grasses comprised 37-87% of Townsend's ground squirrel diets at the four sites. Native species, especially Sandberg's bluegrass ( Poa secunda ), winterfat ( Ceratoides lanata ), big sagebrush ( Artemisia tridentata ) and six-weeks fescue ( Vulpia octoflora ) constituted 7-96% (x = 47.2%) of the diet, whereas exotic species, especially cheatgrass ( Bromus tectorum ), tumbleweed ( Salsola iberica ), and tansymustards ( Descurainia spp.) made up 4-68% (x = 48.0%) of the diet. At each site 2-4 species comprised >90% of the diet. There was no apparent correlation between the importance values of exotic species at a site and their importance in Townsend's ground squirrel diets.     

Survey indicators for pygmy rabbits: temporal trends of burrow systems and pellets

Obtaining estimates of absolute abundance for rare or cryptic species can be challenging. In these cases,methods using indirect indicators such as sign might offer useful indices of population size. Pygmy rabbits ( Brachylagus idahoensis ) are small, burrowing lagomorphs for which methods for population assessment and monitoring are needed. Current tools for estimating relative abundance rely on detecting and assessing fecal pellets and burrow systems. We evaluated temporal changes in each of these indicators to gauge their potential usefulness as indicators of relative and absolute abundance of pygmy rabbits. Pellet persistence was strongly influenced by environmental exposure, and based on our data, we estimated that maximum persistence of fecal pellets would be 24–34 months. Pellet appearance (color) was affected by both time and exposure. Burrow systems were remarkably resilient over the course of the study. Probability of burrow systems transitioning between activity classes (active, recent, and old) did not vary detectably by study site, season, or year. We suggest that 2 protocols currently used for classification of pygmy rabbit burrow systems are most useful for different applications. Further work is needed, however, to link such assessments to quantitative estimates of population size.     

Biodiversity and biogeography of phages in modern stromatolites and thrombolites

Viruses, and more particularly phages (viruses that infect bacteria), represent one of the most abundant living entities in aquatic and terrestrial environments. The biogeography of phages has only recently been investigated and so far reveals a cosmopolitan distribution of phage genetic material (or genotypes). Here we address this cosmopolitan distribution through the analysis of phage communities in modern microbialites, the living representatives of one of the most ancient life forms on Earth. On the basis of a comparative metagenomic analysis of viral communities associated with marine (Highborne Cay, Bahamas) and freshwater (Pozas Azules II and Rio Mesquites, Mexico) microbialites, we show that some phage genotypes are geographically restricted. The high percentage of unknown sequences recovered from the three metagenomes (>97%), the low percentage similarities with sequences from other environmental viral (n = 42) and microbial (n = 36) metagenomes, and the absence of viral genotypes shared among microbialites indicate that viruses are genetically unique in these environments. Identifiable sequences in the Highborne Cay metagenome were dominated by single-stranded DNA microphages that were not detected in any other samples examined, including sea water, fresh water, sediment, terrestrial, extreme, metazoan-associated and marine microbial mats. Finally, a marine signature was present in the phage community of the Pozas Azules II microbialites, even though this environment has not been in contact with the ocean for tens of millions of years. Taken together, these results prove that viruses in modern microbialites display biogeographical variability and suggest that they may be derived from an ancient community.     

Helicobacter exploits integrin for type IV secretion and kinase activation

Integrins are important mammalian receptors involved in normal cellular functions as well as pathogenesis of chronic inflammation and cancer. We propose that integrins are exploited by the gastric pathogen and type-1 carcinogen Helicobacter pylori for injection of the bacterial oncoprotein cytotoxin-associated gene A (CagA) into gastric epithelial cells. Virulent H. pylori express a type-IV secretion pilus that injects CagA into the host cell; CagA then becomes tyrosine-phosphorylated by Src family kinases. However, the identity of the host cell receptor involved in this process has remained unknown. Here we show that the H. pylori CagL protein is a specialized adhesin that is targeted to the pilus surface, where it binds to and activates integrin alpha5beta1 receptor on gastric epithelial cells through an arginine-glycine-aspartate motif. This interaction triggers CagA delivery into target cells as well as activation of focal adhesion kinase and Src. Our findings provide insights into the role of integrins in H.-pylori-induced pathogenesis. CagL may be exploited as a new molecular tool for our further understanding of integrin signalling.     

Rapid,quantitative adipose conversion of chicken fibroblasts by high concentrations of chicken serum or plasma

Summary Rapid, quantitative adipose conversion of chicken fibroblasts occurs when these cells are cultured in undiluted commercial chicken serum or plasma. Fresh serum and plasma acquire this property after ageing.These studies were carried out with grants from the Richardson Foundation, the National Cancer Institute of Canada, and the Canadian Heart Foundations.To whom requests for reprints should be sent.     

基于 VAR 模型的重庆市大气污染物分析及研究

目的 研究重庆市首要空气污染物 PM2. 5 与 PM10 、SO2 、NO2 、CO、O3 的动态影响关系,为政府制定防治大气 污染措施及相关政策提供有价值的建议。 方法 收集重庆市 2021-05-01—2021-10-31 日的 PM2. 5 、PM10 、SO2 、 NO2 、CO、O3 这 6 项大气污染物的日浓度数据,利用 Eviews8. 0 软件,对原始数据进行序列平稳性检验;根据 Granger 因果检验结果选择变量,建立时间序列 VAR 模型,并检验模型的稳定性;利用广义脉冲响应分析和方差分 解分析,研究各污染物浓度对 PM2. 5 的动态影响及相对重要性。 结果 Granger 因果检验表明:PM10 、SO2 、NO2 、O3 是 PM2. 5 的 Granger 原因, CO 不是 PM2. 5 的 Granger 原因;广义脉冲响应分析表明:NO2 对 PM2. 5 的影响最大;方差 分解分析表明:NO2 的浓度对 PM2. 5 的影响最大;O3 对 PM2. 5 的影响次之,对 SO2 的影响作用最小。 所以,从长期 影响效应看,NO2 对 PM2. 5 具有长期较大的影响,SO2 对 PM2. 5 的影响最弱。 结论 防治 PM2. 5 对重庆市空气的污染 应着重控制 NO2 的污染,因此,政府应大力发展绿色交通,控制交通污染;大力监管高污染行业,将烟雾、粉尘、颗粒 物等排放量较大的行业作为工业污染源治理的重点;大力发展清洁能源,加快化石燃料替代资源的开发利用。     

The cosmological density of baryons from observations of 3He+ in the Milky Way.

Primordial nucleosynthesis after the Big Bang can be constrained by the abundances of the light elements and isotopes 2H, 3He, 4He and 7Li (ref. 1). The standard theory of stellar evolution predicts that 3He is also produced by solar-type stars, so its abundance is of interest not only for cosmology, but also for understanding stellar evolution and the chemical evolution of the Galaxy. The 3He abundance in star-forming (H II) regions agrees with the present value for the local interstellar medium, but seems to be incompatible with the stellar production rates inferred from observations of planetary nebulae, which provide a direct test of stellar evolution theory. Here we develop our earlier observations, which, when combined with recent theoretical developments in our understanding of light-element synthesis and destruction in stars, allow us to determine an upper limit for the primordial abundance of 3He relative to hydrogen: 3He/H = (1.1 +/- 0.2) x 10(-5). The primordial density of all baryons determined from the 3He data is in excellent agreement with the densities calculated from other cosmological probes. The previous conflict is resolved because most solar-mass stars do not produce enough 3He to enrich the interstellar medium significantly.