Avidity enhancement of L-selectin bonds by flow: shear-promoted rotation of leukocytes turn labile bonds into functional tethers

L-selectin is a key lectin essential for leukocyte capture and rolling on vessel walls. Functional adhesion of L-selectin requires a minimal threshold of hydrodynamic shear. Using high temporal resolution videomicroscopy, we now report that L-selectin engages its ligands through exceptionally labile adhesive bonds (tethers) even below this shear threshold. These tethers share a lifetime of 4 ms on distinct physiological ligands, two orders of magnitude shorter than the lifetime of the P-selectin-PSGL-1 bond. Below threshold shear, tether duration is not shortened by elevated shear stresses. However, above the shear threshold, selectin tethers undergo 14-fold stabilization by shear-driven leukocyte transport. Notably, the cytoplasmic tail of L-selectin contributes to this stabilization only above the shear threshold. These properties are not shared by P-selectin- or VLA-4-mediated tethers. L-selectin tethers appear adapted to undergo rapid avidity enhancement by cellular transport, a specialized mechanism not used by any other known adhesion receptor.     

Origin and Phylogeny of Microbes Living in Permanent Antarctic Lake Ice

Abstract The phylogenetic diversity of bacteria and cyanobacteria colonizing sediment particles in the permanent ice cover of an Antarctic lake was characterized by analyses of 16S rRNA genes amplified from environmental DNA. Samples of mineral particles were collected from a depth of 2.5 m in the 4-m-thick ice cover of Lake Bonney, McMurdo Dry Valleys, Antarctica. A rRNA gene clone library of 198 clones was made and characterized by sequencing and oligonucleotide probe hybridization. The library was dominated by representatives of the cyanobacteria, proteobacteria, and Planctomycetales, but also contained diverse clones representing many other microbial groups, including the Acidobacterium/Holophaga division, the Green Non-Sulfur division, and the Actinobacteria. Six oligonucleotide probes were made for the most abundant clades recovered in the library. To determine whether the ice microbial community might originate from wind dispersal of the algal mats found elsewhere in Taylor Valley, the probes were hybridized to 16S rDNAs amplified from three samples of terrestrial cyanobacterial mats collected at nearby sites, as well as to bacterial 16S rDNAs from the lake ice community. The results demonstrate the presence of a diverse microbial community dominated by cyanobacteria in the lake ice, and also show that the dominant members of the lake ice microbial community are found in terrestrial mats elsewhere in the area. The lake ice microbial community appears to be dominated by organisms that are not uniquely adapted to the lake ice ecosystem, but instead are species that originate elsewhere in the surrounding region and opportunistically colonize the unusual habitat provided by the sediments suspended in lake ice. Received: 16 August 1999; Accepted: 28 December 1999; Online Publication: 28 April 2000     

Cervical cancer screening, screening errors and reporting

Screening for cervical carcinoma by cervicovaginal cytology has led to a marked reduction in the incidence of and mortality from this tumor over the last 50 years in essentially all countries with a functioning screening program. It is the most successful cancer prevention program of all times. Consequently, approximately 80% of the current incidence of and mortality from this disease occurs in geographic areas of underserved and underscreened women. Essential components of a successful program are a high coverage rate of the female population, screening at regular intervals, well-trained clinical and laboratory staff, and an efficient follow-up and treatment system. Deficiencies in any of these areas may lead to a failing screening system. Thus, the most important reason for the remaining mortality from cervical carcinoma in developed countries is lack of complete coverage. It is questionable if new and more expensive technologies will be able to renmedy the remaining failures of the system if no improvement in the coverage rate is achieved. Screening errors do occur but represent only a small fraction of screening failures. Currently, there are a number of terminology systems around the world; thus, a unified terminology is currently not a realistic goal.     

Sporophytic nondisjunction of the maize B chromosome at high copy numbers

It has been known for decades that the maize B chromosome undergoes nondisjunction at the second pollen mitosis.Fluorescence in-situ hybridization (FISH) was used to undertake a quantitative study of maize plants with differing numbers of B chromosomes to observe if instability increases by increasing B dosage in root tip tissue.B chromosome nondisjunction was basically absent at low copy number,but increased at higher B numbers.Thus,B nondisjunction rates are dependent on the dosage of B's in the sporophyt...     

Sorghum Insect Problems and Management

Sorghum (Sorghum bicolor) has high levels of starch,sugar,and fiber and is one of the most important energy crops in the world.Insect damage is one of the challenges that impacts sorghum biomass production.There are at least 150 insect species that can infest sorghum varieties worldwide.These insects can complete several generations within a growing season,they target various parts of sorghum plants at developmental stages,and they cause significant biomass losses.Genetic research has revealed the existence...     

Energy Crop and Biotechnology for Biofuel Production

Selection of energy crops is the first priority for large-scale biofuel production in China. As a major topic, it was extensively discussed in the Second International Symposium on Bioen-     

拉美城市景观：一种强化的拼贴

拉丁美洲是自然和文化多样性很强的地区。自1492年欧洲殖民者到来至今,这片次大陆像一块“海绵”,持续受到各个时期主导世界经济发展的其他国家的影响。这一过程在某些境况下完全改变了这个地区先前存在的文化景观,而在另一些境况下,则表现为外来模式对本土条件的适应。其结果是城市、景观和建筑形成丰富多样的拼贴,它们共同存在、相互交融,形成了十分独特、变幻万千的拉美色彩。研究这种外国文化对本土的适应和混合过程,可以让其他新兴经济体更好地应对全球化的挑战。值得注意的是,拉美地区在20世纪40—60年代的现代主义运动时期开展了一系列大尺度城市、景观和建筑设计的经典探索。尽管如此,这里依然被认为是社会不平等现象最严重的地区,富人区与贫民窟共存,又形成空间分异。这种社会断裂表现为正规与非正规（自我建构）城市之间的形态和居住标准差异。20世纪80年代以来,通过城市整体规划来调和这些非正规聚落与上层阶级的景观和建筑的实践探索,引起了人们的关注。     

AIDS and associated malignancies

INTRODUCTION It has been over twenty years since the onset of the AIDS epidemic, and in spite of the tremendous progress made towards the understanding of the disease, the virus that causes the disease and the development of highly ef- fective anti-retrov…