The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003

Past studies of cosmological gamma-ray bursts (GRBs) have been hampered by their extreme distances, resulting in faint afterglows. A nearby GRB could potentially shed much light on the origin of these events, but GRBs with a redshift z 相似文献   

Three modes of synaptic vesicular recycling revealed by single-vesicle imaging

Synapses recycle their spent vesicles in order to keep up with on-going neurotransmitter release. To investigate vesicle recycling in the small synapses of hippocampal neurons, we have used an optical recording method that permits us to resolve single-vesicle events. Here we show that an exocytic event can terminate with three modes of vesicle retrieval: a fast (400-860 ms) 'kiss-and-run' mode that has a selective fusion pore; a slow (8-21 s) 'compensatory' mode; and a 'stranded' mode of recycling, in which a vesicle is left on the cell surface until a nerve impulse triggers its retrieval. We have also observed that, in response to a nerve impulse, synapses with low release probability primarily use the kiss-and-run mode, whereas high release probability terminals predominantly use the compensatory mode of vesicle retrieval.     

Change in the sedimentary environment of Wanquan River Estuary,Hainan Island,China

Pb geochronology and sediment core profiles of organic carbon, total sulfur and organic carbon isotope (d 13C) values were used to reconstruct the local environ-mental history of the Shamei Lagoon, located in the Wan-quan River Estuary, eastern Hainan Island, China. Totalsulfur and d 13C values decreased upwards in the top 30 cm of a sediment core that spanned the last 200 years of deposi-tion. Total sulfur concentration and d 13C values respectively decreased upward from 1.92% to 0.36%, and -20.63?to -23.64? The C/S ratio in the 19th century and earlier was relatively stable in the range of 0.47—0.80, and there was a positive correlation between organic carbon and total sulfur. Since around 1900 AD, the C/S ratio increased rapidly to a maximum of 3.94, but no simple correlation was found be-tween organic carbon and total sulfur during this more re-cent period. These results indicated that before 1800 AD, the lagoon had a fully marine character, and the location of to-day抯 Wanquan River Estuary was an open embayment.From 1800 to 1900, the salinity of Shamei Lagoon decreased noticeably. The amount of seawater which could enter thelagoon decreased gradually as the Yudai spit grew. Today,seawater scarcely affects the lagoon; it is essentially a fresh-water basin.     

基于多AGENT的机器人装配系统结构

采用Ａｇｅｎｔ的基本思想,对多Ａｇｅｎｔ系统分别从个体和群体的角度出发,构造系统结构。通过对系统行为方式的定义,将全局运行流程与局部运行流程相分离,将任务的执行和任务间的协调相分离,将任务的选择与自身及状态相结合,从而系统结构可以隔离高层的系统控制与低层的执行过程,使虚拟系统在结构上具有更大灵活性,可扩充性和可重用性。     

Nitric oxide can inhibit apoptosis or switch it into necrosis

Nitric oxide (NO) and its related molecules are important messengers that play central roles in pathophysiology. Redox modulation of thiol groups on protein cysteine residues by S-nitrosylation can modulate protein function. NO has emerged as a potent regulator of apoptosis in many cell types, either preventing cell death or driving an apoptotic response into a necrotic one. NO protects neuroblastoma cells from retinoid- and cisplatin-induced apoptosis, without significantly increasing necrotic cell damage. Nitrosylation of thiol groups of several critical factors may be important for cell survival. Indeed, S-nitrosylation of the active-site cysteine residue of apoptotic molecules, such as caspases and tissue transglutaminase, results in the inhibition of their catalytic activities and has important implications for the regulation of apoptosis by NO. On the other hand, NO is able to shift the anti-CD95- and ceramide-triggered apoptotic response of Jurkat T cells into necrotic cell death. In these apoptotic models, NO is therefore unable to solely inhibit cell death, indicating that it may act below the point of no return elicited by CD95-ligation and ceramide stimulation.     

Transport of lipids from golgi to plasma membrane is defective in tangier disease patients and Abc1-deficient mice

Mutations in the gene encoding ATP-binding cassette transporter 1 ( ABC1) have been reported in Tangier disease (TD), an autosomal recessive disorder that is characterized by almost complete absence of plasma high-density lipoprotein (HDL), deposition of cholesteryl esters in the reticulo-endothelial system (RES) and aberrant cellular lipid trafficking. We demonstrate here that mice with a targeted inactivation of Abc1 display morphologic abnormalities and perturbations in their lipoprotein metabolism concordant with TD. ABC1 is expressed on the plasma membrane and the Golgi complex, mediates apo-AI associated export of cholesterol and phospholipids from the cell, and is regulated by cholesterol flux. Structural and functional abnormalities in caveolar processing and the trans-Golgi secretory pathway of cells lacking functional ABC1 indicate that lipid export processes involving vesicular budding between the Golgi and the plasma membrane are severely disturbed.     

MLH3: a DNA mismatch repair gene associated with mammalian microsatellite instability

DNA mismatch repair is important because of its role in maintaining genomic integrity and its association with hereditary non-polyposis colon cancer (HNPCC). To identify new human mismatch repair proteins, we probed nuclear extracts with the conserved carboxy-terminal MLH1 interaction domain. Here we describe the cloning and complete genomic sequence of MLH3, which encodes a new DNA mismatch repair protein that interacts with MLH1. MLH3 is more similar to mismatch repair proteins from yeast, plants, worms and bacteria than to any known mammalian protein, suggesting that its conserved sequence may confer unique functions in mice and humans. Cells in culture stably expressing a dominant-negative MLH3 protein exhibit microsatellite instability. Mlh3 is highly expressed in gastrointestinal epithelium and physically maps to the mouse complex trait locus colon cancer susceptibility I (Ccs1). Although we were unable to identify a mutation in the protein-coding region of Mlh3 in the susceptible mouse strain, colon tumours from congenic Ccs1 mice exhibit microsatellite instability. Functional redundancy among Mlh3, Pms1 and Pms2 may explain why neither Pms1 nor Pms2 mutant mice develop colon cancer, and why PMS1 and PMS2 mutations are only rarely found in HNPCC families.     

Mutations in RAB27A cause Griscelli syndrome associated with haemophagocytic syndrome

Griscelli syndrome (GS, MIM 214450), a rare, autosomal recessive disorder, results in pigmentary dilution of the skin and the hair, the presence of large clumps of pigment in hair shafts and an accumulation of melanosomes in melanocytes. Most patients also develop an uncontrolled T-lymphocyte and macrophage activation syndrome (known as haemophagocytic syndrome, HS), leading to death in the absence of bone-marrow transplantation. In contrast, early in life some GS patients show a severe neurological impairment without apparent immune abnormalities. We previously mapped the GS locus to chromosome 15q21 and found a mutation in a gene (MYO5A) encoding a molecular motor in two patients. Further linkage analysis suggested a second gene associated with GS was in the same chromosomal region. Homozygosity mapping in additional families narrowed the candidate region to a 3.1-cM interval between D15S1003 and D15S962. We detected mutations in RAB27A, which lies within this interval, in 16 patients with GS. Unlike MYO5A, the GTP-binding protein RAB27A appears to be involved in the control of the immune system, as all patients with RAB27A mutations, but none with the MYO5A mutation, developed HS. In addition, RAB27A-deficient T cells exhibited reduced cytotoxicity and cytolytic granule exocytosis, whereas MYO5A-defective T cells did not. RAB27A appears to be a key effector of cytotoxic granule exocytosis, a pathway essential for immune homeostasis.