SHRIMP dating of zircons from the Caledonian Xiongdian eclogite, western Dabie Mountains, China

This note reports the SHRIMP U-Pb data of zircons from the Caledonian Xiongdian eclogite, western Dabie Mountains. Zircons from the rock occur mainly in garnet and other metamorphic minerals with sharp boundaries and exhibit textures growing under metamorphic conditions. Analyses of 7 grains give ²⁰⁶Pb/²³⁸U ages ranging from 335 to 424 Ma, showing a certain degree of radiogenic lead loss. This suggests a minimum age of (424±5) Ma for the metamorphic zircons, as well as the high-pressure metamorphic event. The outer peripheral zone of a zircon gives ²⁰⁶Pb/²³⁸U age of about 300 Ma. Combined with Sm-Nd, ⁴⁰Ar-³⁹Ar, U-Pb and ²⁰⁷Pb/²⁰⁶Pb ages, the peak metamorphism of the Xiongdian eclogite is documented between 424—480 Ma.     

Galectins in cell growth and apoptosis

Fourteen members of the galectin family, proteins with conserved carbohydrate-recognition domains that bind β-galactoside, have been cloned and more are expected to be discovered in the near future. Many aspects of galectin biology have been thoroughly explored, and functional studies have implicated these proteins in cell growth, differentiation and apoptosis, in addition to cell adhesion, chemoattraction and cell migration. In some cases a galectin can either promote or suppress cell growth, depending on the cell types and doses used. Galectin-3 is the only member known so far to inhibit apoptosis, while galectin-1, -7 and -9 promote this cellular process. Galectins can act either extracellularly or intracellularly to exert effects on cell growth and apoptosis. RID="*" ID="*"Corresponding author.     

Changes in calpastatin localization and expression during calpain activation: a new mechanism for the regulation of intracellular Ca<Superscript>2+</Superscript>-dependent proteolysis

The amount of calpastatin directly available in cytosol is under the control of [Ca²⁺] and [cyclic AMP]. Prolonged calpain activation also promotes degradation of calpastatin. The fluctuation of calpastatin concentration in cell soluble fraction is accompanied by an initial decrease in calpastatin gene expression, followed by a fivefold increase in its expression when the inhibitor protein is degraded. This process can be conceptualized as a mechanism to regulate calpastatin availability in the cell. This conclusion is supported by the fact that calpain, the other component of this proteolytic system, undergoes changes in its levels of expression in a much more limited manner. Furthermore, this process can be observed both in cells exposed to different natural stimuli, or in other cell lines. Modification of calpastatin gene expression might represent a new tool for the in vivo control of the regulatory machinery required for the modulation of Ca²⁺-dependent proteolysis.Received 18 July 2003; received after revision 3 September 2003; accepted 23 September 2003     

Induced recovery of defective membrane expression of a CC chemokine receptor 5 mutant by phytohemagglutinin

CC chemokine receptor 5 (CCR5) is a member of the G-protein-coupled receptor superfamily. It plays an important role in macrophage tropic human immunodeficiency virus-1 entry and in some inflammatory reactions. CCR5-893(–) is a single-nucleotide deletion that results in complete truncation of the C tail of the gene product. We detected CCR5-893(–) in a sample of patients infected with non-tuberculosis mycobacteria and found that it was maintained heterozygously with a frequency of 2%. There is no association between this mutation and any immunodeficiency. Membrane expression of CCR5-893(–) was substantially reduced compared to the wild type, but this defective surface presentation recovered greatly recovered in the presence of 2 mg l-1 phytohemagglutinin (PHA). However, PHA inducement did not affect the total intracellular expression of CCR5-893(–) or wild-type CCR5. Thus we suggest there exist some PHA-induced factor(s) that could mediate the presentation of truncated CCR5.Received 23 July 2003; accepted 18 August 2003     

Structure and morphogenesis of bacteriophage T4

Bacteriophage T4 is one of the most complex viruses. More than 40 different proteins form the mature virion, which consists of a protein shell encapsidating a 172-kbp double-stranded genomic DNA, a tail, and fibers, attached to the distal end of the tail. The fibers and the tail carry the host cell recognition sensors and are required for attachment of the phage to the cell surface. The tail also serves as a channel for delivery of the phage DNA from the head into the host cell cytoplasm. The tail is attached to the unique portal vertex of the head through which the phage DNA is packaged during head assembly. Similar to other phages, and also herpes viruses, the unique vertex is occupied by a dodecameric portal protein, which is involved in DNA packaging.Received 18 February 2003; received after revision 16 April 2003; accepted 9 May 2003     

Early optical emission from the gamma-ray burst of 4 October 2002

Observations of the long-lived emission--or 'afterglow'--of long-duration gamma-ray bursts place them at cosmological distances, but the origin of these energetic explosions remains a mystery. Observations of optical emission contemporaneous with the burst of gamma-rays should provide insight into the details of the explosion, as well as into the structure of the surrounding environment. One bright optical flash was detected during a burst, but other efforts have produced negative results. Here we report the discovery of the optical counterpart of GRB021004 only 193 seconds after the event. The initial decline is unexpectedly slow and requires varying energy content in the gamma-ray burst blastwave over the course of the first hour. Further analysis of the X-ray and optical afterglow suggests additional energy variations over the first few days.     

Antibody neutralization and escape by HIV-1

Neutralizing antibodies (Nab) are a principal component of an effective human immune response to many pathogens, yet their role in HIV-1 infection is unclear. To gain a better understanding of this role, we examined plasma from patients with acute HIV infection. Here we report the detection of autologous Nab as early as 52 days after detection of HIV-specific antibodies. The viral inhibitory activity of Nab resulted in complete replacement of neutralization-sensitive virus by successive populations of resistant virus. Escape virus contained mutations in the env gene that were unexpectedly sparse, did not map generally to known neutralization epitopes, and involved primarily changes in N-linked glycosylation. This pattern of escape, and the exceptional density of HIV-1 envelope glycosylation generally, led us to postulate an evolving 'glycan shield' mechanism of neutralization escape whereby selected changes in glycan packing prevent Nab binding but not receptor binding. Direct support for this model was obtained by mutational substitution showing that Nab-selected alterations in glycosylation conferred escape from both autologous antibody and epitope-specific monoclonal antibodies. The evolving glycan shield thus represents a new mechanism contributing to HIV-1 persistence in the face of an evolving antibody repertoire.     

The effect of aggressiveness on the population dynamics of a territorial bird

A central issue in ecology lies in identifying the importance of resources, natural enemies and behaviour in the regulation of animal populations. Much of the debate on this subject has focused on animals that show cyclic fluctuations in abundance. However, there is still disagreement about the role of extrinsic (food, parasites or predators) and intrinsic (behaviour) factors in causing cycles. Recent studies have examined the impact of natural enemies, although spatial patterns resulting from restricted dispersal or recruitment are increasingly recognized as having the potential to influence unstable population dynamics. We tested the hypothesis that population cycles in a territorial bird, red grouse Lagopus lagopus scoticus, are caused by delayed density-dependent changes in the aggressiveness and spacing behaviour of males. Here we show that increasing aggressiveness experimentally for a short period in autumn reduced recruitment and subsequent breeding density by 50%, and changed population trajectories from increasing to declining. Intrinsic processes can therefore have fundamental effects on population dynamics.