HIV susceptibility conferred to human fibroblasts by cytomegalovirus-induced Fc receptor

The main receptor for the human immunodeficiency viruses type 1 and 2 (HIV-1 and HIV-2) on T and B lymphocytes, monocytes and macrophages is the CD4 antigen 1-3. Infection of these cells is blocked by monoclonal antibodies to CD4(1,2) and by recombinant soluble CD4(4-9). Expression of transfected CD4 on the surface of HeLa and other human cells renders them susceptible to HIV infection 10. HIV-antibody complexes can also infect monocytes and macrophages by means of receptors for the Fc portion of immunoglobulins (FcR)11-13), or complement receptors 14,15. The expression of IgG FcRs can be induced in cells infected with human herpes viruses such as herpes simplex virus type 1 (HSV-1)16,17 and human cytomegalovirus (CMV)18-21. Here we demonstrate that FcRs induced by CMV allow immune complexes of HIV to infect fibroblasts otherwise not permissive to HIV infection. Infection was inhibited by prior incubation with human IgG, but not by anti-CD4 antibody or by recombinant soluble CD4. Once HIV had entered CMV-infected cells by means of the FcR, its replication could be enhanced by CMV transactivating factors. Synergism between HIV and herpes viruses could also operate in vivo, enhancing immunosuppression and permitting the spread of HIV to cells not expressing CD4.     

Towards a transgenic model of Huntington's disease in a non-human primate

Non-human primates are valuable for modelling human disorders and for developing therapeutic strategies; however, little work has been reported in establishing transgenic non-human primate models of human diseases. Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor impairment, cognitive deterioration and psychiatric disturbances followed by death within 10-15 years of the onset of the symptoms. HD is caused by the expansion of cytosine-adenine-guanine (CAG, translated into glutamine) trinucleotide repeats in the first exon of the human huntingtin (HTT) gene. Mutant HTT with expanded polyglutamine (polyQ) is widely expressed in the brain and peripheral tissues, but causes selective neurodegeneration that is most prominent in the striatum and cortex of the brain. Although rodent models of HD have been developed, these models do not satisfactorily parallel the brain changes and behavioural features observed in HD patients. Because of the close physiological, neurological and genetic similarities between humans and higher primates, monkeys can serve as very useful models for understanding human physiology and diseases. Here we report our progress in developing a transgenic model of HD in a rhesus macaque that expresses polyglutamine-expanded HTT. Hallmark features of HD, including nuclear inclusions and neuropil aggregates, were observed in the brains of the HD transgenic monkeys. Additionally, the transgenic monkeys showed important clinical features of HD, including dystonia and chorea. A transgenic HD monkey model may open the way to understanding the underlying biology of HD better, and to the development of potential therapies. Moreover, our data suggest that it will be feasible to generate valuable non-human primate models of HD and possibly other human genetic diseases.     

Localization of the malignant hyperthermia susceptibility locus to human chromosome 19q12-13.2

Malignant hyperthermia (MH) is an inherited human skeletal muscle disorder and is one of the main causes of death due to anaesthesia. The reported incidence of MH varies from 1 in 12,000 in children to 1 in 40,000 in adults. MH is triggered in susceptible people by all commonly used inhalational anaesthetics; it is characterized by a profoundly accelerated muscle metabolism, contractures, hyperthermia and tachycardia. Susceptibility to MH (MHS) is predicted by contracture tests on muscle tissue obtained by biopsy. An almost identical disorder known as porcine MH exists in pigs. The genetics of the porcine syndrome have been extensively studied; the locus controlling expression of porcine MH is genetically linked to the glucose phosphate isomerase locus (GPI). In man, GPI has been mapped to the q12-13.2 region of chromosome 19 (refs 10-12). We have now investigated genetic linkage in several extended Irish pedigrees in which MHS is segregating as an autosomal dominant trait. Here we show linkage between MHS and DNA markers from the GPI region of human chromosome 19 with a maximum log likelihood ratio (lod score) of 5.65 at the CYP2A locus. These results indicate that human and porcine MH are most probably due to mutations in homologous genes, and also provide a potentially accurate and noninvasive method of diagnosis for MHS.     

Linkage of a nasopharyngeal carcinoma susceptibility locus to the HLA region

The frequency of nasopharyngeal carcinoma is nearly 100-fold higher in southern Chinese than in most European populations. Earlier studies have suggested that an increased risk of nasopharyngeal carcinoma is associated with specific haplotypes in the HLA region: relative risks slightly over twofold were found for haplotypes A2, Bw46 and the antigen B17. We now report a linkage study based on affected sib pairs which suggests that a gene closely linked to the HLA locus confers a greatly increased risk of nasopharyngeal carcinoma. The maximum likelihood estimate is of a relative risk of approximately 21. The relationship between this suspected disease susceptibility gene (or genes) and known viral and environmental aetiological factors remains to be elucidated.     

A single class of olfactory neurons mediates behavioural responses to a Drosophila sex pheromone

Insects, like many other animals, use sex pheromones to coordinate their reproductive behaviours. Volatile pheromones are detected by odorant receptors expressed in olfactory receptor neurons (ORNs). Whereas fruit odours typically activate multiple ORN classes, pheromones are thought to act through single dedicated classes of ORN. This model predicts that activation of such an ORN class should be sufficient to trigger the appropriate behavioural response. Here we show that the Drosophila melanogaster male-specific pheromone 11-cis-vaccenyl acetate (cVA) acts through the receptor Or67d to regulate both male and female mating behaviour. Mutant males that lack Or67d inappropriately court other males, whereas mutant females are less receptive to courting males. These data suggest that cVA has opposite effects in the two sexes: inhibiting mating behaviour in males but promoting mating behaviour in females. Replacing Or67d with moth pheromone receptors renders these ORNs sensitive to the corresponding moth pheromones. In such flies, moth pheromones elicit behavioural responses that mimic the normal response to cVA. Thus, activation of a single ORN class is both necessary and sufficient to mediate behavioural responses to the Drosophila sex pheromone cVA.     

肝内胆管结石和胆汁中细菌多样性分析

运用培养法和聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)技术对6个病人肝内胆管结石和胆汁中的细菌群落进行了分析.胰蛋白胨大豆肉汤(TSB)培养法结果显示,从6个胆石和5个胆汁样品中分别分离到15株和12株细菌,均属于Escherichia和Enterococcus两个属,而同一病人胆石及胆汁中细菌种类并不完全相同,其中一份胆汁样在两种方法检测中皆为阴性;PCR-DGGE结果表明,胆石及胆汁样品中除培养法中发现的两个属外,还包含Pseudomonas、Morganella、Citrobacter、Baterioides、Serratia、Clostridiales和Aeromonas共7个属的细菌.在5组PCR阳性的胆石和胆汁的DGGE指纹图谱相似性分析中,每组内胆石和胆汁间细菌群落结构的最高相似性仅为32.3%.两种检测方法的结果表明,Escherichia coli在胆石和胆汁中的检出率最高,胆石和胆汁中细菌多样性存在差异,PCRDGGE技术比培养法能更好检测到胆石和胆汁中的细菌多样性.     

Antibiotic-mediated antagonism leads to a bacterial game of rock-paper-scissors in vivo

Colicins are narrow-spectrum antibiotics produced by and active against Escherichia coli and its close relatives. Colicin-producing strains cannot coexist with sensitive or resistant strains in a well-mixed culture, yet all three phenotypes are recovered in natural populations. Recent in vitro results conclude that strain diversity can be promoted by colicin production in a spatially structured, non-transitive interaction, as in the classic non-transitive model rock-paper-scissors (RPS). In the colicin version of the RPS model, strains that produce colicins (C) kill sensitive (S) strains, which outcompete resistant (R) strains, which outcompete C strains. Pairwise in vitro competitions between these three strains are resolved in a predictable order (C beats S, S beats R, and R beats C), but the complete system of three strains presents the opportunity for dynamic equilibrium. Here we provide conclusive evidence of an in vivo antagonistic role for colicins and show that colicins (and potentially other bacteriocins) may promote, rather than eliminate, microbial diversity in the environment.     

A uniform deleting element mediates the loss of kappa genes in human B cells

Human immunoglobulin light-chain genes become rearranged in an ordered fashion during pre-B-cell development such that rearrangement generally occurs in kappa genes before lambda genes (refs 1,2). This ordered process includes an unanticipated deletion of the constant kappa (C kappa) gene and kappa enhancer sequence which precedes lambda rearrangement, and the site of this deletional recombination was located 3' to the joining (J kappa) segments in 75% of cases studied. We have now characterized the recombinational element responsible for this event on three separate alleles and found them to be identical. This kappa-deleting element recombined site-specifically with a palindromic signal (CACAGTG) located in the J kappa-C kappa intron. All losses of C kappa genes in other human B cells were mediated by this determinant, including the 25% of instances when this element recombined with sequences 5' to J kappa. In contrast, the kappa-deleting element remained in its germline form on all successful kappa-producing alleles. Moreover, kappa loss is an evolutionarily conserved event, as the kappa-deleting element appears to be the human homologue of the murine RS sequence. Our results suggest that this element may help ensure isotypic and allelic exclusion of light chains and may be involved in the ordered use of human light-chain genes.     

X-ray structure of a bacterial oligosaccharyltransferase

Asparagine-linked glycosylation is a post-translational modification of proteins containing the conserved sequence motif Asn-X-Ser/Thr. The attachment of oligosaccharides is implicated in diverse processes such as protein folding and quality control, organism development or host-pathogen interactions. The reaction is catalysed by oligosaccharyltransferase (OST), a membrane protein complex located in the endoplasmic reticulum. The central, catalytic enzyme of OST is the STT3 subunit, which has homologues in bacteria and archaea. Here we report the X-ray structure of a bacterial OST, the PglB protein of Campylobacter lari, in complex with an acceptor peptide. The structure defines the fold of STT3 proteins and provides insight into glycosylation sequon recognition and amide nitrogen activation, both of which are prerequisites for the formation of the N-glycosidic linkage. We also identified and validated catalytically important, acidic amino acid residues. Our results provide the molecular basis for understanding the mechanism of N-linked glycosylation.