Human aminopeptidase N is a receptor for human coronavirus 229E.

Human coronaviruses (HCV) in two serogroups represented by HCV-229E and HCV-OC43 are an important cause of upper respiratory tract infections. Here we report that human aminopeptidase N, a cell-surface metalloprotease on intestinal, lung and kidney epithelial cells, is a receptor for human coronavirus strain HCV-229E, but not for HCV-OC43. A monoclonal antibody, RBS, blocked HCV-229E virus infection of human lung fibroblasts, immunoprecipitated aminopeptidase N and inhibited its enzymatic activity. HCV-229E-resistant murine fibroblasts became susceptible after transfection with complementary DNA encoding human aminopeptidase N. By contrast, infection of human cells with HCV-OC43 was not inhibited by antibody RBS and expression of aminopeptidase N did not enhance HCV-OC43 replication in mouse cells. A mutant aminopeptidase lacking the catalytic site of the enzyme did not bind HCV-229E or RBS and did not render murine cells susceptible to HCV-229E infection, suggesting that the virus-binding site may lie at or near the active site of the human aminopeptidase molecule.     

Protein kinase C reduces Mg2+ block of NMDA-receptor channels as a mechanism of modulation.

The roles of N-methyl-D-aspartate (NMDA) receptors and protein kinase C (PKC) are critical in generating and maintaining a variety of sustained neuronal responses. In the nociceptive (pain-sensing) system, tissue injury or repetitive stimulation of small-diameter afferent fibres triggers a dramatic increase in discharge (wind-up) or prolonged depolarization of spinal cord neurons. This central sensitization can neither be induced nor maintained when NMDA receptor channels are blocked. In the trigeminal subnucleus caudalis (a centre for processing nociceptive information from the orofacial areas), a mu-opioid receptor agonist causes a sustained increase in NMDA-activated currents by activating intracellular PKC. There is also evidence that PKC enhances NMDA-receptor-mediated glutamate responses and regulates long-term potentiation of synaptic transmission. Despite the importance of NMDA-receptors and PKC, the mechanism by which PKC alters the NMDA response has remained unclear. Here we examine the actions of intracellularly applied PKC on NMDA-activated currents in isolated trigeminal neurons. We find that PKC potentiates the NMDA response by increasing the probability of channel openings and by reducing the voltage-dependent Mg2+ block of NMDA-receptor channels.     

Effects of an Rb mutation in the mouse.

The retinoblastoma gene is mutated in several types of human cancer and is the best characterized of the tumour-suppressor genes. A mouse strain has been constructed in which one allele of Rb is disrupted. These heterozygous animals are not predisposed to retinoblastoma, but some display pituitary tumours arising from cells in which the wild-type Rb allele is absent. Embryos homozygous for the mutation die between days 14 and 15 of gestation, exhibiting neuronal cell death and defective erythropoiesis.     

Communal nesting patterns in mice implicate MHC genes in kin recognition.

House mice (Mus musculus domesticus) form communal nests and appear to nurse each other's pups indiscriminately. Communal nesting probably functions to reduce infanticide, but it also makes females vulnerable to exploitation if nursing partners fail to provide their fair share of care. Kinship theory predicts that females will preferentially form communal nests with relatives to minimize exploitation and further increase inclusive fitness. Here we provide evidence from seminatural populations that females prefer communal nesting partners that share allelic forms of major histocompatibility complex genes. Such behaviour would lead to the selection of close relatives as communal nesting partners. Although criteria for the demonstration of kin recognition are currently embroiled in controversy, this is the first vertebrate study to meet Grafen's restrictive requirements: discrimination is based on genetic similarity at highly polymorphic loci, incidental correlations due to relatedness are experimentally controlled, and strong reasons exist for expecting the assayed behaviour to be kin-selected.     

Mutation of the beta-amyloid precursor protein in familial Alzheimer's disease increases beta-protein production.

Progressive cerebral deposition of the 39-43-amino-acid amyloid beta-protein (A beta) is an invariant feature of Alzheimer's disease which precedes symptoms of dementia by years or decades. The only specific molecular defects that cause Alzheimer's disease which have been identified so far are missense mutations in the gene encoding the beta-amyloid precursor protein (beta-APP) in certain families with an autosomal dominant form of the disease (familial Alzheimer's disease, or FAD). These mutations are located within or immediately flanking the A beta region of beta-APP, but the mechanism by which they cause the pathological phenotype of early and accelerated A beta deposition is unknown. Here we report that cultured cells which express a beta-APP complementary DNA bearing a double mutation (Lys to Asn at residue 595 plus Met to Leu at position 596) found in a Swedish FAD family produce approximately 6-8-fold more A beta than cells expressing normal beta-APP. The Met 596 to Leu mutation is principally responsible for the increase. These data establish a direct link between a FAD genotype and the clinicopathological phenotype. Further, they confirm the relevance of the continuous A beta production by cultured cells for elucidating the fundamental mechanism of Alzheimer's disease.     

Mutations in the Caenorhabditis elegans unc-4 gene alter the synaptic input to ventral cord motor neurons.

Identification of the genes orchestrating neurogenesis would greatly enhance our understanding of this process. Genes have been identified that specify neuron type (for example cut and numb in Drosophila and mec-3 in Caenorhabditis elegans) and process guidance (for example, unc-5, unc-6 and unc-40 in C. elegans and the fas-1 gene of Drosophila). We sought genes defining synaptic specificity by identifying mutations that alter synaptic connectivity in the motor circuitry in the nematode C. elegans. We used electron microscopy of serial sections to reconstruct the ventral nerve-cords of uncoordinated (unc) mutants that have distinctive locomotory choreographies. Here we describe the phenotype of mutations in the unc-4 gene in which a locomotory defect is correlated with specific changes in synaptic input to a subset of the excitatory VA motor neurons, normally used in reverse locomotion. The circuitry alterations do not arise because of the inaccessibility of the appropriate synaptic partners, but are a consequence of changes in synaptic specificity. The VA motor neurons with altered synaptic inputs are all lineal sisters of VB motor neurons; the VA motor neurons without VB sisters have essentially the same synaptic inputs as in wild-type animals. The normal function of the wild-type allele of unc-4 may thus be to invoke the appropriate synaptic specificities to VA motor neurons produced in particular developmental contexts.     

Susceptibility of beta 2-microglobulin-deficient mice to Trypanosoma cruzi infection.

The beta 2-microglobulin (beta 2m) protein associates with the products of the class I major histocompatibility (MHC) loci; this combination functions in the thymic development of and antigen presentation to CD8+ T cells. Mice in which the beta 2m gene has been disrupted by homologous recombination fail to express class I MHC gene products, and therefore lack CD8+ T cells and measurable cytotoxic T-cell responses. However, beta 2m- mice appear to have normal development of both CD4+ alpha/beta T-cell receptor (TCR+) and gamma/delta TCR+ T cells and are not overtly more susceptible than beta 2m+ mice to potential environmental agents of infection or to experimental viral infection. Here we show that beta 2m- mice suffer high parasitaemias and early death when infected with the obligate cytoplasmic protozoan parasite Trypanosoma cruzi. Despite this increased susceptibility, the beta 2m- mice are more responsive than their beta 2m+ littermates in terms of lymphokine production, making higher levels of both interleukin-2 and interferon-gamma in response to mitogen stimulation. In addition, the beta 2m- mice show essentially no inflammatory response in parasite-infected tissues. These results confirm previous experiments on mice depleted of CD8+ cells using antibody treatment in demonstrating the importance of CD8+ T cells in immune protection in T. cruzi infection. They also implicate CD8+ T cells and/or class I MHC molecules in regulation of lymphokine production and recruitment of inflammatory cells.