A survey of expressed genes in Caenorhabditis elegans.

As an adjunct to the genomic sequencing of Caenorhabditis elegans, we have investigated a representative cDNA library of 1,517 clones. A single sequence read has been obtained from the 5' end of each clone, allowing its characterization with respect to the public databases, and the clones are being localized on the genome map. The result is the identification of about 1,200 of the estimated 15,000 genes of C. elegans. More than 30% of the inferred protein sequences have significant similarity to existing sequences in the databases, providing a route towards in vivo analysis of known genes in the nematode. These clones also provide material for assessing the accuracy of predicted exons and splicing patterns and will lead to a more accurate estimate of the total number of genes in the organism than has hitherto been available.     

The peripheral myelin protein gene PMP-22 is contained within the Charcot-Marie-Tooth disease type 1A duplication.

Charcot-Marie-Tooth disease (CMT1) is the most common form of inherited peripheral neuropathy. Although the disease is genetically heterogeneous, it has been demonstrated that the gene defect is the most frequent type (CMT1A) is the result of a partial duplication of band 17p11.2. Recent studies suggested that the peripheral hypomyelination syndrome in the trembler (Tr) mouse, a possible animal model for CMT1 disease, is associated with a point mutation in the peripheral myelin protein-22 gene (pmp-22). Expression of pmp-22 is particularly high in Schwann cells, and the protein is found in peripheral myelin. We now report that the human PMP-22 gene is contained within the CMT1A duplication. We therefore, suggest that increased dosage of the PMP-22 gene may be the cause of CMT1A neuropathy.     

Isolation of a candidate gene for Norrie disease by positional cloning.

The gene for Norrie disease, an X-linked disorder characterized by progressive atrophy of the eyes, mental disturbances and deafness, has been mapped to chromosome Xp11.4 close to DXS7 and the monoamine oxidase (MAO) genes. By subcloning a YAC with a 640 kilobases (kb) insert which spans the DXS7-MAOB interval we have generated a cosmid contig which extends 250 kb beyond the MAOB gene. With one of these cosmids, microdeletions were detected in several patients with Norrie disease. Screening of cDNA libraries has enabled us to isolate and sequence a likely candidate gene for Norrie disease which is expressed in retina, choroid and fetal brain. No homologous sequences were found in DNA and protein databases indicating that this cDNA is part of a gene encoding a 'pioneer' protein.     

Telomere-associated chromosome fragmentation: applications in genome manipulation and analysis.

Telomere-associated chromosome fragmentation (TACF) is a new approach for chromosome mapping based on the non-targeted introduction of cloned telomeres into mammalian cells. TACF has been used to generate a panel of somatic cell hybrids with nested terminal deletions of the long arm of the human X chromosome, extending from Xq26 to the centromere. This panel has been characterized using a series of X chromosome loci. Recovery of the end clones by plasmid rescue produces a telomeric marker for each cell line and partial sequencing will allow the generation of sequence tagged sites (STSs). TACF provides a powerful and widely applicable method for genome analysis, a general way of manipulating mammalian chromosomes and a first step towards constructing artificial mammalian chromosomes.     

Clonal expansion of p53 mutant cells is associated with brain tumour progression.

Tumour progression is a fundamental feature of the biology of cancer. Cancers do not arise de novo in their final form, but begin as small, indolent growths, which gradually acquire characteristics associated with malignancy. In the brain, for example, low-grade tumours (astrocytomas) evolve into faster growing, more dysplastic and invasive high-grade tumours (glioblastomas). To define the genetic events underlying brain tumour progression, we analysed the p53 gene in ten primary brain tumour pairs. Seven pairs consisted of tumours that were high grade both at presentation and recurrence (group A) and three pairs consisted of low-grade tumours that had progressed to higher grade tumours (group B). In group A pairs, four of the recurrent tumours contained a p53 gene mutation; in three of them, the same mutation was found in the primary tumour. In group B pairs, progression to high grade was associated with a p53 gene mutation. A subpopulation of cells were present in the low-grade tumours that contained the same p53 gene mutation predominant in the cells of the recurrent tumours that had progressed to glioblastoma. Thus, the histological progression of brain tumours was associated with a clonal expansion of cells that had previously acquired a mutation in the p53 gene, endowing them with a selective growth advantage. These experimental observations strongly support Nowell's clonal evolution model of tumour progression.     

Dynamin is a GTPase stimulated to high levels of activity by microtubules.

Dynamin was initially identified in calf brain tissue as a protein of relative molecular mass 100,000 which induced nucleotide-sensitive bundling of microtubules. Purified dynamin showed only trace ATPase activity. But in combination with an activating factor removed during the purification, it exhibited microtubule-activated ATPase activity and dynamin-induced bundles showed evidence of ATP-dependent force production. Dynamin is the product of the Drosophila gene shibire, which has been implicated in synaptic vesicle recycling and, more generally, in the budding of endocytic vesicles from the plasma membrane. Dynamin also shows extensive homology with proteins that participate in vacuolar protein sorting and spindle pole-body separation in yeast, and in interferon-induced viral resistance in mammals. All members of this family contain consensus sequence elements consistent with GTP binding near their amino termini, although none has been shown to have GTPase activity. We report here that dynamin is a specific GTPase which can be stimulated to very high levels of activity by microtubules.     

Different beta-subunits determine G-protein interaction with transmembrane receptors.

Regulatory GTP-binding proteins (G proteins) are membrane-attached heterotrimers (alpha, beta, gamma) that mediate cellular responses to a wide variety of extracellular stimuli. They undergo a cycle of guanine-nucleotide exchange and GTP hydrolysis, during which they dissociate into alpha-subunit and beta gamma complex. The roles of G-protein alpha-subunits in these processes and for the specificity of signal transduction are largely established; the beta- and gamma-subunits are essential for receptor-induced G-protein activation and seem to be less diverse and less specific. Although the complementary DNAs for several beta-subunits have been cloned, isolated subunits have only been studied as beta gamma complexes. Functional differences have been ascribed to the gamma-subunit on the basis of extensive sequence similarity among beta-subunits and apparent heterogeneity in gamma-subunit sequences. Beta gamma complexes can interact directly or indirectly with different effectors. They seem to be interchangeable in their interaction with pertussis toxin-sensitive alpha-subunits, so we tested this by microinjecting antisense oligonucleotides into nuclei of a rat pituitary cell line to suppress the synthesis of individual beta-subunits selectively. Here we show that two out of four subtypes of beta-subunits tested (beta 1 and beta 3) are selectively involved in the signal transduction cascades from muscarinic M4 (ref. 4) and somatostatin receptors, respectively, to voltage-dependent Ca2+ channels.     

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.     

Neural subsystems for object knowledge.

Critical issues in the cognitive neuroscience of language are whether there are multiple systems for the representation of meaning, perhaps organized by processing system (such as vision or language), and whether further subsystems are distinguishable within these larger ones. We describe here a patient (K.R.) with cerebral damage whose pattern of acquired deficits offers direct evidence for a major division between visually based and language-based higher-level representations, and for processing subsystems within language. K.R. could not name animals regardless of the type of presentation (auditory or visual), but had no difficulty naming other living things and objects. When asked to describe verbally the physical attributes of animals (for example, 'what colour is an elephant?'), she was strikingly impaired. Nevertheless, she could distinguish the correct physical attributes of animals when they were presented visually (she could distinguish animals that were correctly coloured from those that were not). Her knowledge of input stimulus. To explain this selective deficit, these data mandate the existence of two distinct representations of such properties in normal individuals, one visually based and one language-based. Furthermore, these data establish that knowledge of physical attributes is strictly segregated from knowledge of other properties in the language system.     

Uncoupling of hypomyelination and glial cell death by a mutation in the proteolipid protein gene.

Proteolipid protein (PLP; M(r) 30,000) is a highly conserved major polytopic membrane protein in myelin but its cellular function remains obscure. Neurological mutant mice can often provide model systems for human genetic disorders. Mutations of the X-chromosome-linked PLP gene are lethal, identified first in the jimpy mouse and subsequently in patients with Pelizaeus-Merzbacher disease. The unexplained phenotype of these mutations includes degeneration and premature cell death of oligodendrocytes with associated hypomyelination. Here we show that a new mouse mutant rumpshaker is defined by the amino-acid substitution Ile-to-Thr at residue 186 in a membrane-embedded domain of PLP. Surprisingly, rumpshaker mice, although myelin-deficient, have normal longevity and a full complement of morphologically normal oligodendrocytes. Hypomyelination can thus be genetically separated from the PLP-dependent oligodendrocyte degeneration. We suggest that PLP has a vital function in glial cell development, distinct from its later role in myelin assembly, and that this dichotomy of action may explain the clinical spectrum of Pelizaeus-Merzbacher disease.