A three-base-pair deletion in the peripherin-RDS gene in one form of retinitis pigmentosa.

The group of retinopathies termed retinitis pigmentosa (RP) greatly contribute to visual dysfunction in man with a frequency of roughly 1 in 4,000. We mapped the first autosomal dominant RP (adRP) gene to chromosome 3q, close to the gene encoding rhodopsin, a rod photoreceptor pigment protein. Subsequently, mutations in this gene have been implicated as responsible for some forms of adRP. Another adRP gene has been mapped to chromosome 8p. A third adRP gene in a large Irish pedigree has been mapped to chromosome 6p, showing tight linkage with the gene for peripherin, a photoreceptor cell-specific glycoprotein, which is thus a strong candidate for the defective gene. We have now identified a three-base-pair deletion which results in the loss of one of a pair of highly conserved cysteine residues in the predicted third transmembrane domain of peripherin. This deletion segregates with the disease phenotype but is not present in unaffected controls, and suggests that mutant peripherin gives rise to retinitis pigmentosa.     

A coat subunit of Golgi-derived non-clathrin-coated vesicles with homology to the clathrin-coated vesicle coat protein beta-adaptin

Four high-molecular-weight proteins form the main subunits of the coat of Golgi-derived (non-clathrin) coated vesicles. One of these coat proteins, beta-COP, is identical to a Golgi-associated protein of relative mass 110,000 (110K) that shares homology with the adaptin proteins of clathrin-coated vesicles. This connection, and the comparable molecular weights of the coat proteins of Golgi-derived and clathrin-coated vesicles, indicates that they may be structurally related. The identification of beta-COP as the 110K protein explains the blocking of secretion by the drug brefeldin A.     

New use of BCG for recombinant vaccines

BCG, a live attenuated tubercle bacillus, is the most widely used vaccine in the world and is also a useful vaccine vehicle for delivering protective antigens of multiple pathogens. Extrachromosomal and integrative expression vectors carrying the regulatory sequences for major BCG heat-shock proteins have been developed to allow expression of foreign antigens in BCG. These recombinant BCG strains can elicit long-lasting humoral and cellular immune responses to foreign antigens in mice.     

Complex patterns formed by motile cells of Escherichia coli

When chemotactic strains of the bacterium Escherichia coli are inoculated on semi-solid agar containing mixtures of amino acids or sugars, the cells swarm outwards in a series of concentric rings: they respond to spatial gradients of attractants generated by uptake and catabolism. Cells also drift up gradients generated artificially, for example by diffusion from the tip of a capillary tube or by mixing. Here we describe conditions under which cells aggregate in response to gradients of attractant which they excrete themselves. When cells are grown in semi-solid agar on intermediates of the tricarboxylic acid cycle, they form symmetrical arrays of spots or stripes that arise sequentially. When cells in a thin layer of liquid culture are exposed to these compounds, spots appear synchronously, more randomly arrayed. In either case, the patterns are stationary. The attractant is a chemical sensed by the aspartate receptor. Its excretion can be triggered by oxidative stress. As oxygen is limiting at high cell densities, aggregation might serve as a mechanism for collective defence.     

Enhancement of T-cell activation by the CD43 molecule whose expression is defective in Wiskott-Aldrich syndrome

CD43 (sialophorin, leukosialin, leukocyte large sialoglycoprotein), a heavily sialylated molecule found on most leukocytes and platelets, was initially identified as a major glycoprotein of mouse, rat and human T cells. CD43 expression is defective on the T cells of males with the Wiskott-Aldrich syndrome, an X chromosome-linked recessive immunodeficiency disorder. Affected males are susceptible to opportunistic infections and do not respond to polysaccharide antigens, reflecting defects in cytotoxic and helper T-cell functions. Anti-CD43 monoclonal antibodies have a modest costimulatory effect on T cells, natural killer cells, B cells and monocytes, and one such antibody has been shown to activate T cells directly. To investigate a possible physiological role for CD43, a complementary DNA encoding the human protein was introduced into an antigen-responsive murine T-cell hybridoma. We observed that CD43 enhances the antigen-specific activation of T cells and that the intracellular domain of CD43, which is hyperphosphorylated during T-cell activation, is required for this function. We also found that antigen-presenting cells can bind specifically to immobilized purified CD43 and that the binding can be inhibited by liposomes containing CD43 as well as by anti-CD43 monoclonal antibodies.     

Positive selection of CD4+ T cells mediated by MHC class II-bearing stromal cell in the thymic cortex

T lymphocytes differentiate in the thymus, where functionally immature, CD4+CD8+ (double positive) thymocytes develop into functionally mature CD4+ helper cells and CD8+ cytotoxic (single positive) T cells. The thymus is the site where self-reactive T cells are negatively selected (clonally deleted) and where T cells with the capacity to recognize foreign antigens in association with self-proteins encoded by the major histocompatibility complex (MHC) are positively selected. The net result of these developmental pathways is a T-cell repertoire that is both self-tolerant and self-restricted. One unresolved issue is the identity of the thymic stromal cells that mediate the negative and positive selection of the T-cell repertoire. Previous work has pointed to a bone-marrow-derived macrophage or dendritic cell as the inducer of tolerance, whereas a radiation-resistant, deoxyguanosine-resistant thymic cell seems to mediate the positive selection of self-MHC restricted T cells. Thymic stromal cells in the cortex interact with the T-cell antigen receptor on thymocytes. Using several strains of transgenic mice that express the class II MHC molecule I-E in specific regions of the thymus, we show directly that the positive selection of T cells is mediated by an I-E-bearing cell in the thymic cortex.     

Signal transduction through the CD4 receptor involves the activation of the internal membrane tyrosine-protein kinase p56lck

The CD4 T-cell surface antigen is an integral membrane glycoprotein of relative molecular mass 55,000 which binds class II major histocompatibility complex (MHC) molecules expressed on antigen presenting cells (APCs). It is thought to stabilize physical interactions between T cells and APCs (for a review, see ref. 1). Evidence is accumulating that suggests that CD4 can transduce an independent signal during T-cell activation. It has recently been shown that CD4 expressed on human and murine T cells is physically associated with the Src-related tyrosine protein kinase p56lck (refs 7, 8). These results indicate that CD4 can function as a signal transducer and suggest that tyrosine phosphorylation events may be important in CD4-mediated signalling. Here, we present evidence that cross-linking of the CD4 receptor induces a rapid increase in the tyrosine-specific protein kinase activity of p56lck and is associated with the rapid phosphorylation of one of the subunits (zeta) of the T-cell receptor complex on tyrosine residues. These data provide direct evidence for a specific CD4 signal transduction pathway that is mediated through p56lck and suggest that some of the tyrosine phosphorylation events detected during antigen-mediated T-cell activation may result from signalling through this surface molecule.