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S B Snapper

Publications and source records attributed to S B Snapper.

At least 19 recordsLinked to original sources
PubMed2001

Cdc42, Rac1, and the Wiskott-Aldrich syndrome protein are involved in the cytoskeletal regulation of B lymphocytes.

Patients with the immunodeficiency disorder Wiskott-Aldrich syndrome (WAS) have lymphocytes with aberrant microvilli, and their T cells, macrophages, and dendritic cells are impaired in cytoskeletal-dependent processes. WAS is caused by a defective or a missing WAS protein (WASP). Signal mediators interleukin-4 (IL-4) and CD40 are important for actin-dependent morphology changes in B cells. A possible function of WASP and its interacting partners, Cdc42 and Rac1, was investigated for these changes. It was found that active Cdc42 and Rac1 induced filopodia and lamellipodia, respectively, in activated B cells. Evidence is given that IL-4 has a specific role in the regulated cycling of Cdc42 because IL-4 partially and transiently depleted active Cdc42 from detergent extract of activated B cells. WASP-deficient B lymphocytes were impaired in IL-4-- and CD40-dependent induction of polarized and spread cells. Microvilli were expressed on WASP-deficient B cells, but they appeared shorter and less dense in cell contacts than in wild-type cells. In conclusion, evidence is provided for the involvement of Cdc42, Rac1, and WASP in the cytoskeletal regulation of B lymphocytes. Aberrations in WASP-deficient B lymphocytes, described here, provide further evidence that WAS is a cytoskeletal disease of hematopoietic cells. (Blood. 2001;98:1086-1094)

Animals↗
PubMed2001

N-WASP deficiency reveals distinct pathways for cell surface projections and microbial actin-based motility.

The Wiskott-Aldrich syndrome protein (WASP) family of molecules integrates upstream signalling events with changes in the actin cytoskeleton. N-WASP has been implicated both in the formation of cell-surface projections (filopodia) required for cell movement and in the actin-based motility of intracellular pathogens. To examine N-WASP function we have used homologous recombination to inactivate the gene encoding murine N-WASP. Whereas N-WASP-deficient embryos survive beyond gastrulation and initiate organogenesis, they have marked developmental delay and die before embryonic day 12. N-WASP is not required for the actin-based movement of the intracellular pathogen Listeria but is absolutely required for the motility of Shigella and vaccinia virus. Despite these distinct defects in bacterial and viral motility, N-WASP-deficient fibroblasts spread by using lamellipodia and can protrude filopodia. These results imply a crucial and non-redundant role for N-WASP in murine embryogenesis and in the actin-based motility of certain pathogens but not in the general formation of actin-containing structures.

Actins↗
PubMed2001

Efficient uptake of Yersinia pseudotuberculosis via integrin receptors involves a Rac1-Arp 2/3 pathway that bypasses N-WASP function.

Efficient uptake of Yersinia pseudotuberculosis into cultured mammalian cells is the result of high-affinity binding of invasin to beta1 chain integrins. We demonstrate here that uptake requires Rac1 and Arp 2/3 function. Bacterial uptake was stimulated by GTPgammaS, but was inhibited in mammalian cells transfected with the interfering Rac1-N17 derivative. Rac1 was found to be activated in response to integrin engagement by invasin, whereas Rac1 and Arp 2/3 were found to be intensely localized around phagosomes bearing bacteria, indicating a specific role for Rac1 signalling from the nascent phagosome to downstream effectors. To determine whether the Arp 2/3 complex was a component of this proposed pathway, cells overproducing various derivatives of Scar1/WAVE1, an Arp 2/3-binding protein, were analysed. Sequestration of Arp 2/3 away from the phagocytic cup as a result of Scar1/WAVE1 overproduction dramatically inhibited uptake. To determine whether signalling from Rac1 to Arp 2/3 occurred via N-WASP, uptake was analysed in a cell line lacking expression of WASP and N-WASP. Uptake was unaffected by the absence of these proteins, indicating that beta1 integrin signalling from Rac1 to Arp 2/3 can occur in the absence of N-WASP function.

3T3 Cells↗
PubMed2000

Cbl-b is a negative regulator of receptor clustering and raft aggregation in T cells.

Stimulation of T cells via the antigen and costimulatory receptors leads to the organization of a supramolecular activation cluster called the immune synapse. We report that loss of the molecular adaptor Cbl-b in T cells frees antigen receptor-triggered receptor clustering, lipid raft aggregation, and sustained tyrosine phosphorylation from the requirement for CD28 costimulation. Introduction of the cbl-b mutation into a vav1-/- background relieved the functional defects of vav1-/- T cells and caused spontaneous autoimmunity. Wiscott Aldrich Syndrome protein (WASP) was found to be essential for deregulated proliferation and membrane receptor reorganization of cbl-b mutant T cells. Antigen receptor-triggered Ca2+ mobilization, cytokine production, and receptor clustering can be genetically uncoupled in cbl-b mutant T cells. Thus, Cbl-b functions as a negative regulator of receptor clustering and raft aggregation in T cells.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Impaired B cell development and proliferation in absence of phosphoinositide 3-kinase p85alpha.

Phosphoinositide 3-kinase (PI3K) activation has been implicated in many cellular responses, including fibroblast growth, transformation, survival, and chemotaxis. Although PI3K is activated by several agents that stimulate T and B cells, the role of PI3K in lymphocyte function is not clear. The mouse gene encoding the PI3K adapter subunit p85alpha and its splice variants p55alpha and p50alpha was disrupted. Most p85alpha-p55alpha-p50alpha-/- mice die within days after birth. Lymphocyte development and function was studied with the use of the RAG2-deficient blastocyst complementation system. Chimeric mice had reduced numbers of peripheral mature B cells and decreased serum immunoglobulin. The B cells that developed had diminished proliferative responses to antibody to immunoglobulin M, antibody to CD40, and lipopolysaccharide stimulation and decreased survival after incubation with interleukin-4. In contrast, T cell development and proliferation was normal. This phenotype is similar to defects observed in mice lacking the tyrosine kinase Btk.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1999

The Wiskott-Aldrich syndrome protein (WASP): roles in signaling and cytoskeletal organization.

The Wiskott-Aldrich Syndrome (WAS) is a rare X-linked primary immunodeficiency that is characterized by recurrent infections, hematopoietic malignancies, eczema, and thrombocytopenia. A variety of hematopoietic cells are affected by the genetic defect, including lymphocytes, neutrophils, monocytes, and platelets. Early studies noted both signaling and cytoskeletal abnormalities in lymphocytes from WAS patients. Following the identification of WASP, the gene mutated in patients with this syndrome, and the more generally expressed WASP homologue N-WASP, studies have demonstrated that WASP-family molecules associate with numerous signaling molecules known to alter the actin cytoskeleton. WASP/N-WASP may depolymerize actin directly and/or serve as an adaptor or scaffold for these signaling molecules in a complex cascade that regulates the cytoskeleton.

Animals↗
PubMed1998

Wiskott-Aldrich syndrome protein-deficient mice reveal a role for WASP in T but not B cell activation.

The Wiskott-Aldrich syndrome (WAS) is a human X-linked immunodeficiency resulting from mutations in a gene (WASP) encoding a cytoplasmic protein implicated in regulating the actin cytoskeleton. To elucidate WASP function, we disrupted the WASP gene in mice by gene-targeted mutation. WASP-deficient mice showed apparently normal lymphocyte development, normal serum immunoglobulin levels, and the capacity to respond to both T-dependent and T-independent type II antigens. However, these mice did have decreased peripheral blood lymphocyte and platelet numbers and developed chronic colitis. Moreover, purified WASP-deficient T cells showed markedly impaired proliferation and antigen receptor cap formation in response to anti-CD3epsilon stimulation. Yet, purified WASP-deficient B cells showed normal responses to anti-Ig stimulation. We discuss the implications of our findings regarding WASP function in receptor signaling and cytoskeletal reorganization in T and B cells and compare the effects of WASP deficiency in mice and humans.

Animals↗
PubMed1992

Identification of expression signals of the mycobacteriophages Bxb1, L1 and TM4 using the Escherichia-Mycobacterium shuttle plasmids pYUB75 and pYUB76 designed to create translational fusions to the lacZ gene.

Mycobacterial expression signals were cloned using specially constructed gene fusion shuttle plasmid probes carrying a truncated Escherichia coli lacZ (beta-galactosidase) gene which lacked a promoter, a ribosome binding site, and an ATG start codon. Libraries of mycobacteriophage Bxb1, L1 and TM4 DNAs were constructed, and introduced by electroporation into Mycobacterium smegmatis and the 'bacille Calmette-Guérin' (BCG). Clones carrying mycobacterial expression sequences were detected by their blue colour or characteristic fluorescence when plated on media containing chromogenic or fluorogenic substrates. Varying degrees of beta-galactosidase expression were observed, and one Bxb1 expression signal was identified where beta-galactosidase expression is repressed in phage lysogens.

Cloning, Molecular↗
PubMed1990

Isolation and characterization of efficient plasmid transformation mutants of Mycobacterium smegmatis.

Recent development of vectors and methodologies to introduce recombinant DNA into members of the genus Mycobacterium has provided new approaches for investigating these important bacteria. While most pathogenic mycobacteria are slow-growing, Mycobacterium smegmatis is a fast-growing, non-pathogenic species that has been used for many years as a host for mycobacteriophage propagation and, recently, as a host for the introduction of recombinant DNA. Its use as a cloning host for the analysis of mycobacterial genes has been limited by its inability to be efficiently transformed with plasmid vectors. This work describes the isolation and characterization of mutants of M. smegmatis that can be transformed, using electroporation, at efficiencies 10(4) to 10(5) times greater than those of the parent strain, yielding more than 10(5) transformants per microgram of plasmid DNA. The mutations conferring this efficient plasmid transformation (Ept) phenotype do not affect phage transfection or the integration of DNA into the M. smegmatis chromosome, but seem to be specific for plasmid transformation. Such Ept mutants have been used to characterize plasmid DNA sequences essential for replication of the Mycobacterium fortuitum plasmid pAL5000 in mycobacteria by permitting the transformation of a library of hybrid plasmid constructs. Efficient plasmid transformation of M. smegmatis will facilitate the analysis of mycobacterial gene function, expression and replication and thus aid in the development of BCG as a multivalent recombinant vaccine vector and in the genetic analysis of the virulence determinants of pathogenic mycobacteria.

DNA, Bacterial↗
PubMed1989

Development of genetic systems for the mycobacteria.

Requisite to a detailed understanding of the molecular basis of bacterial pathogenesis is a genetic system which allows for the transfer, mutation, and expression of specific genes. Genetic analysis of mycobacteria has been exceedingly difficult since the mycobacteria grow slowly and no natural efficient method of gene transfer within the pathogenic has thus far been found. Using a molecular genetic approach, we have developed both the vectors and the methodology for efficient gene transfer in the mycobacteria. Initially, a novel of type of mycobacteriophage vector was developed, termed a shuttle phasmid. This hybrid shuttle vector replicates in Escherichia coli as a plasmid and in mycobacteria as a phage, capable of introducing foreign DNA into a wide variety of mycobacterial species. A set of shuttle phasmids, constructed from a temperate mycobacteriophage, retained their ability to lysogenize their mycobacterial hosts and could thus introduce foreign DNA stably into mycobacterial cells. An E. coli gene conferring kanamycin-resistance was cloned into these vectors and shown to express in the mycobacteria, thus providing the first selectable marker gene for subsequent genetic studies. Using kanamycin-resistance gene as a selection, the M. fortuitum plasmid pAL5000 replicon, and electroporation; a plasmid transformation system has been developed for both M. smegmatis and BCG. We now plan to use these phage and plasmid systems to analyze, genetically, the virulence attributes of the pathogenic mycobacteria. In addition, by introducing and expressing foreign antigens in BCG, we hope to develop a novel recombinant multi-vaccine vehicle capable of conferring immunity to a variety of bacterial, viral, and parasitic pathogens.

BCG Vaccine↗
PubMed1988

Lysogeny and transformation in mycobacteria: stable expression of foreign genes.

Requisite to a detailed understanding of the molecular basis of bacterial pathogenesis is a genetic system that allows for the transfer, mutation, and expression of specific genes. Because of the continuing importance of tuberculosis and leprosy worldwide, we initiated studies to develop a genetic system in mycobacteria and here report the use of two complementary strategies to introduce and express selectable genetic markers. First, an Escherichia coli cosmid was inserted into the temperate mycobacteriophage L1, generating shuttle phasmids replicating as plasmids in E. coli and phage capable of lysogenizing the mycobacterial host. These temperate shuttle phasmids form turbid plaques on Mycobacterium smegmatis and, upon lysogenization, confer resistance to superinfection and integrate within the mycobacterial chromosome. When an L1 shuttle phasmid containing a cloned gene conferring kanamycin resistance in E. coli was introduced into M. smegmatis, stable kanamycin-resistant colonies--i.e., lysogens--were obtained. Second, to develop a plasmid transformation system in mycobacteria, M. fortuitum/E. coli hybrid plasmids containing mycobacterial and E. coli replicons and a kanamycin-resistance gene were constructed. When introduced into M. smegmatis or BCG (Mycobacterium tuberculosis typus bovinus var. Bacille-Calmette-Guérin) by electroporation, these shuttle plasmids conferred stable kanamycin resistance upon transformants. These systems should facilitate genetic analyses of mycobacterial pathogenesis and the development of recombinant mycobacterial vaccines.

Cloning, Molecular↗
PubMed1984

The distribution of thyrotropin-releasing hormone (TRH) in the rhesus monkey spinal cord.

The distribution of thyrotropin-releasing hormone (TRH) in the Rhesus monkey spinal cord was studied using a highly specific antibody to TRH and the indirect peroxidase-antiperoxidase technique. TRH-positive fibers were found at all levels of the spinal cord and were in greatest concentration in the ventral gray, intermediolateral column and central gray. All motor nuclear groups in lamina IX of the ventral gray were innervated by TRH, frequently in close association with perikarya of alpha-motoneurons. The motor nuclei in the lumbar cord were the most heavily stained and contrasted to the minimal staining in the retrodorsolateral nuclear groups of the cervical, thoracic and sacral cord. Within the intermediolateral column, which contains the majority of preganglionic sympathetic neurons, TRH terminal fields reached their highest density between T2-T4 and T12-L2. Other preganglionic neurons including the nucleus intercalatus spinalis and the dorsal commissural nucleus were also densely innervated. These studies demonstrate the preferential distribution of TRH in the monkey spinal cord to regions containing alpha-motoneurons and preganglionic neurons and indicate that TRH may play an important role in the regulation of motor function and in the autonomic nervous system.

Animals↗
PubMed1983

Evidence that spinal cord thyrotropin-releasing hormone is independent of the paraventricular nucleus.

To determine whether neuronal perikarya containing thyrotropin-releasing hormone (TRH) in the paraventricular nucleus project to the spinal cord, this region of the hypothalamus was ablated by a midline electrolytic lesion and the spinal cord assayed for its content of TRH. In contrast to the marked diminution of TRH in the median eminence, there was no significant change in the TRH content in the spinal cord. These results indicate the absence of significant afferent input of TRH-containing perikarya in the paraventricular nucleus to the spinal cord.

Animals↗
PubMedDate not supplied

Mycobacteriophage vector systems.

Successful application of molecular genetic approaches to the study of mycobacteria necessitates the introduction of recombinant DNA molecules into mycobacterial cells. Efficient methods of introducing DNA into Mycobacterium smegmatis protoplasts have been developed, and the construction of mycobacteriophage recombinant DNA vectors has been initiated. Novel Escherichia coli-Mycobacterium shuttle vectors, termed shuttle phasmids, have been constructed. These vectors were constructed by inserting E. coli cosmids into nonessential regions of mycobacteriophage DNAs. Shuttle phasmids are multifunctional vectors that replicate in E. coli as plasmids and replicate in mycobacteria as phage. The presence of the bacteriophage lambda cos sequences permits the use of the lambda in vitro packaging system for efficient cloning of additional genes into these vectors. Temperate shuttle phasmids have been constructed that can infect and lyse mycobacterial cells or lysogenize mycobacterial cells to stably integrate and express cloned DNA into mycobacterial genomes. Shuttle phasmids can be transduced into a wide variety of mycobacterial species and thus should permit the development of molecular genetic systems for the mycobacteria.

Cloning, Molecular↗