No description available.

Extensive studies indicate that both genetic and epigenetic (physiological and biomechanical) factors play a role in the development of twist state which must correspond to the establishment of cell surface conformational state at the level of cell wall assembly. Therefore, in order to identify the unknown factors that control the macrofiber production, twist states and hand inversion, genetic studies concerning regulation of macrofiber production and macrofiber structural states seemed to be appropriate. Genetic studies were carried out by using an insertional mutagenesis method. Bank(s) of insertions were obtained that carry the Tn917 transposon at random locations in the genome. Selected isolates were characterized with respect to macrofiber production and twist, and helix hand inversion stimulated by various physiological factors. The bank(s) of insertional mutants were searched for those defective or impaired in response to ion-induced hand inversion. None were found to exhibit the desired phenotype. Clones with altered static state were not rare. Another approach was to take advantage of the transposon "lac system" and to use the bank of insertion mutants to study regulation of gene expression. The chromogenic substrate for β-galactosidase, X-gal, made possible the search for factors governing gene expression during macrofiber morphogenesis in a manner similar to the way in which developmental biologists study regulation of gene expression during embryogenesis. First, insertion strains were screened for lac-Z expression on TBAB (Tryptose Blood Agar Base) X-gal plates. Isolates were then characterized by growth in fluid media. One strain (3:1) was found that expressed the E. coli lac-Z structural gene when grown on solid media (TBAB X-gal), but not when grown in fluid media. These observations led us to an examination of the role the medium may play in the regulation of gene expression. Evidence was obtained indicating that a number of insertion strains respond to growth in viscous media by expression of lac-Z+ indicating that different host gene promoters can be regulated by a physical component of the environment. The degree of expression moreover was positively correlated with the degree of viscosity. Environmental physical forces applied to the "body" of a bacterial cell must therefore play a role in gene expression. In at least one strain, 5:7Oring, gene expression was found only in right-handed structures suggesting that either specific genes are involved in the twist state and hand determination or that helix hand itself may govern gene expression. Finally, the 5:7Oring strain shows also the presence of a probable intercellular signalling through a diffusible chemical that causes gene expression to occur only in certain cells found at specific locations within the population.

The leukocyte immunoglobulin like receptors (LILRs) are a group of receptors with immunomodulatory effects. Group 1 LILRs comprise of LILRB1, among others, and bind to class 1 MHC molecules and transmits inhibitory signals. Studies have shown that LILRB1 ligation during the monocyte differentiation process into dendritic cells (DCs) results in the generation of a population of cells that are tolerogenic. Here we hypothesize that this tolerogenic nature of the resultant cells is due to the high expression of nuclear factor kappa – light chain enhancer of activated B cells (NF-κB) inhibitor – A20 binding inhibitor of NF-κB signalling 1 (ABIN1). In this study we analyzed the effect that ABIN1 exerts on the maturation of DCs and CD14+HLA-DRlow/- monocytes - a population of cells that have been recently been identified as myeloid derived suppressor cells (MDSCs) in humans. LILRB1 ligated DCs and CD14+HLA-DRlow/- monocytes, when treated with ABIN1 siRNA, displayed an increase in the expression of antigen presentation and co-stimulatory molecules such as CD80, CD86, HLA-DR and HLA-ABC and displayed a greater capacity to produce cytokines like IL-12 and IFN-α. Additionally, they displayed a greater capacity to stimulate the adaptive component of the immune system in terms of IFN-γ production, cell proliferation and adapter molecule and mitogen activated protein kinase (MAPK) activation in T cells. Based on the results we obtained, it can be concluded that ABIN1 plays a significant role in maintaining the immature and suppressive phenotype of immature myeloid cells (IMCs) by dampening NF-κB signalling, while also exerting a negative effect on antiviral signalling.

Sepsis affects hundreds of thousands each year in the United States alone, with an estimated 20-30% mortality rate in spite of current treatment regimens. Sepsis mortality was originally understood to be the caused by overproduction of inflammatory cytokines in response to pathogen detection by the host. However, recent studies suggest that with modern treatments, secondary infection, rather than inflammatory shock, may be of greater concern. In either case, the failure of a large number of anti-inflammatory agents to produce beneficial outcomes in sepsis treatment during clinical trial suggests that the development of a new class of immunomodulatory agents may be required for effective treatment. In experimental models, pre-treatment with sub-lethal doses of lipopolysaccharide (LPS, previously referred to as endotoxin) induces a state of "LPS tolerance" that reduces septic shock lethality. Paradoxically, LPS tolerance also results in increased antimicrobial gene expression and resistance to secondary infection in some models. Further exploration of this process may provide drug targets capable of limiting inflammation without dampening antimicrobial immunity, which could be of great benefit in the treatment of sepsis and chronic inflammatory disease. Many groups have studied signaling changes that occur during LPS tolerance. However, mediators of tolerance that can account for the changes in LPS-induced gene expression that result in increased microbial resistance are not well described. This has prevented proper testing of the physiological effects of tolerance on disease, and it remains unclear if this process could be artificially induced or is of any benefit to sepsis patients. Recent in vitro work suggests that tolerant gene expression patterns are the result of large scale changes in chromatin organization that occur in macrophages after prolonged LPS stimulation. Because microRNAs (miRNAs), a new class of gene regulator, have been found to regulate chromatin modifying complexes in other systems, LPS-induced miRNAs were screened to identify potential mediators of tolerance that could cause changes in gene expression patterns without necessarily impacting LPS signaling itself. Several tolerance-associated miRNAs were identified. One miRNA in particular, miR-222, was found to repress tumor necrosis factor (Tnf) and Brahma-related gene one (Brg1) expression. This attenuates expression of genes dependent on nucleosome remodeling, primarily affecting inflammatory genes. Consequently, miR-222 expression effectively limits septic shock lethality. However, low-level responses, as well as NF-κB signaling and the expression of a subset of antimicrobial and antiviral genes, are left intact. Thus, although miR-222 does not entirely recapitulate the tolerance response, by directing the LPS response into a less damaging expression profile, miR-222 may accelerate the onset of tolerance and be a promising target for therapeutics aiming to treat inflammatory disease without compromising host immunity.

No description available.

Moloney Murine Leukemia Virus (M-MLV) proviral DNA is transcriptionally silenced in mouse embryonic cells by a repressor complex containing tripartite-motif-containing 28 (Trim28). Trim28 depends on post-translational modifications, such as sumoylation and phosphorylation, and its interactions with several co-repressor proteins to regulate its repressive activity. YY1 is one such Trim28 co-repressor protein, recently found to tether the Trim28 silencing complex to the M-MLV promoter. Here, we investigated the biochemical interaction of Trim28 and YY1, and the role of sumoylation and phosphorylation of Trim28 in mediating M-MLV silencing. Experiments probing the binding of YY1 and Trim28 in vitro suggested that their interaction occurs indirectly. Mutational studies demonstrated that the RBCC domain of Trim28 is sufficient for interaction with YY1 while the acidic region 1 and zinc fingers of YY1 were necessary and sufficient for its interaction with Trim28. Additionally, we found that the K779 residue was critical for Trim28-mediated silencing of M-MLV in embryonic cells. The repressor complex that silences M-MLV is very large and likely consists of many protein subunits. A few proteins contained in the repressor complex have been identified, including Trim28, but the identity of most of the components forming the repressor complex are unknown. We detected a new form of the complex that is of even high molecular weight and likely contains additional associated cofactors. We reported an approach for purifying this larger repressor complex and identified new candidates for cofactors that may potentially function in the silencing of M-MLV. We also examined the regulation of sumoylation in embryonic cells. Sumoylation conjugation is a post-translational modification that affects a diverse range of processes and is important for embryo survival. Overall inhibition of the SUMO pathways results in embryonic lethality demonstrating the importance of the SUMO pathways for embryonic viability; however, our understanding of SUMO function in embryos at the cellular and molecular level is still greatly lacking. We demonstrated that SUMO1 cannot be overexpressed in embryonic carcinoma and embryonic stem cells and that SUMO1 overexpression is prevented at a post-transcriptional level. This occurred specifically for SUMO1 and not for SUMO2 overexpression. Furthermore, blocking conjugation or increasing the deconjugation of SUMO1 to substrates significantly improved SUMO1 overexpression. The results indicate that the overexpression of SUMO1 protein, in itself, is tolerated in embryonic cells, but the accumulation of substrate(s) modified by SUMO1 appears to be strongly prevented by an embryonic-specific post-transcriptional mechanism.

No description available.

The successive activation of tissue-specific genes during cellular differentiation is orchestrated by the formation of transcriptional complexes consisting of cellspecific and ubiquitous transcription factors. Understanding the molecular events associated with normal megakaryocyte (Mk) differentiation is an issue of central importance to haematology. The aims of this study were therefore to: (i) define the transcription factors responsible for regulating the expression of Mkspecific genes such as Glycoprotein IX, (ii) identify the protein partners of such important Mk-regulatory transcription factors and (iii) examine the mechanisms utilised by these factors to regulate gene expression. First, the regulatory elements in the GPIX promoter required for basal and inducible expression were examined in megakaryoblastic Dami cells stimulated to undergo differentiation. The resulting data suggested that an Ets site in the GPIX promoter binding the Ets-family member Fli-1 was crucial in regulating both constitutive and inducible GPIX expression. Second, a two-hybrid screen of a K-562 cDNA library was used to identify transcription factors that interacted with Fli-1 and were potential regulators of Mk development. Results of this screen identified a novel protein-protein interaction with GATA-1, a previously well-characterised zinc finger transcription factor also implicated in erythroid and Mk development. Mapping of the domains required for the interaction show that the zinc fingers of GATA-1 interact with the Ets domain of Fli-1. The biological significance of the Fli-1/GATA-1 interaction was demonstrated in transient transfection assays, which resulted in synergistic activation of Mkspecific promoters. Analysis of Fli-1 and GATA-1 expression in a series of erythroleukaemic and megakaryoblastic cell lines demonstrated that the Fli- 1/GATA-1 combination correlates with a Mk-phenotype. Moreover, expression of Fli-1 in K-562 cells (a line rich in GATA-1 but normally lacking Fli-1) induces endogenous GPIX expression. Quantitative mobility shift assays reveal that Fli- 1 and GATA-1 exhibit cooperative DNA-binding in which the binding of GATA-1 to DNA is increased approximately 26 fold in the presence of Fli-1. This data provides a mechanism for the observed transcriptional synergy. In conclusion, this work suggests that Fli-1 and GATA-1 work together through protein-protein interaction and cooperative DNA-binding to activate the expression of genes associated with the terminal differentiation of Mks.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 87-102.