No description available.

No description available.

No description available.

The scaffolding protein anillin plays a crucial role during cytokinesis – the physical separation of daughter cells following chromosome segregation. Anillin binds filamentous F-actin, non-muscle myosin II and septins, and in cell culture models has been shown to restrict actomyosin contractility to the cleavage furrow. Whether anillin also serves this function during the incomplete cytokinesis that occurs in developing germ cells has remained unclear. Localization of anillin to several actin-rich structures in developing male germ cells also suggests potential roles for anillin outside of cytokinesis. In this study, I demonstrate that anillin is required for cytokinesis in dividing Drosophila spermatocytes. In addition, spermatid individualization is defective in anillin-depleted cells, although similarities to another cytokinesis mutant, four wheel drive, suggest this may be a secondary effect of failed cytokinesis. Anillin, septins and myosin II stably associate with the cleavage furrow in wild-type dividing spermatocytes. Anillin is necessary for recruitment of septins to the cleavage furrow, and for maintenance of Rho, F-actin and myosin II at the equator in late stages of cytokinesis. Membrane trafficking appears unaffected in anillin-depleted cells, although, unexpectedly, ectopic expression of one membrane trafficking marker, DE-cadherin-GFP, suppresses the cytokinesis defect. DE-cadherin-GFP recruits β-catenin (armadillo) and α-catenin to the cleavage furrow and stabilizes F-actin at the equator. Taken together, my results suggest that the anillin-septin and cadherin-catenin complexes can serve as alternative means to promote tight physical coupling of F-actin and myosin II to the cleavage furrow and successful completion of cytokinesis.

Cell adhesion is a critical process that allows the organisation and functioning of tissues in three-dimensions. However, the replenishing of cells, via cell division, within tissues is equally important for functioning complex life. Both cell adhesion and division are tightly controlled processes and rely on a complex network of signals that, as yet, are not wholly understood. This Thesis presents a structural analysis of several proteins involved in these processes. In the case of cell adhesion, we have made use of high-throughput (HTP) cloning and expression screening technologies in the Oxford Protein Production Facility (OPPF) for the study of the Kindlin protein family – a recently discovered set of proteins essential for integrin-mediated cell adhesion. As a direct result of the HTP pipeline used we were able to determine the high resolution crystal structure of a single domain, the Pleckstrin Homology Domain, from the isoform Kindlin-1. Deletion of this domain in the full-length protein resulted in impaired integrin activation in vivo. This structure, in combination with molecular dynamics simulation demonstrated that, unlike other well characterised PH domains, the binding of secondary messenger lipids (phosphoinositides) is dictated by a, previously unseen, salt bridge that occludes the putative binding site. Mutation of the salt bridge alters the binding characteristics of this domain in vitro. In addition to the PH domain, we have also studied and biophysically characterised full-length Kindlin-3, a blood cell specific isoform. By optimising baculovirus-infected Sf9 cell expression systems we were able to obtain, for the first time, sufficient quantities of protein for characterisation. Furthermore, by using small-angle X-ray scattering (SAXS) in solution we were able to determine a low resolution solution structure of Kindlin-3, revealing a linear arrangement of its FERM domain - a novel conformation known only otherwise in talin. We characterised the interaction of full-length Kindlin-3 with β-integrin cytoplasmic tails using nuclear magnetic resonance spectroscopy, which confirmed that a direct interaction with a membrane distal NPxY motif occurs, and demonstrated the importance of a preceding Serine/Threonine rich region in peptide binding. In the case of cell division, we have determined the crystal structure of the cell cycle checkpoint control related protein, Cid1, a terminal uridine tranferase from Schizzosaccharomyces pombe, alone and in complex with UTP. Structural and biochemical analysis of Cid1 identified a novel Uridine selection mechanism that is suggested to be conserved in metazoan ZCCHC enzymes involved in let-7 miRNA biogenesis, which are important for proliferation, differentiation and cell fate. We have also demonstrated that Cid1 is an RNA binding protein, a property essential for activity that employs a novel mechanism of RNA binding in the absence of RNA binding motifs. The structural work undertaken in this thesis has focussed on two distinct, but interwoven, aspects of cell biology and has significantly added to both fields of research. Excitingly, this has opened many new avenues of investigation and, in the case of Cid1, has the strong potential to lead to the development of novel anticancer therapies.

DNA replication is a key process required by organisms during cell division, with a concomitant requirement for genome synthesis by DNA polymerases. Biotechnological exploitation of thermostable DNA polymerases for DNA amplification by the Polymerase Chain Reaction (PCR), provides a significant market for novel enzymes or those with improved properties. An approach was taken to isolate alternative thermostable DNA polymerases, by enriching thermophilic bacteria from a novel thermal environment, aerobically spoiling silage. In addition, a novel DNA polymerase (Abr polBl) was cloned from the thermoacidophilic archaeon, Acidianus brierleyi, with the intention of characterising its in vivo role and application to PCR. Protein sequence analysis suggested a proofreading (high fidelity) DNA synthesis activity most related to polBl DNA polymerases from Crenarchaeota. Abr polBl was heterologously expressed in bacteria and protein purified to homogeneity. Biochemical assays confirmed high-temperature DNA polymerase and 3'-5'exonuclease activities of Abr polBl, with an accompanying proofreading ability. Sequence analysis, processivity, strand displacement and lesion bypass activities indicated potential roles in genome replication and DNA repair. Abr polBl could not amplify DNA under a range of PCR conditions, presumably following its low intrinsic thermostability. Biophysical analyses confirmed irreversible unfolding of Abr polBl at temperatures required for PCR. Supplementation with organic compounds and ionic salts stabilised Abr polBl, promoting retention of conformational stability and DNA synthesis activity following thermal incubation, but could not promote DNA amplification with Abr polB 1.

No description available.

Thesis advisor: Marc Jan Gubbels / Thesis advisor: Thomas Chiles / The length of the tachyzoite cell cycle, in particular G1, is an important virulence factor in Toxoplasma gondii. Cdk and Cyclin activities ultimately control the cell cycle; however, the checkpoint control mechanisms diverge from higher eukaryotes and are poorly understood. In order to elucidate these mechanisms, temperature sensitive (ts) mutants were generated by chemical mutagenesis. One of these mutants, called FV-P6, dies within one cell cycle in the G1 phase upon transfer from the permissive (35°C) to the restrictive temperature (40°C). Cosmid complementation identified the gene responsible for this G1 arrest as a `Cactin' ortholog. A single point mutation in this gene that resulted in an amino acid substitution from Tyrosine to Histidine at position 661 in the highly conserved C-terminus was shown to underlay the temperature sensitive effect. Cactin is highly conserved across eukaryotes and plays a role in embryonic development of metazoa although its mechanism of action is poorly understood. In agreement with the predicted nuclear localization signal in the N-terminus, expression of a fluorescent reporter gene fusion resulted in nuclear localization. Genome-wide expression profiling analysis of mutant and wild type at the permissive and restrictive temperatures confirmed the G1 arrest and furthermore demonstrated up-regulation of bradyzoite and Toxoplasma cat life cycle stage genes, hinting at TgCactin's role as a repressor. Since DNA binding domains or enzymatic domains are absent in TgCactin, TgCactin must act in a complex. Native blue gel electrophoresis demonstrated that TgCactin is present in large complexes of 720 and 800 kDa. A yeast two-hybrid screen (YTH) identified 40 potential TgCactin-interacting proteins of which 10 were selected for further validation. Eight out of these ten candidates are involved in DNA/RNA processes pertaining to transcription and translation, respectively. One-on-one YTH interactions between mutated and N-terminal deletion mutants of TgCactin and the above 10 interactors were abolished except for a single RNA helicase. Studies in Toxoplasma of four of these interactors demonstrated that only the RNA helicase localized to the nucleus; however, co-immunoprecipitation experiments to demonstrate that this protein is present in a complex with TgCactin were inconclusive. Furthermore, TgCactin self interactions identified domains necessary for TgCactin-TgCactin binding. Taken together, these findings indicate that TgCactin likely functions as a repressor of gene expression, possibly through an epigenetic mechanism reminiscent of an RNA/DNA helicase- based system in plants. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

by Chan Shuk Chong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 135-142). / Statement --- p.i / Acknowledgment --- p.ii / Abbreviations --- p.iii / Abstract --- p.iv / Chapter Chapter 1: --- General Introduction / Chapter 1.1 --- Haematopoiesis --- p.1 / Chapter 1.1.1 --- Sites of haematopoiesis / Chapter 1.1.1.1 --- Bone marrow stroma / Chapter 1.1.1.2 --- Thymus / Chapter 1.1.1.3 --- Spleen and lymph node / Chapter 1.1.1.3.1 --- Spleen / Chapter 1.1.1.3.2 --- Lymph Nodes / Chapter 1.1.2 --- Blood Cell / Chapter 1.1.2.1 --- Development of T and B cells / Chapter 1.1.2.1.1 --- T cells / Chapter 1.1.2.1.2 --- B cells / Chapter 1.1.2.2 --- Development of Granulocytes and monocytes / Chapter 1.2 --- White Cell Disorder -Leukemia --- p.13 / Chapter 1.2.1 --- Leukemia - general concept / Chapter 1.2.1.1 --- Classification of leukemia / Chapter 1.2.1.2 --- Pathophysiology and Clinical features / Chapter 1.2.1.3 --- Etiology of myeloid leukemia / Chapter 1.2.2 --- Genetic basis of leukemia / Chapter 1.3 --- Acute myeloid leukemia (AML) cell model --- p.19 / Chapter 1.3.1 --- Cell Model for human acute myeloid leukemia / Chapter 1.3.2 --- Murine leukemia cell lines / Chapter 1.4 --- Induction of leukemia cell differentiation --- p.21 / Chapter 1.4.1 --- Overview of different inducers / Chapter 1.4.2 --- Cytokines as Inducers / Chapter 1.5 --- Objectives and Research Strategy --- p.26 / Chapter 1.5.1 --- Objectives / Chapter 1.5.2 --- Research strategy / Chapter Chapter 2 : --- Materials and Methods / Chapter 2.1 --- Materials --- p.29 / Chapter 2.1.1 --- Cell line / Chapter 2.1.2 --- Tissue culture medium / Chapter 2.1.3 --- Tumor necrosis Factor - alpha (TNF-α) / Chapter 2.1.4 --- Interleukin 1- alpha (IL-lα)and Interleukin 1- beta (IL-1β) / Chapter 2.1.5 --- "Monoclonal hamster anti-mouse IL-lα monoclonal hamster anti-mouse IL-1β, and Polyclonal rabbit anti-mouse TNF-α antibodies" / Chapter 2.1.6 --- Lipopolysaccharides (LPS) / Chapter 2.1.7 --- Buffers and solutions / Chapter 2.2 --- Methods : --- p.33 / Chapter 2.2.1 --- Cell culture / Chapter 2.2.2 --- Cytotoxicity assay / Chapter 2.2.3 --- Proliferation assay / Chapter 2.2.4 --- Cell morphology / Chapter 2.2.5 --- Phagocytosis assay / Chapter 2.2.6 --- Preparation of undifferentiated and differentiated murine leukemia WEHI3B (JCS) cells for cell lysate / Chapter 2.2.7 --- Isolation of total cellular RNA / Chapter 2.2.8 --- Extraction of the total RNA / Chapter 2.2.9 --- Spectrophotometry / Chapter 2.2.10 --- Electrophoresis of RNA in agarose gel containing formaldehyde / Chapter 2 2.11 --- First strand cDNA synthesis / Chapter 2.2.12 --- Cytokines phenotyping of the uninduced and induced WEHI 3B (JCS) by The Reverse Trancription Polymerase Chain Reaction method / Chapter 2.2.13 --- Gel electrophoresis of PCR- product / Chapter 2.2.14 --- Southern blot / Chapter 2.2.15 --- Dot blot / Chapter 2.2.16 --- Hybridization with oligonucleotides / Chapter 2.2.17 --- Chemiluminescent detection / Chapter Chapter 3 : --- Growth Inhibitory and Differentiation Effects of Lipopolysaccharides ( LPS ) on WEHI 3B (JCS) cells / Chapter 3.1 --- Introduction --- p.51 / Chapter 3.1.1 --- Chemical structure of LPS / Chapter 3.1.2 --- Biological activity of LPS / Chapter 3.2 --- Results --- p.55 / Chapter 3.2.1 --- Anti-proliferative effects of LPS / Chapter 3.2.2 --- Differentiation inducing effect of LPS on WEHI 3B (JCS) cells / Chapter 3.2.3 --- Phagocytic activity LPS treated WEHI 3B (JCS) cells / Chapter 3.2.4 --- Anti-proliferative effect of TNF-α / Chapter 3.2.5 --- Differentiation inducing effect of TNF-α / Chapter 3.2.6 --- Phagocytic activity of TNF-α treated WEHI3B (JCS) cells / Chapter 3.3 --- Discussion --- p.67 / Chapter 3.4 --- Summary --- p.69 / Chapter Chapter 4 : --- The Cytokine Genes Expression of the TNF-α and LPS Treated WEHI 3B (JCS) cells / Chapter 4.1 --- Introduction --- p.70 / Chapter 4.1.1 --- Differentiation of leukemia cell line / Chapter 4.1.2 --- Study of the cytokine genes expression of WEHI 3B (JCS) cells / Chapter 4.2 --- Results --- p.72 / Chapter 4.2.1 --- Isolation of total RNA from uniduced and induced WEHI 3B (JCS) cells / Chapter 4.2.2 --- The cytokine genes expression during differentiation / Chapter 4.2.2.1 --- "Up-regulation of IL-lα, IL-1β,TNF-α and IFN-γ in both TNF-α induced and LPS induced WEHI 3B (JCS) cells" / Chapter 4.2.2.1.1 --- Southern blot / Chapter 4.2.2.1.2 --- Semi-quantitation of PCR-products by gel electrophoresis and dot-blot hybridization / Chapter 4.2.2.2 --- up-regulation of GM-CSF and G-CSF in LPS induced WEHI 3B (JCS) cells / Chapter 4.3 --- Discussion --- p.92 / Chapter 4.4 --- Summary --- p.95 / Chapter Chapter 5 : --- Growth inhibitory and Differentiation Inducing Effect of IL-l( IL-1α and IL-1β) on WEHI 3B (JCS) cells / Chapter 5.1 --- Introduction --- p.96 / Chapter 5.1.1 --- The interleukin 1 (IL-1) family / Chapter 5.1.1.1 --- Structure of IL-1 / Chapter 5.1.1.2 --- The biological function of IL-1 / Chapter 5.1.2 --- Tumor necrosis factor - alpha ( TNF-α) / Chapter 5.1.2.1 --- Structure of TNF-α / Chapter 5.1.2.2 --- Biological functions of TNF-α / Chapter 5.1.3 --- The similarity between TNF and IL-1 / Chapter 5.2 --- Results --- p.102 / Chapter 5.2.1 --- Anti-proliferative effect of IL-1 / Chapter 5.2.2 --- Differentiation inducing effect of IL-1 / Chapter 5.2.3 --- Phagocytic activity of IL-1 treated JCS cells / Chapter 5.2.4 --- "Role of endogenously produced IL-lα, IL-1β and TNF-α in LPS cytokines differentiation of WEHI 3B (JCS) cells" / Chapter 5.2.4.1. --- "Effect of neutralizing anti- ILl-α,anti - IL-l-β, and anti-TNF-α antibodies on the growth inihbition of the treated WEHI 3B (JCS) cells" / Chapter 5.2.4.2 --- "Effects of neutralizing anti-IL-lα, anti- IL-1β, and anti-TNF-α antibodies on differentiation of the treated WEHI 3B (JCS) cells" / Chapter 5.3 --- Discussion --- p.124 / Chapter 5.4 --- Summary --- p.127 / Chapter Chapter 6 --- : Concluding Discussion --- p.128 / References --- p.135

Cell division is an important biological process, thus it is always an active field in biological research. To complete cell division, plant cells form a new cell wall that separates the two new cells. In contrast to the contractile ring of animal cells, plant cells form the new cell wall from their interior. Vesicles containing the new cell wall fuse at the cell plate between the two cells. The formation of the cell plate is guided by the phragmoplast, a microtubule and filamentous actin-containing structure. Because vesicles are known to be transported by myosin motors during interphase and little is known about the role of myosin XI during cell division, I investigated the participation of the plant specific myosin XI in cell division. For this work I used the moss Physcomitrella patens as a model organisms because of its simple cytology and powerful genetics. Using a fluorescent protein fusion of myosin XI, I found that this molecule associates with the mitotic spindle immediately after nuclear envelope breakdown. Myosin XI stays associated with the spindle during mitosis, and when the phragmoplast is formed, it concentrates at the cell plate, forming a fine line. Using an actin polymerization inhibitor, latrunculin B, I found that the associations of myosin XI with the mitotic spindle and the phragmoplast are independent of the presence of filamentous actin. After using double-labeled lines for myosin XI the endoplasmic reticulum and vesicle markers, I found the myosin XI on the spindle is not colocalized with the endoplasmic reticulum and two types of vesicle markers. Furthermore, I also found the vesicle trafficking inhibitor, brefeldin A, does not inhibit the localization of myosin XI at the mitotic spindle and the phragmoplast. These observations suggest a new actin-independent behavior of myosin XI during cell division, and provide novel insights to our understanding of the function of myosin XI during plant cell division.