• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 370
  • 211
  • 176
  • 67
  • 19
  • 19
  • 10
  • 9
  • 1
  • 1
  • 1
  • Tagged with
  • 11571
  • 4161
  • 476
  • 253
  • 176
  • 172
  • 170
  • 166
  • 165
  • 163
  • 159
  • 151
  • 144
  • 129
  • 120
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
331

Developmental profile and investigation into potential functional roles of sumoylation in brain

Prado, Fernando Josa January 2014 (has links)
Protein SUMOylation is a posttranslational modification event with various effects over its substrates, including modification of their turnover equilibrium, intracellular sorting, blocking interactions or facilitating new ones. Although most cellular SU MOylation has been linked to the nucleus and nuclear functions, in the past years an increasing number of cytosolic and membrane proteins have been reported as SUMO substrates. Compared to other modifications such ubiquitination or phosphorylation, very little is known of the role of SUMOylation in brain and its possible substrates. Also, its role in development of the central nervous system is poorly understood. In this work it is shown that levels of global SUMOylation of substrates for SUMOl and SUM02/3 decrease during development, as do most of the examined SUMOylation machinery proteins, which interestingly show an increased presence in cerebellum over the rest of the brain. PIAS3, a SUMOE3 ligase, was further characterised in brain and a new putative candidate PIAS3-PINIT-domain interactor was found : Ago2. Ago proteins are the core components of the RNA-induced silencing complexes (RISe) and mediate RNA interference. It was found that Ago2 can be SUMOylated under certain conditions, being its major acceptor site the lysine K402. Slight RNAi effect alleviation was observed in a SUMOylation-deficient mutant of Ago2. Finally I also hypothesize about a new mechanism for SUMOylation of Iysines other than the one at the consensus site. This opens an interesting avenue of research regarding the effects of SUMOylation in the RNAi pathway.
332

In vitro and in vivo electrophysiological investigations into the role of nicotinic receptors in the rat hippocampus

Bratley, Claire Tamsyn January 2014 (has links)
Nicotinic cholinergic receptors within the hippocampus are hypothesised to modulate memory: nicotinic agonists can enhance hippocampal dependent memory. Moreover, nicotine is an addictive drug whose removal produces an extended withdrawal state. Extracellular electro physiological recordings were conducted in vitro to assess nicotinic actions upon synaptic transmission and intrinsic neuronal excitability in subfield CAl of the hippocampus. Agonists (PNU-282987 and SSR180711) and a positive allosteric modulator (PNU-120596) of the alpha7 nicotinic receptor were bath applied. PNU- 120596 in presence of nicotine caused a sustained depression of CAl synaptic responses. Recordings of local field potentials (includ ing theta and gamma oscillations) and action potential firing were made from the hippocampus of awake freely moving rats. An acute dose of SSR180711 was without effect. Effects were then sought of chronically administered nicotine and its withdrawal. Chronic nicotine administration enhanced performance of an object location (Ol) recognition memory task in which a rat spontaneously explores an object in a novel and a familiar location. Hippocampal theta-gamma phase amplitude coupling (PAC) was greater during exploration of an object in the familiar than in the novel location. However, PAC changes did not parallel nicotine's effect on performance of the Ol task. During the Ol task, PAC in CAl and the dentate gyrus was enhanced following nicotine administration but did not return to baseline following withdrawal. Nicotine withdrawal was associated with an increase in the firing rate of CAl and CA3 neurones. Nicotine enhanced theta-gamma phase amplitude coupling (PAC) in CAl, whereas in CA3 it decreased PAC when the animal was mobile but under no cognitive load. PAC, theta and gamma power were lower in CAl than in CA3; they were highest in the dentate gyrus. In sum, nicotine administration was found to enhance object location memory and produce long lasting changes to hippocampal oscillations and theta-gamma coupling.
333

Towards consistent evolutionary descriptions of complete proteomes

Sardar, Adam J. January 2015 (has links)
By means of introduction, I look here to vignette the general structure of my thesis and how it represents the body of work conducted over my PhD. Abstracts that more generally place individual pieces of work within the context of the rest of the scientific literature prepend each chapter. Figure 1 describes the projects that I have been involved in, the time periods that work was conducted over and where in this thesis those projects are documented. They detail: • 'The Impact Of Horizontal Gene Transfer (HGT) Upon The Tree Of Life', where I attempt to refute claims that rampant HGT renders ,even the concept of a bifurcating tree of evolutionary relation obsolete. This is presented in Part ii: Chapter 2 & Chapter 3. • 'Evolution Of The Transcribed Human Proteome' in Chapter 4 (Part iii), where I investigate the history of use of structural protein innovation in Homo sapiens using cell-type specific digital expression data from the FANTOM5 consortium. • 'Multicellular Phenotype In Yeast' in Chapter 5 (Part iv), which describes attempts to create a multicellular phenotype of Saccharomyces cerevisiae by directed evolution before extracting nucleic material so as to study. the genetic underpinnings of such behaviour. • 'The Gene Core Of E. Coli' in Chapter 1 (Part i), where I investigate anomalous values for a consensus gene set in the bacterial species Escherichia coli and show that confusion arises from a misunderstanding of the meaning of a significant E-value for popular biological sequence search tools.
334

Regulation of COX-2 expression by the BCL-3:NF-KappaB homodimeric complex : implications for colorectal carcinogenesis

Fallatah, Hafsah M. January 2014 (has links)
Cyclooxygenase-2 (COX-2) is an enzyme that plays a key role in the synthesis of prostaglandin (PGE2). COX-2 has been widely investigated in cancer progression studies generally and in colorectal cancer (CRC) specifically, not only because it is regulated by various signalling pathways, but also because it is one of the main players in the inflammation/cancer link. The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-KB) is among the transcription factors that have been repOlied to regulate the transcriptional activity of the COX-2 gene. Constitutive activity of NF-KB clearly results in the over-expression observed of COX-2. Although there are two KB sites localised at the promoter region of COX-2, the definitive mechanism by which COX-2 is regulated by NF-KB needs more elucidation. Several modulators have been repOlied that control NF-KB activity in order to maintain the selectivity or specificity of responses to the trigger. B-cell lymphoma-3 (BCL-3) is an oncogene that is up-regulated by inflammatory cytokines, such as tumour necrosis factor-a (TNF-a) and interleukin-l ~ (IL-l ~). It functions as a co-activator protein that binds favourably to the homodimer' subunits of NF-KB, namely pSO/pSO or pS2/pS2. Those two dimers are found to have repressor roles in the regulation of NF-KB target genes. However, when they bind to BCL-3, their action switches to an activator role. Therefore, understanding the exact role ofBCL-3: NF-KB homodimers complex in the context ofCOX-2 regulation by NF-KB signalling is crucial. Initially, I investigated the expression of BCL-3 and COX-2 in a range of different adenoma and carcinoma cells. I chose HCA 7/P and HT29 cells to be included in subsequent studies. In studying the effect of BCL-3 suppression in the level of COX-2 protein and its activity, potential regulation of COX-2 and PGE2 by BCL-3 has been revealed. This regulation has also been observed after the treatment of cells with TNF-a. Interestingly, the mRNA level of COX-2 has also been regulated by BCL-3 suppression, especially at 48 hours of BCL-3 silencing. Dual-Luciferase assay results of COX-2 gene also support this finding. Transfecting the cells with mutant BCL-3 (which cannot bind the homodimer pSO/pSO) has shown no change to the promoter activity of COX-2 as compared with cells transfected with wild-type BCL-3 protein; this suggests an addition to requirement amount of pSO to regulate COX-2 by BCL-3. Results obtained from Chromatin Immunoprecipitation (ChIP) experiments emphasised the presence of both BCL-3 and pSO in the predicted KB site of the COX-2 promoter. In vivo, there was a marked increase of both BCL-3 and COX-2 expression in carcinoma tissue as compared to healthy normal tissue, indicating the important role they play in the progression from adenoma to carcinoma. Because BCL-3 has been shown to regulate the level of PGE2, it was important to investigate whether this had . any consequence on the role played by PGE2 in the proliferation and sternness of the adenoma cell RG/C2. It was also significant to study the effect of Nonsteroidal anti-inflammatory drugs (NSAIDs) on the function of BCL-3 in regards to the COX-2/PGE2 signalling pathway. Treating cells with aspirin results in a decrease in the protein level of BCL-3 and COX-2, which strengthens the notion of aspirin chemoprevention 's role in tumour regression. This study is proposing, for the first time, the potential use of BCL-3: COX-2/PGE2 as a therapeutic target of CRC prevention and treatment.
335

The regulation of cell migration and invasion by Eph-ephrin signalling

Campbell, Jessica January 2015 (has links)
Cell migration and invasion are essential aspects of normal cellular behaviour, however abnormal cell migration can lead to defects in essential cell processes, such as wound healing, or can also promote diseases such as cancer. Cell migration can be regulated by many factors and, importantly, can depend upon a cells interaction with its surrounding cellular microenvironment. Eph receptors are the largest family of receptor tyrosine kinases and are essential in transmitting signals between cells as, uniquely to this family, the ephrin ligands are cell surface bound, therefore signalling is cell-cell contact dependent. Although Eph and ephrin functions have been studied for many years, much of the mechanisms by which they signal are still unclear. In this thesis, I have investigated the role of Eph-ephrin signalling in regulating different aspects of cell migration and invasion in prostate cancer cells and during keratinocyte cell wound healing. I find that the activity of EphB4 is regulated by the expression of PTEN phosphatase both in DU145 and PC-3 prostate cancer cells. This regulation leads to altered heterotypic cell contact inhibition of locomotion, in a co-culture assay between DU145 cells and fibroblasts. I also find that PTEN expression regulates the number of DU145 cells invading from a tumour cell spheroid, towards fibroblasts, in a 3D collagen gel. I suggest these cell behaviours may be as a consequence of altered Rac activity, downstream of EphB4 and PTEN signalling. I also use SILAC based phosphoproteomics to investigate some of the proteins regulated downstream of PTEN expression ilnd EphB4 activity. Furthermore I find that Ephrin-Bs are essential in regulating keratinocyte cell reepithelialisation during tissue culture wound healing, by regulating the actin cytoskeleton structure and E-cadherin processing. Finally, I have attempted to investigate the role of EphB2 in regulating prostate cancer cell migration and invasion, and find that EphB2 depletion does not alter PC-3 cell migration velocity in two dimensions.
336

Modelling the reactivity of glutamate mutase and heme dioxygenase enzymes

Glehn, Patrick von January 2014 (has links)
Adenosylcobalamin (AdoCbl) serves as a reservoir for the 5'-deoxyadenosyl radical, which is generated in enzyme by the homolytic cleavage of a Co-C bond and harnessed to initiate radical reactions by abstracting a hydrogen from the substrate. How these enzymes increase the rate of Co-C bond cleavage by an estimated 12 orders of magnitude, whether the 5' -deoxyadenosyl radical exists as a metastable or transient intermediate and how the first steps of the reaction are coupled are key unresolved questions. The Co-C bond breaking and hydrogen abstraction steps were modelled in AdoCbl dependent glutamate mutase with MD simulations, adiabatic mapping and umbrella sampling simulations using a novel empirical valence bond (EVB) potential, which was calibrated to high level ab initio and DFT calculations. This potential was found to compare favourably with the results of QM/MM calculations. Hydrogen bonding with the protein stabilises the dissociated 5' -deoxyadenosyl radical and induce conformational change, guiding the C5' radical centre towards the substrate hydrogen to be abstracted. The heme dioxygenase enzymes Indoleamine 2,3 -dioxygenase (lDO) and tryptophan 2,3-dioxygenase (TDO) catalyse the first step in the metabolism of L-tryptophan (L-Trp) by insertion of both atoms of heme-bound O2 into the substrate. In an attempt to improve understanding of the differences in substrate binding and reactivity between these enzymes, molecular dynamics (MD) simulations, MMIPBSA binding free energy calculations and reaction modelling with hybrid quantum mechanics/molecular mechanics (QMlMM) adiabatic mapping calculations were performed. Starting with crystal structures for a bacterial TDO (XcTDO) and human IDO (hIDO), reactivity and binding of IDO, TDO and the H55A mutant TDO with L-Trp, D-tryptophan (D-Trp) and I-methyl-L-tryptophan (l -Me-L-Trp) were investigated. Differences in experimental KMs were partially rationalised by analysis of substrate-protein interactions and calculated binding free energies. Although the calculated barriers were unable to rank correctly the active systems, they were able to predict whether a particular system was active, slightly active or inactive. Differences in reactivity were related to the varying ability of the systems to position optimally the substrate in relation to the heme-bound 02.
337

The molecular basis of substrate translocation by monocarboxylate transporters and their isoform specific inhibition

Nancolas, Bethany Amilia January 2014 (has links)
The transport of lactate and other monocarboxylates across the plasma membrane is mediated by the proton linked Monocarboxylate Iransporters (MCTs), members of the Solute Carrier family (SLC16) and the wider Major Facilitator Superfamily (MFS) of secondary active transporters. MCTs require an ancillary protein, basigin in the case of MCTl, for trafficking to and activity at the plasma membrane. Recently the importance of MCTs in tumour cell metabolism and their potential as drug targets for cancer therapy have been recognised. The work in this thesis has used molecular modelling and dynamic simulation techniques to understand the mechanisms responsible for substrate translocation by MCTl. An important role for K38, D302, R306 and F360 was confirmed and conformational changes associated with translocation proposed that involve protonation/deprotonation of other key residues. In addition, preliminary studies on the purification of the MCT1-anciliary protein complex from mammalian erythrocytes are reported with an ultimate goal of structural determination. The labelling of an extracellular cysteine residue of basigin with an organomercurial-biotin conjugate was shown to be a promising initial step for purification. The inhibition of MCTs by isoform-specific inhibitors has also been investigated. Site directed mutagenesis and molecular modelling have been employed to indicate a possible binding site for AR-C155858 in MCTl with key roles proposed for residues D302 and R306. In addition, Ki values of~ 30-50 nM were determined in both Xenopus laevis oocytes and mammalian cell lines for some novel MCT4 specific inhibitors recently developed by AstraZeneca .
338

Characterization of synapsins SUMOylation

Tang, Leo Tsz-Ho January 2014 (has links)
Synapsins are neuron-specific phosphoproteins that are key components of the presynaptic neurotransmitter release machinery. Their main role is to cluster synaptic vesicles (SVs) to each other and anchor them to the actin cytoskeleton, thereby establishing the reserve vesicle pool, and then release them in response to appropriate membrane depolarisation. Here we demonstrate that, in addition to phosphorylation, SUMOylation of Synapsin la (Synla) at K687R is necessary for Synla function. SUMOylation refers to the covalent attachment of a small protein SUMO onto one of its lysine residue. The attachment of SUMO in turn causes changes in the behavior of the protein. Fluorophore-based exocytosis assay showed that replacement of endogenous Synla in neurons with a non-SUMOylatable mutant impairs stimulated SV exocytosis, primarily through a change in size of the releasable vesicle pool. Through SV binding assay and Synla dispersion assay, we found that SUMOylation enhances Synla association with SVs to promote efficient reclustering of Synla following neuronal stimulation. Co-localization assays also showed that SUMOylation aids in Synla targeting to the presynaptic terminal. Finally, the A548T mutation in Synla is strongly associated with autism spectrum disease (ASD) and epilepsy and we identify that A548T causes defective Synla SUMOylation. We further demonstrate the similar phenotype displayed by the non-SUMOylatable mutant and the A548T mutant. These results identify SUMOylation as a fundamental regulator of Synla function and reveal a novel link between reduced SUMOylation of Synla and neurological disorders.
339

A molecular analysis of endosome to plasma membrane recycling mediated by retromer

Gallon, Matthew January 2015 (has links)
The endosomal network is a crucial hub in the trafficking of proteins through the cellular endomembrane system. Cargo proteins enter endosomes by endocytosis from the plasma or by trafficking from the trans-Golgi network (TGN). Here, cargo proteins face one of two fates: retention in the endosome, leading ultimately to lysosomal degradation, or export from the endosome for re-use ("recycling"). The balance of protein degradation and recycling is crucial to cellular homeostasis; inappropriate sorting of proteins to either fate leads to cellular dysfunction. Retromer is an endosome-membrane-associated protein complex central to the recycling of many cargo proteins from endosomes, both to the TGN and the plasma membrane. Retromer function is reliant on a number of proteins from the sorting nexin (SNX) family, one of which is SNX27. SNX27 is unique among SNXs in its bearing a POZ domain that binds POZ binding motifs (PDZbms) in the cytoplasmic tails of trans-membrane cargo proteins. SNX27 is required for retromer-mediated endosome-plasma-membrane recycling of POZbm-containing cargo proteins. In this thesis I firstly investigate the role of SNX27 in the trafficking of transmembrane proteins that control planar cell polarity. I next show that SNX27 interacts directly with retromer and dissect the molecular details of this interaction. I then identify other proteins that interact with retromer using SILAC-based proteomics and investigate three of the proteins identified in greater detail. Overall, these data add to the growing appreciation of retromer as a master regulator of endosomal recycling.
340

Investigations into the descending control of primary and secondary inflammatory hyperalgesia : a pronociceptive role for prostaglandin signalling in the periaqueductal grey

Drake, Robert Andrew Rodger January 2015 (has links)
The periaqueductal grey (PAG) together with downstream nuclei in the rostral ventral medulla (RVM) and adrenergic nuclei in the pons (e.g. Locus coeruleus) form the archetypal descending control network that is able to bi -directionally regulate the ascending flow of nociceptive information and so the level of perceived pain. Tissue damage leads to nociceptor sensitisation and an increase in sensitivity to noxious stimuli (hyperalgesia), which can develop within the site of tissue damage (primary hyperalgesia) as well as outside it (secondary hyperalgesia). Previous work from our laboratory demonstrates that COX activity and prostaglandin signalling within the ventrolateral PAG (vIPAG) facilitates spinal nociceptive processing in the normal animal. Work herein utilises a complete Freund's adjuvant (CFA) model of primary (s.c. paw) and secondary (La. knee joint) hyperalgesia to explore the hypothesis that this prostanergic descending facilitation (PDF) enhances spinal nociceptive processing and contributes to both primary and secondary hyperalgesia. Additionally, any differential control of A- and C-nociceptor inputs by the PAG was determined by using a ramping thermal stimulus protocol that preferentially activates A- or C-nociceptor inputs. Acute inflammation of the dorsal hind-paw (hairy skin) produced a primary mechanical, but not thermal hyperalgesia, and only a transient (-1h) sensitisation of reflex withdrawal evoked by A- and C-heat nociceptor activation. An equivalent inflammation in glabrous skin produced a persistent hyperalgesia (thermal/mechanical) and reflex sensitisation. The transience of reflex sensitisation in acute inflammation (<4h) was attributed to a rapidly acting descending noradrenergic inhibition, which could be blocked by the alpha-2-adrenoceptor antagonist yohimbine, affecting nociceptor inputs arriving from inflamed hairy, but not from glabrous, skin. There was no evidence for a contribution of PDF from the PAG to acute primary hyperalgesia in hairy skin. Prolonged (7 days) inflammation of the knee joint led to a secondary mechanical and thermal hyperalgesia of the hind-paw that was associated with a sensitisation of spinal processing of A-nociceptor inputs from the secondary site. Delivery of the non-selective COX inhibitor, ketoprofen, or a prostaglandin EP1 or EP3 receptor antagonist into the vIPAG, but not dIPAG, increased withdrawal thresholds to both A- and C-nociceptor activation in an area of secondary hyperalgesia. Moreover, antagonism of vIPAG EP3 receptors increased the firing threshold and reduced the stimulus encoding capacity of spinal dorsal horn wide dynamic range neurones to C-, but not A-, nociceptor activation in an area of secondary hyperalgesia. It was concluded that during prolonged inflammation, prostaglandin signalling in the vIPAG enhances spinal nociceptive processing of inputs arriving from the secondary hyperalgesic site and so contributes to secondary hyperalgesia.

Page generated in 0.0269 seconds