2,284 research outputs found
NKalpha: Non-uniform epistatic interactions in an extended NK model
No full textKauffman’s seminal NK model was introduced to relate the properties of fitness landscapes to the extent and nature of epistasis between genes. The original model considered genomes in which the fitness contribution of each of N genes was influenced by the value of K other genes located either at random or from the immediately neighbouring loci on the genome. Both schemes ensure that (on average) every gene is as influential as any other. More recently, the epistatic connectivity between genes in natural genomes has begun to be mapped. The topologies of these genetic networks are neither random nor regular, but exhibit interesting structural properties. The model presented here extends the NK model to consider epistatic network topologies derived from a preferential attachment scheme which tends to ensure that some genes are more influential than others. We explore the consequences of this topology for the properties of the associated fitness landscapes
Plan shewing the position of 500 acres of land on the Murray Estuary [cartographic material] : the gift of Thomas Peel Esquire to the church of that district [Western Australia] /
No full textInset: Detail of property. Scale 1:23 760.; Map of area given to church by Thomas Peel on the Serpentine River in the vicinity of Peel's Inlet. Local landholders named and tracks shown.; Rex Nan Kivell Collection Map NK 2456/167
A study of NK-3 tachykinin receptors
No full textThe aim of this thesis was to determine the pharmacological characteristics and biochemical properties of NK-3 tachykinin receptors in the mammalian central nervous system (cerebral cortex and spinal cord) and periphery (guinea-pig ileum; GPILM). The affinities of naturally-occurring tachykinins and several receptorselective analogues, for peripheral (GPILM) and central (guinea-pig cortex) NK-3 receptors (labelled with the selective NK-3 receptor ligand, [3H]-senktide) have been determined. A good correlation between affinities of the above peptides for NK-3 sites in the two tissues was obtained. The inhibition of [3H]-senktide binding by guanine nucleotides, in addition to the correlation between affinities of tachykinins at NK-3 sites and their biological potencies in contracting the rat portal vein (RPV; data from the literature), suggest that [3H]-senktide binding sites represent functional receptors. Evidence for the coupling of GPILM and neonatal rat spinal cord (but not RPV or rat cerebral cortex) NK-3 receptors, to the hydrolysis of inositol phospholipids has been obtained. In GPILM, morphine was found to inhibit the formation of [3H]-inositol phosphates in response to the NK-3 agonist, senktide. This finding is in agreement with the hypothesis that the indirect contractile action of tachykinins in GPILM is due to the activation of neuronal NK-3 receptors and the release of acetylcholine (ACh). This idea has also been confirmed by contractile and [3H]-ACh release studies. Autoradiographical studies in spinal cord, using [3H]-senktide, have shown the presence of NK-3 sites in the dorsal horn. These findings, taken together with the recent report that NK-3 agonists may be analgesic, suggest that the guinea-pig ileum might be a useful bioassay for the evaluation of potent and selective NK-3 agonists which may represent novel analgesic agents
Characterisation and ontogeny of natural killer cells in Xenopus laevis
No full textThe initial aim of the work described in this Thesis was to investigate the lymphoid organ distribution, phenotype and function of the lymphocyte population identified by candidate anti-Xenopus natural killer (NK) cell monoclonal antibodies (mAb's). Since removal of the thymus gland early in larval life (thymectomy) results in the eradication of T-cells and subsequent increase in the proportion of candidate NK cells, thymectomised (Tx) Xenopus were integral in the study of this subset of lymphocytes. Phenotypic and functional studies respectively demonstrated that mAb-defined candidate NK cells do not belong to the B- or T-cell lineage and display cytotoxic activity towards MHC class-Ia-deficient tumour target cells, strengthening the contention that these cells represent the NK subset in Xenopus. The ontogeny of NK cells was investigated in relation to the emergence of the NK cell inhibitory ligand, MHC class-L Splenic NK cells were found to emerge in 6-7 week-old larvae (stage 56-58), which is ≈5 weeks after T- and B-cells become detectable, and some 2 weeks after MHC-Ia is first detected. However, these cells do not appear to be functionally competent until 6 months of age. The expression and ontogeny of recently cloned β2m (the molecule essential for MHC class-I expression) was also briefly investigated. β2m (both RNA and protein) was detectable in all adult tissues and cell lines, even class-I-deficient tumour cells; β2m transcripts were found in 5 week-old larvae that lack MHC class-I. The emergence of NK antigen on a population of T-cells following in vitro stimulation of splenocytes with PMA and calcium ionophore presented the opportunity to biochemically characterise (through immunoprecipitation) the mAb-defined NK antigen. Proteins precipitated using the anti-NK mAb were either surface labelled with biotin, or metabolically labelled with (^35)S. Both techniques resulted in the detection of a protein 55kDa in size
Natural killer cell evolution: cellular and molecular studies on Xenopus
No full textThe presence of natural killer cells at lower evolutionary levels was investigated in the amphibian Xenopus laevis. Chromium release microcytotoxicity assays revealed that fresh splenocytes from early-thymectomised Xenopus displayed significant spontaneous cytotoxicity against allogeneic B(_3)B(_7) thymic tumor cell targets, unlike those from control Xenopus, suggesting that 'NK-like' activity is greater in thymectomised (T cell-deficient) animals. Addition of Concanavalin A- derived active supernatants to splenocytes from a thymectomised animal caused a significant increase in cytolytic activity, but had no effect on cells from a control animal. This finding of enhanced cytotoxicity was indicative of lymphokine-activated killing in Xenopus, and supported the concept that tumour cell lysis was mediated by NK - like cells. Attempts were made to enrich the splenocytes for natural killer cells through the selective depletion of other lymphocyte subsets, using the techniques of 'panning’ and 'magnetic bead' separation following monoclonal antibody labelling of cells. On comparison of the two techniques, it was found that both were able to deplete a splenocyte culture of B cells to the same extent, but that magnetic sorting produced far superior results for depletion of T cells. Optimum conditions for magnetic sorting were determined, and used to generate 'purified' populations which were tested for their cytolytic activity. Such preliminary investigations suggested that natural killer like activity in Xenopus is likely to be mediated by a 'non-T / non-B' lymphoid subset. Finally, preliminary work was undertaken into the development of 'phage display' technology for the generation of single chain Fy antibody fragments (ultimately against NK cell surface antigens). PGR amplification of the V(_H) and Kappa chains was attempted on RNA extracted (using various methods) from Carboxypeptidase Y-injected-, B(_3)B(_7)-injected-, and unimmunised mice. Following RNA extraction under optimum conditions. Kappa chains were successfully amplified from experimental spleens, but the heavy chains still require more development
Development of antibody technology to identify natural killer cell surface antigens in Xenopus Laevis
No full textNatural killer (NK)-like lymphocytes have recently been identified in thymectomised (Tx) Xenopus which are capable of spontaneous cytotoxicity towards the MHC- deficient, allogeneic thymus tumour cell line B(_3)B(_7). This Thesis describes attempts to raise antibodies to Xenopus NK cell surface antigens by phage display and hybridoma technology. The phage display technique was optimised for raising antibodies to novel, cellular antigens in a trial run using the Xenopus thymus tumour cell line B(_3)B(_7). Having isolated a phage antibody which was shown by flow cytometry to bind B(_3)B(_7) cells, the technique was then used to try and raise antibodies to Xenopus NK cells. Isolation of an NIC-specific phage antibody was not achieved but phage antibody XL-6 was raised, which bound an antigen on Xenopus lymphocytes. Phage antibody XL-6, and soluble scFv derived from this, were able to identify a putative mature T cell population in the thymus and may be specific for an amphibian homologue of the mammalian leukocyte common antigen CD45. Hybridoma technology was used to isolate three monoclonal antibodies, 1F8, 4D4 and 1G5, which were shown by flow cytometric analysis to identify a putative NK cell population in control and Tx Xenopus. Following immunomagnetic purification, 1F8- positive spleen cells from control and Tx animals were shown to kill the MHC- deficient tumour target B(_3)B(_7), confirming that this antibody was specific for Xenopus NK cells. Western blotting experiments showed that 1F8, 4D4 and 1G5 identified a doublet of protein bands at 72 and 74 kilodaltons in Xenopus gut lymphoid lysates. Initial attempts to isolate cDNA encoding a Xenopus NK cell surface antigen through immunoscreening a xenopus gut cDNA expression library with antibody 1G5 were unsuccessful as was an attempt to clone a Xenopus homologue of the mammalian NK receptor NKR-Pl by PGR
Das Hühner CLEC-2 Homolog
No full textDas Hühner CLEC-2 Homolog: Ein Thrombozytenrezeptor mit aktivierender Funktion
Der Natürliche Killer Gen Komplex (NKC) des Huhnes ist auf dem Chromosom 1 lokalisiert und weist zwei C-typ Lektine auf, von denen das eine als Homolog zu CD69 und das andere zu CD94 und NKG2 beschrieben worden ist. Diese Studie trägt durch die Generierung eines spezifischen monoklonalen Antikörpers zur Charakterisierung des Hühner C-typ Lektin ähnlichen Proteins CD94/NKG2 als potentiellen NK Zellrezeptor bei. Durchflußzytometrische Messung von lymphatischem Gewebe des Huhnes ergab, dass das C-typ Lektin von einer Vielzahl von Zellen des PBMC, wenigen Milzzellen und keinerlei Bursa- oder Thymuszellen exprimiert wird. In PBMC von Huhn und Pute konnte der monoklonale Antikörper auf Thrombozyten nachgewiesen werden. Die biochemische Analyse konnte zeigen, dass das Molekül als ein glykosyliertes Homodimer auf der Zelloberfläche exprimiert wird und durch Kreuzvernetzung Thrombozyten aktiviert werden, was über CD107 Expression gemessen wurde. Die Sequenzanalyse deutete auf ein Motiv im Zytoplasma hin, welches als hem Immunrezeptor Tyrosin-basierendes aktivierendes Motiv bei C-typ Lekinen wie DECTIN1 und CLEC-2 vorkommt, aber nicht für CD94/NKG2 beschrieben ist. In der Sequenz konnte ein zusätzliches Cystein im extrazellulären Bereich gefunden werden. Zusammengenommen geben diese Ergebnisse Hinweise darauf, dass das Gen nicht einem CD94/NKG2 Hybrid ähnlich ist, sondern ein CLEC-2 Homolog darstellt.Chicken CLEC-2 homologue: a thrombocyte receptor with activation function
The chicken NKC was described to consist of only two C-type lectins, CD69 and a CD94/NKG2 hybrid, both encoded on chromosome 1. This study contributes to the characterisation of the chicken C-type lectin CD94/NKG2 by production of a specific monoclonal mab which was used to analyse the potential function on NK cells. Immunofluorescent analysis of lymphoid chicken tissues revealed in expression of the C-type lectin on a large percentage of PBMC, a small percentage of splenocytes and no reactivity in bursa and thymus. In chicken and turkey PBMC, the mab reacted with virtually all thrombocytes. The biochemical analyses demonstrated that CLEC-2 is presented on the cell surface as a highly glycosylated homodimer, which upon mab crosslinking induced thrombocyte activation, as measured by CD107 expression. Sequence analysis indicated a cytoplasmic motif known as hem immunoreceptor tyrosine-based activation motif (hemITAM), which was found to be presented in C-type lectins like DECTIN1 and CLEC-2 but not CD94/NKG2. In addition the sequence exhibits a further extracellular cysteine residue. These findings indicate that the gene may not resemble CD94/NKG2 but rather CLEC-2 homologue
Country lands in the Parishes of Codrington & Eumeralla, Counties of Normanby & Villiers [cartographic material] /
No full textMap of Parish of Codrington and Eumeralla with description of topography, cadastral information and relief shown by hachures.; No 252.; No 55/464.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.map-nk2456-216; Rex Nan Kivell Collection Map NK 2456/216
Plan of part of the Parishes of Talangatta and Panmure at the junction of the Emu Creek with the Hopkins River [cartographic material] /
No full textMap of Parish of Talangatta and Panmure with description of topography, cadastral information and relief shown by hachures. Shows dray track, Mr Skenes road, township of Panmure, falls and stockyard on Emu Creek.; No. 114.; Rex Nan Kivell Collection Map NK 2456/248
There's more to a model than code: understanding and formalizing in silico modeling experience
No full textMapping biology into computation has both a domain specific aspect -- biological theory -- and a methodological aspect -- model development. Computational modelers have implicit knowledge that guides modeling in many ways but this knowledge is rarely communicated. We review the challenge of biological complexity and current practices in modeling genetic regulatory networks with the aim of understanding characteristics of the in silico modeling process and proposing directions for future improvements. Specifically, we contend that the modeling of complex biological systems can be made more efficient and more effective by the use of structured methodologies incorporating experience about modeling algorithms and implementation. We suggest that an appropriate formalism is Complex Systems Patterns, adopted from Design Patterns in software engineering. First steps towards building community resources for such patterns are described
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