No description available.

During development of tissues, cells collectively organize to form complex patterns and morphologies. A general feature of many developing epithelia is their distinct organization into cellular compartments of different cell lineages. The interfaces between these compartments, called compartment boundaries, maintain straight and sharp morphologies. The interfaces play key roles in tissue development and pattern formation. An important model system to study the morphology of compartment boundaries during development is the wing disc of the fruit fly. Two compartment boundaries exist in the fly wing disc, the anteroposterior (AP) boundary and the dorsoventral (DV) boundary. A crucial question is how compartment boundaries are shaped and remain stable during growth. In this work, we discuss the dynamics and mechanisms of compartment boundaries in developing epithelia. We analyze the general features of interfacial phenomena in coarse- grained models of passive and active fluids. We introduce a continuum description of tissues with two cell types. This model allows us to study the propagation of interfaces due to the interplay of cell dynamics and tissue mechanics. We also use a vertex model to describe cellular compartments in growing epithelia. The vertex model accounts for cell mechanics and describes a 2D picture of tissues where the network of adherens junctions characterizes cell shapes. We use this model to study the general physical mechanisms by which compartment boundaries are shaped. We quantify the stresses in the cellular network and discuss how cell mechanics and growth influence the stress profile. With the help of the anisotropic stress profile near the interfaces we calculate the interfacial tension. We show that cell area pressure, cell proliferation rate, orientation of cell division, cell elongation created by external stress, and cell bond tension all have distinct effects on the morphology of interfaces during tissue growth. Furthermore, we investigate how much different mechanisms contribute to the effective interfacial tension. We study the mechanisms shaping the DV boundary in wing imaginal disc at different stages during the development. We analyze the images of wing discs to quantify the roughness of the DV boundary and average cell elongation in its vicinity. We quantify increased cell bond tension along the boundary and analyze the role of localized reduction in cell proliferation on the morphology of the DV boundary. We use experimentally determined values for cell bond tension, cell elongation and bias in orientation of cell division in simulations of tissue growth in order to reproduce the main features of the time-evolution of the DV boundary shape.

PolyHistidine repeats and DYRK1A: from the localization to the functionEl principal objectiu d'aquesta tesi ha estat el d'esbrinar noves funcions de la proteína quinasa DYRK1A en el nucli cel.lular. Donat que el domini de repetició d'histidines de DYRK1A dirigeix la proteína al compartiment d'speckles nuclears, aquesta propietat ha estat utilitzada per adreçar aquesta pregunta. Els resultats obtinguts en aquesta tesi han permès proposar els homopolímers d'histidina com una nova i general senyal de localització a speckles nuclears. Proteïnes amb segments de polihistidines, la majoria d'elles factors de transcripció, mostren un comportament intranuclear dinàmic, compatible amb un model en el quèl diferents dominis d'interacció competeixen entre ells pel reclutament de la proteína a diferents subcompartiments nuclears. El mecanisme molecular que media l'acumulació a speckles de les proteïnes amb polihistines s'ha estudiat utilitzant DYRK1A com a model. Els resultats obtinguts exclouen la unió a l'RNA com a mecanisme de reclutament i concloure que, aquest, ocorre mitjançant la interacció amb proteïnes residents. S'han identificat dues noves proteïnes interactores per a DYRK1A, l'RNA polimerasa II i el factor de transcripció Brn-3b. La fosforilació de DYRK1A sobre el domini C-terminal o CTD de l'RNA polimerasa II suggereix una funció directa de la quinasa en el procés de transcripció o del seu acoblament al processament d'RNAs missatgers. La fosforilació de DYRK1A sobre el domini d'activació de Brn-3b sembla regular positivament l'activitat transcripcional d'aquest factor. Aquests resultats indiquen una funció activa de DYRK1A en la regulació de la transcripció gènica, tant directament sobre la maquinària transcripcional com indirectament, modulant l'activitat de factors de transcripció. PolyHistidine repeats and DYRK1A: from the localization to the functionThe main objective of this thesis work has been to identify new roles for the protein kinase DYRK1A in the cell nucleus. Given that a histidine repeat in DYRK1A targets the protein to the nuclear speckle compartment, this property has been used as a tool to approach the question. The results obtained in this thesis work have allowed proposing homopolymeric histidine runs as a novel and general nuclear speckle-directing signal. Proteins with polyHistidine segments, mostly transcription factors, present a dynamic intranuclear behaviour compatible with a model in which distinct interacting domains compete for recruiting elements within the nucleus. The molecular mechanisms that mediate speckle accumulation have been studied in DYRK1A as a model system. The results allow excluding RNA binding as the recruiting mechanism and concluding that targeting is mediated by interaction with speckle-resident proteins. Two novel DYRK1A interactors have been identified during the study, the RNA polymerase II and the transcription factor Brn-3b. DYRK1A phosphorylation of the C-terminal domain or CTD of the RNA polymerase II suggests a direct role of DYRK1A on transcription or coupling of transcription with RNA processing. DYRK1A phosphorylation of Brn-3b within its activation domain seems to positively regulate Brn-3b transcriptional activity. These results confirm an active role for DYRK1A in gene transcription regulation both direct on the transcriptional machinery and indirect by modulating the activity of transcription factors.

No description available.

An understanding of compartment fire behaviour is important for fire protection engineers. For design purposes, whether to use a prescriptive code or performance based design, life safety and property protection issues are required to be assessed. The use of design fires in computer modelling is the general method to determine fire safety. However these computer models are generally limited to the input of one design fire, with consideration of the complex interaction between fuel packages and the compartment environment being simplified. Of particular interest is the Heat Release Rate, HRR, as this is the commonly prescribed design parameter for fire modelling. If the HRR is not accurate then it can be subsequently argued that the design scenario may be flawed. Therefore the selection of the most appropriate fire design scenario is critical, and an increased level of understanding of compartment behaviour is an invaluable aid to fire engineering assumptions. This thesis details an experimental study to enhance the understanding of the impact and interaction that the size and location of pool fires within an enclosure have upon the compartment fire behaviour. Thirty four experiments were conducted in a reduced scale compartment (½ height) with dimensions of 3.6m long by 2.4m wide by 1.2m high using five typical ventilation geometries (fully open, soffit, door, window and small window). Heptane pool fires were used, located in permutations of three evenly distributed locations within the compartment (rear, centre and front) as well as larger equivalent area pans located only in the centre. This thesis describes the experimental development, setup and results of the experimental study. To assist in the classification of compartment fire behaviour during the experiments, a ‘phi’ meter was developed to measure the time dependent equivalence ratio. The phi meter was developed and configured to measure O₂, CO₂ and CO. The background development, calibration, and experimental results are reported. A review of compartment fire modelling using Fire Dynamics Simulator, has also been completed and the results discussed. The results of this experimental study were found to have significant implications for Fire Safety Engineering in that the size of the fire is not as significant as the location of the fire. The effect of a fire near the vent opening was found to have a significant impact on compartment fire behaviour with the vent located fuel source increasing the total compartment heat release rate by a factor of 1.7 to that of a centrally placed pool fire of the same total fuel area. The assumption that a fire located in the centre of the room provides for the highest heat release rate is not valid for post-flashover compartment fires. The phi meter was found to provide good agreement with the equivalence ratio calculated from total compartment mass loss rates, and the results of FDS modelling indicate that the use of the model in its current form can not be applied to complex pool fire geometries.

During development of tissues, cells collectively organize to form complex patterns and morphologies. A general feature of many developing epithelia is their distinct organization into cellular compartments of different cell lineages. The interfaces between these compartments, called compartment boundaries, maintain straight and sharp morphologies. The interfaces play key roles in tissue development and pattern formation. An important model system to study the morphology of compartment boundaries during development is the wing disc of the fruit fly. Two compartment boundaries exist in the fly wing disc, the anteroposterior (AP) boundary and the dorsoventral (DV) boundary. A crucial question is how compartment boundaries are shaped and remain stable during growth. In this work, we discuss the dynamics and mechanisms of compartment boundaries in developing epithelia. We analyze the general features of interfacial phenomena in coarse- grained models of passive and active fluids. We introduce a continuum description of tissues with two cell types. This model allows us to study the propagation of interfaces due to the interplay of cell dynamics and tissue mechanics. We also use a vertex model to describe cellular compartments in growing epithelia. The vertex model accounts for cell mechanics and describes a 2D picture of tissues where the network of adherens junctions characterizes cell shapes. We use this model to study the general physical mechanisms by which compartment boundaries are shaped. We quantify the stresses in the cellular network and discuss how cell mechanics and growth influence the stress profile. With the help of the anisotropic stress profile near the interfaces we calculate the interfacial tension. We show that cell area pressure, cell proliferation rate, orientation of cell division, cell elongation created by external stress, and cell bond tension all have distinct effects on the morphology of interfaces during tissue growth. Furthermore, we investigate how much different mechanisms contribute to the effective interfacial tension. We study the mechanisms shaping the DV boundary in wing imaginal disc at different stages during the development. We analyze the images of wing discs to quantify the roughness of the DV boundary and average cell elongation in its vicinity. We quantify increased cell bond tension along the boundary and analyze the role of localized reduction in cell proliferation on the morphology of the DV boundary. We use experimentally determined values for cell bond tension, cell elongation and bias in orientation of cell division in simulations of tissue growth in order to reproduce the main features of the time-evolution of the DV boundary shape.

Indiana University-Purdue University Indianapolis (IUPUI) / We present a novel, variational and statistical approach for model-based segmentation. Our model generalizes the Chan-Vese model, proposed for concurrent segmentation of multiple objects embedded in the same image domain. We also propose a novel shape descriptor, namely the Multi-Compartment Distance Functions or mcdf. Our proposed framework for segmentation is two-fold: first, several training samples distributed across various classes are registered onto a common frame of reference; then, we use a variational method similar to Active Shape Models (or ASMs) to generate an average shape model and hence use the latter to partition new images. The key advantages of such a framework is: (i) landmark-free automated shape training; (ii) strict shape constrained model to fit test data. Our model can naturally deal with shapes of arbitrary dimension and topology(closed/open curves). We term our model Active Geometric Model, since it focuses on segmentation of geometric shapes. We demonstrate the power of the proposed framework in two important medical applications: one for morphology estimation of 3D Motor Neuron compartments, another for thickness estimation of Henle's Fiber Layer in the retina. We also compare the qualitative and quantitative performance of our method with that of several other state-of-the-art segmentation methods.

Volume overload is a common feature in patients on haemodialysis (HD). This contributes significantly to the cardiovascular disease burden seen in these patients. Clinical assessments of the volume state are often inaccurate. Techniques such as interdialytic blood pressure, relative blood volume monitoring, bioimpedance are available to improve clinical effectives. However all these techniques exhibit significant shortcomings in their accuracy, reliability and applicability at the bed side. We evaluated the usefulness of a dual compartment monitoring technique using Continuous Segmental Bioimpedance Spectroscopy (CSBIS) and Relative Blood Volume (RBV) as a tool to assess hydration status and determine dry weight. We also sought to evaluate the role of Atrial Natriuretic Peptide (ANP) and B-type Natriuretic Peptide (BNP) as a volume marker in dialysis patients. The Retrospective analysis of a historical cohort (n = 376, 55 Diabetic) showed a significant reduction in post-dialysis weights in the first three months of dialysis (72.5 to 70kg, p<0.027) with a non-significant increase in weight between months 6-12. The use of anti-hypertensive agents reduced insignificantly in the first 3 months, increased marginally between months 3-6 and significantly increased over the subsequent 6 months. The residual urea clearance (KRU) fell and dialysis times increased. The cohort was very different to that dialysing at Tassin and showed a dissociation between weight reduction and BP control. This may relate to occult volume overload. CSBIS-RBV monitoring in 9 patients with pulse ultrafiltration (pulse UF) showed distinct reproducible patterns relating to extra cellular fluid (ECF) and RBV rebound. An empirical Refill Ratio was then used to define the patterns of change and this was related to the state of their hydration. A value closer to unity was consistent with the attainment of best achievable target weight. The refill ratio fell significantly between the first (earlier) and third (last) rebound phase (1.97 ± 0.92 vs 1.32 ± 0.2). CSBIS monitoring was then carried out in 31 subjects, whilst varying dialysate composition, temperature and patient posture to analyse the effects of these changes on the ECF trace and to ascertain whether any of these interventions can trigger a change in the slope of the ECF trace distinct to that caused by UF. Only, isovolemic HD caused a change in both RBV and ECF in some patients that was explained by volume re-distribution due to gravitational shifts, poor vascular reactivity, sodium gradient between plasma and dialysate and the use of vasodilating antihypertensive agents. This has not been described previously. These will need to be explored further. The study did demonstrate a significant lack of comparability of absolute values of RECF between dialysis sessions even in the same patient. This too has not been described previously. This is likely to be due to subtle changes in fluid distribution between compartments. Therefore a relative changes must be studied. This sensitivity to subtle changes may increase the usefulness of the technique for ECF tracking through dialysis. The potential of dual compartment monitoring to track volume changes in real time was further explored in 29 patients of whom 21 achieved weight reductions and were able to be restudied. The Refill Ratio decreased significantly in the 21 patients who had their dry weights reduced by 0.95 ± 1.13 kg (1.41 ± 0.25 vs 1.25 ± 0.31). Blood pressure changes did not reach statistical significance. The technique was then used to examine differences in vascular refill between a 36oC and isothermic dialysis session in 20 stable prevalent patients. Pulse UF was carried out in both these sessions. There were no significant differences in Refill Ratios, energy removed and blood pressure response between the two sessions. The core temperature (CT) of these patients was close to 36oC and administering isothermic HD did not confer any additional benefit. Mean BNP levels in 12 patients during isovolemic HD and HD with UF did not relate to volume changes. ANP concentrations fell during a dialysis session in 11 patients from a mean 249 ± 143 pg/ml (mean ± SD) at the start of dialysis to 77 ± 65 pg/ml at the end of the session (p<0.001). During isolated UF levels did not change but fell in the ensuing sham phase indicating a time lag between volume loss and decreased generation. (136±99 pg/ml to 101±77.2 pg/ml; p<0.02) In a subsequent study ANP concentrations were measured throughout dialysis and in the post-HD period for 2 hours. A rebound in ANP concentration was observed occurring at around 90 min post-HD. The degree of this rebound may reflect the prevailing fluid state and merit further study. We have shown the utility of dual compartment monitoring with CSBIS-RBV technique and its potential in assessing volume changes in real time in haemodialysis patients. We have also shown the potential of ANP as an independent marker of volume status in the same setting. Both these techniques merit further study.