In Gram-negative bacteria, the three-layered cell envelope, including the cell wall, outer and inner membranes, is essential for cell survival in the changing, and often hostile environments. Conserved in all prokaryotes, the cell wall is incredibly thin, yet it functions to prevent osmotic lysis in diluted conditions. Based on observations obtained by genetic and chemical perturbations, time-lapse live cell imaging, quantitative imaging and statistical analysis, Part I of this dissertation explores the molecular and physical events leading to cell lysis induced by division-specific beta-lactams. We found that such lysis requires the complete assembly of all essential components of the cell division apparatus and the subsequent recruitment of hydrolytic amidases. We propose that division-specific beta-lactams lyze cells by inhibiting FtsI (PBP3) without perturbing the normal assembly of the cell division machinery and the consequent activation of cell wall hydrolases. On the other hand, we demonstrated that cell lysis by beta-lactams proceeds through four physical phases: elongation, bulge formation, bulge stagnation and lysis. Bulge formation dynamics is determined by the specific perturbation of the cell wall and outer membrane plays an independent role in stabilizing the bulge once it is formed. The stabilized bulge delays lysis, and allows escape and recovery upon drug removal. Asymmetrical in structure and unique to Gram-negative bacteria, outer membrane prevents the passage of many hydrophobic, toxic compounds. Together with inner membrane and the cell wall, three layers of the Gram-negative cell envelope must be well coordinated throughout the cell cycle to allow elongation and division. Part II of this dissertation explores the essentiality of the LPS layer, the outer leaflet of the outer membrane. Using a conditional mutant severely defective in LPS transport, we found that mutations in the initiation phase of fatty acid synthesis suppress cells defective in LPS transport. The suppressor cells are remarkably small with a 70% reduction in cell volume and a 50 % reduction in growth rate. They are also blind to nutrient excess with respect to cell size control. We propose a model where fatty acid synthesis regulates cell size in response to nutrient availability, thereby influencing growth rate. / Chemistry and Chemical Biology

The goal of my research was to obtain a quantitative understanding of the mechanisms of DNA double-strand break (DSB) repair, and the activation of the tumor suppressor p53 in response to DSBs in human cells. In Chapter 2, we investigated how the kinetics of repair, and the balance between the alternate DSB repair pathways, nonhomologous end-joining (NHEJ) and homologous recombination (HR), change with cell cycle progression. We developed fluorescent reporters to quantify DSBs, HR and cell cycle phase in individual, living cells. We show that the rates of DSB repair depend on the cell cycle stage at the time of damage. We find that NHEJ is the dominant repair mechanism in G1 and in G2 cells even in the presence of a functional HR pathway. S and G2 cells use both NHEJ and HR, and higher use of HR strongly correlates with slower repair. Further, we demonstrate that the balance between NHEJ and HR changes gradually with cell cycle progression, with a maximal use of HR at the peak of active replication in mid-S. Our results establish that the presence of a sister chromatid does not affect the use of HR in human cells. Chapter 3 examines the sensitivity of the p53 pathway to DNA DSBs. We combined our fluorescent reporter for DSBs with a fluorescent reporter for p53, to quantify the level of damage and p53 activation in single cells. We find that the probability of inducing a p53 pulse increases linearly with the amount of damage. However, cancer cells do not have a distinct threshold of DSBs above which they uniformly induce p53 accumulation. We demonstrate that the decision to activate p53 is potentially controlled by cell-specific factors. Finally, we establish that the rates of DSB repair do not affect the decision to activate p53 or the dynamical properties of the p53 pulse. Collectively, this work emphasizes the importance of collecting quantitative dynamic information in single cells in order to gain a comprehensive understanding of how different DNA damage response pathways function in a coordinated manner to maintain genomic integrity.

Throughout their life cycle, plants adjust growth in response to their developmental and environmental situation within the limits of their energetic capacities. This capacity is defined by the local sugar availability, which is constantly modulated through synthesis, transport and consumption of sugar. The monitoring of sugar presence is carried out by a complex signalling network in which simple sugars (e.g. glucose, fructose and sucrose) act as metabolic signals for the modulation of physiological processes. However, often it remains unclear whether the regulation is induced by the simple sugars themselves or by their derivatives generated during sugar metabolism. This thesis focuses on the dissection of distinct sugar signals, their generation, perception and impact on the modulation of gene expression and cell division both in cell culture and young seedlings. Based on a stem-cell-like A. thaliana cell culture, which could be sustained in a hormone-free media, a new biological system, supplied with Xyl as the only carbon source was developed. The performance of a variety of sugar and sugar analogue treatments in this novel system allowed for the identification of sugar-responsive candidate genes, which were specifically regulated by glucose, fructose and sucrose. For several genes (e.g. bZIP63, AT5g22920, TPS9, MGD2 and BT2), this regulation required both sugar transport into the cytosol and metabolisation for the generation of the signal. Furthermore, gene expression analyses in young A. thaliana seedlings indicated the requirement for the catalytic activity of hexokinase 1 in the regulation of bZIP63, Atg22920 and BT2 under conditions of a perturbed carbohydrate balance. These findings have been combined in a proposed model for the transcriptional regulation of bZIP63, AT5g22920, TPS9, MGD2 and BT2, which further proposes a function of those genes in the regulation of cell division. The optimisation of a protocol for long-term real-time live-cell imaging provided a valuable tool to show that, similar to gene expression, the progression of cell division depended on a sugar-type-specific regulation at the single-cell level; this regulation was most likely caused by prolongation of the interphase. Together with the observation of cell death and growth arrest of the primary root in intact seedlings in response to the glucose analogue 2dog, this led to the conclusion that sugar signals themselves were sufficient to induce cell division. However, the continuation of cell cycle progression and consequently organ growth over long-time required the availability of the energy contained in the sugar.

No description available.

Regenerative medicine is a rapidly developing field, merging engineering and biological life sciences to create biological replacements for damaged tissue and organ function. Development of cellular based therapies has the potential of curing present untreatable diseases and conditions, such as diabetes. The identification of protein expression patterns, that guide undifferentiated cells to different lineages, can provide important information about the progression of cellular differentiation at various stages. This research project utilizes proteomics and in vitro live-cell microscopy to investigate two distinct cellular systems: (1) the signaling pathways of calmodulin (CaM) in the differentiation of a human glioblastoma cell line; and (2) the effect of islet neogenesis associated protein (INGAP) on human islet-derived progenitor cells (hIPCs). Using a proteomic readout with a long term live-cell imagining approach, it was hypothesized that highly specific binding proteins of a CaM-mutant, and proteins in hIPCs perturbed by INGAP, could be identified and studied in vitro, characterizing specific signaling pathways which control the function of CaM in brain tumour cells and the mechanism(s) of INGAP in islet-derived progenitor cells. This thesis presents the utility of a proteomics and an in vitro cell microscopy approach to investigate therapeutic proteins, such as INGAP, on cell culture systems. The results have established the limitations and the utility of DIGE, differential binding of a CaM-mutant versus calcium-CaM, and the cell specific uptake feasibility of using the TAT-binding domain. In the hIPC system, proteomic, phenotypic, motility, proliferation and nuclear effects of INGAP were determined. Specifically, hIPCs exposed to INGAP had 50% decrease in average nuclear speed, the translocation of two identified proteins caldesmon and tropomyosin and INGAP was found to bind specifically to hIPCs. However, hIPCs had no changes in insulin specific hormone expression.

L'analyse de l'organisation à grande échelle des chromosomes, par des approches d'imagerie et de biologie moléculaire, constitue un enjeu important de la biologie. Il est maintenant établi que l'organisation structurelle du génome est un facteur déterminant dans tous les aspects des " transactions " génomiques: transcription, recombinaison, réplication et réparation de l'ADN. Bien que plusieurs modèles aient été proposés pour décrire l'arrangement spatial des chromosomes, les principes physiques qui sous-tendent l'organisation et la dynamique de la chromatine dans le noyau sont encore largement débattus. Le noyau est le compartiment de la cellule dans lequel l'ADN chromosomique est confiné. Cependant, la mesure quantitative de l'influence de la structure nucléaire sur l'organisation du génome est délicate, principalement du fait d'un manque d'outils pour déterminer précisément la taille et la forme du noyau. Cette thèse est organisée en deux parties: le premier axe de mon projet était d'étudier la dynamique et les propriétés physiques de la chromatine dans le noyau de la levure S. cerevisiae. Le deuxième axe visait à développer des techniques pour détecter et quantifier la forme et la taille du noyau avec une grande précision. Dans les cellules de levure en croissance exponentielle, j'ai étudié la dynamique et les propriétés physiques de la chromatine de deux régions génomiques distinctes: les régions codant les ARN ribosomiques regroupés au sein d'un domaine nucléaire, le nucléole, et la chromatine du nucléoplasme. Le mouvement de la chromatine nucléoplasmique peut être modélisé par une dynamique dite de " Rouse ". La dynamique de la chromatine nucléolaire est très différente et son déplacement caractérisé par une loi de puissance d'exposant ~ 0,7. En outre, nous avons comparé le changement de la dynamique de la chromatine nucléoplasmique dans une souche sauvage et une souche porteuse d'un allèle sensible à la température (ts) permettant une inactivation conditionnelle de la transcription par l'ARN polymérase II. Les mouvements chromatiniens sont beaucoup plus importants après inactivation transcriptionnelle que dans la souche témoin. Cependant, les mouvements de la chromatine restent caractérisés par une dynamique dite de " Rouse ". Nous proposons donc un modèle biophysique prenant en compte ces résultats : le modèle de polymère dit "branched-Rouse". Dans la deuxième partie, j'ai développé "NucQuant", une méthode d'analyse d'image permettant la localisation automatique de la position de l'enveloppe nucléaire du noyau de levures. Cet algorithme comprend une correction post-acquisition de l'erreur de mesure due à l'aberration sphérique le long de l'axe Z. "NucQuant" peut être utilisée pour déterminer la géométrie nucléaire dans de grandes populations cellulaires. En combinant " NucQuant " à la technologie microfluidique, nous avons pu estimer avec précision la forme et la taille des noyaux en trois dimensions (3D) au cours du cycle cellulaire. "NucQuant" a également été utilisé pour détecter la distribution des regroupements locaux de complexes de pore nucléaire (NPCs) dans des conditions différentes, et a révélé leur répartition non homogène le long de l'enveloppe nucléaire. En particulier, nous avons pu montrer une distribution particulière sur la région de l'enveloppe en contact avec le nucléole. En conclusion, nous avons étudié les propriétés biophysiques de la chromatine, et proposé un modèle dit "branched Rouse-polymer" pour rendre compte de ces propriétés. De plus, nous avons développé "NucQuant", un algorithme d'analyse d'image permettant de faciliter l'étude de la forme et la taille nucléaire. Ces deux travaux combinés vont permettre l'étude des liens entre la géométrie du noyau et la dynamique de la chromatine. / Chromosome high-order architecture has been increasingly studied over the last decade thanks to technological breakthroughs in imaging and in molecular biology. It is now established that structural organization of the genome is a key determinant in all aspects of genomic transactions. Although several models have been proposed to describe the folding of chromosomes, the physical principles governing their organization are still largely debated. Nucleus is the cell’s compartment in which chromosomal DNA is confined. Geometrical constrains imposed by nuclear confinement are expected to affect high-order chromatin structure. However, the quantitative measurement of the influence of the nuclear structure on the genome organization is unknown, mostly because accurate nuclear shape and size determination is technically challenging. This thesis was organized along two axes: the first aim of my project was to study the dynamics and physical properties of chromatin in the S. cerevisiae yeast nucleus. The second objective I had was to develop techniques to detect and analyze the nuclear 3D geomtry with high accuracy. Ribosomal DNA (rDNA) is the repetitive sequences which clustered in the nucleolus in budding yeast cells. First, I studied the dynamics of non-rDNA and rDNA in exponentially growing yeast cells. The motion of the non-rDNA could be modeled as a two-regime Rouse model. The dynamics of rDNA was very different and could be fitted well with a power law of scaling exponent ~0.7. Furthermore, we compared the dynamics change of non-rDNA in WT strains and temperature sensitive (TS) strains before and after global transcription was actived. The fluctuations of non-rDNA genes after transcriptional inactivation were much higher than in the control strain. The motion of the chromatin was still consistent with the Rouse model. We propose that the chromatin in living cells is best modeled using an alternative Rouse model: the “branched Rouse polymer”. Second, we developed “NucQuant”, an automated fluorescent localization method which accurately interpolates the nuclear envelope (NE) position in a large cell population. This algorithm includes a post-acquisition correction of the measurement bias due to spherical aberration along Z-axis. “NucQuant” can be used to determine the nuclear geometry under different conditions. Combined with microfluidic technology, I could accurately estimate the shape and size of the nuclei in 3D along entire cell cycle. “NucQuant” was also utilized to detect the distribution of nuclear pore complexes (NPCs) clusters under different conditions, and revealed their non-homogeneous distribution. Upon reduction of the nucleolar volume, NPCs are concentrated in the NE flanking the nucleolus, suggesting a physical link between NPCs and the nucleolar content. In conclusion, we have further explored the biophysical properties of the chromatin, and proposed that chromatin in the nucleoplasm can be modeled as "branched Rouse polymers". Moreover, we have developed “NucQuant”, a set of computational tools to facilitate the study of the nuclear shape and size. Further analysis will be required to reveal the links between the nucleus geometry and the chromatin dynamics.

The perfusion chamber for long term observing of live cells by the means the Coherence-Controlled Holographic Microscope (CCHM) was designed. CCHM was built and designed at the Laboratory of the optical microscopy at the Institute of Physical Engineering, Brno University of Technology. CCHM can quantitatively evaluate dynamical changes inside live cells thanks to the quantitative information about phase shift in each pixel of the image. In order to demonstrate advantages of CCHM experimentally, it is important to keep the live cells in the good conditions. This is made by adding the fresh cultivation medium for studied cells directly in the microscope. In contrast to the stationary chamber the perfusion chamber allows both the cultivation medium exchange and the application of biological reagents without the necessity of removing the chamber from the microscope. Therefore we can study the vital signs of cells before and after the application of reagents. An original perfusion system with accessories compatible with CCHM was designed. The design is based on the previously published perfusion system solutions that are referred to in this thesis. The flow characteristics and medium exchange process was discussed and a modification of the internal geometry, based on numerical simulations, was introduced. The applicability of this perfusion chamber has been proven for the CCHM and even for different types of microscopes. The reactions of tumor and epithelial cells during the change of the environment from the cultivation medium to the physiologically solution were studied.

No description available.

Mitochondria are the power plant of most non-green eukaryotic cells. In order to understand mitochondrial functions and their regulation, knowledge of the spatiotemporal organization of their proteins is important. Mitochondrial membrane proteins can diffuse within membranes. They are involved in diverse functions e.g. protein import, cell respiration, metabolism, metabolite transport, fusion, fission or formation of the mitochondrial architecture. Furthermore, mitochondria compose of different subcompartments with different tasks. Especially, the inner mitochondrial membrane (IM), where the oxidative phosphorylation (OXPHOS) takes places, has a complex architecture with cristae extending into the matrix. The present work revealed the restricted localization of some mitochondrial proteins to specific membrane sections and linked it to their function or bioenergetic circumstances in the living cell. 
Single particle tracking (SPT) techniques like tracking and localization microscopy (TALM) allow to localize proteins with a precision below 20 nm. Additionally, tracking single proteins provides information about their mobility, dynamic and their spatiotemporal organization. TALM uses proteins, which were genetically tagged either with the HaloTag® (HaloTag) or the fSnapTag® (fSnapTag). These tags can be orthogonally and posttranslationally stained with specific and self-marking dyes. If the dyes are conjugated to the respective substrate of the tag. Single molecule labeling of mitochondrial proteins was performed substoichiometrically using membrane permeable rhodamine dyes, either tetramethylrhodamine (TMR) or silicon rhodamine (SiR). TALM allowed to localize proteins in different mitochondrial subcompartments. The gained trajectories and trajectory maps of mitochondrial proteins revealed their spatiotemporal organization. In the case of IM proteins like F1FO ATP synthase (Complex V - CV) a restricted diffusion in the CM, which is part of the continuous IM, was determined. The unimpeded diffusion of mitochondrial proteins in the outer mitochondrial membrane (OM) was compared with the mobility of IM proteins. The diffusion of mitochondrial IM proteins was restricted by the IM architecture and their diffusion coefficients were lower. Furthermore, significant differences of different mitochondrial IM proteins were compared, showing different localizations in the IM often coupled to their function, accompanied by different spatiotemporal organization and diffusion coefficients. Furthermore, a distinction was made between diffusion of proteins in the inner boundary membrane (IBM) and proteins that preferentially diffuse in the cristae membrane (CM). Evaluating trajectory maps, the different subcompartments in the IM were revealed by trajectories and the trajectory directionality, allowing the identification of mitochondrial proteins, which mark these subcompartments.
The morphology of mitochondria / mitochondrial networks and their bioenergetic parameters are linked to the metabolic states of the cell. In this work, the connection of the spatiotemporal protein organization of CV and the IM architecture was uncovered on the micro- and nanoscopic level and linked to the metabolic state of the cell. It was determined that the spatiotemporal organization of the CV was altered, when CV was inhibited. In addition, the bioenergetic influence of cells on the spatiotemporal behavior of CV and the reorganization of the IM architecture was investigated by TALM and compared with results of electron microscopy images. It was shown that starvation of cells led to a loss of cristae and thus to an increased mobility and spatiotemporal reorganization of CV. Taken together, the results presented in this work showed that a correctly functioning and active CV helps to maintain the IM architecture and both, the spatiotemporal organization of CV and the IM architecture were coupled to the metabolic state.. 
In order to investigate putative protein-protein interactions by colocalization and co-locomotion studies on single molecule level, dual color SPT is needed. Therefore, posttranslational and substoichimetric labeling as performed in TALM was tested for its potential of protein-protein interaction studies of mitochondrial membrane proteins. Here, a genetically double tagged translocase of the outer membrane subunit-20 (Tom20) (Tom20:HaloTag:fSnapTag) acted as a positive control. It turned out that substoichimetric, posttranslational labeling of mitochondrial proteins was not suitable for protein-protein interaction studies on mitochondrial proteins, because it was restricted by the low labeling degrees needed for TALM. However, dual-color TALM still allowed to study effects of proteins influencing the IM architecture and to study their influence on the spatiotemporal organization of CV. The co-transfection of Mic10, as the central protein of the mitochondrial inner membrane organizing system / mitochondrial contact site complex / mitochondrial organizing structure (MINOS / MICOS / MitOS (MINOS/MICOS)), altered the regular and aligned organization of the cristae. This was measured by a changed spatiotemporal organization of the CV, such as the loss of the perpendicular oriented of CV subunit-γ (CV-SUγ) cristae trajectories. In contrast to this, co-transfection of CV subunit-e (CV-SUe), important for dimerization of CV, increased the number of cristae trajectories. 
Mitochondria are three-dimensional (3D) cell organelles. Consequently, subcompartments like the IBM and CM are a 3D space in which CV is localized and diffuses. Thus, the diffusion of mitochondrial proteins is underestimated by two-dimensional SPT e.g. lateral confined diffusion can result from mitochondrial proteins diffusing along the z-axis of the microscope. In order to reveal the 3D spatiotemporal organization of CV, the potential of TALM to be extended to a 3D-SPT technique was investigated. Therto a cylindrical lens was installed in the emission path of a total internal reflection fluorescence (TIRF) microscope. This leads to an astigmatically distorted point spread function (PSF) of the fluorescent single molecule signals. This distortion allowed the reconstruction of single molecule localizations of CV to a superresolved image of the IM, in living cells. In addition, 3D-TALM enabled to display the 3D architecture of the IM by 3D trajectories of CV. 3D-TALM was able to detect whether CV diffuses in the IBM or in the CM, and extended the information about its mobility in the CM that it takes place in a disc-like manner. In this way it could be shown that CV is mobile within the cristae in all directions. Finally, 3D-TALM revealed an altered IM architecture caused by the metabolic state of the cell. As performed in two-dimensional TALM, the cells were kept under starving conditions. Here the now tubular IM architecture was revealed by 3D-TALM. The reversed metabolic state under improved respiratory conditions unexpectedly led to a more diverse IM architecture. These ultrastructural changes were also revealed by electron microscopy. Consequently, 3D-TALM enabled the study of IM architecture by tracking CV under different metabolic conditions, allowing an ultrastructural analysis of mitochondria in living cells. In addition, 3D TALM provided the spatiotemporal organization of CV under different metabolic conditions, so that the diffusion coefficients of CV could be related to changes in IM architecture caused by the metabolic condition.

No description available.