Leaf size and shape are strongly influenced by the growth patterns of the epidermal tissue. Pavement cells are the prevalent cell type in the epidermis and during cell expansion they undergo a drastic shape change from a simple polyhedral cells to puzzled-shaped cell. The role of these cell protrusions, more commonly referred to as lobes, remains unknown but their formation has been proposed to help increase the structural integrity of the epidermal tissue. How the symmetry breaking event that initiates a lobe is controlled remains unknown, however pharmacological and genetic disruption of the microtubule system has been shown to interfere not only with lobe initiation but also with lobe expansion. Additionally, the role of microtubules in the pattering of microfibril deposition, the load-bearing structure of the cell wall, makes the microtubule system a good candidate to evaluate its dynamics as a function of shape change. Two main mechanical models for lobe initiation are evaluated here, one where microtubules serve as stable features suppressing local expansion and one where microtubules, similarly to the anisotropic expansion patterning in hypocotyl cells, pro-mote the local anisotropic expansion of the cell resulting in lobe formation. The main method to evaluate these models was through the use of long-term time-lapse image analysis using a plasma-membrane marker for accurate shape change quantification and a microtubule marker to quantify their location, persistence, and density as a function of cell shape change. Using the junctions where three cells come together,cells were sub-divided into segments and the shape of these segments were tracked using a new coordinate system that allowed the detection of new lobes as which can arise from ∼300 deflections. By mapping sub-cellular processes, such as microtubule persistence, to this coordinate system, correlations of microtubule organization and shape change was possible. Additionally, a subset of microtubules bundles that splay across the anticlinal and periclinal walls, perpendicular and parallel to the leaf surface respectively, were identified as marking the location and direction of lobe formation.Disrupting the cell boundary by partially digesting pectin, a main component in the middle lamella, revealed the cell-autonomous morphogenesis mechanism in pavementcells. Under pectinase treatment, cell invaginations were produced and similarly to lobes their initiation was microtubule and cellulose dependent. Lastly, stress prediction using finite-element models, based from live-cell images, co-localized regions of high cell wall stress with both microtubule persistence and shape shape locations in both lobing and invaginated segments. Together, a model of cellular shape change is presented where microtubules translate cell wall stresses to tissue morphogenesis.

The chicken bursa of Fabricius is a primary lymphoid tissue important for B-cell development. Our long-term goal is to understand the role of bursal microenvironment in an early B-cell differentiation event initiating repertoire development through immunoglobulin gene-conversion in the chick embryo. We hypothesize that early bursal B-cell differentiation is guided by signals through cytokine receptors. Our theory is based on previous evidence for expression of the receptor tyrosine kinase superfamily members and interleukin receptors in unseparated populations of bursal B-cells and bursal tissue. Knowledge of the expressed genes that are responsible for B-cell differentiation is a prerequisite for understanding the bursal microenvironment’s function. This project uses transcriptomic analysis to examine gene expression across an early B-cell differentiation event. RNA-seq was performed with total RNA isolated from developing B-cells at embryonic day (ED) 16 and ED 19 (n=3). Approximately 90 million high quality clean reads where obtained from the cDNA libraries. The analysis revealed differentially expressed genes involved in Wnt signaling pathway, Jak-STAT pathway, metabolic pathways, tyrosine metabolism, Toll-like receptor signaling pathway, MAPK signaling pathway, and cellhesion molecules. The transcripts for surface receptors, signal transduction and transcription factors identified in this study represent gene candidates for controlling B-cell differentiation in response to bursal microenvironmental factors.

<p>Bioelectricity, or endogenous electrical signaling mediated by the dynamic distribution of charged molecules, is an ancient signaling mechanism conserved across living organisms. Increasing evidence has revealed that bioelectric signals play a critical role in many diverse aspects of biology such as embryonic development, cell migration, regeneration, cancer, and other diseases. However, direct visualization and manipulation of bioelectricity during development are lacking. Neuroscience has developed tools such as GEVIs (genetically encoded voltage indicators) and chemogenetics like DREADDs (designer receptor exclusively activated by designer drugs) which allow for real–time voltage monitoring and activation of mutated receptors by inert molecules for perturbing membrane potential (Vm). To uncover bioelectric activity during development, we generated a whole-zebrafish transgenic GEVI reporter line and characterized the electrical signaling during early embryogenesis using light sheet microscopy (LSM). Additionally, we generated tissue-specific transgenic lines that combined GEVIs and chemogenetic DREADD tools to manipulate Vm. We found zebrafish embryos display stage-specific characteristic bioelectric signals during the cleavage, blastula, gastrula, and segmentation periods. Furthermore, activation of DREADDs was able to alter cell-specific GEVI fluorescence intensity and could cause a melanophore hyperpigmentation phenotype. Ultimately, these results provide the first real-time systematic analysis of endogenous bioelectricity during vertebrate embryonic development. Additionally, we generated and tested zebrafish transgenic lines for simultaneous visualization and chemogenetic manipulation of Vm during development. These results provide a better understanding of developmental bioelectricity and new tools for future studies, which could eventually help uncover the cellular electric mechanisms behind tissue patterning and disease.</p>

No description available.

<p dir="ltr">The pancreas is composed of a variety of cell types such as acinar, endocrine, and ductal cells, as well as endothelial cells and adipocytes. Whereas we understand the distinct functions of each, there remains an incomplete understanding of the molecular pathways and communications that exist between these cells that may influence development, growth, and function. Given that diabetes is characterized by the destruction or dysfunction of the insulin-producing pancreatic beta cell, a better understanding of the mechanisms that influence cell growth and maintenance in the pancreas is of therapeutic interest. Genome-wide association studies identified eukaryotic initiation factor 5A (eIF5A) to be within a type 1 diabetes susceptibility locus, which also suggests this translation factor may play a role in maintaining beta cell health. EIF5A is active once post-translationally modified by the rate-limiting enzyme deoxyhypusine synthase (DHPS) in a process known as hypusination, producing hypusinated eIF5A (eIF5A^HYP). The functional loss of eIF5A^HYP via pancreas-specific genetic deletion of <i>Dhps</i> or <i>Eif5a</i> within multipotent pancreatic progenitor cells (MPPCs) results in an mRNA translation defect detectable at E14.5 causing the decreased expression of many proteins required for exocrine growth and function. Moreover, DHPS^ΔPANCmice die by 6 weeks-of-age; however, eIF5A^ΔPANCmice survive up to 2 years-of-age. The postnatal phenotype of the eIF5A^Δ^PANCmodel was investigated in this thesis.</p>

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by abnormalities in multiple components of the immune system resulting in progressive damage to multiple organs. Current treatments for SLE are often intensive and result in side effects and the potential for continued flares and progression of disease. Histone deacetylase (HDAC) enzymes control multiple cellular functions by removing acetyl groups from lysine residues in various proteins. HDAC inhibitors have been investigated as a potential treatment for SLE with promising results, however selective HDAC6 inhibition (HDAC6i) has become a leading candidate for pharmacologic inhibition to reduce the potential for side effects. We hypothesize that HDAC6i will decrease SLE disease by targeting substrates of HDAC6 in multiple components of immunity and organ systems. NZB/W mice were treated with ACY-738 or ACY-1083, followed by evaluation of multiple disease parameters and mechanisms involved in disease pathogenesis within the kidney, bone marrow, and spleen. Within the kidney, HDAC6i decreased glomerular pathology scores, proteinuria, and IgG and C3 deposition. Within glomerular cells, HDAC6i increased alpha-tubulin acetylation and decreased nuclear NF-κB. Within the spleen, there was a dose-dependent decrease in the frequency of Th17 cells and a mild decrease in the frequency of Treg cells. Concurrently, there were decreased levels of IL-12/IL-23 and minimal decreases in TGF-β in the serum. Within the bone marrow, B cell development through Hardy fractions exhibited accelerated progression through later stages as NZB/W mice aged. This accelerated progression may allow B cells to bypass important regulatory checkpoints in maintaining immune tolerance and contribute to autoimmunity. Treatment with an HDAC6i corrected the aberrant B cell development in the bone marrow and RNAseq analysis unveiled six genes (Cebpb, Ccr9, Spib, Nfil3, Lgals1, and Pou2af1) that may play a role in the aforementioned abnormalities. Overall, these findings show that HDAC6i decreased disease in NZB/W mice by targeting multiple components of the immune response, including glomerular cells, T cell subsets in the spleen, and bone marrow B cells. In conclusion, selective HDAC6i is an excellent candidate for pharmacologic therapy for SLE because it targets multiple immune abnormalities involved in SLE pathogenesis while remaining selective and safe. / Ph. D. / Systemic Lupus Erythematosus (SLE) is an autoimmune disease characterized by multiple abnormalities in the immune system resulting in progressive immune-mediated damage to multiple organs. Current treatment regimens are often intensive, result in side effects, and may only provide temporary relief of disease. Histone deacetylase (HDAC) inhibition is currently being investigated as a new treatment modality for SLE with aims for improved efficacy and decreased potential for unwanted side effects. HDAC enzymes remove acetyl groups from multiple proteins (substrates) and subsequently regulate their function. HDAC6 is a specific HDAC enzyme that is of particular interest and are the subject of the following studies. These studies hypothesize that HDAC6 inhibition will decrease SLE by targeting multiple protein targets involved in the immune-mediated pathway of disease initiation and progression. NZB/W mice were utilized as a model of the human disease, and were treated by HDAC6 inhibitors during various stages of disease progression. Long-term treatment initiated early in disease decreases disease as evidenced by decreased renal pathology scores, immune complex deposition in the kidneys, decreased T cell subtypes in the spleen, and decreased inflammatory cytokines. HDAC6 inhibition corrects abnormal B cell development within the bone marrow of NZB/W mice, which is otherwise altered during disease progression. Furthermore, HDAC6 inhibition altered gene expression within the bone marrow, and deep sequencing analysis revealed multiple genes that may be involved in the pathway of disease progression. Overall, HDAC6 inhibition targets multiple pathways involved in SLE disease initiation and progression in various organs including the bone marrow, spleen, and kidneys. Because SLE is a disease that is multi-factorial and effects multiple organs, it would be ideal that a potential drug therapy also targets multiple targets and organ systems while remaining safe to use. Based on these studies, HDAC6 inhibitors are excellent candidates for the treatment of SLE.

T lymphocytes are considered an essential and advanced component of the immune system, since these cells are able to discriminate self from non-self, start up an immune reaction and further develop into memory cells. However, therapies based on the use of patient derived newly generated T cells reinoculated into humans do not exist. This is due to difficulties in replicating the peculiar conditions required for T cell development in vitro. The systems developed so far are based on the use of animal or unrelated human thymic tissue and therefore they would not be adequate to be used in any clinical application. Having conjectured that human skin cells, rearranged in a threedimensional fashion, would be able to support the development of human T lymphocytes from hematopoietic stem cells, we developed a model consisting of human skin keratinocytes and fibroblasts arrayed on a synthetic matrix so to create a prototype suitable to be translated into the clinic. In this way we were able to induce few hundred cord blood CD34⁺ haematopoietic stem cells to entirely develop into mature CD4⁺ or CD8⁺ T lymphocytes in vitro. However, circulating adult peripheral CD34⁺ precursors failed to survive in the same conditions. Finally we were able to explain our success as consequence of strong induction of the Notch delta ligand Dll-4 by the keratinocytes cultured in the construct. In synthesis, we report here for the first time that skin keratinocytes, in the presence of fibroblasts and reconfigured in a three-dimensional arrangement, are able to induce the differentiation of a minimal amount of cord but not adult blood stem cells into fully differentiated T cells by acting through the Dll-4 Notch signaling pathway in vitro.

Pathogenesis of autoimmune and auto-inflammatory diseases is induced by auto-aggressive helper T (Th) cells (i.e. Th1 and Th17 cells), and can be controlled by regulatory T cells (Tregs) characterized by expression of the transcription factor Foxp3. Thus, development of autoimmunity is regulated by the balance of Tregs and Th1/Th17 cells. Prostaglandin E₂ (PGE₂) is a bioactive lipid mediator with immune-modulatory potential that acts through 4 receptors (EP1-4). It has been shown that PGE₂ facilitates Th1 and Th17 cell development and expansion, therefore promoting autoimmune inflammation. However, the role of PGE₂ in Treg development and function is largely unclear. The aim of this PhD was to test the hypothesis that PGE₂ regulates Treg development, function and subsequent immune response. I observed that in vivo inhibition of endogenous PGE₂ biosynthesis using a COX inhibitor resulted in increased Foxp3+ Tregs in various lymphoid organs. This response was prevented by addition of an EP4 agonist. PGE₂-EP4 signalling particularly inhibits RORγt+ Tregs in the intestine. This was not observed in either antibiotic-treated mice or MyD88/TRIF double-knockout mice, suggesting gut commensal microbiota involvement. In addition, PGE₂ has a role in microbiota-dependent regulation of intestinal CD11c+MHCII+CD11b+CD103- mononuclear phagocytes (MNPs) which drive intestinal Treg expansion through production of type 1 interferons. Consistent with these in vivo observations, gut microbial metabolites from indomethacin treated mice enhanced in vitro RORγt+ Treg differentiation in the dendritic cell- T cell co-culture system. Adoptive transfer of caecal microbiota from COX inhibitor- treated mice into naïve mice also provided protective benefits in a chemical (DSS)-induced colitis disease model. In summary, this work has demonstrated that PGE₂ affects intestinal Tregs, indicating a novel mechanism for interaction of PGE₂, the adaptive immune system and the gut microbiota in homeostasis within this environment. These findings increase our understanding of the role of PGE₂ in development of inflammatory bowel disease and offer potential therapeutic strategies for treating this disease.

T lymphocytes comprise one arm of the adaptive immune system and are critical for immunity to neoplasia and infection. A full understanding of their development has important implications for the treatment of autoimmunity, immunodeficiency, and leukemias arising from T cell developmental intermediates. The Notch signaling pathway is already known to be absolutely required for T cell commitment and development, but its collaboration with other factors is poorly understood. Unfortunately, deficiency in many of the genes critical to hematopoiesis, including Notch, causes early embryonic lethality by disrupting multiple developmental processes. This complicates the study of such genes by in vivo models or ex vivo hematopoietic progenitors. To circumvent these difficulties, this thesis describes the use of in vitro-differentiated embryonic stem cell-derived T progenitors to examine the roles of two GATA family members during early T cell development. GATA-2, while not required for T cell development, is shown to act downstream of Notch signals to inhibit myelopoiesis. These findings both characterize a novel role for GATA-2, and demonstrate that T progenitor maturation and exclusion of non-T cell fates are distinct and separable events. GATA-3, in contrast to GATA-2, is absolutely required for T lymphopoiesis. However, the current literature does not distinguish between a requirement for GATA-3 in homing to the thymic environment, committing to the T cell fate, or surviving such a commitment event. This thesis demonstrates that GATA-3 is dispensable for commitment itself, but required to permit survival and proliferation after commitment. Taken together, the results presented in this thesis employ a novel model system to characterize the interactions of two important collaborators with Notch signals during T cell development, and further dissect the stages through which early T cell development is enacted.

T lymphocytes comprise one arm of the adaptive immune system and are critical for immunity to neoplasia and infection. A full understanding of their development has important implications for the treatment of autoimmunity, immunodeficiency, and leukemias arising from T cell developmental intermediates. The Notch signaling pathway is already known to be absolutely required for T cell commitment and development, but its collaboration with other factors is poorly understood. Unfortunately, deficiency in many of the genes critical to hematopoiesis, including Notch, causes early embryonic lethality by disrupting multiple developmental processes. This complicates the study of such genes by in vivo models or ex vivo hematopoietic progenitors. To circumvent these difficulties, this thesis describes the use of in vitro-differentiated embryonic stem cell-derived T progenitors to examine the roles of two GATA family members during early T cell development. GATA-2, while not required for T cell development, is shown to act downstream of Notch signals to inhibit myelopoiesis. These findings both characterize a novel role for GATA-2, and demonstrate that T progenitor maturation and exclusion of non-T cell fates are distinct and separable events. GATA-3, in contrast to GATA-2, is absolutely required for T lymphopoiesis. However, the current literature does not distinguish between a requirement for GATA-3 in homing to the thymic environment, committing to the T cell fate, or surviving such a commitment event. This thesis demonstrates that GATA-3 is dispensable for commitment itself, but required to permit survival and proliferation after commitment. Taken together, the results presented in this thesis employ a novel model system to characterize the interactions of two important collaborators with Notch signals during T cell development, and further dissect the stages through which early T cell development is enacted.