Granulocytes represent the first line of defense against bacteria and fungi. Daily production of granulocytes is sustained by steady state granulopoiesis but under stress (e.g., bacterial infection) this program switches to emergency granulopoiesis (EG) which ensures the production of granulocytes at enhanced and accelerated rates. Very little is known about the regulation of EG. In this thesis, we showed that disruption of the β-catenin-TCF/LEF mediated transcription impairs EG in vivo. Further, we demonstrated that lipopolysaccharide (LPS) administration in mice induces accumulation of active β-catenin in hematopoietic stem and progenitor cells (HSPCs) as early as 4 hours (H) after stimulation, with highest increase at 24H. This effect was at least partially mediated in a niche independent manner, since LPS stimulation in vitro induced β-catenin accumulation in c-Kit+ cells after 2H, with a peak activation at 4H. Using single cell RNA sequencing, we determined the cell cluster dynamics of HSPCs following 4H LPS stimulation. Interestingly, we identified a possible upstream activator of β- catenin in one of the clusters - Wnt10b. Indeed, Wnt10b showed a similar expression pattern as EG master regulator Cebpb and β-catenin activation, following in vitro treatment with LPS. Altogether, our data point...

4 Abstract The Wnt pathway is one of the major signaling cascades contributing to multiple cellular processes during embryogenesis, and adult tissue homeostasis and regeneration. Moreover, aberrant activation of the Wnt signaling pathway is connected with development of neoplasia, notably colorectal cancer. The aim of the thesis was to identify new ways of the Wnt pathway regulation to understand better physiological as well as non-physiological mechanisms of Wnt signaling. The results are summarized in four publications. The first article deals with TROY, a member of tumor necrosis factor receptor family. We identified TROY as a Wnt target gene during our search for Wnt responsive genes in colorectal cancer cell lines. Additionally, we detected expression of Troy in tumors of two mouse models of intestinal cancer. In the healthy gut, Troy is produced in fast cycling intestinal stem cells where negatively regulates the Wnt pathway. The second study focuses on processing and posttranslational modification of murine Wnt1 and Wnt3a. Wnts are glycosylated and double acetylated by lipid adducts and our results revealed that O-linked acylation of serine is required for the subsequent S-palmitoylation of cysteine. Moreover, acylation of Wnts is connected with their signaling activity which is related to Wnt1 and...

Lens development and differentiation are strictly regulated processes. Various disturbances of these processes can lead to vision-limiting pathologies. The vertebrate lens is composed of epithelial cells and terminally differentiated fiber cells. Differentiation of fiber cells is connected with expression of fiber cell specific proteins (such as crystallins), cell cycle exit, and finally with the degradation of cell nucleus and organelles. Wnt/β-catenin signaling plays important roles during early eye development as well as later during the lens differentiation. To investigate the consequences of constitutive activation of Wnt/β-catenin signaling in lens fiber cells transgenic mouse strain, called CLEF, was created. Constitutive activation of Wnt/β-catenin signaling in fiber cells of CLEF mouse is achieved by transgenic protein CLEF that contains C-terminal activation domain of β-catenin fused to the amino terminus of full-length protein Lef1. The expression of CLEF transgene is under the control of αA-crystallin promoter. As a result of constitutive activation of Wnt/β-catenin signaling in fiber cells, adult CLEF mice develop cataracts and microphthalmia, and the morphology of adult mutant lenses is disrupted. Transgenic CLEF mRNA is expressed starting from E13.5 and by E16.5 transgenic CLEF protein is...

Colon cancer causes approximately seven percent of all cancer-related deaths in the world and presumably due to modern lifestyle, it is also one of the most frequently diagnosed cancers. The inefficiency of standard treatment indicates the need for intensive research of molecular mechanisms of cancer development. The canonical Wnt signaling pathway is essential for maintenance of the progenitor phenotype of stem cells in crypts of the intestine and controls repopulation of the epithelia, in physiological conditions. However, aberrant activation leads to tumor formation. Although Wnt signaling in cancer has been subjected to thorough investigation, there is still a lot of questions concerning further branching of the pathway. As a model of Wnt/β-catenin triggered colorectal cancer, we use mice with mutated APC, which is the tumor suppressor involved in this pathway. Previous expression profiling of the intestinal tumors from relevant mice revealed two transcription factors: ETV4 and MSX1 which are significantly overexpressed in cancer cells. In this project we elucidate whether the overexpression is really tumor restricted and Wnt dependent or there is a crosstalk with another signal transduction pathway. We investigate the function and regulation of these transcription factors by synthetic reporter assays,...

Wnt signalling represents an important mechanism participating in control of cellular and developmental processes, including establishment of cell polarity, cell fate specification, stem cell self-renewal, tissue patterning and organogenesis, homeostasis maintenance and regeneration. Misregulation of the Wnt signalling during embryogenesis leads to developmental defects while aberrant activation later in development is associated with degenerative diseases and a number of cancers. The presented PhD thesis is based on four original publications that deal with the post-translational modifications of Wnt ligands and molecular mechanisms contributing to the regulation of a transcriptional profile of the so-called canonical Wnt pathway. Wnt signalling pathway is used repetitively both in time and different cellular contexts throughout development of multicellular organisms. Inevitably, in each single situation -catenin/TCF complexes, the downstream effectors, induce only subsets of all potential target genes. How this differential tissue- and stage-specific control over various subsets of target genes is achieved with such a limited number of nuclear effectors is not fully understood. Along with the expression of specific LEF/TCF family members or their variants containing different functional domains...

The canonical Wnt/β-catenin signalling pathway plays an important role in proliferation and differentiation of neural progenitors during embryogenesis as well as postnatally. In the present study, the effect of the Wnt signalling pathway on the differentiation potential of neonatal and adult neural stem cells (NS/PCs) isolated from subventricular zone (SVZ) of lateral ventricles and their membrane properties were studied eight days after the onset of in vitro differentiation. To manipulate Wnt signalling at different cellular levels, three transgenic mouse strains were used, which enabled inhibition or activation of the pathway using the Cre- loxP system. We showed that the activation of the Wnt signalling pathway leads to higher expression of β-catenin in both postnatal as well as adult NS/PCs, while Wnt signalling inhibition results in the opposite effect. To follow the fate of NS/PCs, the patch-clamp technique, immunocytochemistry, and Western blot were employed. After eight days of NS/PCs differentiation we identified three electrophysiologically and immunocytochemically distinct cell types of which incidence was significantly affected by the canonical Wnt signalling pathway, only in differentiated neonatal NS/PCs. Activation of this pathway suppressed gliogenesis, and promoted neurogenesis,...

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