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Expression and Function of Plexin-B Ligands in the Intestinal Epithelium
The gastrointestinal tract is of central importance, due to its role in digestion, nutrient uptake and as a first line of defense against microbial and parasitic food contaminants. The intestine is the longest section, in which these processes take place. Its inner lining, the intestinal epithelium...
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| Format: | Dissertation |
| Sprache: | Englisch |
| Veröffentlicht: |
Philipps-Universität Marburg
2020
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| Online Zugang: | PDF-Volltext |
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| Zusammenfassung: | The gastrointestinal tract is of central importance, due to its role in digestion, nutrient uptake and as a first line of defense against microbial and parasitic food contaminants. The intestine is the longest section, in which these processes take place. Its inner lining, the intestinal epithelium is a complex tissue with highly diverse cell types. The cellular turnover is the fastest in the human body, the entire epithelium completely renews itself every 4 to 7 days. Consequently, intestinal epithelial proliferation and differentiation need to be carefully balanced to maintain homeostasis, a process in which intestinal stem cells play a crucial role. Once disturbed, a plethora of intestinal diseases develop, including colorectal cancers, which account for 10 % of new cancer cases every year. The semaphorin-plexin system consists of a family of ligands, the semaphorins and their corresponding receptors, the plexins. These molecules have been described to play an important role in epithelial homeostasis in other organs and are known to be involved in cancer development. Since plexins B1 and B2 are known to be expressed in the intestine, the expression of their class 4 semaphorin ligands and angiogenin in the intestinal epithelium was systematically analyzed. These experiments revealed the ligands to be expressed in partially overlapping patterns. Next, a bacterial artificial chromosome was constructed to express Cre under the enterocyte-specific Alpi promoter. This construct enabled the generation of a novel Alpi-Cre mouse line for future breeding of enterocyte-specific knockout mice. Studying stem cell function, intestinal crypts were isolated from Plexin B1/B2 knockout mice and analyzed for their ability to form organoids. Organoid formation was reduced, pointing to a defect in stem cell function. To identify the relevant ligands, semaphorin knockout organoids were analyzed in the same manner, but failed to replicate the receptor knockout phenotype. To target multiple ligands simultaneously by inducible RNAi, a lentiviral transduction method was established for future organoid studies. To explore the role of semaphorins in human intestinal physiology and disease, colonic organoids from normal and tumor tissue samples of patients were established. These results precisely lay out the overlapping expression patterns of B-plexin ligands in the intestinal epithelium, highlight their redundancies, and enable further functional studies, including translational research in the human intestinal epithelium. |
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| Umfang: | 161 Seiten |
| DOI: | 10.17192/z2020.0406 |