| dc.description.abstract | Tightly regulated gene expression is essential for normal development and maintenance of tissue homeostasis. RNA-binding proteins (RBPs) are essential facilitators of spatiotemporal gene expression control by regulating post-transcriptional activity of target RNAs. Of particular interest to our lab is the RBP Musashi1 (Msi1), which displays aberrant expression in multiple cancer types, including colorectal cancers. Msi1 controls translation, stability, and alternative splicing of developmentally relevant target mRNAs. Previous in-vitro studies in our lab implicated Msi1 in the regulation of intestinal tissue homeostasis. To elucidate functions of Msi1 in the intestinal epithelium, our lab generated a mouse model that allows conditional and inducible Msi1 overexpression. In this dissertation, I report that young mice ubiquitously overexpressing Msi1 (Msi1O/E) had an overall stunted growth phenotype and experienced premature death. These Msi1O/E mice failed to maintain normal organ proportions, with particular organs either too small or too large when compared to control mice. For example, the small intestine tissue of Msi1O/E mice was smaller, whereas the brain was larger. Therefore, my work suggests a potential role of Msi1 in regulating postnatal development of various mouse organs. Focusing on the intestinal tissue, I demonstrate that ubiquitous Msi1O/E mice had decreased proportions of proliferating intestinal epithelial cells (IECs) and reduced growth of small intestine villi and colon crypts. These findings were consistent with the shortened intestinal tissue phenotype. Furthermore, I show that dampened Cdc20 expression could underlie the intestinal growth defects and diminished IEC proliferation. Most importantly, I report novel results showing that Msi1 controls IEC differentiation in a region-specific manner. The ileum sections of Msi1O/E mice displayed more pronounced alterations in IEC differentiation and Notch signaling when compared to the jejunum and colon sections. In addition, I observed enhanced expression of intestinal ion transporters in Msi1O/E mice. These ion transporters regulate movement of ions across the intestinal epithelia and facilitate reabsorption of water into IECs. Taken together, my findings implicate Msi1 in intestinal tissue development, and homeostasis, as well as highlight distinct roles of Msi1 along the intestinal tract. Using an intestine-specific Msi1 overexpressing mouse line (Vil-Msi1O/E), I show that our novel mouse model is a versatile tool that can be utilized to elucidate developmental and pathological functions of Msi1 in any tissue of interest. Notably, the Vil-Msi1O/E mice had a greater longevity than ubiquitous Msi1O/E mice. This finding suggests that the early premature death observed in ubiquitous Msi1O/E mice might be due to contributions from tissues or cell types distinct from intestinal epithelia. Furthermore, the greater longevity of Vil-Msi1O/E mice indicates that this model will be a useful tool in studies which require mice to be viable for a longer time, such as those focusing on tumor formation and screening of new therapeutics. Lastly, Msi1 is an attractive therapeutic target due to its enhanced expression in various cancer types and association with tumor progression. In this dissertation, I tested several small molecule inhibitors of Msi1 in tissue culture and identified three compounds that were effective at pharmacologically-relevant concentrations. | |
