Year: 2020
Type: dissertation
Abstract: The role of extracellular signaling pathways and transcription factor cascades have been well studied during organogenesis but microRNAs (miRs) remain poorly investigated, due to their complex genomic arrangement and redundancy. In this dissertation, I begin to fill this gap in knowledge with my examination of the miR-200 family, which was inhibited using a Plasmid based miR Inhibitor System (PMIS) in developing murine embryos. We found that the miR-200 family directly regulated the differentiation of Dental Epithelial Stem Cells (DESCs), which failed to exit the cell cycle when the miR-200 family was inhibited. Two transcription factors, Sox2 and Pitx2, have been shown by our lab and others to both be required for tooth development, and to be direct targets of miR-200c (Sox2) or miR-200a(Pitx2). Upon inhibition of the miR-200 family, these factors were ectopically expressed in expanded regions of the lower incisor. We show that the miR-200c functional group regulates the level of autophagy which occurs at low levels normally in the lower incisor. Inhibition of miR-200c resulted in an increase in autophagy accompanied by epithelial cell death, in a caspase independent manner. The embryonic lethality of the PMIS-miR-200 double inhibitor embryos suggested that the miR-200 family functions in the development of other organs as well. We examined heart and lung development and found defects in progenitor cell differentiation, and an increase in proliferation, in PMIS-miR inhibitor embryos. We noted defects in the expression of proteins required for contractility in the heart, and hyperproliferation of cells in the lung. We found that increased levels of Pitx2 in the heart promoted the expression of other transcription factors, including Gata4, which promoted cardiomyocyte proliferation and prevented differentiation. In the lung, we found a miR-200c-Irx1-Sox9 regulatory loop that promotes the differentiation of distal airway epithelial cells.
DOI: 10.17077/etd.005400
Language: English
Subfield: Cancer Research
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3211793710