Book Description

Epithelial-to-mesenchymal transition (EMT) is a highly conserved cellular process through which polarized and stationary epithelial cells become highly motile mesenchymal cells. EMT is an essential cellular process during embryogenesis, such as mesoderm induction, and more recently has been shown to be an important step in cancer metastasis. In both cases, epithelial cells must break away from neighboring cells and migrate to a distant location. Even though EMT has an important role in development and pathogenesis, the molecular machinery that drives EMT in mesoderm development and cancer metastasis is far from being fully understood. Therefore, for my dissertation, I sought to characterize the mechanism of EMT in both processes to gain a better understanding of cell migration and morphogenesis. Twist is a known inducer of EMT and tumor invasion and metastasis. To understand how Twist regulates target gene expression, we applied chromatin immuno-precipitation coupled with high-throughput sequencing to characterize its genome-wide DNA binding patterns. Using this approach, we found that through cooperative binding, Twist recognizes an evolutionarily conserved double E-box motif to regulate transcription of target genes. Furthermore, we show that the highly conserved WR domain of Twist mediates the high affinity cooperative binding of Twist to the double E-box motif. Functionally, the WR domain is essential for the ability of Twist to promote EMT. To characterize EMT in mammalian mesoderm formation, we utilized the in vitro embryoid body model system that forms all three germ layers during differentiation. After establishing the embryoid body system as an effective ex vivo model to study mesoderm formation, I first characterized the expression profile of known EMT-inducing transcription factors during mesoderm development. By knocking down individual genes using shRNA, I identified several EMT transcription factors to be essential for mesoderm formation and began to elucidate how a group of EMT-inducing transcription factors function together to orchestrate mesoderm formation. By studying the molecular mechanism of EMT in development and cancer metastasis, we have gained a better understanding of EMT as an essential cellular process and as a possible therapeutic target to inhibit cancer progression.