Molecular Mechanisms Mediating Morphogenesis of the Basal Epithelial Tissue Fold During Midbrain-hindbrain Boundary Formation in Zebrafish

Abstract

ABSTRACT MOLECULAR MECHANISMS MEDIATING MORPHOGENESIS OF THE BASAL EPITHELIAL TISSUE FOLD DURING MIDBRAIN-HINDBRAIN BOUNDARY FORMATION IN ZEBRAFISH by Mike Roger Visetsouk The University of Wisconsin-Milwaukee, 2019 Under the Supervision of Jennifer H. Gutzman, PhD The formation of a fully functional organism requires the morphogenesis of cell and tissue structures during development. It is important to understand the mechanisms that mediate morphogenesis, since cell and tissue structures are crucial to physiological function. Here, we studied basal epithelial tissue folding as a model to determine the mechanisms of morphogenesis. We investigated a highly conserved basal tissue fold known as the midbrain-hindbrain boundary (MHB) using zebrafish. MHB formation relies on cell shape changes in a single-cell layered epithelial structure called the neural tube. The molecular mechanisms that mediate cell shaping during basal tissue folding are not well understood. Our studies revealed that calcium and Wnt5b, known morphogens in development, mediate MHB tissue folding. We found that calcium, via Calmodulin 1a, regulates cell length at the deepest point of the MHB fold through myosin light chain kinase and actomyosin. Furthermore, we demonstrated that cells at the deepest MHB fold point decrease in cell width and increase in cell depth, generating anisotropic cell shape. Wnt5b modulates this MHB anisotropic cell shape. However, basally at the MHB, Wnt5b regulates microtubule stability, potentially through JNK, to mediate anisotropic cell shape. Together, these studies are important for the future development of preventative and therapeutic approaches to structural birth defects and for the future of tissue engineering in regenerative medicine.