An investigation of the molecular mechanisms regulating zebrafish hindbrain morphogenesis

The central aim of my thesis research was to advance our understanding of hindbrain morphogenesis, more specifically hindbrain ventricle formation, cerebellar development and neuronal migration.;The embryonic brain begins as a simple tube, the lumen of which forms the brain ventricles, a highly conserved system of cavities with important functions. The first part of my thesis describes my work focused on investigating the roles of zebrafish Zic1 and Zic4 in dorsal neural tube development. I hypothesized that Zic1 and Zic4 proteins function in hindbrain ventricle formation. Using morpholino knockdown and a battery of molecular markers I provide evidence that zebrafish Zic1 and Zic4 function cooperatively to promote normal hindbrain ventricle morphogenesis. Based on morphological and molecular characterization, I showed that in Zic1 and/or Zic4 morphants the ventricle does not open properly due in part to a reduction in dorsal hindbrain progenitor cell proliferation and I determined that Zic1 and Zic4 function is required for the development of the dorsal roof plate and dorsal rhombomere boundary signaling centers. I showed that roof plate formation and patterning from rhombomere boundaries are critical components of ventricle development. My findings suggest that fundamental Zic functions are likely conserved throughout vertebrates, and aspects of zebrafish Zic1 and Zic4 gene function may inform future studies of DWM.;In the second part of my thesis I explored the molecular mechanisms underlying early cerebellum development in zebrafish by addressing the role of the cMet signaling in this process. In mouse, cMet signaling has been shown to regulate cerebellum development. Interestingly, abnormalities in cerebellar structure have been reported in some autistic patients, and altered regulation of human cMET expression has been implicated in autism. I showed that zebrafish cmet is expressed in the cerebellar primordium and the hgf ligand genes expressed in surrounding tissues. Morpholino knockdown of either cMet or its Hgf ligands leads to reduction of the cerebellum, as a consequence of reduced proliferation, disrupted cell-type specification of VZ progenitors and thus differentiation of VZ-derived cell types, and impaired granule cell development. I provide further evidence that cMet signaling regulates the migration of a subpopulation of hindbrain neurons.