Identification and validation of proteins with Siah-degron-motifs that are essential for neuronal migration.
Final Report Abstract
During my time in the lab of Dr. David Solecki at the St. Jude Children’s Research Hospital I worked on the principle mechanisms of oxygen tension and homeostasis during the development of the cerebellum. I was able to show that especially the neurgenic niche in the cerebellum is highly hypoxic and hypoxia abates in later stages of the development. This relief of hypoxia is accompanied with the development of an elaborated blood vessel system. Hypoxia is predominantly sensed and transmitted to a physiological response through the transcriptional regulator hypoxia-inducible factor (Hif). In vivo gain and loss of function experiments of Hif1 showed that Hif1 and thereby oxygen tension tunes neuron precursor generation. Moreover, through organotypic cerebellar ex vivo slices I could demonstrate that appropriate oxygen concentrations also regulate germinal zone exit and migration of postmitotic cerebellar granule neurons (CGN). While overexpression of Hif1 in CGN in cerebellar slice cultures showed a similar phenotype, deleting of Hif1 rescued the hypoxia-induced migration deficiency indicating that elevated Hif1 levels transmit the hypoxic signal in CGNs and trigger transcriptional events that lead to the observed migration deficiency. A transcriptomic screen in Hif1-overexpressing CGN revealed the transcriptional repressor Zeb1 as a major candidate that mediates the inhibition of germinal zone exit and migration. Consequently, downregulation of Zeb1 restored germinal zone exit and migration in hypoxia or in CGN that overexpress Hif1. Additionally, overexpression of Par3, Par6 and Chl1, polarity and adhesion proteins that are downregulated by Zeb1, restored germinal zone exit and migration in hypoxia or in Hif1-overexpressing CGNs. In total, my results show that hypoxia is a major determinant of the cerebellar development and needs to be tightly controlled. Changes in oxygen tension influence neuron precursor generation and reduced oxygen availability lead to impaired germinal zone exit and migration mediated by an upregulation of the Hif1-Zeb1 axis of transcription factors.
