Using zebrafish as a model organism, we will study mechanisms by which mechonsensory hair cells and neurons of the inner ear are formed and maintained. Fgf and Wnt signaling pathways cooperate to establish hair cells, and at the same time Fgf and Wnt work in opposition during formation of neurons. How Fgf and Wnt are coordinated to regulate these diverse responses is poorly understood. This will be investigated in three specific aims. 1) We will study how transcription factors Pax2, Pax5, Sp5a, and Sp5l mediate discrete aspects of Fgf and Wnt signaling. We will examine how mutations in these genes alter the response to Fgf and Wnt. We will also will rely on transgenic lines in which these genes can be overexpressed by simply incubating embryos at elevated temperatures. 2) We will explore how Pax2 and Pax5 promote hair cell survival. In embryos lacking Pax2 or Pax5, hair cells initially form but are later extruded from the developing inner ear. We will test the idea that Pax2 and Pax5 are required to maintain cell adhesion molecules that normally hold hair cells in place. This will be tested by treating embryos with drugs that stabilize adhesion complexes, and by using transgenic lines to overexpress cell adhesion molecules to see whether hair cell loss is prevented. 3) We recently discovered a completely novel mechanism by which cells in the developing ear undergo a change in metabolism similar to the ?Warburg Effect? seen in metastatic tumors. Specifically, ear cells upregulate glycolysis and fermentation (despite abundant oxygen) in order to produce and secrete high levels of lactate. Disruption of lactate production impairs production of hair cells and neurons, in part by weakening the response to Fgf. We will further explore how lactate impacts Fgf signaling, and also test whether lactate affects Wnt signaling. In addition, we will test the function of Foxm1, a transcription factor often responsible for activating the Warburg Effect in tumors. Foxm1 also mediates Wnt and Fgf in tumors, so we will investigate how mutations in Foxm1 or misexpressing Foxm1 affects Fgf and Wnt signaling in the ear. Together, these studies will provide fundamental insights into mechanisms of hair cell and neural development. Because developmental mechanisms are broadly conserved, studying how these genes work in zebrafish could suggest candidates for ?gene therapy? to restore hearing in mammals.
Loss of hearing is a common affliction and results from permanent loss of sensory hair cells and/or neurons of the inner ear. It is widely believed that it may be possible to restore hearing in humans using ?gene therapy? to activate genes found to regulate the development or regeneration of sensory hair cells or neurons in other species. Using zebrafish as a model, we are investigating the functions of genes believed to regulate these processes in all vertebrates.
