Genetic Hierarchy Underlying Photoreceptor Regeneration

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In most vertebrates, the adult retina is unable to regenerate lost neurons, which results in loss of vision. In contrast, the zebrafish retina possesses the ability to regenerate any class of retinal neurons that are lost due to a variety of insults. For example, constant intense light causes rod and cone photoreceptor death. Photoreceptor regeneration originates from the M¿ller glia that reenter the cell cycle and divide to produce neuronal progenitors, which continue to proliferate and then differentiate into the regenerated neurons. The human retina also possesses M¿ller glia, but fails to regenerate any retinal cell class. We are interested in identifying the processes that regulate retinal regeneration of photoreceptors in the light-damaged zebrafish retina. In this proposal, we will investigate the molecular mechanisms that generate and maintain the neuronal progenitor cell population in an undifferentiated and proliferating state during regeneration, which will identify approaches to induce a full regeneration response in the damaged mammalian retina. This could provide a strategy to restore vision to individuals who suffer from genetic forms of blindness, such as retinitis pigmentosa or macular degeneration. We will explore the roles of the Pax6a, Pax6b, and Olig2 proteins during proliferation of neuronal progenitors in the light-damaged zebrafish retina. We will use a technique that we developed to electroporate antisense morpholinos into the regenerating retina. This technique gives us the powerful ability to conditionally block the translation of specific proteins during regeneration of the light-damaged retina. We will test the hypothesis that the Pax6b protein is required for the initiation of neuronal progenitor cell proliferation, but is not required for the subsequent expression of progenitor cell transcription factors, and ultimately, photoreceptor cell opsins (S. A. 1). We will then determine if Pax6a is required for the continued proliferation of the neuronal progenitors and the transcription of the olig2 gene (S. A. 2). Finally, we will determine if Olig2 is also required for the continued proliferation of the neuronal progenitor cells and, if, in the absence of Olig2, the neuronal progenitors prematurely differentiate into photoreceptors at the expense of M¿ller glial cells (S. A. 3).