Molecular Mechanisms of Zebrafish Photoreceptor Regeneration.

Abstract

Unlike mammals, which have only limited capabilities to replace damaged tissues and organs, teleost fishes, such as zebrafish, are highly regenerative. Adult zebrafish can regenerate retinal neurons following damage and thereby restore visual function. The objective of this dissertation research was to investigate the molecular basis of zebrafish photoreceptor regeneration by using a diverse range of genetic techniques. Since regeneration of retinal neurons in adult zebrafish depends on the activation of retinal stem cells, which are the Müller glial cells, I first generated gene expression profiles of isolated Müller glia during the early stages of zebrafish photoreceptor regeneration. Two of the genes up-regulated in injury-activated Müller glia were previously identified as essential factors for fin and heart regeneration. I showed that these genes are also required for retinal regeneration, suggesting that a common molecular program triggers regeneration of diverse tissues in zebrafish. Another gene up-regulated in injury-activated Müller glia, six3b, is one of three zebrafish six3-related homeobox transcription factors, which are required for forebrain and eye development in all vertebrates studied. Expression patterns of six3b during the early stages of zebrafish photoreceptor regeneration as shown by qRT-PCR and in situ hybridization suggested that it might also play a central role in reprogramming Müller glia to regenerate retinal neurons. In addition, by using a candidate gene approach, I tested the role of Fgf signaling during zebrafish photoreceptor regeneration. Together, these studies have advanced our understanding of the molecular mechanisms that activate a retinal stem cell program in mature glial cells, resulting in regeneration of photoreceptor neurons in the adult zebrafish retina.