Elucidating the role of DNA methyltransferases in epigenetic regulation of retinal regeneration in zebrafish

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Project Abstract According to the National Eye Institute, there are currently over 12 million Americans suffering from diseases affecting the retina. To present, therapeutic attempts to reduce retinal death or replace lost neurons have been met with limited success, highlighting the need for an alternative approach to this problem. The zebrafish is becoming an increasingly popular model to study mechanisms of stem-cell based tissue regeneration. In response to extensive retinal injury, zebrafish are able to completely regenerate the retina. This is accomplished through the induction of Müller glial cells which undergo an asymmetric division to generate a pool of progenitor cells that go on to regenerate all cell types of the retina with no evidence of the glial scarring observed in mammalian species. While the remarkable capacity of the zebrafish to regenerate tissues has been known for years, our understanding of the comparative biology between mammalian and teleost responses to retinal damage remains poorly understood. To present, studies of retinal regeneration in the zebrafish have largely focused on identifying signaling pathways and individual genes involved in retinal regeneration. The epigenetic orchestration of these pathways, however, remains to be investigated in the zebrafish. DNA methyltransferases (Dnmts) have been studied extensively in mammals and have been identified as critical in the homeostatic maintenance of adult stem cell processes such as hematopoietic stem cell development. The limited literature of epigenetic regulators in zebrafish reveals that teleost species appear to utilize the same mechanisms of epigenetic regulation as mammalian species, with zebrafish Dnmts baring considerable sequence homology to mammalian Dnmts. It is known that immediately following retinal injury in the zebrafish there is an initial global DNA hypomethylation and subsequent increase in DNA methylation as the pools of progenitor cells begin to differentiate, indicating the importance of the epigenetic landscape during these processes. With the experiments planned in this proposal, we aim to identify the role of Dnmts in orchestrating the process of adult retinal regeneration in the zebrafish, with the goal of elucidating pathways regulated in Müller glial derived progenitor cells at the epigenetic level. We also plan to develop a new tool that will be an important addition to the zebrafish community for investigation of the consequences of targeted epigenetic modulation of specific genes. These proposed studies will illuminate candidate genes for targeted therapeutic approaches to identify and “unlock” pathways in mammalian systems that are epigenetically silenced, opening new avenues for future studies in the field of regenerative medicine.