Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Anatomy and Cell Biology

First Advisor

Ryan Thummel

Abstract

Unlike mammals, zebrafish can regenerate all of their retinal neurons through Müller glial cells, which respond to retinal damage by re-entering the cell cycle to create clusters of progenitor cells. The progenitors continue to proliferate as they migrate to the site of damage, where they ultimately differentiate into new retinal neurons. In contrast, Müller glia of the mammalian retina respond to injury with reactive gliosis, which if persistent, can lead to loss of Müller cell function and devastating vision loss. Despite this, multiple lines of evidence suggest that mammalian Müller glial cells possess a latent ability to regenerate retinal neurons. This work examines various the signaling pathways that trigger the Müller glia to re-enter the cell cycle and which molecules are required for retinal progenitors to differentiate into new neurons during adult zebrafish retinal regeneration. First, we show the Tg(nrd:egfp)/alb zebrafish line is expressed in multiple areas of the developing zebrafish. In the adult light damaged retina, Neurod is not expressed in Müller glial cells as they reenter the cell cycle or their immediate progeny, but is expressed in progenitors of regenerating rod photoreceptors as they exit the cell cycle and begin differentiating. Next, we provide evidence that combining two previously described light damage paradigms results in more extensive and consistent across the dorsal and ventral retina, and a more robust proliferation response from Müller glial cells. Further, we show that zebrafish Müller glial cells, like the mammalian retina, posses both regenerative and gliotic potential. Finally, we show that Shh signaling is not required for Müller glial cell entry into the cell cycle, but is required for progenitor cell amplification. Additionally, Shh is required for proper amacrine and ganglion cell differentiation following Ouabain damage. In summary, these experiments will elucidate the molecular requirements at critical stages in retinal regeneration in the zebrafish and reveal targets for advances in sight-saving treatments.

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