PhD Exit Seminar for Amanda Miles (Tropepe Lab)

The Role of dmbx1 and pcdh15 in Zebrafish Retinal Development and Disease

Abstract

The retina is a thin neural tissue found at the back of the eye that is organized into layers of multiple retinal cells, including photoreceptors, which are responsible for vision. Improper development or maintenance of retinal cells are responsible for many retinal dystrophies. Precise development of the retina requires (1) the coordinated expression of many genetic regulatory networks to promote the proper differentiation of each retinal cell type from multipotent retinal progenitor cells (RPCs), and (2) adaptation of structural features to elaborate unique cell morphologies necessary for their function. Degeneration of photoreceptors can lead to diseases like Retinitis Pigmentosa (RP) which causes blindness, and Usher syndrome (USH) which causes deaf-blindness. In this thesis, I explore two genes that exemplify gene regulatory and structural stability processes including the homeobox transcription factor, dmbx1, and putative adhesion molecule and USH gene, pcdh15, in the retina.

Using CRISPR genome editing technology, I created the first and currently only described zebrafish mutants for the paralogs dmbx1a/b and pcdh15b that display retinopathic features. Despite previous accounts that suggest dmbx1 is required for RPC cell cycle exit, I find that although there are some early defects in RPC proliferation and cell death, the retina initially forms normally in the mutant context. However, specifically in dmbx1a mutants, I find novel phenotypes showing greater amounts of retinal cell death, failure of post-embryonic retinal growth, and the progressive development of dystrophic photoreceptors. RNA-seq analysis indicates that these phenotypes can be attributed to dysregulation of a small subset of genes associated with retinal disease and ciliogenesis.

Although reports of pcdh15 mice mutants fail to mimic retinopathy, I show that zebrafish pcdh15b mutants, generated in this thesis, display defects in the outer segment (OS) regions of photoreceptors, and the synapse. Zebrafish pcdh15b mutants show abnormal photoreceptor integrity, including detachment of OS from the cell body, and abnormal growth of OS disks, which are both exacerbated under bright light conditions, as well as disorganization of synaptic elements. Furthermore, the current model of USH-associated retinal disease suggests that USH is a degenerative issue, however, the detection of these defects in early developing photoreceptor cells indicates a progressive developmental pathology. Together, my work highlights new finding of these genes using zebrafish models, and the importance of establishing proper transcriptional gene networks, as well as maintaining structural molecules in the prevention of retinal dystrophies.

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Join Zoom Meeting

Friday, December 17^th, 2021 @ 2:10pm

https://utoronto.zoom.us/j/83033239558

Meeting ID: 830 3323 9558

Host: Vince Tropepe (v.tropepe@utoronto.ca)

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