Semester

Fall

Date of Graduation

2019

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Biochemistry

Committee Chair

Visvanathan Ramamurthy

Committee Member

Ronald Gross

Committee Member

John Hollander

Committee Member

Maxim Sokolov

Committee Member

Peter Stoilov

Abstract

RNA binding proteins (RBPs) have emerged as important regulators of gene expression. RBPs typically contain RNA binding domains that recognize a specific sequence and/or structural motifs within the RNA. This allows them to modulate metabolism of RNAs in several possible ways including regulation of alternative splicing and processing, polyadenylation, translocation, localization, modification, stability, or translation. Previous studies have shown the Musashi (MSI) RBP family to be highly expressed in the retina, and more specifically, photoreceptors, but the importance of this expression remains largely unknown. We identified the MSI proteins as potential regulators of alternative exon splicing in murine photoreceptors. We hypothesized that the MSI proteins are essential splicing factors needed to produce photoreceptor-specific transcripts and that inactivation of the Msi genes would lead to decreased photoreceptor function and survival subsequent to aberrant splicing. We also predicted that the MSI proteins were regulating splicing of transcripts involved in ciliogenesis and outer segment morphogenesis.

To test our hypothesis, I generated Cre-LoxP conditional knockout mice to inactivate the Msi genes either in the entire retina and ventral forebrain or specifically rod photoreceptors. I found that both rod and cone photoreceptor function was completely absent after pan-retinal inactivation of both Msi genes. I also discovered alterations in retinal progenitor cell proliferation and decreased retinal cell survival at later ages in the absence of the MSI proteins. When analyzing the morphology of the outer segment and connecting cilium in the absence of MSI, I found defects only in outer segment morphology. Furthermore, I found that the MSI proteins regulate the photoreceptor-specific splicing of several outer segment and cilia-related transcripts including Bbs8, Cc2d2a, Cep290, and Prom1. Lastly, we found that deletion of these photoreceptor-specific exons in C57BL6/J mice did not significantly affect photoreceptor function.

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