Date Available

12-11-2015

Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Biology

First Advisor

Dr. Ann C. Morris

Abstract

Proper visual system function requires tightly controlled proliferation of a pool of relatively homogeneous retinal progenitor cells, followed by the stepwise specification and differentiation of multiple distinct cell types. These retinal cells, both neuronal and glial, must be generated in the correct numbers, and the correct laminar location to permit the formation of synaptic connections between individual cell types. After synapses are made, constant signaling is required as part of normal retinal function, and to maintain cellular identity and connectivity. These processes rely on both extrinsic and intrinsic signaling, with regulation of gene expression by cascades of transcription factors having a key role. While considerable work has been done to identify key regulators of retinal development, maturation, and homeostasis, many factors remain unidentified or poorly characterized, either at large or within the retina.

One such factor is Insulinoma-associated 1 (Insm1). Known to function in endocrine cell, sympathetic and monoaminergic neuron, and olfactory epithelial cell differentiation and maturation, Insm1 is also a regulator of cell cycle progression in the adrenal system and cerebral cortex. Although Insm1 was previously considered a transcriptional regulator, recently, non-nuclear functions have also been identified. However, the retinal function of Insm1 remained a mystery. To determine the role of Insm1 in retinal development, I characterized the retinal expression pattern of Insm1, as well as the effect of perturbation of Insm1 expression levels at both the cellular and molecular level. Chapter 1 of this dissertation provides an overview of the retina and its development, vision and retinal degenerative diseases, and a review of Insm1 expression and function in tissues outside the retina. Chapter 2 presents data generated from the knockdown of the retinal-expressed zebrafish co-ortholog of Insm1, insm1a, which demonstrated a requirement for insm1a in proper differentiation of photoreceptor cells. Additionally, these experiments showed a cell cycle regulatory function for insm1a in retinal development. Characterization of a zebrafish insm1a mutant and functional examination of insm1a truncation variants is discussed in Chapter 3. Chapter 4 presents data from an RNA-Seq analysis of wild-type and Insm1 knockout mouse retinas at two developmental time points, and details transcriptional changes during retinal development in the absence of Insm1. Finally, Chapter 5 discusses the conclusions from the data generated for this dissertation, additional studies identified as the result of this work, and the implications of these results on our understanding of retinal development.

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