Dissertations, Theses, and Capstone Projects

Date of Degree

9-2021

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Mark Emerson

Committee Members

Andreas H. Kottmann

Mark Pezzano

Nathalia Glickman Holtzman

Jane Johnson

Subject Categories

Developmental Biology | Genetics | Molecular and Cellular Neuroscience

Keywords

retinal development, cone photoreceptors, Notch signaling, cell fate determination

Abstract

In the vertebrate retina, cone photoreceptors are crucial for high acuity color vision. Several retinal diseases lead to loss of cones and there is a need to identify the normal developmental genesis of these cells to inform the development of stem cell-based therapies. Cone genesis has previously been shown to be repressed by Notch signaling, however, the mechanism by which Notch signaling controls cone fate determination is still unclear. It has been identified that cone photoreceptors are formed from multipotent retinal progenitor cells (RPCs) that first generate genetically-defined, restricted RPCs with limited mitotic and fate potential to preferentially form cones and horizontal cells. We used cell type specific inhibition of Notch signaling to localize the primary role of Notch signaling in the formation of cone restricted retinal progenitor cells from multipotent retinal progenitor cells. Our data supports a model in which Notch signaling regulates the formation of restricted RPCs from multipotent RPCs and is not involved in later steps of cone formation. We also determined that cell cycle promotion is not a primary effect of Notch signaling but an indirect effect of progenitor cell state transitions that leads to depletion of the multipotent progenitor cell population. This project aims to elucidate the mechanisms by which the Notch signaling pathway regulates the formation of cone photoreceptors during retinal development.

Our study has identified the step that Notch functions to repress cone formation: the transition from multipotent RPCs to restricted RPCs. We also tested effects of non-canonical Notch inactivation mediated by Deltex4 on cone development using dominant negative and CRISPR knockout strategies. We are interested in Deltex4 because a transcriptome analysis identified Deltex4 as highly enriched in multipotent RPCs as compared to restricted RPCs. We tested whether Deltex4 expression in multipotent RPCs activates Notch signaling independent of ligand-binding and represses the formation of restricted RPCs. Overall, this project suggests that the role of Notch signaling in cone photoreceptor formation and proliferation are both mediated by a localized function of Notch in multipotent RPCs to repress the formation of restricted progenitor cells and provides preliminary information of molecular changes during different time points in retinal development.

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