Investigating emc1 in Photoreceptor Outer Segments and Inherited Retinal Disease using the raf Zebrafish Model

Inherited retinal diseases constitute a rare and heterogeneous group of eye disorders affecting more than four million people worldwide, characterised by progressive dysfunction of the retina and degeneration of retinal cells causing subsequent vision loss. They collectively represent the leading cause of blindness in the working-age population with varying inheritance patterns, clinical phenotypes and ages of onset, and treatment options for patients are limited. The causative factor is one or more pathogenic variants in more than 280 retinal genes with diverse functions in visual perception. In the retina at the back of the eye, the photoreceptor cells (rods and cones) contain outer segments; specialized and modified cilia which are imperative to the visual process of phototransduction. Their importance in vision necessitates their regular renewal to maintain their structural health and function. As a result of disruptions to genes involved in the structure, function or renewal of outer segments, there is progressive dysfunction of photoreceptors causing visual impairment. This thesis aims to phenotypically characterise a novel zebrafish model of inherited blindness, known as the raifteirí (raf) model which was first identified in an N-ethyl-N-nitrosourea mutagenesis screen. Mutant zebrafish harbour a single point mutation in the emc1 gene, the largest subunit of the ubiquitously expressed endoplasmic reticulum membrane protein complex which functions in protein folding and synthesis. This includes crucial retinal proteins which are synthesised and trafficked through photoreceptors for localisation in outer segments to function in vision-associated processes. Previous genetic studies have implicated human EMC1 variants in numerous blindness phenotypes, but there is a need for additional studies employing animal research models to uncover the disease-associated cellular and molecular mechanisms.