Identification of Molecular Interactions between Usher Syndrome Type 2 Proteins in the Zebrafish Retina

Abstract

Usher syndrome is the most common cause of hereditary deaf-blindness. Usher type 2A is the most common form of the disease and is caused by mutations in the gene USH2A, which encodes the large multi-domain protein Usherin. Mutations in Usherin are also the most common cause of an inherited form of retinal degeneration called Retinitis Pigmentosa. Other genes associated with Usher type 2 (USH2) include ADGRV1 and WHRN. Physical protein-protein interactions among all three USH2 proteins have been demonstrated in other systems, and the cooperative function of this multi-protein complex is thought to be required for retinal cell function. This study characterizes zebrafish models of USH2 using strains with mutations in ush2a and adgrv1, alone and in combination. In the single ush2a mutant, Whirlin protein localization in the retina is notably defective, providing us with important information regarding what regions of Usherin are most important for maintaining a stable USH2 protein complex. Subsequently, these studies showed that the stability of this complex in the ush2a mutant background fluctuates according to time spent in daylight. This study further explored light-dependent effects on retinal cells and revealed that elevated light levels exacerbate retinal cell death in young fish defective in either ush2a or adgrv1. Collectively, this thesis research has enriched our understanding of the functional roles and relationships of the USH2 proteins Usherin, Adgrv1, and Whirlin and provided new data to direct preventative and therapeutic efforts toward improving clinical outcomes in patients with mutations in USH2 genes.