An exploration of functional domains in the zebrafish ortholog of human Usher syndrome gene USH2A

Abstract

Usher syndrome is the most prevalent cause of hereditary deafblindness. Usher type 2A is the most widespread form of the syndrome, caused by mutations in the USH2A gene. USH2A patients experience congenital hearing impairment due to defects in the mechanosensory hair cells of the inner ear and progressive retinal degeneration. USH2A consists of 72 exons encoding the protein Usherin. Several functional domains have been identified and human mutations causing Usher Syndrome have been located in multiple regions of the protein. Determining the relative importance of these functional domains is crucial to the development of effective therapies.We designed morpholino oligonucleotides to interfere with pre‐mRNA splicing at the 5′ and 3′ regions of the transcript. Protein levels in sensory cells were visualized with antibody staining. Both morpholinos achieved a similar degree of Usherin depletion, suggesting that altered splicing at either the 5′ or 3′ region can impact Usherin production or stability. We noted circle‐swimming and failure to inflate the swim bladder in morphant larvae, both common phenotypes indicating hair cell defects. Because of the retinal degeneration seen in human Usher syndrome, we analyzed retinal cells in morphants and saw significant increases in photoreceptor death. These results will enable further functional analyses of zebrafish Usher proteins.