Tag: Jennifer Phillips

Using Zebrafish Models of Usher Syndrome Type 2A to Investigate Retinal Cell Function and Survival

Presenter: Kimberly Lerner

Mentors: Monte Westerfield and Jennifer Phillips, Biology

Poster: 42

Major: Biology 

Usher syndrome is a hereditary disorder and the main cause of deaf-blindness. Patients diagnosed with Usher syndrome experience hearing loss and progressive blindness due to photoreceptor degeneration. The most common form of Usher syndrome is type 2A, which is caused by mutations in the USH2A gene. Although gene therapies for some forms of Usher syndrome are being actively researched, current gene replacement methods are not feasible for USH2A patients due to the large size of the USH2A gene. Zebrafish orthologues of Usher genes can be used as models of human Usher syndrome, and our research will contribute to the use of zebrafish as a model of USH2A. Three different mutations targeting different regions of the gene will be characterized in this study, with a specific focus on the ush2asa1881 mutant. Usherin forms a complex with other Usher type 2 proteins at the base of the connecting cilium in order to load ciliary cargo on this transport system between the inner and outer segments of the photoreceptor cells. We studied the co-localization of other known Usher proteins in the ush2asa1881 mutant background, to see if a mutant form of Usherin disrupted the normal localization of these other proteins. The accumulation of photoreceptor cell death in the retina over time leads to progressive vision loss in human USH2A patients. It may be difficult to see progressive retinal degeneration occur over the much shorter life span of the zebrafish, and mouse models of Usher syndrome have a mild retinal phenotype compared to the degree of vision loss that human patients experience. We devised a system that would challenge the retina to see if we could accelerate the damage that is normally accumulated over a longer period of time. Our findings will be useful in that we have created a functional zebrafish model of USH2A, and our results provide the foundation for a potential treatment though the protection of the retina.

Examining the Feasibility of Exon Skipping as a Potential Gene Therapy for USH1F Patients

Presenter: Willem Griffiths

Faculty Mentor: Jennifer Phillips, Judy Pierce

Presentation Type: Poster 65

Primary Research Area: Science

Major: Biology

Usher syndrome (USH) is the most frequent cause of hereditary deaf-blindness, accounting for over 50% of the deaf- blind population. USH type 1F, one of the most severe forms of USH, is rare globally, but the Founder effect has made it the most prevalent type of USH in the Ashkenazi Jewish population. USH1F patients have profound congenital deafness and early-onset progressive vision loss due to photoreceptor degeneration. USH1F is caused by mutations in the PCDH15 gene, which encodes a large, multidomain cell adhesion protein. The truncated PCDH15 protein disrupts the organization of stereocilia in the inner ear and leads to dysfunction and eventual death in photoreceptor cells. Due to the size and complex alternative splicing of PCDH15, the straightforward gene-replacement therapies being pursued for other forms of USH are not feasible for this gene. We are testing the feasibility of using an antisense splice-inhibitor to delete Exon 8 from the PCDH15 transcript. Although the resulting protein would be slightly shorter than normal, all downstream functional domains would remain intact, so it is possible that this modified form of PCDH15 would maintain its functional integrity in the absence of Exon 8. Zebrafish mutants with nonsense mutations in the orthologous pcdh15 exon have been generated via targeted mutagenesis using CRISPR/Cas9 gene editing. These loss of function mutants display phenotypes characteristic of human USH1F. The Exon 8 splice-blocking oligonucleotides will be tested on these mutants in order to determine whether the modified pcdh15 protein can rescue the phenotype.