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Camille Inez Prejean, Katelyn N Robillard, Marianne Hathaway, Jennifer J Lentz; Harmonin expression in the retina of rodents and nonhuman primates over time. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1265.
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© ARVO (1962-2015); The Authors (2016-present)
Usher syndrome Type 1C (USH1C) is a deaf-blinding disease caused by mutations in the USH1C gene, which encodes harmonin. The function of harmonin in the retina and the cause of retinitis pigmentosa (RP) following its mutation remain unclear. The goal of this study was to characterize Ush1c transcript and harmonin protein expression in rodents (both wild type and USH1C mutants) and nonhuman primates (NHP) over time. Previous studies have localized harmonin to photoreceptor segments (IS/OS) and ribbon synapses (OPL) in wild type mice. We hypothesized that harmonin is also expressed in the photoreceptors of rhesus macaques (Macaca mulatta). Furthermore, we predicted abnormal Ush1c expression and localization in the retinas of USH1C mice compared to wild type controls.
Ush1c transcript and harmonin protein expression were analyzed in retinal tissues at three different ages in mice and NHP that correlate to infancy (P0-21; 0-12mo), juvenile (P21-35; 1-3yr), and adulthood (P90-180; >8yr), respectively. Ush1c transcript expression in the retina was quantified in wild type and mutant mice up to 1 year of age using Next Generation Sequencing (NGS) RNA-Seq. Immunohistochemistry (IHC) was performed on both longitudinal sections and whole-mounts to determine patterns of harmonin expression across ages and between genotypes. The same assays were repeated for wild type rhesus macaque eyes obtained from the Tulane National Primate Research Center.
NGS RNA-Seq showed increasing abundance of total (full-length + truncated) Ush1c transcripts in mutant retinas over time, compared to wild type retinas with stable Ush1c expression (full-length only). Interestingly, IHC localized harmonin protein to synaptic layers of the mouse retina (OPL, IPL, GCL axons) at all ages tested, which did not support the original hypothesis. In NHP, IHC localized harmonin to photoreceptor segments (IS/OS) at all ages tested, which correlated with previous staining in mice.
This study successfully detected Ush1c and harmonin expression in both rodents and NHP at three distinct age groups. Our data reveal differences in harmonin expression between mice and rhesus macaques that will (1) improve our understanding of the pathophysiology of RP and (2) aid in the development of therapeutics for vision loss in Usher syndrome.
This is a 2020 ARVO Annual Meeting abstract.
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