The genetic disorder Usher syndrome (USH) causes hearing and visual impairment. Mice have provided biologists with a fantastic model of hearing impairment in USH patients, specifically those with the most severe form of the syndrome, USH1. The five USH1 proteins (myosin VIIa, harmonin, cadherin-23, protocadherin-15, sans) all play a role in the development of the hair bundle, the structure that drives the conversion of sounds into electrical responses in the ear. Mice with USH1 mutations do not, however, experience the same visual degeneration as human USH1 patients. A recent study finds differences in USH1 protein localization in the photoreceptors of different animal models. Sahly and colleagues found that the photoreceptors of macaques (monkeys) show localization of all USH1 proteins at membrane interfaces, while photoreceptors in mice lack any USH1 network proteins. Sahly and colleagues suggest that the USH1 network found in humans and other primates forms an adhesion belt around the basolateral region of photoreceptors, and this structure may be the key to understanding the visual impairment experienced by USH1 patients. In the images above of macaque retina photoreceptors, the USH1 network protein protocadherin-15 (green) is localized at the junction between the inner (IS) and outer segments (OS) of rods and cones.
Sahly, I., Dufour, E., Schietroma, C., Michel, V., Bahloul, A., Perfettini, I., Pepermans, E., Estivalet, A., Carette, D., Aghaie, A., Ebermann, I., Lelli, A., Iribarne, M., Hardelin, J., Weil, D., Sahel, J., El-Amraoui, A., & Petit, C. (2012). Localization of Usher 1 proteins to the photoreceptor calyceal processes, which are absent from mice originally published in the Journal of Cell Biology, 199 (2), 381-399 DOI: 10.1083/jcb.201202012
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