Combined Retinal Degeneration and Deafness in the Ush1c216AA Knock-in Mouse

Abstract

Purpose: : Combined deaf-blindness is the hallmark of Usher syndrome. Patients with Usher I suffer retinitis pigmentosa beginning in early adolescence, congenital deafness and vestibular areflexia. Mouse models exist for all of the known Usher I-related genes; however they all lack retinitis pigmentosa. The purpose of this study is to examine the cochlear and retinal phenotypes in our knock-in mouse model containing the human USH1C216G→A mutation (216AA).

Methods: : Cochleae from one month old 216AA and control mice were examined using whole-mount preparation, SEM, and ABRs. Retinal function and structure were analyzed over a one year time course in 216AA and age-matched control mice by scotopic ERG, histology, and immunohistochemistry. Eye cups from 8 and 15 month old 216AA and control mice were light-stressed and photoreceptor apoptotic cell death was measured histologically by TUNEL analysis.

Results: : Disorganized inner and outer hair cell rows and abnormal hair cell bundle morphology were apparent in all regions of the 216AA cochlea at one month and elevated ABRs indicated profound deafness. Mutant a- and b-wave maximum amplitudes were significantly attenuated at all time points tested. Degeneration of rod photoreceptors in mutant retinas was observed between 6.5 and 12 months of age. By one year of age, severely affected central regions of mutant retinas have an outer nuclear layer (ONL) of 4-5 nuclei in thickness compared to 8-9 in wild type controls. Harmonin immunolocalization shows transretinal labeling in wild type adult mice, typical of Müller cell distribution, while mutants show little or no signal. Light-stressed mutant eye cups show 3 times as many TUNEL-positive photoreceptors.

Keywords: retinal degenerations: cell biology • transgenics/knock-outs • retina: distal (photoreceptors, horizontal cells, bipolar cells)