Crb1 and Crb2 in Retinal Development - Part 2

Abstract

Purpose: : To assess the effects of Crb1 and Crb2 protein deficiency on retinal morphology and layer integrity as well as retinal function.

Methods: : Crb1-Crb2 double knock-out (DKO) mice were generated as described in part 1, examined functionally and morphologically as presented here, and subsequently underwent histological analysis (part 1). Whereas Crb1 was a full knockout, Crb2 was a conditional knockout line (Crb2-Chx10Cre). The examination of retinal morphology and vasculature was performed with confocal scanning-laser ophthalmoscopy (SLO), and that of retinal layer composition with the Spectralis^TM spectral domain optical coherence tomography (OCT). The functional analysis was done in the same mice with Ganzfeld electroretinography (ERG) under both scotopic and photopic conditions. The data presented here include Crb2 KO mice at the age of 1, 3 and 6 months and respective controls.

Results: : Initially (one month of age), DKO mice had a regular fundus appearance in the SLO, but the retina lacked any structured layers in OCT imaging. At that time point, overall retinal thickness appeared almost normal. With increasing age, a significant decrease of retinal thickness was observed in OCT analysis. This was paralleled in SLO imaging by the appearance of spotty and patchy areas scattered all over the fundus. However, no vascular changes were observed. ERG signals were severely reduced already at one month of age under both scotopic and photopic conditions, indicating that both rod and cone system components were initially affected, and further decreased until at the age of six months no retinal responses were detectable.

Conclusions: : The lack of both CRB1 and CRB2 protein resulted in an absence of ordered retinal layering (see also part 1 for the histological workup) and subsequently a progressive retinal degeneration, demonstrated functionally with electroretinography (ERG) and morphologically with SLO / OCT imaging. The particularly severe phenotype in DKO mice suggests some degree of functional interchangeability between CRB1 and CRB2 in the retina.

Keywords: electroretinography: non-clinical • imaging/image analysis: non-clinical • retina