Electrophysiological and Morphological Characterization of a Mouse Model of Muscle-Eye-Brain Disease Generated by Targeting Disruption of POMGnT1

Abstract

Purpose: : POMGnT1 is an enzyme that transfers N-acetylglucosamine to O-mannose of glycoproteins. Alpha-dystroglycan is a substrate of POMGnT1 and is concentrated in the outer plexiform layer (OPL), around blood vessels, and at the inner limiting membrane (ILM) of the retina. Mutations of the POMGnT1 gene cause muscle-eye-brain (MEB) disease. Several ocular abnormalities including retinal dysplasia and retinal detachment were reported in patients with MEB. We have analyzed the eyes of POMGnT1-deficient mice to study the mechanism of retinal abnormalities caused in patients with MEB.

Methods: : We analyzed eyes of POMGnT1-deficient mice generated by standard gene targeting technique. Morphology of the mutant mice was evaluated by light and electron microscopy. Immunohistochmical analysis was conducted using antibodies against dystrophin-associated glycoproteins (DAG). Fundus camera was used to record the change in the retina of the mutant mice. ERG analysis was performed on adult mutant mice.

Results: : The ILM of the mutant mice was disrupted with ectopic cells in the vitreous. Focal retinal detachment was also found by light microscopy. Abnormal synaptic ribbon was found in the OPL of the mutant mice by electron microscopy. A monoclonal antibody that reacts with the sugar moiety of alpha-dystroglycan gave no signal in either OPL or ILM of the mutant mice. Fundus photography showed sheathing of retinal vessels and ectopic fibrous tissues around optic nerve. ERG analysis showed decreased amplitude of the a- and b-wave and prolonged implicit time of the b-wave of the mutant mice.

Conclusions: : POMGnT1-deficient mice showed disorganization of the OPL, the ILM and the perivascular sheaths where alpha-dystroglycan is concentrated. Abnormal ERGs recorded from the mutant mice may be associated with both disorganization of the OPL and focal retinal detachment caused by fibrous change in the ILM and the perivascular sheaths. Similar mechanisms may cause the retinal changes in human MEB.

Keywords: genetics • retinal detachment • immunohistochemistry