-syntrophin Is Expressed in Horizontal Cells but Is Not Part of the Photoreceptor Dystrophin Glycoprotein Complex in the Mouse Retina

Abstract

Purpose:: In the mouse retina, at least three isoforms of dystrophins (Dp427, Dp260 and Dp140) are expressed in the triadic synapse between photoreceptors, bipolar and horizontal cells. However, their function remains unknown, despite the fact that the electroretinogram b-wave amplitude is strongly reduced in the dystrophins deficient mice (mdx^3cv). To gain insight in the origin of the b-wave reduction, we verified the sub-cellular localization of classical constituents of the dystrophin-associated protein (DAPs) complex, α-syntrophin and dystrobrevins in wild-type (WT) and mdx^3cv mice retinas.

Methods:: The localizations of α-syntrophins and dystrobrevins were determined in the outer retina of wild-type C57BL/6J and mdx^3cv mice by double immunohistochemistry with either a pan-dystrophin or a calbindin antibody followed by confocal microscopy observation.

Results:: We found that α-syntrophin, thought to be expressed in photoreceptor terminals with dystrophins, is in fact expressed in the processes of horizontal cells that enter cone and rod terminals, and that its localization is unchanged in the mdx^3cv retina, in opposition to dystrobrevin, which co-localize with dystrophins in the photoreceptor terminals and is mis-localized in the mdx^3cv retina.

Conclusions:: Our results indicate that the composition of the DAPs complex in the outer retina differs from the one found in muscle. The eventual involvement of another syntrophin should be tested.

Keywords: horizontal cells • in situ hybridization • immunohistochemistry