Dystrophin and the dystrophin-associated glycoprotein, beta-dystroglycan, co-localize in photoreceptor synaptic complexes of the human retina.

Mutations in the gene encoding for dystrophin, a membrane-associated cytoskeletal protein of muscle and several non-muscle cells, are the cause of Duchenne muscular dystrophy and Becker muscular dystrophy. Patients suffering from Duchenne muscular dystrophy have recently been shown to display an abnormal b-wave of the electroretinogram, suggesting that dystrophin is important for normal retinal transmission. In the retina, dystrophin has been localized in the outer plexiform layer where dystrophin co-localizes with postsynaptic markers of photoreceptor synaptic complexes. In the present study we addressed the question of whether two major dystrophin-associated integral membrane proteins of the muscular plasma membrane, beta-dystroglycan and adhalin, are also present in photoreceptor synaptic complexes. By double immunostaining and immunoblotting we show here that beta-dystroglycan is expressed in the human retina where it co-localizes with dystrophin in photoreceptor synaptic complexes most likely on the postsynaptic side. Adhalin was not detected in the retina. Since beta-dystroglycan is a member of a transmembrane supramolecular complex thought to be important for differentiation of the neuromuscular junction, it is an attractive hypothesis that dystroglycan (linked to dystrophin) might also play a similar role in differentiation of the photoreceptor synapse. A further outcome of this study is that beta-dystroglycan is not only present in the neuromuscular junction but also associated with a well-defined synaptic complex of the central nervous system. These findings indicate a more general role of this dystrophin-associated membrane protein in synaptic functions.