Dystroglycan distribution in adult mouse brain: a light and electron microscopy study

Dystroglycan, originally identified in muscle as a component of the dystrophin-associated glycoprotein complex, is a ubiquitously expressed cell-surface receptor that forms a transmembrane link between the extracellular matrix and the cytoskeleton. It contains two subunits, alpha and beta, formed by proteolytic cleavage of a common precursor. In the brain, different neuronal subtypes and glial cells may express dystroglycan in complex with distinct cytoplasmic proteins such as dystrophin, utrophin and their truncated forms. To examine the distribution of dystroglycan in adult mouse brain, we raised antibodies against the recombinant amino- and carboxyl-terminal domains of alpha-dystroglycan. On western blot, the antibodies recognized specifically alpha-dystroglycan in cerebellar extracts. Using light microscopy, alpha-dystroglycan was found in neurons of the cerebral cortex, hippocampus, olfactory bulb, basal ganglia, thalamus, hypothalamus, brainstem and cerebellum, where dystrophin and its truncated isoforms are also known to be present. Electron microscopy revealed that alpha-dystroglycan immunoreactivity was preferentially associated with the postsynaptic specializations. Dystroglycan immunostaining was also detected in perivascular astrocytes and in those facing the pia mater, where utrophin and dystrophin truncated isoforms are present. The cell body and endfeet of astrocytes around blood vessels and the endothelial cells at the blood-brain barrier also expressed dystroglycan. From these data, we suggest that dystroglycan, by bridging the extracellular matrix and the cytoskeleton, may play an important functional role at specialized intercellular contacts, synapses and the blood-brain barrier, whose structural and functional organization strictly depend on the integrity of the extracellular matrix-cytoskeleton linkage.