Identification of a beta-dystroglycan immunoreactive subcompartment in photoreceptor terminals.
OBJECTIVE
Mutations in the dystrophin-associated glycoprotein complex (DGC) cause various forms of muscular dystrophy. These diseases are characterized by progressive loss of skeletal muscle tissue and by dysfunctions in the central nervous system (CNS). The CNS deficits include an altered electroretinogram, caused by an impaired synaptic transmission between photoreceptors and their postsynaptic target cells in the outer plexiform layer (OPL). The DGC is concentrated in the OPL but its exact distribution is controversial. Therefore, the precise distribution of beta-dystroglycan, the central component of the DGC, within the OPL of the mature chick retina, was determined.


METHODS
Double immunolabeling with antibodies against beta-dystroglycan and against Bassoon, a component of the presynaptic cytomatrix, concentrated at the insertion point of the synaptic ribbon into the active zone of the photoreceptor synapses, showed a nonoverlapping distribution of both proteins within individual rod and cone photoreceptor terminals. The three-dimensional distribution of the DGC within the photoreceptor terminals was determined by reconstruction of the beta-dystroglycan immunoreactivity from serial electron microscopic sections.


RESULTS
We found that beta-dystroglycan was not directly associated with the ribbon synapse but instead concentrated perisynaptically in processes extending from the photoreceptors into the OPL. The processes displayed dystroglycan immunoreactivity primarily along their lateral sides and at their tips. Processes from bipolar or horizontal cells were not labeled.


CONCLUSIONS
The perisynaptic concentration of beta-dystroglycan in photoreceptor terminals suggests a novel domain within photoreceptor terminals with functions in synaptic transmission.
Jastrow
Holger
H
Department of Anatomy and Cell Biology, University of Mainz, Mainz, Germany.
Koulen
Peter
P
Altrock
Wilko D
WD
Kröger
Stephan
S
D000818:Animals; D002451:Cell Compartmentation / Q000502:physiology; D002645:Chickens; D049030:Dystroglycans / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000378:metabolism; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D051245:Retinal Bipolar Cells / Q000378:metabolism; D051248:Retinal Horizontal Cells / Q000378:metabolism
D009419:Nerve Tissue Proteins; D049030:Dystroglycans