Neurexin is expressed on nerves, but not at nerve terminals, in the electric organ.
Neurexins are highly variable transmembrane proteins hypothesized to be nerve terminal-specific cell adhesion molecules. As a test of the hypothesis that neurexin is restricted to the nerve terminal, we examined neurexins in the electric organ of the elasmobranch electric fish. Specific antibodies generated against the intracellular domain of electric fish neurexin were used in immunocytochemical and Western blot analyses of the electromotor neurons that innervate the electric organ. Our results indicate that neurexin is not expressed at electric organ nerve terminals, as expected by the neurexin hypothesis. Instead, neurexin is expressed by electromotor neurons and on myelinated axons. This neurexin has a molecular weight of 140 kDa, consistent with an alpha-neurexin. In addition, we find that perineurial cells of the electromotor nerve also express a neurexin. These cells surround bundles of axons to form a diffusion barrier and are thought to be a special form of fibroblast. The results of the study argue against a universal role for neurexins as nerve terminal-specific proteins but suggest that neurexins are involved in axon-Schwann cell and perineurial cell interactions.
Russell
A B
AB
Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, USA.
Carlson
S S
SS
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D001483:Base Sequence; D002417:Cattle; D017931:DNA Primers; D004555:Electric Fish; D004557:Electric Organ / Q000294:innervation*; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism*; D009411:Nerve Endings / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D016133:Polymerase Chain Reaction; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014101:Torpedo
D000911:Antibodies, Monoclonal; D017931:DNA Primers; D009419:Nerve Tissue Proteins