Aggregates of acetylcholine receptors are not observed under anti-agrin staining Schwann cell processes at the frog neuromuscular junction
✍ Scribed by Werle, Michael J. ;Jones, Melissa A. ;Stanco, Anne M.
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 196 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0022-3034
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✦ Synopsis
The frog neuromuscular junction offers a unique structure in which to observe fine details in the relationship between the motor neuron, muscle, and Schwann cell, which together comprise the neuromuscular junction. Schwann cell processes that extended from the synapse stained positively with anti-agrin antibodies. Immunocytochemistry revealed strong antiagrin staining of the extracellular matrix surrounding the entire Schwann cell and the Schwann cell processes come in close contact with the muscle fiber. Dual-labeling experiments revealed a lack of acetylcholine receptor (AChR) aggregates on the surface of the muscle fiber directly under these anti-agrin-staining Schwann cell processes. The cDNA that codes for the C-terminal portion of agrin in frog (Rana pipiens) was cloned and sequenced. Polymerase chain reaction of frog brain, nerve, and muscle cDNA revealed that like other species, agrin transcripts that contain the B 8 , B 11 , or B 19 inserts were observed only in brain tissue. Unlike other species, the exact site of the B inserts in frog was slightly altered, with the B insertion site occurring within a codon sequence. Our data are consistent with the hypothesis that Schwann cells produce agrin which lacks inserts at the B region, and that agrin lacking B inserts does not direct the aggregation of AChRs in vivo under physiological conditions and concentrations.