Figure 2.

GFP enables vital imaging of synaptic glia at the NMJ and provides evidence of their stability. A-F, Images of the same NMJ in the sternomastoid muscle of a living Kosmos transgenic mouse obtained 30 d apart. A-C, Junction at first view. D-F, Same junction reimaged 30 d later. A, D, AChRs labeled with a nonblocking concentration of rhodamine-bungarotoxin (BTX). B, E, Schwann cells viewed by their GFP fluorescence. C, F, Merged images with receptors pseudocolored red and Schwann cells green. Schwann cells wrapping the nerve entering the junction can be identified (B, E, asterisks). This junction grew somewhat in size between viewings, but the geometry of its receptors and TSCs remained remarkably constant. The Schwann cells did not change the location of their cell bodies, except for the topmost Schwann cell (B, E, arrow), which moved to occupy a position further back along the top preterminal branch entering the junction. A small portion of the receptor area near the site of nerve entry was lost between the two views (A, C, D, F, arrowheads). G, H, Images of a single NMJ in the soleus of the Kosmos line. Despite their overall stability, TSCs extend and retract short processes. Processes present on the first day (G, arrowhead) that are extended beyond the AChRs (data not shown) were absent when a second image was collected 3 d later (H). Scale bar: A-F, 30 μm; G, H, 20 μm.