SIRPα1's regulation of pre-patterned AChR cluster dispersal. R-BTX labeled muscle cells expressing GFP alone (A-C) or GFP and wild-type SIRPα1 (SIRP-FL; D-F) or dominant-negative SIRPα1 (SIRP-TR, G-I) were exposed to HB-GAM beads overnight. In the muscle cell expressing dominant-negative SIRPα1, a large pre-patterned AChR cluster was detected (I; arrow) in addition to the bead-induced clusters, which were present in control and Shp2-expressing cells (C, F, I; asterisks). Results, quantified as described in Fig. 7, revealed that the expression of wild-type SIRPα1 promoted the dispersal of pre-patterned AChR clusters whereas expression of dominant-negative SIRPα1 inhibited dispersal (panel J). GFP-cells, n = 198; SIRP-FL, n = 156; SIRP-TR, n = 169; *p < 0.05 relative to GFP-cells.