Effects of over-expression of wild-type or constitutively active Shp2 on pre-patterned AChR cluster formation. Wild-type and mutant Shp2 proteins were over-expressed in Xenopus muscle cells by mRNA injection. Muscle cells expressing green fluorescent protein alone (GFP; A, B) or GFP together with wild-type Shp2 (Shp2 WT; C, D), constitutively active Shp2 (Shp2 E76A; E, F) or dominant-negative Shp2 (Shp2 deltaP; images not shown) were stained with R-BTX (B, D, F) to visualize pre-patterned AChR clusters. In muscle cells expressing GFP, normal pre-patterned AChR clusters were found (B; arrow), but in cells with wild-type or constitutively active Shp2 fewer clusters were detected (D, F). G. Data from multiple micro-injection experiments were quantified and the numbers of pre-patterned clusters in cells expressing wild-type and active Shp2 were normalized relative to the number obtained from GFP-expressing cells. GFP-cells, n = 356; Shp2 WT, n = 98; Shp2 E76A, n = 327; Shp2 deltaP, n = 356; *p < 0.05; **p < 0.001 relative to GFP-cells.