Double-labeling detects co-expression of clc and clf or clc and cntfr in individual muscle cells. Single sections of E16.5 muscles were hybridized with two probes. Dig-labeled clc (A-D) and Fluo-labeled clf (A, B) or cntfr (C, D). Anti-Dig antibodies were applied first and stained using NBT/BCIP to reveal cells expressing clc (A, C). Anti-Fluo antibodies were then applied and detected using Fast red to reveal cells expressing clf (B) and cntfr (D), after removal of the first red reaction product. Most muscle cells express clc and clf or clc and cntfr (examples indicated by arrows). Bars: 100 μm.