Figure 3.

Defasciculation of intercostal nerves and abnormal axonal arborization in the intercostal and limb muscles. (A–E) controls and (F–J) mutants. In the control (A), the intercostal nerve trunk formed bundles, with many collateral branches emanating from the main nerve trunk (arrowheads in A); in the mutants (F), the intercostal nerves were defasciculated and nerve branches were disorganized (arrowheads). Note the tip of intercostal nerves terminated aberrantly in the mutants (arrow in F), as compared with the controls (arrow in A). B, C, G, and H show E18.5 intercostal muscles double-labeled with neurofilament antibodies (B and G) and Texas Red-conjugated α-BTX (C and H). In the controls, nerve terminals extended from the nerve bundle (arrow in B) and terminated at a central band labeled by α-BTX (C). In the mutants, the intercostal nerves were defasciculated (arrow in G), and nerve terminals aberrantly projected to the center of muscle fibers (G). As in control embryos, an AChR clustering band was present at the center of muscle fibers in the mutant (H). D, E, I, and J show sections of leg muscle, double-labeled with neurofilament antibodies and α-BTX. In the controls (D and E), neurofilament antibody-labeled nerve terminals were colocalized with α-BTX-labeled AChR clusters (arrowheads in D and E); in the mutants (I and J), only a small number of nerve terminals remained (arrowheads in I and J). [Bars = 100 μm (A and F), 50 μm (B, C, G, and H), and 50 μm (D, E, I, and J).]