Figure 4.

Absence of Schwann cells in erbB2-deficient embryos. (A–F) Whole-mount preparations from controls (A, C, and E) and erbB2 mutants (B, D, and F) were labeled with antibodies against S100. In the control preparations, S-100-labeled Schwann cells delineated the entire phrenic nerves as early as E13.5 (A), and were readily detectable at E15.5 (C). S100-positive cells were also found in the intercostal nerve in the controls (arrowheads in E). In contrast, there were no Schwann cells detectable in the mutants in the phrenic nerves (B and D), or in the intercostal nerves (F). Ribs (r) also stained positively for S100. (G and H) Electron micrographs of the intercostal nerves at E18.5. In the control (G), every single axon (ax) was wrapped by Schwann cell processes (SC). Axons were separated apart by extracellular matrix (ec). In the mutant (H), axons were tightly packed together. There were no Schwann cells or extracellular matrix. Note that the density of axons in the mutants is higher, and overall axon diameters are smaller. [Bars = 50 μm (A, B, E, and F), 100 μm (C and D), and 1 μm (G and H).]