A CNPase promoter directed expression of Ha-RasV12 to peripheral nerve Schwann cells. Staining of teased fibers from adult sciatic nerve detects Ras (anti-HA, red) at the membrane of thick myelinated fibers; Schwann cell cytoplasm is counterstained with anti-S100 (green). Thinner unmyelinated fibers containing small axons and Schwann cells also express Ha-RasV12 (red). Nerves from these mice enabled identification of Ras-driven gene expression, which was used to define therapeutic targets in Schwann cell tumors. Photograph was taken by Tilat A. Rizvi. For details, see the article by Patel and colleagues on page 5020 of this issue.