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Cover Figure

COVER This week features a Perspective on Sonic Hedgehog signaling during limb morphogenesis. The image shows Wolpert's spatial morphogen gradient model of digit specification. [Image: Rolf Zeller, University of Basel Medical School]

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Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882