Molecular Biology Of The Cell 6th Edition by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter

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6 The extracellular protein factor Decapentaplegic (Dpp) is critical for proper wing development in Drosoph- ila (Figure Q21-3A). It is normally expressed in a narrow stripe in the middle of the wing, along the anterior-pos- terior boundary. Flies that are defective for Dpp form stunted "wings" (Figure Q21-3B). If an additional copy of the gene is placed under control of a promoter that is active in the anterior part of the wing, or in the posterior part of the wing, a large mass of wing tissue composed of normal-looking cells is produced at the site of Dpp expres- sion (Figure Q21-3C and D). Does Dpp stimulate cell divi- sion, cell growth, or both? How can you tell?