PerspectiveDevelopmental Biology

Gradient Scaling and Growth

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Science  04 Mar 2011:
Vol. 331, Issue 6021, pp. 1141-1142
DOI: 10.1126/science.1203270

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What determines the final size of an animal? Secreted molecules called morphogens control tissue and organ growth during development (1). As morphogens diffuse away from their source, a concentration gradient forms. Target cells “read” the local concentration and activate genes involved in differentiation. One such morphogen is Decapentaplegic (Dpp), a member of the transforming growth factor–β family that controls fly (Drosophila melanogaster) development (26). Paradoxically, although Dpp forms a concentration gradient, it promotes seemingly uniform growth across its target tissue. Earlier studies argued that the slope rather than the concentration of the Dpp gradient may control growth (7), or that cell proliferation is modulated by mechanical constraints (8, 9). On page 1154 of this issue, Wartlick et al. (10) propose instead that cells control growth by computing the relative temporal variation in Dpp activity.