Hand Over Heart

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Science  16 Jan 2009:
Vol. 323, Issue 5912, pp. 310
DOI: 10.1126/science.323.5912.310a

Although each of us likes to feel unique, many of the physical characteristics that define us are not all that different from those of our neighbors. In particular, the size of one's body and the relative sizes of the component parts vary within a narrow range, but the guiding mechanisms are not well understood. For instance, after hepatectomy, the remaining liver cells divide only until the organ is fully regenerated and not beyond. How are the boundaries between individual organs and appendages controlled during development and regeneration? Evidence suggesting that cross talk between organs contributes to size determination comes from heritable congenital syndromes that affect multiple organs. Retinoic acid, a derivative of vitamin A, is part of a universal pathway involved in many aspects of vertebrate organogenesis. In zebrafish embryos, defective retinoic acid signaling causes an expansion of the heart and a reduction of the forelimb, but whether these two processes are coordinately regulated is unknown; although the heart and forelimbs are far apart in the adult, they are juxtaposed during early stages of development. Waxman et al. show that retinoic acid signaling in the developing forelimb restricts the size of the adjacent cardiac progenitor field; the downstream factor hoxb5b, which is expressed in response to retinoic acid in the forelimb, mediates this restrictive effect on the heart. The coordinated development of heart and limbs would explain their correlated defects in some syndromes and suggests a mechanism whereby communication between adjacent organs helps to regulate size. — HP*

Dev. Cell 15, 923 (2008).

  • *Helen Pickersgill is a locum editor in Science's editorial department.

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