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Hox Control of Organ Size by Regulation of Morphogen Production and Mobility
Michael A. Crickmore1 and
Richard S. Mann2*
Selector genes modify developmental pathways to sculpt animalbody parts. Although body parts differ in size, the ways inwhich selector genes create size differences are unknown. Wehave studied how the Drosophila Hox gene Ultrabithorax (Ubx)limits the size of the haltere, which, by the end of larvaldevelopment, has fivefold fewer cells than the wing. We findthat Ubx controls haltere size by restricting both the transcriptionand the mobility of the morphogen Decapentaplegic (Dpp). Ubxrestricts Dpp's distribution in the haltere by increasing theamounts of the Dpp receptor, thickveins. Because morphogenscontrol tissue growth in many contexts, these findings providea potentially general mechanism for how selector genes modifyorgan sizes.
1 Department of Biological Sciences, Columbia University, New York, NY 10027, USA. 2 Department of Biochemistry and Molecular Biophysics, Columbia University, HHSC 1104, 701 West 168th Street, New York, NY 10032, USA.
* To whom correspondence should be addressed. E-mail: rsm10{at}columbia.edu
fivefold fewer cells than the wing. We find that Ubx controls haltere size by restricting both the transcription and the mobility of the morphogen Decapentaplegic (Dpp). Ubx restricts Dpp's distribution in the haltere by increasing the amounts of the Dpp receptor, thickveins. Because morphogens control tissue growth in many contexts, these findings provide a potentially general mechanism for how selector genes modify organ sizes. 
