First published online October 30, 2006
Development 133, 2201e (2006)
© The Company of Biologists Limited
Sizing up size control
The developmental mechanisms that control the growth and final size of
organs are poorly understood. What, for example, determines the different
sizes of halteres and wings, homologous thoracic structures in
Drosophila? Two papers in this issue of Development provide
new insights into this process. On
p. 4421,
Martín and Morata show that the control of growth and final size is an
autonomous feature of the Drosophila wing imaginal disc and of its
anterior and posterior compartments. They used Minute mutations,
which prolong the larval period of heterozygous animals (M/+) without
affecting the size of the larvae or adults, in a complex genetic strategy to
generate slow-growing M/+ larvae that contained fast-growing, wild-type
Minute+ (M+) discs or compartments. These wild-type,
M+ tissues have 
20 hours more development time than is normal,
enough to quadruple in size, yet they grow only to a normal size in M/+
larvae. And although adjoining M/+ and M+ wing disc compartments in
M/+ larvae initially grow at different rates, they form adult wings of the
correct shape and size. The researchers conclude that an autonomous mechanism
within the wing disc compartments arrests their growth once they reach the
right size, probably by lengthening the cell division cycle. On
p. 4495, de Navas,
Garaulet and Sánchez-Herrero tackle the question of what controls the
size difference between halteres and wings, and show that the
Ultrabithorax (Ubx) Hox gene controls haltere size by
regulating Decapentaplegic (Dpp) signalling. Ubx is expressed in the
haltere disc but not in the wing disc, and Ubx mutations increase
haltere size, transforming them into wings. Because changes in Dpp signalling
affect wing size, the authors wondered whether Ubx fixes haltere size
by modifying the Dpp pathway. Their results indicate that Ubx
downregulates dpp expression and alters Dpp activity in halteres. It
also reduces Dpp spread, they report, by controlling the expression of the Dpp
receptor thick veins and of division abnormally delayed,
which encodes a cell-surface molecule. Thus, they suggest, changes in Dpp
signalling that are induced by Ubx might partly account for the
different size of halteres and wings.
Related articles in Development:
- Compartments and the control of growth in the Drosophila wing imaginal disc
- Francisco A. Martín and Ginés Morata
Development 2006 133: 4421-4426.
[Abstract]
[Full Text]
- The Ultrabithorax Hox gene of Drosophila controls haltere size by regulating the Dpp pathway
- Luis F. de Navas, Daniel L. Garaulet, and Ernesto Sánchez-Herrero
Development 2006 133: 4495-4506.
[Abstract]
[Full Text]
