Development 124, 125-132 (1997)
Printed in Great Britain © The Company of Biologists Limited 1997
DEV7536
Specification of the embryonic limb primordium by graded activity
of Decapentaplegic
Satoshi Goto and Shigeo Hayashi
SUMMARY
Two thoracic limbs of Drosophila, the leg and the wing, originate
from a common cluster of cells that include the source of two secreted
signaling molecules, Decapentaplegic and Wingless. We show that Wingless,
but not Decapentaplegic, is responsible for initial specification of the
limb primordia with a distal identity. Limb formation is restricted to
the lateral position of the embryo by negative control of the early function
of Decapentaplegic and the EGF receptor homolog that determine the global
dorsoventral pattern. Late function of Decapentaplegic locally determines
two additional cell identities in a dosage dependent manner. Loss of Decapentaplegic
activity results in a deletion of the proximal structures of the limb,
which is in contrast to the consequence of decapentaplegic mutations
in the imaginal disc, which cause a deletion of distal structures. The
results indicate that the limb pattern elements are added in a distal to
proximal direction in the embryo, which is opposite to what is happening
in the growing imaginal disc. We propose that Wingless and Decapentaplegic
act sequentially to initiate the proximodistal axis.
Key words: imaginal disc, wing, leg, cell allocation, wingless, pattern
formation, Drosophila