Abstract
Drosophila appendages develop from imaginal discs which become subdivided into distinct regions during normal patterning. At least 3 axes of asymmetry are required to produce a chiral appendage such as a leg. The A/P compartments provide one axis of asymmetry in all discs. In leg and antennal discs, the anterior compartment becomes asymmetric in the D/V axis with decapentaplegic (dpp) expression defining dorsal anterior leg, and wingless (wg) expression defining ventral anterior leg. However, unlike wing discs, no D/V compartment has been demonstrated in legs or antennae. How are the dorsal anterior and ventral anterior territories defined and maintained? Here we show that wg inhibits dpp expression and dpp inhibits wg expression in leg and eye/antennal discs. This mutual repression provides a mechanism for maintaining separate regions of wg and dpp expression in a developing field. We propose the term 'territory' to describe regions of cells that are under the domineering influence of a particular morphogen. Territories differ from compartments in that they are not defined by lineage but are dynamically maintained by continuous morphogen signaling. We propose that the anterior compartment of the leg disc is divided into dorsal and ventral territories by the mutual antagonism between WG and DPP signaling.
Highlights
The generation of at least three axes of asymmetry in appendage primordia is an essential element of patterning
The A/P axes in Drosophila appendages are established by the A/P compartments (Garcia-Bellido et al, 1973, 1976; GarciaBellido, 1975; Steiner, 1976; Wieschaus and Gehring, 1976; Lawrence and Morata, 1977) which are defined by non-overlapping expression of cubitus interruptus(ci) in the anterior compartment (Eaton and Kornberg, 1990; Dominguez et al, 1996) and engrailed in the posterior compartment (Kornberg et al, 1985; Sanicola et al, 1995; Zecca et al, 1995)
The D/V restriction of wg and dpp divides the anterior compartment into dorsal and ventral territories, creating a D/V axis of asymmetry that is necessary for generating a chiral appendage
Summary
The generation of at least three axes of asymmetry in appendage primordia is an essential element of patterning (see Postlethwait, 1978; Cohen, 1993). After the establishment of A/P asymmetry, the wing disc is further subdivided into dorsal and ventral compartments (Bryant, 1970; Garcia-Bellido et al, 1976; Blair, 1993) by the activity of the apterous (ap) gene (Blair, 1993; Diaz-Benjumea and Cohen, 1993; Lawrence and Morata, 1993; Williams et al, 1993; Blair et al, 1994) but it has not been possible to demonstrate a D/V lineage restriction in the leg (Steiner, 1976).
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