Establishment of Medial Fates along the Proximodistal Axis of the Drosophila Leg through Direct Activation of dachshund by Distalless

Abstract

Summary The proximo-distal (PD) axis of the Drosophila leg is thought to be established by the combined gradients of two secreted morphogens, Wingless (Wg) and Decapentaplegic (Dpp). According to this model, high [Wg+Dpp] activates Distalless (Dll) and represses dachshund (dac) in the distal cells of the leg disc while intermediate [Wg+Dpp] activates dac in medial tissue. To test this model we identified and characterized a dac cis-regulatory element (dac RE) that recapitulates the dac’s medial expression domain during leg development. Counter to the gradient model, we find that Wg and Dpp do not act in a graded manner to activate RE. Instead, dac RE is activated directly by Dll and repressed distally by a combination of factors including the homeodomain protein Bar. Thus, medial leg fates are established via a regulatory cascade in which Wg+Dpp activate Dll and then Dll directly activates dac, with Wg+Dpp as less critical, permissive inputs.

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…Before the end of embryogenesis, the leg imaginal disc is divided between a central zone of cells expressing Dll , which gives rise to all leg segments except the coxa, and a peripheral zone of cells expressing hth , which gives rise to the coxa and surrounding body wall. Late in the second larval instar, a dac domain emerges at the boundary of the Dll and hth domains, in response to Dll (Giorgianni and Mann 2011 ). Interactions between the leg gap genes initially establish largely mutually exclusive domains along the PD axis of the leg (Abu-Shaar and Mann 1998 ;Wu and Cohen 1999 ).…”

Evolution of sex comb from the primitive bristle pattern in drosophila is associated with modification in the developmental regulatory protein dachshund

“…As studied in D. melanogaster, it is needed for proper formation of the segments along the proximo-distal axis of the leg (Lecuit and Cohen, 1997;Mardon et al, 1994). Without its function, particularly the medial cell fate specification suffers and results in a shortened leg (Giorgianni and Mann, 2011). In species, which do not have sex comb, still the segmentation of the leg has been properly formed indicating that this aspect of the DAC function is taken care of.…”

Ras-activated Dsor1 promotes Wnt signaling in Drosophila development

“…Wg and Dpp activate dachshund (dac) in the medial cells, followed by EGFR signaling in the distal cells in the early third instar, through inducing expression of the EGFR ligand vein and the protease rhomboid (Campbell, 2002;Galindo et al, 2002). The EGFR target gene Bar, in turn, represses dac expression in the distal cells (Giorgianni and Mann, 2011), resulting in refinement of Dac to a distinct domain of medial cells and its absence in the active distal EGFR domain (Fig. 5A‴, arrow).…”