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Fig. 6. Known genetic interactions that define/maintain the notum/dorsal hinge
subdivision of the wing disc. (A) In the second instar, EGFR signaling
activates the `pronotum' genes Iro-C (Wang
et al., 2000; Zecca and
Struhl, 2002a; Zecca and
Struhl, 2002b), and Dpp signaling, which is active only in the
distal part of the disc, confines the expression of Iro-C to the proximal part
of the disc (Cavodeassi et al.,
2002), thus defining the notum territory. Also in the second
instar, EGFR signaling, by means of ap, activates msh in the
dorsal hinge. The proximal border of the msh domain abuts the Iro-C
territory and the mutual repression between these genes contributes to
maintain and stabilize the border between the Iro-C and the Msh territories.
As discussed in the text, this border should define and/or maintain the
notum/dorsal hinge subdivision of the disc (red line). (B,C) In support of
this model, B and C show the expressions (red) in first/second instar discs of
dpp-lacZ (B), which occurs mostly in the distal part of the disc, and
of ap-lacZ (C), which takes place most strongly in a more central
region. Within this region, msh will later be activated at high
levels (Fig. 1A, and not
shown). The contour of the discs has been marked with broken lines. (D) Adult
structures that correspond to the domains of Iro-C (notum, orange) and
msh (dorsal hinge, blue). The dorsal hinge has been equated to the
msh domain. Its distal limit with the proximal wing (light blue),
approximately corresponds with the inner circle of Wg expression
(Fig. 1C)
(del Álamo Rodríguez et al.,
2002).
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