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First published online 5 January 2005
doi: 10.1242/dev.01585

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Patterning function of homothorax/extradenticle in the thorax of Drosophila

Centro de Biología Molecular, CSIC-UAM, Universidad Autónoma de Madrid, Madrid, 28049, Spain

View larger version (49K): [in a new window]   Fig. 1. Expression of hth/exd in the Drosophila notum. (A) Single staining for hth expression in a middle third instar disc. hth expression (red) covers most of the notum but some modulation is already visible. (B-D) Notum region of a mature disc doubly stained for hth (red) and exd (green). The two regions of high hth expression are the and the ß subdomains. The image in C shows only exd staining and in D the red and green channels are merged. The hth and exd expression patterns are almost identical. (E) Third instar disc doubly stained for hth (red) and en (green). Part of the ß subdomain is included in the postnotum. (F) Notum part of a mature disc stained for hth (red) and eyg (green). The ß subdomain and the eyg expression domain abut and form a sharp border, but the subdomain is included within the eyg domain. (G) Double staining with anti-Hth (red) and anti-pMad (green). The ß subdomain contains high levels of Dpp signalling. (H) A schematic of hth expression in the adult thorax. (I) Thorax of an hth-Gal4 > UAS-lacZ stained with X-gal to reveal hth expression in adult structures.

View larger version (74K): [in a new window]   Fig. 2. Developmental effects of the loss of hth/exd function. (A) Adult notum containing a exd- clone (arrow) in the lateral region. The clone differentiates several macrochaetes that are not normally present in that zone. (B) A large M+ exd- clone showing alterations of the bristle pattern in the scutellum region and the disappearance of the suture between the scutum and the scutellum. (C) Idealised image of the phenotype of an entire exd- heminotum (right) compared with a normal heminotum (left). The two sutures are lost and the pattern of macrochaetes is different from the normal one. dc, dorsocentral; pa, postalar; s, suture; sc, scutellum. (D-F) Notum region of the disc containing several hth- clones, marked black. The red staining marks the activity of the DC enhancer (see main text for details), which is expressed in the precursors of the dorsocentral bristles. The normal activity of this line is indicated in the inset in D. The clone in the posterior region (arrows in D,F) shows ectopic activity of the DC enhancer, indicating a change of the identity towards scutum.

View larger version (83K): [in a new window]   Fig. 3. Effect of uniform hth expression in the notum pattern. (A) Uniform expression of hth in an ap-Gal4>UAS-hth notum. (B) Notum structures differentiated by the same genotype. Some scutellum structures remain but most of the scutum is lacking. There is a general lack of microchaetes and the few that remain are in the lateral region.

View larger version (133K): [in a new window]   Fig. 4. Regulation of hth expression by eyg. (A) Mutant eyg disc stained with an anti-Hth antibody showing generalised hth expression. (B,C) A mutant eyg- clone (arrows, labelled by the loss of GFP) in the inter-subdomains zone, exhibiting ectopic hth expression. (D-F) Notum region with many clones of eyg-expressing cells, marked with GFP. The clones in the subdomain do not affect hth expression, in contrast to those in the ß subdomain where hth is lost. (G-I) Disc of genotype 248-Gal4>UAS-eyg doubly labelled with anti-Eyg (green) and anti-Hth (red), showing loss of hth in the ß but not in the subdomain.

View larger version (98K): [in a new window]   Fig. 5. Regulation of hth by the Dpp pathway. (A-C) Disc containing several Mad- clones marked by the loss of GFP (green). In the subdomain, they do not affect hth (red) but those in the inter-subdomains zone (small arrows) show gain of hth, although not in all the cells. The clone inside the ß subdomain (large arrows) shows loss of hth. (D-F) Several TkvQD-containing clones marked by the gain of GFP (E). The clones in the subdomain (arrows) show loss of hth (red) but the clones in the ß subdomain do not affect hth.

View larger version (36K): [in a new window]   Fig. 6. (A) Adult thorax of genotype 248-Gal4>UAS-hth. Although the scutellum remains approximately normal, most of the scutum is lacking. Many microchaetes are missing. (B) Thorax of a 248-Gal4>UAS-eyg fly. As described previously (Aldaz et al., 2003), the scutellum is replaced by a scutum-like pattern in mirror-image orientation. Macrochaetes are present in the duplicated structure. (C) 248-Gal4>UAS-hth UAS-eyg thorax. The only macrochaetes that remain are those in the lateral region (where the Gal4 line is not expressed), while the central region only differentiates microchaetes. (D) Pull-down assay. All three lanes are tested with the Eyg antibody for the presence of Eyg product (80 kDa band). The first lane corresponds to crude extracts. The second lane to the extract incubated with His-agarose, and in the third lane the extract was incubated with His-Hth protein. Eyg is detected in the larval extract and in a complex formed with Hth.

View larger version (21K): [in a new window]   Fig. 7. Model for hth regulation. The two horizontal bars indicate expression of the two regulators: the Dpp signalling pathway and eyg. In the anterior (A) part of the disc, eyg is expressed but the levels of Dpp signalling are too low to repress hth. In the inter-subdomain region, eyg is present and the levels of Dpp signalling are sufficient to repress hth. Close to the posterior (P) border of the disc, high levels of Dpp signalling are present, but there is no eyg activity and hence hth is not repressed.