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First published online 12 December 2007
doi: 10.1242/dev.009662

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Common functions of central and posterior Hox genes for the repression of head in the trunk of Drosophila

Institut de Biologie du Développement de Marseille Luminy, UMR6216 CNRS Université de la Méditerranée, Case 907 Parc Scientifique de Luminy, 13288 Marseille Cedex 09, France.

View larger version (151K): [in this window] [in a new window]   Fig. 1. Hox genes repress head and promote trunk. Cuticles of (A) wild type, (B) HoxCP, (C) tsh- HoxCP, (D) tsh- Hox- Scr+, (E) tsh- Hox- Antp+, (F) tsh- Hox- Ubx+, (G) tsh- Hox- abdA+ and (H) tsh- Hox- AbdB+, larvae. White arrows, denticles; black arrows, naked cuticle; arrowheads, crinkled head cuticle. Head cuticle is mostly in the posterior part of each trunk segment in B, but occasionally also differentiates in the anterior (left and right arrowheads). Inset in A shows the pigmented crinkled cuticle typical of the head skeleton. Inset in C highlights the crinkled cuticle. In D, the distance from the anterior border of the crinkled cuticle to the anterior trunk (line) is larger than that in C. The inset in E shows the small thoracic denticles (white arrow) invisible in the larger photograph. Head-like cuticle develops in A5-8 (arrowheads). Anterior is on the left for all panels.

View larger version (75K): [in this window] [in a new window]   Fig. 2. HoxCP and tsh genes repress optix expression in the trunk. (A-C) optix expression (green) in wild type, stage 6 (A), 11 (B) and 14 (C). Arrows, early expression domain in the labrum; arrowheads, patches of optix-expressing cells in maxillary and labial segments. Clbr, Clypeolabrum; Spog, Supra oesophagial ganglia. (D,E) Expression of optix in HoxCP and tsh- HoxCP embryos at retraction. Elav (red) highlights the ventral side of the embryo. White arrows indicate ectopic patches of optix (green) in the trunk. The expression domain of optix in the ventral labial segment is not visible in this section (D, asterisk, see E and F). (F) tsh- HoxCP embryo showing optix compared with engrailed (red) at stage 12. The patterns are complementary, indicating that optix ectopic stripes are located in the anterior region of each segment. There is an ectopic patch of optix in the labial (Lb) and ninth abdominal segments (A9). B, D and E are ventral views; A, C and F are lateral views.

View larger version (49K): [in this window] [in a new window]   Fig. 3. optix is required for the development of the labrum and mouth hooks during embryogenesis. (A) Genomic region of optix showing the insertions and the probes (red lines) used for the RNAi experiments. (B-G) Cuticle preparations of wild type (B, dorsal; C, lateral), Df/optix (D, laterodorsal; E, ventral) head skeletons, tsh- optixC01718 HoxCP (F, ventral) and nullo-Gal4 UAS-optix (G, lateral) larva. Derivatives of the labrum (red; lr, labrum; es, epistomal sclerite) and labral sense organ are absent and the maxillary-derived, mouth hooks (MH) are missing (E) or reduced (D) in Df/optix (compare B-E). All sense organs, apart from the labral one, are unaffected in the different optix alleles (D,E) and RNAi-treated larvae (not shown). In E, the asterisk indicates head cuticle in place of the mouth hooks, labral and adjacent structures normally found in this position (see B,C). H piece (H), hypostomal sclerite (hys) and lateralgräten (LG) derive from segments posterior to the labrum (Jürgens et al., 1986). The head-like cuticle present on the ventral side of tsh- optixC01718 HoxCP (arrowhead in F) and tsh-HoxCP (Fig. 1C) embryos are indistinguishable. In G, early ectopic expression of optix results in a failure in retraction of the germ band.

View larger version (71K): [in this window] [in a new window]   Fig. 4. Each Hox CP gene represses optix in its ventral, anterior ectodermal activity domain. Expression of optix (green) in (A) tsh- HoxCP, (B) tsh- Hox- Scr+, (C) tsh- Hox- Antp+, (D) tsh- Hox- Ubx+, (E) tsh- Hox- abdA+, (F) tsh- Hox- AbdB+, (G) Dfd, (H) lab. (A) Elav staining (red) highlights the ventral side. (B-F) The distribution of Hox proteins is in red. Arrows delimit the boundaries between optix expression and Hox domains. Scr+ (B) has one patch less (Lab segment) compared with A; Antp+ (C) presents only two (Lab and T1), Ubx+ (D) four (Lab to T3), abdA+ (E) five (Lab to A1) and AbdB+ (F) has eight (Lab to A4) ectopic patches of optix. (G) Loss of Dfd induces an ectopic optix patch in the maxillary segment (white arrow); arrowheads indicate the two normal domains of optix in the gnathal segments. (H) optix distribution is normal in lab (compare Fig. 2B). All panels are ventral aspects.

View larger version (101K): [in this window] [in a new window]   Fig. 5. Effects of ubiquitous Hox activation on optix expression. (A) Wild-type, (B) 69B-Gal4>UAS-Ubx and (C) 69B-Gal4>UAS-tsh embryos: the gnathal patches of optix (arrowheads) are missing in the mutants but the head domains are largely as in wild type following late Hox induction. (D) nullo-Gal4>UAS-Ubx and (E) nullo-Gal4>UAS-AbdB. Early activation of Hox proteins eliminates both the head (asterisk) and gnathal expression domains of optix (compare with Fig. 2B,C). (F) 69-Gal4>UAS-Dfd. Late Dfd expression induces ectopic patches of optix in small lateral groups of cells in the thoracic segments (arrows) and enlarged gnathal patches (arrowheads, compare with Fig. 2B,C and 5A). (G) nullo-Gal4>UAS-lab. Early, but not late (not shown), induction of Lab results in lateral patches of optix in the thoracic segments (arrows) and enlarged optix patches in the maxillary and labial segments (arrowheads, compare with A). B,E-G are ventral views; A, C and D are lateral views.

View larger version (73K): [in this window] [in a new window]   Fig. 6. Expression of optix in mutations for exd and hth. Expression of optix (green) in exd (A,C) and hth (B,D) mutant embryos, and cuticle preparations (E,F). (A,B) Stage 12; (C,D) retracted germ band stage. Expression of optix is strongest in the maxillary (Mx), labial (Lb) and thoracic segments and weaker in A1-7. There is no significant expression of optix in the A8, where AbdB is detected (A,B), nor in A9 segments. There is a stronger segmentation defect in exd compared with hth embryos. In the thorax of exd and hth (E,F insets), crinkled head-like cuticle differentiates. A and B are lateral views, C-F are ventral views.

View larger version (68K): [in this window] [in a new window]   Fig. 7. The role of Engrailed and Wingless signalling in the repression of optix. Expression of wg (red) and optix (green) in HoxCP (A) and tsh- HoxCP (B) embryos at the retracted germ band stage. optix and wg patterns of expression are complementary in each trunk segment and are colocalised in parts of the labrum and gnathal domains (yellow). (C,D) Expression of optix in wg- tsh- HoxC (C) and tsh- en- HoxC (D) embryos; optix expression covers a larger region of the ventral side of each trunk segment compared with B. (A,B) ventral views; (C) lateral view. (E) Summary of the repression activities of HoxCP, Tsh and Wg in a typical trunk segment.

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