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First published online 23 January 2008
doi: 10.1242/dev.018317

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Delimiting the conserved features of hunchback function for the trunk organization of insects

Henrique Marques-Souza^1,*, Manuel Aranda^1,* and Diethard Tautz^2,

¹ Department of Genetics, University of Cologne, Zülpicherstrasse 47, 50674 Köln, Germany.
² Max-Planck Institute for Evolutionary Biology, August-Thienemannstrasse 2, 24306 Plön, Germany.

View larger version (65K): [in this window] [in a new window]   Fig. 1. Tribolium hunchback phenotypic series. Cuticular preparation of wild-type larvae (A,E) and hunchback-depleted larvae (B-D,F). (B) All body segments are formed but gnathal and thoracic segments are transformed to abdominal identity. The thoracic segments appear to be partially transformed, showing underdeveloped limbs (arrow). (C) Larva displaying approximately 10 segments with abdominal identity and fusion of segments (arrowhead). (D) Larva displaying the strongest phenotype. Antennae and mandible are still formed and the segments following these have abdominal identity up to the fusion point (arrowhead), after which no further segments are seen. (E,F) Comparison of the anterior region of a wild-type larva (E) and a larva with a weak phenotype (F). The latter shows a normal antenna (an) and mandibular (md) segment, while the prospective remaining segments (mx, maxilla; lb, labium; T1-T3, thoracic; A1, A2, abdominal) are transformed into segments of abdominal identity. Some leg stumps are still visible in T2 and T3, indicating that the transformation towards abdominal segments was not complete in these segments.

View larger version (42K): [in this window] [in a new window]   Fig. 2. Changes in Hox gene expression in Tc'hbpRNAi embryos. Wild-type expression is shown in A,C,E,G,I; expression in loss of hunchback embryos (strongest phenotypes) is shown in B,D,F,H,J. All embryos are double stained with a Tc'gsb probe, which serves as a segmental reference marker. Tc'gsb staining is brown in A-F and dark purple in G-J. Hox gene staining is the reverse. (A,B) Tc'Dfd expression extends over the mandibular and maxillary segment in wild type (A) and is lost from the maxillary segment in Tc'hbpRNAi embryos (B). (C,D) Tc'Scr expression covers the labial segment (arrow) in wild type (C) and is lost in Tc'hbpRNAi embryos (D). (E,F) Tc'Antp expression covers the thoracic and abdominal region in wild type (E) with a stronger expression in the thoracic segment (double-headed arrow). In Tc'hbpRNAi embryos, Tc'Antp expression is shifted towards anterior up to the mandibular segment, but its intensity is comparable with the wild-type expression of Tc'Antp in the abdominal segments (F). (G,H) Tc'Ubx expression starts in the third thoracic segment and extends throughout the abdominal region in wild-type embryos (G), with a stronger expression in the first abdominal segment (arrowhead). In Tc'hbpRNAi embryos, Tc'Ubx expression is shifted towards anterior up to the mandibular segment (H), but its intensity is comparable with the wild-type expression of Tc'Ubx in the abdominal segments (arrows in G,H). (I,J) Tc'Antp expression starts in the second abdominal segment and extends throughout the abdominal region in wild-type embryos (I). In Tc'hbpRNAi embryos, Tc'Antp expression is shifted towards anterior up to the mandibular segment (J).

View larger version (23K): [in this window] [in a new window]   Fig. 3. Expression of Tc'Kr. Wild type (A,C,E) and Tc'hbpRNAi embryos (B,D,F). (A,B) Blastoderm stage embryos. Tc'Kr is expressed at the posterior end in wild-type embryos (A) and this expression is strongly reduced (and often absent) in Tc'hbpRNAi embryos (B). (C,D) Early germband stages. Tc'Kr is expressed in a central domain in wild-type embryos (C) and this expression is absent in Tc'hbpRNAi embryos (D). (E,F) Extended germband stages. Tc'Kr is secondarily expressed in segmental stripes in wild-type embryos (E), an expression aspect that is not changed in Tc'hbpRNAi embryos (F), but these develop fewer segments (compare with Fig. 1).

View larger version (47K): [in this window] [in a new window]   Fig. 4. Expression of Tc'gt. Wild-type (A,B) and in Tc'hbpRNAi embryos (C,D), at early (A,C) and late (B,D) germband stages. The embryos are double stained with a Tc'gsb probe (brown), which serves as a segmental reference marker. (A,B) Tc'gt (purple) is expressed in an anterior domain and two posterior stripes in wild-type embryos. (C,D) In Tc'hbpRNAi embryos, the anterior domain is not significantly affected, but the posterior expression of Tc'gt in T3 and A2 (arrows in B) is absent in Tc'hbpRNAi embryos. The segments where Tc'gt should have been expressed are partially fused in Tc'hbpRNAi embryos, indicated by the partial fusion of the Tc'gsb stripes (arrowheads in D).

View larger version (57K): [in this window] [in a new window]   Fig. 5. Expression of Tc'hb. Wild type (A,D), Tc'KrpRNAi (B,E) and Tc'gtpRNAi embryos (C,F). Early (A-C) and late (D-F) germband stages. In wild-type embryos, Tc'hb is expressed in an anterior domain at early germband stages (A) and in a segmental register and a posterior domain at later germband stages (D). In Tc'KrpRNAi embryos, Tc'hb is expressed ectopically in a strong domain posterior to the maxillary segment (B; this embryo is much less stained than the one in A, i.e. the anterior expression domain of hunchback shows up only weakly). At later stages, the posterior expression is restricted to the prospective growth zone (E), although it remains broader than in wild-type embryos (compare with D). In Tc'gtpRNAi embryos, Tc'hb is not significantly affected (C,F), only a partial fusion of segments in the posterior region becomes visible (arrowheads in F).

View larger version (65K): [in this window] [in a new window]   Fig. 6. Expression of Tc'runt. Double staining with Tc'gsb (A-F) (brown) and Tc'eve (G-M) in wild type and in Tc'hbpRNAi embryos. It is evident that the first stripes are not affected in Tc'hbpRNAi embryos, while the patterning beyond the second stripe appears to be disrupted for both genes. Tc'eve expression is very dynamic, i.e. the first stripe disappears fast and the primary stripes split directly into two secondary stripes.

View larger version (29K): [in this window] [in a new window]   Fig. 7. Schematic drawing of the effects of hunchback on the expression of the target genes in Tribolium. (A) Wild type. (B) Tc'hbpRNAi. Arrows indicate activation and bars indicate repression. Unbroken lines indicate a possible direct interaction and broken lines indicate a probable indirect effect. The red lines indicate the actions of hunchback that appear to be conserved in all insects.

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