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Genetic evidence for the transcriptional-activating function of Homothorax during adult fly development

¹ Unit of Genetics and the Rappaport Family Institute for Research in the Medical Sciences,
² Department of Biochemistry, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel

View larger version (96K): [in a new window]   Fig. 1. Phenotypic effects of EN-HTH1-430. Phenotypes characteristic of dpp-Gal4/UAS-EN-HTH1-430 flies grown at 24°C. (A-B) Ectopic eyes form in various positions on the ventral head cuticle, including the region of the maxillary palp (A) and the antennal foramen (B). (C,D) Hyperplasia of the eye is evident in adult flies (C) and eye imaginal discs dissected from a third instar larva (D). (E,F) Expression of EN-HTH1-430 in the eye-antenna disc causes tufts of large bristles to appear in ectopic positions along the eye margin. (G,H) Cuticle preparations of antennae from dpp-Gal4/UAS-EN-HTH1-430 flies showing an antenna-to-leg transformation. (G) The a2 antennal segment is relatively normal. The distal portion of the a3 segment is replaced by a leg-like structure. (H) Higher magnification of the transformed antenna reveals the presence of bracted bristles (arrows) typical of distal leg segments. (I,J) Cuticle preparations of a third (I) and second (J) leg of dpp-Gal4/UAS-EN-HTH1-430 flies. The proximal leg segments are reduced in size and fused together (arrow in I). Distal parts of the truncated legs consist of disfigured leg structures with bristle patterns typical of tibia (arrow in J) or pretarsus (arrowheads in I and J). (K-L) Third leg discs from wild-type (K) or dpp-Gal4/UAS-EN-HTH1-430 (L) third instar larvae shown at the same magnification. The EN-HTH1-430 expressing disc is significantly enlarged and exhibits abnormal pattern of epithelial folds.

View larger version (108K): [in a new window]   Fig. 2. Phenotypic effects of VP16-HTH1-487. (A) Head of a dpp-Gal4/UAS-VP16-HTH1-487 fly exhibiting a complete loss of the eye. (B) Cuticle preparation of antennae from a dpp-Gal4/UAS-VP16-HTH1-487 fly. The a2 and a3 segments appear relatively normal, however the arista is either spineless and fused to the a3 segment (arrow) or completely missing. (C) A typical antenna of a dpp-Gal4/UAS-hth12 fly. The a3 segment is reduced in size and the arista is missing. (D-E) Cuticle preparations of a first leg (D) and a second leg (E) of a dpp-Gal4/UAS-VP16-HTH1-487 fly. C, coxa; Tr, trochanter; F, femur. The coxa, trochanter and proximal femur are unaffected. Distal leg structures are deformed and condensed together. The arrows indicate the claws. (F) First leg of a dpp-Gal4/UAS-hth12 fly. Proximal segments are intact, as they are in the leg in D. The leg is truncated and the remaining distal structures are malformed.

View larger version (83K): [in a new window]   Fig. 3. VP16-HTH1-487 can rescue the loss of native HTH. The pattern of PNS neurons in stage 15-16 embryos as revealed by mAb 22C10 staining. In all panels anterior is to the left and dorsal is up. The boxed areas in A-C are shown in higher magnification in D-F; segment identity is indicated. (A,D) A heterozygous hth64-1 embryo showing a normal pattern of the PNS. The abdominal lateral chordotonal (LCh5) neurons can be clearly seen in the lateral PNS cluster of each abdominal segment A1-A7 (asterisks). (B,E) Similar views of a homozygous hth64-1 embryo. A loss of neurons and dorsal localization of the LCh5 neurons (indicated by arrows) are evident in all abdominal segments. (C,F) Expression of UAS-VP16-HTH1-487 was driven by Kr-Gal4 in a hth64-1 background. The LCh5 neurons are correctly positioned in abdominal segments A1-A4 (asterisks) where the transgene is expressed. More posterior segments do not exhibit such a rescue. Note the dorsal position of the LCh5 neurons in A5-A7 (arrows in C and F).

View larger version (85K): [in a new window]   Fig. 4. EN-HTH1-430 localizes EXD to the nucleus. Lateral view of stage 13 embryos stained with anti-EXD antibody. The thoracic segments are indicated. (A) A wild-type embryo. (B) An arm-Gal4/UAS-EN-HTH1-430 embryo. Nuclear localization of EXD is clearly evident in both types of embryos.

View larger version (126K): [in a new window]   Fig. 5. Phenotypic effects of EN-XMeis31-333. (A,B) Phenotypes characteristic of dpp-Gal4/UAS-EN-XMeis31-333 flies grown at 24°C. Ectopic eyes are frequently observed in the ventral head region (arrows). (C) An eye-antenna disc from a third instar larva stained with anti-ELAV antibody. Ectopic photoreceptors are present in the presumptive ventral head region (arrow). (D) A typical antenna-to-leg transformation. The a2 segment appears normal. The a3 segment is transformed distally to distal leg tissue, as suggested by the presence of bracted bristles. (E) The distal region of a deformed and truncated third leg. Bristle patterns suggest that these structures are of tibial (arrow) and pretarsal (arrowheads) identities.

View larger version (132K): [in a new window]   Fig. 6. The effects of EN-HTH1-430 and EN-XMeis31-333 on derivatives of the wing, labial and genital discs. (A-C) Cuticle preparations of wings from dpp-Gal4/UAS-EN-HTH1-430 flies. (A) Low magnification showing the general organization of the affected wing. The arrow indicates the bristles of the anterior wing margin. (B) Higher magnification of the proximal region, which is covered by bracted bristles (arrowheads). The arrow indicates the bristles of the anterior wing margin. (C) Higher magnification of the anterior wing margin bristles concentrated in a small region of the proximal portion of the wing. (D) A dpp-Gal4/UAS-EN-HTH1-430 fly exhibiting a duplication of the wings. Extra wings are indicated by arrows. (E-F) Cuticle preparation of mouth parts of a wild-type (E) and a dpp-Gal4/UAS-EN-HTH1-430 fly (F). Note the outgrowths with bracted bristles on the labellum in F (arrow). (G) Cuticle preparation of a dpp-Gal4/UAS-EN-XMeis31-333 fly showing a typical outgrowth from the anal region (arrows). (H-I) Genital discs of a wild-type (H) and a dpp-Gal4/UAS-EN-XMeis31-333 (I) larvae. Note the abnormal morphology and hyperplasia of the presumptive anal region in I (arrows).