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Fig. 7. Functional relationships between LIM-HOM, Prd-HOM, Chip and Dlmo proteins in the pretarsus. (A) Ectopic expression of Al using the apGal4 driver produces a loss of the fourth tarsal segment. (B) Co-expression of Bar in an apGal4/UAS-al background partially rescues the dominant-negative effect on the development of the fourth tarsal segment (compare with A). (C) Ectopic expression of Islet using the dppGal4 driver causes fusion of the femur, tibia and first tarsal segment. In the pretarsus only one claw develops (arrowhead). (D,D') A dppGal4/UAS-GFP;UAS-islet leg disc showing Lim1 protein distribution (D, blue) and Lim1 protein distribution plus the Gal4 pattern of expression (D', green). Ectopic expression of Islet does not repress Lim1 expression; therefore the dominant-negative effect on Lim1 function seems to be posttranslational. (E) Ectopic expression of a truncated Chip protein lacking the LIM interaction domain with the DllGal4 driver produces a similar phenotype in the pretarsus to that seen in DllGal4;UAS-Chip flies: lack of the claws (arrowhead), and fusion of the fifth and fourth tarsal segments (compare with Fig. 1G). (F) A DllGal4;UAS-dlmo leg. Ectopic expression of the dlmo gene mimics the Lim1 lack-of-function phenotype. Arrowhead denotes the pretarsus lacking the claws. (G) Ectopic expression of Lim1 driven by the dppGal4 driver disrupts leg development causing the fusion of femur, tibia, and tarsus one to three. In the pretarsus it produces a similar phenotype to that seen in Lim1 mutants, or after ectopic expression of Lim1 antagonists (arrowhead; compare with C). (H) Pattern of Lim1 expression in a wild-type leg imaginal disc. (I) Lim1 protein distribution in a DllGal4;UAS-dlmo leg imaginal disc. The Lim1 protein is detected in a normal number of pretarsal cells, suggesting that the ectopic Dlmo effect on Lim1 function is not transcriptional, although part of the Lim1 domain is disorganised (compare with H). The white dotted line denotes the proximal limit of the DllGal4 pattern of expression.