Fig. 6. Genetic relationships between the tarsal gene Bar and the pretarsal genes al and Lim1. (A) Pattern of expression of a reporter Bar-lacZ in a wild-type late third instar leg imaginal disc. (B) A Lim1^R12.4 mutant leg imaginal disc showing Bar-lacZ reporter expression invading the pretarsal region (arrow, compare with A). (C) Bar-lacZ expression in an al strong mutant (al^ex/al^ice), which lacks al and loses Lim1 expression (Pueyo et al., 2000). Bar expression invades the whole pretarsal region at the centre of the disc. (D) Bar-lacZ expression in an al^ice/al^ex mutant background expressing Lim1 driven by the dppGal4 driver. Expression of Lim1 is not able to repress Bar expression in the absence of Al function (compare with Fig. 3C,D-D''). (E) Leg from a dppGal4/UAS-Bar fly. Ectopic expression of Bar produces fusion of the proximal segments, such as femur, tibia and the first tarsal segment (arrow), and in the pretarsus one claw is missing (arrowhead). (F) Ectopic Al expression (arrow) produced by dppGal;UAS-Lim1. (G) High magnification of the pretarsal region from a leg imaginal disc with a clone of cells deficient for Bar (outlined in white). Lim1 expression (red) extends into the clone. (H-H''') A dppGal4/UAS-GFP leg disc showing Lim1 protein in blue (H), Al protein in red (H'), and the pattern of Gal4 expression in green (H''), in an otherwise wild-type leg. (H''') Merged image. (I-I''') A dppGal4/UAS-GFP;UAS-Bar leg disc stained as in H. Ectopic expression of Bar represses Lim1 and Al in the pretarsus (compare with H).