Fig. 1. The role of Chip and dlmo in leg development, and their genetic relationships with apterous. (A) The distal region of a wild-type prothoracic leg showing the distal part of the tibia (Tb), tarsal segments one to five (t1-t5), and the distalmost organ, the claw, in the pretarsus (c). (B-B''') Each segment of the distal part of the leg is characterised by differential expression of the LIM-HOM Ap and Lim1 and the Prd-HOM Bar transcription factors. The images show a side view of an everting leg imaginal disc. B shows the merged triple staining; B'-B''' show the separate channels. Expression of a Bar reporter gene in tarsus four and five is shown in green (B'); Lim1 protein distribution in the pretarsus is shown in blue (B''); and Ap protein distribution is shown in red (B'''; yellow in overlap in B). (C) Wild-type leg imaginal disc showing Chip protein distributed ubiquitously in the disc epithelium. (D) Dlmo protein distribution in a late third instar leg imaginal disc. Specific staining can be detected in a few cells in the peripodial membrane (arrow). (E) Minute+ Chip^e55 clones in leg. The tissue lacking Chip is marked by its yellow (y) phenotype and is outlined in black. Clones in the tibia, femur, coxa and pretarsus show a phenotype similar to strong Lim1 mutants. The fourth tarsal segment fails to develop, as in strong ap mutants. (F) Higher magnification of the tip of the leg shown in E. The majority of the distal part of the leg is y^– apart from two bristles that are y⁺ (asterisks). In the pretarsus no claws develop (arrowhead). In addition, only a remnant part of a joint is observed between the last tarsal segments (arrow). (G) Leg of a DllGal4;UAS-Chip fly. Only four tarsal segments develop and the claw organ is absent, similar to the phenotype of Chip lack of function, which is shown in E. (H) Ap (red) and Lim1 (green) protein expression are normal in a DllGal4;UAS-Chip leg disc. The white dotted line denotes the edge of the distal domain of expression of the DllGal4 line. (I) Leg of an apGal4;UAS-dlmo fly (29°C). Although the LIM-only gene (dlmo) is not expressed in the leg imaginal disc, Dlmo overexpression produces loss of the fourth tarsal segment. (J) Co-expression of UAS-Chip in an apGal4;UAS-dlmo genetic background rescues the loss of the fourth tarsal segment.