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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+ Chipe55 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.
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