Fig. 2. brk is required for PD axis specification. (A) A brk^- clone originating in the ventral proximal femur marked by yellow and forked (arrow, outlined in white) creating a cell-autonomous outgrowth. (A') The entire outgrowth appears to have a single, tibia-like DV identity. co, coxa; tro, trochanter; fem, femur; tibia, tib; tib', tibia-like outgrowth; t, tarsal segments 1-5; cl, tarsal claw. (B) brk^- clone proximal to the Dll and Dac domains (absence of GFP, arrow) showing cell-autonomous derepression of Dll and dac. No effects on Dll or dac are observed in brk^- clones within their normal domains (asterisks). (C-D''') gro^- (C) or CtBP^- (D) clones (absence of GFP, green) derepress Dll and dac in proximoventral regions of the disc (arrows and clones labeled `2'; isolated clones are outlined in white and shown in C'', C''', D'' and D'''). No derepression is observed in dorsal gro<sup>-</sup> or CtBP<sup>-</sup> clones (arrowheads and clones labeled `1'; isolated clones are outlined in yellow and shown in C' and D'). Clones within the Dac or Dll domains (outlined, but not numbered) have no effect on Dac or Dll expression.