Fig. 2. The Ds and Stan systems are different and independent. Comparison of the effects of over-producing Fz, Ft and ectoDs (a particularly potent signalling form of Ds) in clones in flies lacking either the Ds (A,C,E) or the Stan (B,D,F) systems. (A) Clones overexpressing Fz (UAS.fz) reverse the polarity of wild-type cells over a short range (Lawrence et al., 2004) but they reverse polarity of ds^- cells over a longer range. (B) UAS.fz clones have no effect in stan^- flies. (C) UAS.ft clones reverse the polarity of wild-type cells in front of the clone (see Fig. 3A), but have no effect in ds^- flies; (D) the same clones reverse polarity of stan^- flies. (E) Clones overexpressing ectoDs reverse the polarity of wild-type cells behind the clone (see Fig. 3C), but have no effect in ds^- flies. (F) These UAS.ectoDs clones reverse polarity in stan^- flies. Clones are marked with pwn (A-D) and pwn sha (E,F). Anterior is towards the top, red lines outline the clone and red arrows indicate the polarity imposed on cells outside the clone.