Fig. 5. Ftz converts Runt from an activator to a repressor of slp1. (A) Embryos mutant for ftz express slp1 in the anterior half of the even-numbered parasegments, resulting in six-cell wide stripes. (B) The ftz mutant phenotype and the way in which this expanded expression is accounted for by Runt+Opa dependent activation. Note that run expression is not significantly altered in ftz mutant embryos at this stage (Klingler and Gergen, 1993). (C) Ectopic Runt expression in ftz mutant embryos activates slp1 throughout the presegmental region. This embryo was obtained from a cross between a female heterozygous for NGT40, NGTA and the ftz[11] mutation with a male homozygous for UAS-runt[232] and heterozygous for ftz[11]. The level of NGT-driven Runt obtained with this combination does not fully overcome Eve-dependent repression, resulting in a few thin stripes of cells with reduced slp1 expression. Runt+Opa-dependent activation (D) results in the slp1 pattern shown in C. The effects of NGT-driven Ftz on slp1 is shown in E and interpreted in F. The embryo in E is from a mating between homozygous NGT40 females and homozygous UAS-ftz[261] males. The effects of co-expressing Runt and Ftz are shown in G and interpreted in H. The embryo in G is from a mating between homozygous NGT40 females and males homozygous for both UAS-runt[232] and UAS-ftz[261].