Fig. 1. slp1 is a sensitive target of Runt. In situ hybridization reveals the segmentally repeated expression patterns of different segmentation genes in gastrula stage embryos. Embryos in this and other figures are shown anterior towards the left, dorsal side upwards. Each row shows expression of a different segmentation gene as labeled on the right. The wild-type expression patterns are shown in the left column of embryos. Embryos in the middle and right column of embryos have intermediate and high levels of NGT-driven ectopic Runt expression, respectively. Intermediate and high levels of ectopic Runt were obtained by mating females homozygous for NGT11 and NGT40, respectively to homozygous UAS-runt[232] males. These are the same combinations used to demonstrate that high, but not intermediate, levels of Runt alter expression of eve and ftz (Tracey et al., 2000). Not shown in this panel are the responses of the pair-rule genes hairy and odd-paired (opa). NGT-driven Runt expression leads to stripe-specific repression of hairy similar to that obtained in hs-runt embryos, but only at high levels of expression. The opa pattern is unique amongst the pair-rule genes and is expressed in a broad band spanning the presegmental region of the embryo, rather than in a series of stripes. This pattern is not altered by ectopic Runt.