Fig. 4. Runt and Opa cooperate to activate slp1transcription. In situ hybridization showing the expression of slp1 (A-I) and ftz (J-L) mRNAs in embryos with varying levels of NGT-driven Runt and Opa. In all cases, ectopic expression was obtained in crosses using females homozygous for both NGT40 and NGTA. Variations in expression were obtained using different UAS-runt and UAS-opa lines. Embryos in the first row carry UAS-runt[14] in combination with (A) UAS-opa[36], (B) UAS-opa[12] and (C) UAS-opa[10], which are ordered in increasing strength from left to right. Embryos in the second row (D-F) carry UAS-runt[232] in combination with the same three UAS-opa transgenes. Embryos in the third and fourth rows (G-L) carry UAS-runt[15], also in combination with the same three UAS-opa transgenes. The different levels of ectopic Runt expression are organized in increasing strength from top to bottom, UAS-runt[232] and UAS-runt[15], giving approximately two- and fivefold increases, respectively, over the level obtained with UAS-runt[14] (Li and Gergen, 1999).