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Fig. 2. Conserved bap expression and activities of bap enhancers from D. melanogaster and D. virilis. (A-H) Lateral views, (I-L) dorsal views, (M-O) cross-sections and (P) ventral view. (I-P) Arrows indicate the dorsal mesoderm and arrowheads indicate the dorsal ectoderm. (A) Stage 10 D. melanogaster embryo hybridized with a D. melanogaster bap probe, which detects bap mRNA expression in the trunk visceral mesoderm (TVM) and hindgut visceral mesoderm (HVM) primordia (foregut/FVM expression out of focus). (B) Hybridization of a stage 10 D. virilis embryo with a D. virilis bap probe shows an identical expression pattern as in D. melanogaster. (C) D. melanogaster bapDS3.5-lacZ (stage 10) recapitulating bap expression in HVM and FVM. Low levels of TVM expression are also seen. (D) D. virilis bapDS4.6-R-lacZ activity is nearly identical to that of D. melanogaster bapDS3.5-lacZ. (E,F) Stage 14 embryos carrying the same constructs as embryos in C,D, respectively, show foregut and hindgut visceral mesoderm expression. (G) D. melanogaster bap3-lacZ recapitulates the TVM pattern of bap mRNA expression during stage 10. (H) D. virilis bapDS2.7-R-lacZ activity is similar to D. melanogaster bap3-lacZ activity. (I) D. melanogaster bap3.2-lacZ activity in stage 11 embryo is largely confined to the TVM primordia, although there are traces of ectopic activity in the dorsal ectoderm (arrowhead). (J) D. virilis bapV1-lacZ activity is similar to D. melanogaster bap3.2-lacZ activity. (K) D. melanogaster bap3.2.1-lacZ embryo (stage11) showing ectopic segmented enhancer activity in the dorsal ectoderm in addition to normal mesodermal expression. (L) D. virilis bapV2-lacZ showing ectopic ectodermal and largely normal mesodermal enhancer activity, similar to D. melanogaster bap3.2.1. (M) Cross-sectioned bap3-lacZ embryo (stage 10) showing exclusive dorsal-mesodermal enhancer activity. (N) bap3.2-lacZ with largely mesodermal expression but weak ectopic ectodermal expression. (O) bap3.2.1-lacZ showing equally strong activity in dorsal mesoderm and dorsal ectoderm. (P) Stage 9 embryo stained for bap mRNA (green) and phospho-Mad (red), showing coincidence of the ventral borders of nuclear pMad and bap mRNA expression.