Fig. 10. The lab550 enhancer contains multiple elements that are all required for its HOX- and DPP-dependent regulation in the developing midgut endoderm. (A) Schematic representation of the developing midgut, depicting the visceral mesoderm (VM) and the endoderm. Cells in which DPP is transcribed are shown in dark blue; apparent distribution of the DPP ligand is indicated by the light blue squares. The expression of the endogenous lab gene in the endoderm is indicated by the stripes. The expression domains driven by lab550, HOMRE, DPPRE and DPPREm300 are shown below with brown bars. Embryos depicting the situation in stage 14 embryos are shown in B-D; DPP mRNA is in blue, and ß-gal expression driven by lab550 (B), HOMRE (C) and DPPREm300 (D) in brown. A schematic summary of the factors that have been demonstrated or proposed to regulate lab550 expression is shown in E.