FoxK and Dfos regulate Lab independently of Mad. FoxK (A, arrow) and Dfos (B, arrow) colocalize in the midgut endoderm of wild-type embryos (C, arrow). Homozygous FoxK¹⁶ embryos lack FoxK (D) but accumulate Dfos (E, arrow). (F) Dfos^1/Sro mutant embryos maintain FoxK expression in the endoderm (arrow). Wild-type expression of FoxK (G, arrow), Lab (H, arrowhead), and pSmad (I, arrow) in the midgut endoderm in stage 15 embryos. A Z-axis projection of all the endoderm is shown. The arrowhead in I indicates pSmad staining in PS3. (J–L) FoxK and Dfos coexpression in the endoderm (48Y-Gal4) induces anterior expansion of Lab (K, arrow). The arrowhead indicates the normal position of Lab. Coexpression of FoxK and tkv^DN (M, green) in the endoderm results in loss of Lab (N, arrowhead) and pSmad in PS7 (O, arrow). Coexpression of FoxK, Dfos, and tkv^DN in the endoderm restores midgut constrictions (P, arrowhead) and Lab accumulation (Q, arrowhead), whereas pSmad expression is still missing in PS7 (R, arrow). Note that the expression of pSmad in PS3 is still present (R, arrowhead).