Fig. 1. Generation of mutants lacking specific phases of tin expression. (A-C) Schematic embryo drawings illustrating main areas and phases of tin expression and their assignment to enhancer elements, color-coded as in D. (D) tin locus with its enhancers tinA-tinD (white boxes: introns) (Yin et al., 1997). Constructs used in transgenes are shown below. As expected, tinD did not have any rescuing activity in tin^- because the Dpp response requires the presence of Twist-dependent Tin (Xu et al., 1998). (E) tin-null mutant embryos expressing Tin from tin-AB show uniform mesodermal Tin expression at stage 9. (F) tin-null mutant embryos with tin-ABD show dorsal mesodermal Tin expression at stage 10.