Fig. S1. Characterization of the tup^isl-1 allele. (A-D) Immunostaining of tup^isl-1 mutants for Tup shows that the protein is in principle absent (asterisks in B,D). (E,F) tup mRNA expression is also strongly reduced. as, amnioserosa.

Fig. S2. Tup is not required for visceral mesoderm formation but may play a role in the development of dorsal somatic muscle. (A,B) The visceral mesoderm marker FasIII is expressed normally in tup^isl-1 mutants. (C,D) Formation of Kr-expressing dorsal somatic muscle cells is affected in tup^isl-1 mutants (arrows in D).

Fig. S3. Time course of Tin expression after early pan-mesodermal inhibition of Tup function and in tup^isl-1 mutants. (A-C) Tin expression is strongly reduced in stage 12 embryos (lateral view) after expressing UAS-tupΔHD (B) and in tup^isl-1 mutants (C). (D-I) At later stages (14-16), the Tin phenotype does not completely match the strong reduction of Tin-expressing cells observed at early stages. This is especially true for the embryos in which mesodermal Tup was inhibited by expressing the UAS-tupΔHD construct (E,H), but can also be observed in tup^isl-1 mutants (F,I). These findings imply an early Tup-sensitive time period for Tin expression. A-F, lateral views; G-I, dorsal views.