Fig. 4. Germ layer-specific requirement of pnr and ush for heart formation. (A,B) Histograms of tin expression in stage 13 pnr and ush mutants with (`rescue') or without mesodermal overexpression of wild-type cDNA for pnr and ush, respectively (see Materials and Methods). (A) Mesodermal (yellow) and ubiquitous (blue) pnr restores tin expression when compared with pnr mutants (red); however, ectodermal rescue (orange) moderately restores tin expression in a small percentage of embryos. (B) Mesodermal (blue) ush rescue also restores tin expression in a large proportion of embryos when compared with ush mutants (red). (C) pnr mesodermal rescued embryo shows restored tin expression, when compared with wild type (Fig. 2E). (D) pnr ectodermal rescued embryo exhibits moderately decreased tin expression (brackets indicate the embryonic domain affected with the ZKr-Gal4 driver). (E-L) Overexpression of UAS-pnrEnR (see Materials and Methods) in either the mesoderm or the ectoderm. tin (E,F) and Eve (G-L) expression. (E,G-I) Late stage 11. (F,J-L) Stage 13. (E) Mesodermal overexpression of pnrEnR causes a dramatic reduction in tin expression already at late stage 11. (F) Ectodermal overexpression causes a moderate reduction in tin expression that occurs only in later stage embryos. (G,J) Wild type. (H,K) Mesodermal overexpression of pnrEnR causes a decrease in mesodermal Eve, similar to pnr mutants (Fig. 2N). (I,L) Ectodermal overexpression causes a moderate reduction of Eve only in later stage embryos (L).

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