Fig. 1. Mesodermal expression pattern of Dorsocross. Dorsocross protein (shown in green) was detected by immunofluorescent staining using antisera recognizing Doc2 and Doc3 (anti-Doc2+3 or anti-Doc3+2 as indicated), except in A, which shows Doc3 RNA detection by in situ hybridization. Images are merged optical sections of embryonic trunk mesoderm (lateral views, anterior towards the left and dorsal upwards, unless noted otherwise). Broken lines indicate borders between mesoderm (mes) and ectoderm (ect). (A) Stage 10 wild-type embryo showing overlapping expression of Doc3 RNA and phospho-Mad in dorsal mesoderm. (B) Ventral view of late stage 10 wild-type embryo with alternating expression of Doc2+3 and the early visceral mesoderm marker Bap (red). as, amnioserosa. (C) Mesodermal expression of Doc and Bap extend towards the ventral midline (center) upon 2xPE-twi-GAL4-driven ectopic expression of Tkv^Q253D. (D) Early stage 10 wild-type embryo stained for Doc2+3, Tin (red) and Wg (blue) proteins. Co-localized Doc and Tin in dorsal mesoderm appears yellow. Doc is strictly aligned with the Wg stripes. (E) Expanded Doc expression upon ectopically expressed wg (via 2xPE-twi-GAL4) in the dorsal mesoderm at stage 10. (F) Wild-type stage 11 embryo stained as in D. Clusters of Doc⁺ cells in the dorsal mesoderm are marked by white arrowheads, a Doc^– Eve cluster by a red arrowhead and lateral (somatic) mesodermal clusters by arrows. (G) Mutually exclusive expression of Doc (white arrowheads) and Eve (red arrowheads) proteins along the dorsal mesodermal margin in wild type at stage 11. (H) Stage 11 tinD-lacZ embryo, labeled with anti-Doc2+3 (green), anti-Pnr (red) and anti-ß-Galactosidase antibodies (blue). Overlap (white; arrowheads) occurs near the dorsal margin of the mesoderm. Additional Pnr⁺ nuclei (red) are from ectodermal invaginations. (I) Stage 12 wild-type embryo stained for Doc and Pnr proteins showing co-expression along the dorsal edge of the mesoderm (overlap appears yellow). (J) High magnification view of early stage 12 svp-lacZ embryo stained for Doc2+3 proteins, mid RNA (blue) and ß-Galactosidase (red). All cardioblasts, which are either positive for mid (Tin-CB) or svp-LacZ (Svp-CB), express Doc, as do svp-lacZ⁺ pericardial cells (Svp-PC). Differences in Doc levels within svp-lacZ-clusters (arrow) probably reflect continued expression of Doc in Svp-CBs versus its termination in Svp-PCs.