Fig. 2. Muscle founders/precursors are determined correctly in rols mutants. All nuclei of muscle founder cells are visualized at late stage 13 in the enhancer trap line rP298 by the anti-ß-galactosidase antibody. The expression of rP298 was monitored in embryos homozygous for the deficiency Df(3L)BK9 (B) and revealed essentially a wild-type pattern (A). However, at stage 15/16, the number of rP298 positive nuclei in rols mutant embryos (D) is significantly reduced compared with wild type (C). Eve expression in wild-type embryos marks the nuclei of dorsal muscle 1 (DA1, marked by a white circle in one segment) and pericardial cells (pc) (E). In rols^P1729 mutants, Eve staining in DA1 is visible only in two to five nuclei (F, marked by a white circle in one segment). This is shown for a younger embryo homozygous for the deficiency (H) where two to three nuclei of dorsal muscle 1 are stained compared with a wild-type embryo with five to ten Eve-positive nuclei (G).