Fig. 7. rols mutant cells are able to fuse with wild-type myoblasts as fusion-competent cells and exhibit fusion defects as muscle precursor cells. Descendants of the transplanted cells are visualized by histochemical ß-galactosidase staining only in syncytial tissues that co-express GAL4 and UAS-lacZ. Clones in the ventral and lateral larval muscles after transplantation of homozygous rols null mutant cells are shown. (A) Ventrolateral larval muscle clone spanning two segments derived from a transplantation of three to five homozygous mutant cells. (B) Most descendants of rols mutant cells behave normally in wild-type background. This ventral muscle clone shows two additional structures, one spindle-like (arrow) and one more compact (arrowhead) with two to three nuclei each. (C) Ventral bilateral clone in two larval muscles, a normal syncytium and a small elongated striated syncytium with four nuclei, probably representing a muscle precursor. (D) Part of a ventral muscle clone with a very shortened mini-muscle attached correctly to the epidermis.