Fig. 2. The GAL4/UAS transplantation system exclusively labels syncytia. A clone in a stage 17 embryo that overlaps fat body and somatic musculature. All descendants of the transplanted cell are labelled red by the cell-lineage marker RITC-dextran (A), whereas syncytia containing both donor- and recipient-derived nuclei express GFP (B). The superimposition (C) reveals that the syncytia marker GFP is not expressed in the mononuclear fat body (asterisk). This tissue is solely labelled by the cell-lineage marker. Most somatic muscles are double labelled and therefore represent syncytia consisting of clonally non-related nuclei. The muscle indicated by the arrowhead is labelled only by the cell-lineage marker, indicating that this syncytium consists exclusively of donor-derived nuclei.