aret location in the transcriptional pathway specifying flight muscle identity. (A) Immunological detection of Aret expression in control (WT), hth KD (hth ↓), and salm KD (salm ↓) flight muscles, counterstained for F-actin and nuclei (blue). Note that the KD muscles do not accumulate Aret and have transformed myofibrils resulting from identity transformation. Low-magnification views of the images for WT were shown previously in Fig. 2 A. (B) Localization of Aret in jump muscles of control (left), jump muscles ectopically expressing exd plus hth (exd/hth ↑), and jump muscles expressing salm (salm ↑). Note the transformed fibrillar-type jump muscles accumulate Aret in the nuclei. Muscle morphology was assessed using phalloidin to highlight actin filaments and DAPI to stain nuclei. (C) Scheme of genetic interactions in the flight muscle identity pathway. The identity genes exd/hth and salm encode proteins that regulate expression of flight muscle structural genes; salm is genetically upstream of aret. Aret promotes flight muscle–specific alternative splicing of muscle transcripts. Bars, 20 µm.