Figure 1. Induction of splicing reporter by the Transformer‐2 (Tra2) protein. Shown is an imaginal disc in which a large clone of cells expressing the Drosophila Tra2 protein from a UAS‐cDNA transgene was generated using the flip‐out system. A lacZ splicing reporter, pCZPORF3, transcribed by a promoter active throughout the disc, is designed to detect the amount of retention of an intron that is known to be regulated by Tra2 [ 9, 10]. (a) A diagram of transcripts from the reporter construct with the regulated intron (M1) retained. The position of AUG initiation codons and β‐galactosidase reporter sequences are indicated. Expression of the reporter occurs when the intron is retained; (b) The position of the clone is marked by expression of EGFP from a UAS‐EGFP transgene; (c) Elevated expression of LacZ in the clone indicates that intron retention is increased in the presence of elevated Tra2.