Stop codon readthrough of a POU transcription factor regulates steroidogenesis and developmental transitions

Translational stop codon readthrough generates C-terminally extended protein isoforms. While evidence mounts of readthrough as a global phenomenon, proofs of its functional consequences are scarce. We show that readthrough of the Drosophila POU/Oct transcription factor gene drifter (dfr) occurs at a high rate and in a spatiotemporal manner in vivo, reaching more than 50% in the larval prothoracic gland. Phylogenetic analyses suggested that readthrough of dfr is conserved among Dipterans, with C-terminal extensions harboring intrinsically disordered regions and amino acids streches implied in transcriptional activation. The extended Dfr isoform is required for maintaining normal levels of the growth hormone ecdysone through regulation of its biosynthetic genes, acting in synergy with the transcription factor Molting defective (Mld). A 14-bp deletion that abolished readthrough, caused prolonged larval development and delayed metamorphosis. This study provides a striking example of alternative genetic decoding that feeds into the progression from one life cycle stage to another. Overall design: Two biological replicates were analyzed for each of 6 conditions (three genotypes; two treatments per genotype)