The selector genes midline and H15 control ventral leg pattern by both inhibiting Dpp signaling and specifying ventral fate

mid and H15 encode Tbx20 transcription factors that specify ventral pattern in the Drosophila leg. We find that there are at least two pathways for mid and H15 specification of ventral fate. In the first pathway, mid and H15 negatively regulate Dpp, the dorsal signal in leg development. mid and H15 block the dorsalizing effects of Dpp signaling in the ventral leg. In loss- and gain-of-function experiments in imaginal discs, we show that mid and...