When expression is driven by Scer\GAL4hs.2sev heat shocked 2.5hr after egg laying, tracheal development in the embryo is abnormal, no lumen appears. Invaginations of a few tracheal cells that express a small patch of lumen material are occasionally observed. Effects are only seen with two copies of P{UAS-trh.DN}. Induction 4hr AEL does not perturb the development of the tracheal pits, though cells in the dorsal trunk in each segment fail to fuse with their neighbours.