Transcriptional activator. In tracheal terminal cells, regulates the transcription of factors involved in the formation of a mature apical extracellular matrix (aECM) which is essential for the integrity and shape of seamless tubes. Expressed in embryo from stage 10 in all ectodermally-derived epithelia secreting cuticle. During germband retraction, epidermal expression is strongest in the T2, T3, and A8 epidermal parasegments, but not detected during primary branching. Pan-tracheal expression is first detected at stage 14 and continues during later stages coinciding with lumen growth and cuticle deposition. In addition to tracheal expression, expressed in epidermis, foregut, and hindgut. Embryonic lethal. RNAi-mediated knockdown in the trachea of first instar larvae results in discontinuous tubes. RNAi-mediated knockdown in the tracheal terminal cells of first instar larva results in lumen devoid of taenidiae and occluded with disorganized electron-dense material, pan-tracheal liquid clearance defect as well as a breaks in the dorsal trunks.