Transmembrane protein that plays a key role in trachea development by regulating crb localization and maintenance at the apical cell membrane (PubMed:30645584). Required for anisotropic apical surface expansion important for tracheal tube elongation and lumen stability at larval stages (PubMed:30645584). Interacts with crb. In tracheal cells, colocalizes with crb in the subapical region, a small region of the apical membrane apical to the adherens junctions. Expressed in embryos at stage 13 in tracheal fusion cells (at protein level). During embryonic stages 15 and 16, detected in the dorsal and lateral trunks, in the visceral and dorsal branches and in the transverse connective branches (at protein level). In the larvae, continuously expressed in the entire tracheal system (at protein level). Dies at second instar larval stage (PubMed:30645584). Shows reduced larval body size and shortened dorsal trunk probably due to defective membrane growth in larval tracheae (PubMed:30645584). Results in defective tracheal tube maturation including liquid clearance and gas filling resulting in twisted and uninflated tracheal tubes (PubMed:30645584). Results in mislocalization of crb from the subapical region to Vsp35/retromer-positive vesicles in the cytoplasm (PubMed:30645584). RNAi-mediated knockdown in the trachea results in a similar phenotype (PubMed:30645584). Apnoia means lack of air in Greek.