Essential for ensuring the polarized growth of tracheal seamless tubes. During seamless tube morphogenesis, likely to act as a GTPase-activating protein (GAP) for Rab35 to regulate vesicle trafficking from the recycling endosomes to the lumenal apical membrane to ensure the polarized dynein motor complex-dependent growth of seamless tubes along the proximodistal axis in tracheal terminal cells. When the terminal branch lumen is growing, Rab35-GTP is active and likely directs the transport of apical membrane vesicles from the soma to the distal tip of elongating terminal cell branches thus providing a continuous supply of apical membrane components as the lumen grows. Whereas when Rab35-GDP is inactivated, presumably by this GAP, apical membrane vesicles are transported to a central location adjacent to the terminal cell nucleus. Restricted to the lumenal membrane of tracheal terminal cells with increased accumulation at the growing tips of seamless tubes. Colocalizes with Rab35 at the apical membrane, cytoplasmic puncta (likely to be vesicles) and filopodia. RNAi-mediated knockdown in the trachea results in a U-turn phenotype in which the seamless tubes undergo a series of 180 degree turns in terminal tip cells.