Abstract
Distinct tube size is critical for the function of human tubular organs such as the lung, vascular system, and kidney. Aberrant tube sizes can lead to devastating human illnesses, including polycystic kidney disease. The Drosophila trachea provides a premier genetic system to investigate the fundamental mechanisms that regulate tube size. Here we describe the function of a novel gene, apnoia, in tube-size regulation. apn encodes an apical membrane protein, Apnoia (Apn), with three helical transmembrane domains. Loss-of-function apn mutants show shorter-tube and air-filling defects in larval trachea, whereas there are no obvious defects in embryonic trachea. Conversely, overexpression of apn in trachea leads to significant tube over-elongation. We analyzed apical luminal matrix and cell polarity in these longer tubes. It is interesting to note that we observed normal establishment of cell polarity, whereas all luminal matrix components are significantly reduced. In addition, we observed that some matrix components are localized in cytoplasmic vesicles, suggesting secretion defects in apn overexpressing trachea. Taken together, these results strongly suggest the possibility that apn is directly or indirectly involved in vesicular trafficking to regulate tube size.
