General Biology Seminar

The apical plasma membranes in many polarized epithelial cells show highly specialized morphological adaptations, such as villi in the gut or rhabdomeres in photoreceptors, which enable them to fulfill distinct physiological functions. The terminal cells of the Drosophila tracheal system generate an extreme plasma membrane specialization, the intracellular tubules that form the lumen of the oxygen transporting cell branches. The actin cytoskeleton has been suggested to be necessary for the formation and maintenance of the lumen, but it is not known how actin interacts with the luminal plasma membrane. We have found that the membranes forming the intracellular tubules contain lipids and proteins typical of apical plasma membranes in polarized epithelial cells. The Drosophila synaptotagmin-like protein Bitesize (Btsz) and the activated form of its interaction partner Moesin are also located at the growing luminal membrane. Depletion of either Btsz or Moesin leads to actin mis-localisation and defects in branch and lumen formation. We propose that the actin cytoskeleton, through its interaction with Btsz via Moesin directs apical membrane morphogenesis to create and maintain distinct intracellular tubules. The role of other proteins in the mechanism of tube formation will also be discussed.