Maintaining the mechanochemical properties of the cell membrane is essential for a vast number of cellular processes including the selective uptake of material and signaling, which are the essence of cellular homeostasis in every living cell. Yet, how membrane homeostasis is maintained in secretory tissues where a continuous fusion of vesicles with the apical membrane takes place is incompletely understood.
This is most dramatically demonstrated in tissues that secrete viscous cargoes from large vesicles, ranging up to 8 microns in diameter. These include the exocrine pancreas, surfactant-secreting cells in the lung, VWF-secreting endothelial cells and the tear secreting lacrimal gland cells.
In such tissues, maintaining the homeostasis of the apical surface becomes a major challenge and it is not fully understood how this is accomplished because of the inherent difficulties to manipulate and visualize these tissues by live imaging. To overcome these challenges we are studying this process in the Drosophila larval salivary gland which secrets an adhesive glycoprotein (mucin) that is used to attach the fly pupa to a solid surface during its metamorphosis.
To resolve the fate of the vesicular membrane, we are using state-of-the-art live imaging and correlative light and 3D electron microscopy. Together with the wide range of genetic and pharmacological tools available, this experimental system provides a powerful toolkit to dissect the molecular mechanisms through which secretory cells sustain the integrity of their apical surface and to maintain membrane and cellular homeostasis.
Secretory giant vesicles coated in actin (red), releasing mucin (green) in the lumen of Drosophila salivary gland. Video by Tom Biton