Polarized exocyst-mediated vesicle fusion directs intracellular lumenogenesis within the C. elegans excretory cell

• DOI: 10.1016/j.ydbio.2014.07.019
• Publication Date: 2014-08-04T23:16:43Z
• Authors: Stephen T. Armenti; Emily Chan; Jeremy Nance
• Keywords: 0301 basic medicine; Secretory Vesicles; Vesicular Transport Proteins; Vesicle trafficking; Cell Biology; Protein Serine-Threonine Kinases; Lumenogenesis; Tubulogenesis; Membrane Fusion; 03 medical and health sciences; Osmoregulation; Animals; PAR proteins; RNA Interference; ral GTP-Binding Proteins; Exocyst; RNA, Small Interfering; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Molecular Biology; Protein Kinase C; Developmental Biology

Lumenogenesis of small seamless tubes occurs through intracellular membrane growth and directed vesicle fusion events. Within the Caenorhabditis elegans excretory cell, which forms seamless intracellular tubes (canals) that mediate osmoregulation, lumens grow in length and diameter when vesicles fuse with the expanding lumenal surface. Here, we show that lumenal vesicle fusion depends on the small GTPase RAL-1, which localizes to vesicles and acts through the exocyst vesicle-tethering complex. Loss of either the exocyst or RAL-1 prevents excretory canal lumen extension. Within the excretory canal and other polarized cells, the exocyst co-localizes with the PAR polarity proteins PAR-3, PAR-6 and PKC-3. Using early embryonic cells to determine the functional relationships between the exocyst and PAR proteins, we show that RAL-1 recruits the exocyst to the membrane, while PAR proteins concentrate membrane-localized exocyst proteins to a polarized domain. These findings reveal that RAL-1 and the exocyst direct the polarized vesicle fusion events required for intracellular lumenogenesis of the excretory cell, suggesting mechanistic similarities in the formation of topologically distinct multicellular and intracellular lumens.