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

Dev Biol. 2014 Oct 1;394(1):110-21. doi: 10.1016/j.ydbio.2014.07.019. Epub 2014 Aug 4.


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.

Keywords: Exocyst; Lumenogenesis; Osmoregulation; PAR proteins; Tubulogenesis; Vesicle trafficking.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Caenorhabditis elegans / embryology*
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism
  • Membrane Fusion / physiology*
  • Osmoregulation / genetics
  • Protein Kinase C / genetics
  • Protein Kinase C / metabolism
  • Protein Serine-Threonine Kinases
  • RNA Interference
  • RNA, Small Interfering
  • Secretory Vesicles / metabolism*
  • Vesicular Transport Proteins / genetics
  • ral GTP-Binding Proteins / genetics*


  • Caenorhabditis elegans Proteins
  • RNA, Small Interfering
  • Vesicular Transport Proteins
  • par-6 protein, C elegans
  • PAR-3 protein, C elegans
  • Protein Serine-Threonine Kinases
  • PKC-3 protein
  • Protein Kinase C
  • ral GTP-Binding Proteins