Elsevier

Developmental Biology

Volume 394, Issue 1, 1 October 2014, Pages 110-121
Developmental Biology

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

https://doi.org/10.1016/j.ydbio.2014.07.019Get rights and content
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Highlights

  • The exocyst and RAL-1 are required for single-cell lumen extension.

  • The exocyst and RAL-1 mediate polarized vesicle fusion in the canal cell.

  • RAL-1 recruits the exocyst to the cell membrane.

  • PAR proteins polarize the membrane distribution of the exocyst.

Abstract

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
PAR proteins
Lumenogenesis
Tubulogenesis
Vesicle trafficking
Osmoregulation

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