The exocyst complex regulates C. elegans germline stem cell proliferation by controlling membrane Notch levels

Area of Science:

• Cell Biology
• Developmental Biology
• Stem Cell Biology

Background:

• The exocyst complex is crucial for vesicle transport and plasma membrane fusion in eukaryotic cells.
• Germline stem cell (GSC) proliferation is tightly regulated by conserved Notch signaling pathways.
• The specific role of the exocyst complex in stem cell proliferation remained largely uncharacterized.

Purpose of the Study:

• To investigate the role of the exocyst complex in regulating germline stem cell (GSC) proliferation in Caenorhabditis elegans.
• To elucidate the molecular mechanisms by which the exocyst complex influences Notch signaling in GSCs.
• To determine if this exocyst-mediated regulation is conserved in mammalian cells.

Main Methods:

• Utilized Caenorhabditis elegans as a model organism to study GSC proliferation.
• Employed knockdown techniques for exocyst complex subunits and associated GTPases (Rab5, Rab11).
• Assessed Notch signaling pathway activity, membrane localization, and interactions with polarity proteins (Par6, Par5) and exocyst components.

Main Results:

• Knockdown of exocyst components or Rab GTPases disrupted asymmetric Notch distribution on GSCs, leading to cytoplasmic redistribution.
• The anterior polarity protein Par6 is essential for maintaining niche-facing Notch and exocyst levels on GSCs.
• The exocyst complex interacts with Par5 and Notch, and its components are necessary for Notch plasma membrane localization and signaling in both C. elegans and human cells.

Conclusions:

• The exocyst complex plays a critical, cell-autonomous role in regulating C. elegans GSC proliferation.
• Exocyst function is required for maintaining proper plasma membrane levels and signaling of Notch.
• This study uncovers a conserved mechanism involving the exocyst complex in stem cell proliferation and membrane protein regulation.