An ESCRT grommet cooperates with a diffusion barrier to maintain nuclear integrity

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The endosomal sorting complexes required for transport (ESCRT) machinery is crucial for membrane remodeling, but its role in nuclear envelope (NE) integrity is not fully understood.
• Nuclear envelope discontinuities can compromise nucleocytoplasmic compartmentalization, a fundamental aspect of cellular function.

Purpose of the Study:

• To elucidate the molecular mechanisms by which ESCRT proteins maintain nuclear envelope barrier integrity.
• To investigate the distinct roles of ESCRT-III proteins and CHMP7/Cmp7 in sealing nuclear envelope holes.

Main Methods:

• Utilizing the Schizosaccharomyces pombe model system with a single NE hole generated during mitotic extrusion.
• Employing microscopy and biochemical approaches to analyze ESCRT protein function and NE sealing dynamics.
• Investigating the role of spindle pole body proteins in forming diffusion barriers.

Main Results:

• Identified two distinct modes of ESCRT-mediated NE repair: a grommet-like function in anaphase B and a sealing module in interphase, both dependent on CHMP7/Cmp7.
• Demonstrated that CHMP7/Cmp7 is essential for restricting NE hole size and eventual sealing.
• Showed that nucleocytoplasmic compartmentalization is maintained even with large NE discontinuities (up to 540 nm) in the absence of CHMP7/Cmp7, suggesting alternative diffusion barriers.
• Implicated spindle pole body proteins as key components of a diffusion barrier acting with CHMP7/Cmp7 during anaphase B.

Conclusions:

• ESCRT proteins, specifically distinct ESCRT-III complements and CHMP7/Cmp7, play critical roles in maintaining nuclear envelope integrity through dual mechanisms of NE hole restriction and sealing.
• Spindle pole body proteins contribute to diffusion barriers that cooperate with ESCRT machinery to preserve nucleocytoplasmic compartmentalization.
• These findings reveal novel mechanisms of nuclear envelope remodeling and barrier maintenance beyond canonical nuclear pore complexes.