Three-dimensional organization of chromatids by nuclear envelope-associated structures

Area of Science:

• Cell Biology
• Evolutionary Biology
• Biophysics

Background:

• The nuclear envelope (NE) evolved from prokaryotic plasma membranes.
• NE-associated structures, including nuclear pore complexes (NPCs), nuclear lamina, and nuclear envelope junctions (NEJs), organize chromatids within the nucleus.
• NEJs align inner and outer NE membranes via protein interactions, linking chromatids to the cytoskeleton.

Purpose of the Study:

• To explore the evolutionary origins and functional roles of NE-associated structures.
• To elucidate the mechanics of nuclear envelope junctions (NEJs) and nuclear pore complexes (NPCs) in organizing nuclear contents and responding to mechanical forces.
• To understand how NEJs and NPCs facilitate nuclear movement and internal nuclear processes like DNA repair, replication, and transcription.

Main Methods:

• Comparative analysis of NE structure and protein interactions across evolution.
• Biophysical modeling of mechanical force buffering by NEJs and NPCs.
• Examination of nucleoporin plasticity through crystallographic data.

Main Results:

• NEJs link heterochromatin to the cytoskeleton, buffering mechanical forces to protect the NE during nuclear movement.
• Mechanical forces transmitted through NEJs can induce nuclear distortions, facilitating chromatid fluctuations for DNA metabolism.
• NPCs interact with euchromatin and exhibit plasticity, coevolving to buffer mechanical forces and facilitate transport of large molecules.

Conclusions:

• NEJs and NPCs are crucial for nuclear organization, mechanical stability, and dynamic nuclear processes.
• The plasticity of NPCs is essential for both mechanical force dissipation and macromolecular transport.
• The evolution of NE-associated structures reflects a sophisticated adaptation for nuclear function in eukaryotic cells.