Structural changes in chromosomes driven by multiple condensin motors during mitosis.

Area of Science:

• Cell Biology
• Computational Biology
• Polymer Physics

Background:

• Understanding chromosome organization during mitosis is crucial for cell division.
• Condensin I and II motors play key roles in shaping mitotic chromosomes through loop extrusion.
• Previous models have limitations in fully capturing the dynamic nature of chromosome folding.

Purpose of the Study:

• To develop a parameter-free computational framework to predict chromosome organization during mitosis.
• To investigate the role of multiple condensin motors (I and II) in loop extrusion and chromosome folding.
• To elucidate the helical scaffold structure formed by condensin motors during mitosis.

Main Methods:

• Utilizing a computational framework based on loop extrusion (LE) by condensin I/II motors.
• Employing a polymer physics-based, data-driven method using Hi-C contact maps as input.
• Analyzing the formation of a dynamically changing helical scaffold and random helix perversions (RHPs).

Main Results:

• The framework accurately reproduces experimental contact probability profiles for mitotic chromosomes in HeLa and DT40 cells.
• The loop extrusion rate increases as cells approach metaphase.
• Condensin II-mediated loops are significantly larger than condensin I-mediated loops, forming overlapping structures stapled to a helical scaffold.

Conclusions:

• The developed computational framework provides a robust, parameter-free model for mitotic chromosome organization.
• The study reveals the dynamic helical scaffold and random helix perversions as key features of chromosome folding.
• The findings offer testable predictions for future imaging experiments, advancing our understanding of chromosome structure and dynamics.