# Robust Gap Repair in the Contractile Ring Ensures Timely Completion of Cytokinesis

## TL;DR

This study shows that contractile rings in C. elegans embryos can repair gaps and continue cell division even after being cut.

## Contribution

The study reveals that contractile rings can autonomously repair and maintain timely cytokinesis despite structural discontinuities.

## Key findings

- Laser cutting of contractile rings causes tension release but not disintegration.
- Contractile rings repair gaps by recruiting new material and continue constriction.
- Cytokinesis timing remains unaffected even after multiple cuts to the ring.

## Abstract

Cytokinesis in animal cells requires the constriction of an actomyosin contractile ring, whose architecture and mechanism remain poorly understood. We use laser microsurgery to explore the biophysical properties of constricting contractile rings in C. elegans embryos. Laser cutting causes rings to snap open, which is a sign of tension release. However, instead of disintegrating, ring topology recovers and constriction proceeds. In response to severing, a finite gap forms that is proportional to ring perimeters before cutting, demonstrating that tension along the ring decreases throughout constriction. Severed rings repair their gaps by recruiting new material and subsequently increase constriction rate and complete cytokinesis with the same timing as uncut rings. Rings repair successive cuts and exhibit substantial constriction when gap repair is prevented. Our analysis suggests that cytokinesis is accomplished by contractile modules that assemble and contract autonomously, enabling local repair of the actomyosin network throughout constriction. Consequently, cytokinesis is a highly robust process impervious to discontinuities in contractile ring structure.