Background

Chromatin bridges are strands of incompletely segregated DNA connecting the anaphase poles or daughter nuclei. If unresolved, chromatin bridges can break in cytokinesis leading to micronuclei formation and accumulation of DNA damage. To prevent this, human cells form accumulations of polymerized actin (actin patches) at the base of the intercellular canal to stabilize chromatin bridges; however, the molecular mechanisms involved are incompletely understood.

Method

To investigate this, we used site directed mutagenesis, RNA silencing, replacement of endogenous proteins with transfected wild-type or mutant transgenes, confocal microscopy, live cell imaging and biochemistry techniques.

Results

In the present study, we show that RhoA, a member of the Rho family of small GTPases which control the growth or contraction of filamentous actin fibers, localizes to actin patches and is required for stable chromatin bridges in cytokinesis. Inhibition of RhoA reduces actin patch formation and promotes chromatin bridge breakage by confocal microscopy analysis of fixed cells or live-cell fluorescence microscopy. Furthermore, chromatin breakage in RhoA-deficient cells is not caused by premature abscission but likely correlates with reduced actin patches compared with wild-type cells.

Conclusion

We propose a novel role for RhoA in preventing chromatin bridge breakage by promoting actin patch formation in cytokinesis.

Impact statement

Because chromatin breakage can lead to genomic instability that is associated with cancer formation or progression, understanding the mechanisms by which human cells stabilize chromatin bridges may help us understand mechanisms of tumorigenesis.