The H4K20 demethylase DPY-21 regulates the dynamics of condensin DC binding

Abstract

Condensin is a multi-subunit SMC complex that binds to and compacts chromosomes. Unlike cohesin, in vivo regulators of condensin binding dynamics remain unclear. Here we addressed this question using C. elegans condensin DC, which specifically binds to and represses transcription of both X chromosomes in hermaphrodites for dosage compensation. Mutants of several chromatin modifiers that regulate H4K20me and H4K16ac cause varying degrees of X chromosome derepression. We used fluorescence recovery after photobleaching (FRAP) to analyze how these modifiers regulate condensin DC binding dynamics in vivo. We established FRAP using the SMC4 homolog DPY-27 and showed that a well-characterized ATPase mutation abolishes its binding. The greatest effect on condensin DC dynamics was in a null mutant of the H4K20me2 demethylase DPY-21, where the mobile fraction of the complex reduced from ~30% to 10%. In contrast, a catalytic mutant of dpy-21 did not regulate condensin DC mobility. Separation of catalytic and non-catalytic activity is also supported by Hi-C data in the dpy-21 null mutant. Together, our results indicate that DPY-21 has a non-catalytic role in regulating the dynamics of condensin DC binding, which is important for transcription repression.

Condensin I folds theC. elegansgenome

“…The X-specific increase in gene expression thereby demonstrates that condensin I/I DC ongoing presence on chromatin is essential to maintain X-linked gene regulation, and not the consequence of secondary chromatin modifications which in turn regulate gene expression independently of condensin I DC . As condensins have been shown to be able to extrude both DNA and chromatin loops in vitro (Ganji et al 2018; Kong et al 2020), these results, together with a recent analysis showing that the ATPase activity of DPY-27 is necessary for its binding to the X chromosome (Breimann et al 2021) strongly suggest that condensin I DC constantly extrudes loops to regulate gene expression.…”