The histone H4 lysine 20 demethylase DPY-21 regulates the dynamics of condensin DC binding

Abstract

Condensin is a multi-subunit SMC complex that binds to and compacts chromosomes. Here we addressed the regulation of condensin binding dynamics using C. elegans condensin DC, which represses X chromosomes in hermaphrodites for dosage compensation. We established fluorescence recovery after photobleaching (FRAP) using the SMC4 homolog DPY-27 and showed that a well-characterized ATPase mutation abolishes its binding. Next, we performed FRAP in the background of several chromatin modifier mutants that cause varying degrees of X-chromosome derepression. The greatest effect was in a null mutant of the H4K20me2 demethylase DPY-21, where the mobile fraction of condensin DC reduced from ∼30% to 10%. In contrast, a catalytic mutant of dpy-21 did not regulate condensin DC mobility. Hi-C data in the dpy-21 null mutant showed little change compared to wild type, uncoupling Hi-C measured long-range DNA contacts from transcriptional repression of the X chromosomes. 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 DC loads and spreads from recruitment sites to create loop-anchored TADs inC. elegans

“…The repressive effect of condensin DC may be local and loop extrusion independent. In agreement with this, a null mutant of dpy-21 (a non condensin DCC subunit) results in X upregulation without significantly altering Hi-C interactions [75]. Future work separating Hi-C features and dosage compensation should shed light on how a condensin complex was co-opted to repress transcription of an entire chromosome.…”

“…One explanation is that such off-target loading is skewed towards the X-chromosome by the increased condensin DC ‘local concentration’ produced by SDCs. However, the loss of SDC-2 does not result in global redistribution of condensin DC; in the absence of SDC-2, the FRAP recovery of condensin DC shows similar dynamics to that of free-floating molecules [75]. Therefore, the simplest conclusion reconciling many observations is that the rex sites act as condensin DC loading sites and additional features of the DCC system explain the non- rex loops within TADs.…”

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 Xlinked 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. Number of significantly up and down regulated genes (AdjP<0.05, |LFC|>0.5) per chromosome upon cleavage of condensin I/I DC (dpy-26 cs ), condensin II (kle-2 cs ), or the alternative kleisin subunits of cohesin, scc-1 cs and coh-1 cs individually or together.…”

Latest trends in bioimaging and building a proactive network of early-career young scientists around bioimaging in Europe

“…Among the many high-quality oral presentations, we would like to put in the spotlight that of Laura Breimann (Harvard Medical School, Boston, MA, USA), who uses fluorescence microscopy to study mechanisms of transcription repression by an X-specific condensin in Caenorhabditis elegans ( Breimann et al, 2022 ). Laura won the Oral Presentation Contest and was awarded a prize sponsored by BioAxial.…”