Dynamic loss of H2B ubiquitylation without corresponding changes in H3K4 tri-methylation during myogenic differentiation.
Vasupradha Vethantham, Yan Yang* , Christopher Bowman*, Patrik Asp, Jeong-Heon Lee, David G. Skalnik, and Brian D. Dynlacht

Mol. Cell. Biol. published 17 January 2012, 10.1128/MCB.06026-11
http://mcb.asm.org/cgi/content/abstract/MCB.06026-11v1?etoc

Abstract

Ubiquitylation of H2B on lysine 120 (H2Bub) is associated with active transcriptional elongation. H2Bub has been implicated in histone cross-talk and is generally regarded to be a prerequisite for H3K4 and H3K79 tri-methylation in both yeast and mammalian cells. We performed a genome-wide analysis of epigenetic marks during muscle differentiation, and, strikingly, we observed a near-complete loss of H2Bub in the differentiated state. We examined the basis for global loss of this mark and found that the H2B ubiquitin E3 ligase, RNF20, was depleted from chromatin in differentiated myotubes, indicating that recruitment of this protein to genes substantially decreases upon differentiation. Remarkably, during the course of myogenic differentiation, we observed retention and acquisition of H3K4 tri-methylation on a large number of genes in the absence of detectable H2Bub. The Set1 H3K4 trimethylase complex was efficiently recruited to a subset of genes in myotubes in the absence of detectable H2Bub, accounting in part for H3K4 tri-methylation in myotubes. Our studies suggest that H3K4me3 deposition in the absence of detectable H2Bub in myotubes is mediated via Set1 and, perhaps, MLL complexes, whose recruitment does not require H2Bub. Thus, muscle cells represent a novel setting in which to explore mechanisms that regulate histone cross-talk.

Cell 2011 May 26; Epub 2011 May 26

doi10.1016/j.cell.2011.04.028

Centriolar Kinesin Kif24 Interacts with CP110 to Remodel Microtubules and Regulate Ciliogenesis.

Tetsuo Kobayashi, WY Tsang, J Li, William Lane and Brian David Dynlacht

We have identified a protein, Kif24, that shares homology with the kinesin-13 subfamily of motor proteins and specifically interacts with CP110 and Cep97, centrosomal proteins that play a role in regulating centriolar length and ciliogenesis. Kif24 preferentially localizes to mother centrioles. Loss of Kif24 from cycling cells resulted in aberrant cilia assembly but did not promote growth of abnormally long centrioles, unlike CP110 and Cep97 depletion. We found that loss of Kif24 leads to the disappearance of CP110 from mother centrioles, specifically in cycling cells able to form cilia. Kif24 is able to bind and depolymerize microtubules in vitro. Remarkably, ectopically expressed Kif24 specifically remodels centriolar microtubules without significantly altering cytoplasmic microtubules. Thus, our studies have identified a centriolar kinesin that specifically remodels a subset of microtubules, thereby regulating cilia assembly. These studies also suggest mechanistic differences between the regulation of microtubule elongation associated with centrioles and cilia.