Epigenetic countermarks in mitotic chromosome condensation

Mitosis in metazoans is characterized by abundant phosphorylation of histone H3 and involves the recruitment of condensin complexes to chromatin. The relationship between the 2 phenomena and their respective contributions to chromosome condensation in vivo remain poorly understood. Recent studies have shown that H3T3 phosphorylation decreases binding of histone readers to methylated H3K4 in vitro and is essential to displace the corresponding proteins from mitotic chromatin in vivo. Together with previous observations, these data provide further evidence for a role of mitotic histone H3 phosphorylation in blocking transcriptional programs or preserving the ‘memory’ PTMs. Mitotic protein exclusion can also have a role in depopulating the chromatin template for subsequent condensin loading. H3 phosphorylation thus serves as an integral step in the condensation of chromosome arms.Research in K.v.W. laboratory is supported in part by grant SAF2013–42289-R from the Spanish Ministry of Economics and Competitiveness. C.M.G. is a CSIC predoctoral fellow financed by FPI grant BES-2014–068580. Research in the T.G.K. laboratory is supported by grants from the NIH, GM101664, GM106416, and GM100907.Peer reviewe