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DNA methylation is an essential epigenetic chromatin modification, and its maintenance in mammals requires the protein UHRF1. It is yet unclear if UHRF1 functions solely by stimulating DNA methylation maintenance by DNMT1, or if it has important additional functions. Using degron alleles, we show that UHRF1 depletion causes a much greater loss of DNA methylation than DNMT1 depletion. This is not caused by passive demethylation as UHRF1-depleted cells proliferate more slowly than DNMT1-depleted cells. Instead, bioinformatics, proteomics and genetics experiments establish that UHRF1, besides activating DNMT1, interacts with DNMT3A and DNMT3B and promotes their activity. In addition, we show that UHRF1 antagonizes active DNA demethylation by TET2. Therefore, UHRF1 has non-canonical roles that contribute importantly to DNA methylation homeostasis; these findings have practical implications for epigenetics in health and disease. [ABSTRACT FROM AUTHOR]

Author(s): Giulia Saredi [sup.1] , Hongda Huang [sup.2] , Colin M. Hammond [sup.1] , Constance Alabert [sup.1] , Simon Bekker-Jensen [sup.3] , Ignasi Forne [sup.4] , Nazaret Reverón-Gómez [sup.1] , [...], We have a limited understanding of how cells mark and identify newly replicated genomic loci that have a sister chromatid; here, unmethylated K20 in the tail of new histone H4 is shown to serve as a signature of post-replicative chromatin, which is specifically recognized by the homologous recombination complex TONSL-MMS22L. A marker for post-replicative chromatin We have a limited understanding of how cells mark and identify newly replicated genomic loci that have a sister chromatid. Here, Anja Groth and colleagues show that histone H4 tails unmethylated at lysine 20 (H4K20me0) serve as a signature of post-replicative chromatin and are specific to new histones incorporated during DNA replication. H4K20me0 is specifically recognized by a 'reader' domain of the TONSL-MMS22L homologous recombination complex, enabling differentiation of pre- and post-replicative chromatin, and allowing TONSL to function as a histone chaperone or guide repair of damaged replication forks. After DNA replication, chromosomal processes including DNA repair and transcription take place in the context of sister chromatids. While cell cycle regulation can guide these processes globally, mechanisms to distinguish pre- and post-replicative states locally remain unknown. Here we reveal that new histones incorporated during DNA replication provide a signature of post-replicative chromatin, read by the human TONSL-MMS22L.sup.1,2,3,4 homologous recombination complex. We identify the TONSL ankyrin repeat domain (ARD) as a reader of histone H4 tails unmethylated at K20 (H4K20me0), which are specific to new histones incorporated during DNA replication and mark post-replicative chromatin until the G2/M phase of the cell cycle. Accordingly, TONSL-MMS22L binds new histones H3-H4 both before and after incorporation into nucleosomes, remaining on replicated chromatin until late G2/M. H4K20me0 recognition is required for TONSL-MMS22L binding to chromatin and accumulation at challenged replication forks and DNA lesions. Consequently, TONSL ARD mutants are toxic, compromising genome stability, cell viability and resistance to replication stress. Together, these data reveal a histone-reader-based mechanism for recognizing the post-replicative state, offering a new angle to understand DNA repair with the potential for targeted cancer therapy.

JAK2 signalling is implicated in various biological processes, including cell cycle progression, apoptosis, mitotic recombination, genetic instability and alteration of heterochromatin (10-13). The most common somatic alteration of JAK2 is [...], Activation of Janus kinase 2 (JAK2) by chromosomal translocations or point mutations is a frequent event in haematological malignancies (1-6). JAK2 is a non-receptor tyrosine kinase that regulates several cellular processes by inducing cytoplasmic signalling cascades. Here we show that human JAK2 is present in the nucleus of haematopoietic cells and directly phosphorylates Tyr41 (Y41) on histone H3. Heterochromatin protein 1α (HP1α), but not HP1β, specifically binds to this region of H3 through its chromo-shadow domain. Phosphorylation of H3Y41 by JAK2 prevents this binding. Inhibition of JAK2 activity in human leukaemic cells decreases both the expression of the haematopoietic oncogene lmo2 and the phosphorylation of H3Y41 at its promoter, while simultaneously increasing the binding of HP1 α at the same site. These results identify a previously unrecognized nuclear role for JAK2 in the phosphorylation of H3Y41 and reveal a direct mechanistic link between two genes, jak2 and lmo2, involved in normal haematopoiesis and leukaemia (1-9).

KDM2A is a histone demethylase associated with transcriptional silencing, however very little is known about its in vivo role in development and disease. Here we demonstrate that loss of the orthologue kdm2aa in zebrafish causes widespread transcriptional disruption and leads to spontaneous melanomas at a high frequency. Fish homozygous for two independent premature stop codon alleles show reduced growth and survival, a strong male sex bias, and homozygous females exhibit a progressive oogenesis defect. kdm2aa mutant fish also develop melanomas from early adulthood onwards which are independent from mutations in braf and other common oncogenes and tumour suppressors as revealed by deep whole exome sequencing. In addition to effects on translation and DNA replication gene expression, high-replicate RNA-seq in morphologically normal individuals demonstrates a stable regulatory response of epigenetic modifiers and the specific de-repression of a group of zinc finger genes residing in constitutive heterochromatin. Together our data reveal a complex role for Kdm2aa in regulating normal mRNA levels and carcinogenesis. These findings establish kdm2aa mutants as the first single gene knockout model of melanoma biology. [ABSTRACT FROM AUTHOR]

Induction of gene expression in yeast and human cells involves changes in the histone modifications associated with promoters. Here we identify a histone H3 endopeptidase activity in Saccharomyces cerevisiae that may regulate these events. The endopeptidase cleaves H3 after Ala21, generating a histone that lacks the first 21 residues and shows a preference for H3 tails carrying repressive modifications. In vivo, the H3 N terminus is clipped, specifically within the promoters of genes following the induction of transcription. H3 clipping precedes the process of histone eviction seen when genes become fully active. A truncated H3 product is not generated in yeast carrying a mutation of the endopeptidase recognition site (H3 Q19A L20A) and gene induction is defective in these cells. These findings identify clipping of H3 tails as a previously uncharacterized modification of promoter-bound nucleosomes, which may result in the localized clearing of repressive signals during the induction of gene expression. [ABSTRACT FROM AUTHOR]