RESUMO
The inactive X chromosome (Xi) is inherently susceptible to genomic aberrations. Replication stress (RS) has been proposed as an underlying cause, but the mechanisms that protect from Xi instability remain unknown. Here, we show that macroH2A1.2, an RS-protective histone variant enriched on the Xi, is required for Xi integrity and female survival. Mechanistically, macroH2A1.2 counteracts its structurally distinct and equally Xi-enriched alternative splice variant, macroH2A1.1. Comparative proteomics identified a role for macroH2A1.1 in alternative end joining (alt-EJ), which accounts for Xi anaphase defects in the absence of macroH2A1.2. Genomic instability was rescued by simultaneous depletion of macroH2A1.1 or alt-EJ factors, and mice deficient for both macroH2A1 variants harbor no overt female defects. Notably, macroH2A1 splice variant imbalance affected alt-EJ capacity also in tumor cells. Together, these findings identify macroH2A1 splicing as a modulator of genome maintenance that ensures Xi integrity and may, more broadly, predict DNA repair outcome in malignant cells.
Assuntos
Processamento Alternativo , Reparo do DNA , Epigênese Genética , Instabilidade Genômica , Histonas/fisiologia , Anáfase , Animais , Linhagem Celular , Instabilidade Cromossômica , Cromossomos Humanos X , Feminino , Histonas/genética , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos KnockoutRESUMO
Recent integrative epigenome analyses highlight the importance of functionally distinct chromatin states for accurate cell function. How these states are established and maintained is a matter of intense investigation. Here, we present evidence for DNA damage as an unexpected means to shape a protective chromatin environment at regions of recurrent replication stress (RS). Upon aberrant fork stalling, DNA damage signaling and concomitant H2AX phosphorylation coordinate the FACT-dependent deposition of macroH2A1.2, a histone variant that promotes DNA repair by homologous recombination (HR). MacroH2A1.2, in turn, facilitates the accumulation of the tumor suppressor and HR effector BRCA1 at replication forks to protect from RS-induced DNA damage. Consequently, replicating primary cells steadily accrue macroH2A1.2 at fragile regions, whereas macroH2A1.2 loss in these cells triggers DNA damage signaling-dependent senescence, a hallmark of RS. Altogether, our findings demonstrate that recurrent DNA damage contributes to the chromatin landscape to ensure the epigenomic integrity of dividing cells.
Assuntos
Carcinogênese/genética , Cromatina/genética , Dano ao DNA/genética , Reparo do DNA/genética , Replicação do DNA/genética , Histonas/genética , Recombinação Homóloga/genética , Proteína BRCA1/metabolismo , Divisão Celular/genética , Células Cultivadas , Senescência Celular/genética , Instabilidade Genômica/fisiologia , Humanos , Transdução de Sinais/genéticaRESUMO
We have previously shown that macro histone variants (macroH2A) are expressed at low levels in stem cells and are up-regulated during differentiation. Here we show that the knockdown of macro histone variants impaired the in vitro and in vivo differentiation of human pluripotent cells, likely through defects in the silencing of pluripotency-related genes. ChIP experiments showed that during differentiation macro histone variants are recruited to the regulatory regions of pluripotency and developmental genes marked with H3K27me3 contributing to the silencing of these genes.