RESUMO
Most autosomal genes are thought to be expressed from both alleles, with some notable exceptions, including imprinted genes and genes showing random monoallelic expression (RME). The extent and nature of RME has been the subject of debate. Here we investigate the expression of several candidate RME genes in F1 hybrid mouse cells before and after differentiation, to define how they become persistently, monoallelically expressed. Clonal monoallelic expression is not present in embryonic stem cells, but we observe high frequencies of monoallelism in neuronal progenitor cells by assessing expression status in more than 200 clones. We uncover unforeseen modes of allelic expression that appear to be gene-specific and epigenetically regulated. This non-canonical allelic regulation has important implications for development and disease, including autosomal dominant disorders and opens up therapeutic perspectives.
Assuntos
Alelos , Desequilíbrio Alélico , Epigênese Genética , Doenças Musculares/genética , Células-Tronco Neurais/metabolismo , Doenças Neurodegenerativas/genética , Hidrolases Anidrido Ácido/genética , Hidrolases Anidrido Ácido/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Proteínas Reguladoras de Apoptose/genética , Proteínas Reguladoras de Apoptose/metabolismo , Diferenciação Celular , Quimera , Células Clonais , Metilação de DNA , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Modelos Animais de Doenças , Feminino , Dosagem de Genes , Frequência do Gene , Loci Gênicos , Impressão Genômica , Masculino , Camundongos , Doenças Musculares/metabolismo , Doenças Musculares/patologia , Neoplasias/genética , Neoplasias/metabolismo , Neoplasias/patologia , Células-Tronco Neurais/patologia , Doenças Neurodegenerativas/metabolismo , Doenças Neurodegenerativas/patologia , Osteoporose/genética , Osteoporose/metabolismo , Osteoporose/patologia , Receptores de Ácido Caínico/genética , Receptores de Ácido Caínico/metabolismo , Receptor de GluK2 CainatoRESUMO
The chromosomal protein SMCHD1 plays an important role in epigenetic silencing at diverse loci, including the inactive X chromosome, imprinted genes, and the facioscapulohumeral muscular dystrophy locus. Although homology with canonical SMC family proteins suggests a role in chromosome organization, the mechanisms underlying SMCHD1 function and target site selection remain poorly understood. Here we show that SMCHD1 forms an active GHKL-ATPase homodimer, contrasting with canonical SMC complexes, which exist as tripartite ring structures. Electron microscopy analysis demonstrates that SMCHD1 homodimers structurally resemble prokaryotic condensins. We further show that the principal mechanism for chromatin loading of SMCHD1 involves an LRIF1-mediated interaction with HP1γ at trimethylated histone H3 lysine 9 (H3K9me3)-modified chromatin sites on the chromosome arms. A parallel pathway accounts for chromatin loading at a minority of sites, notably the inactive X chromosome. Together, our results provide key insights into SMCHD1 function and target site selection.
Assuntos
Cromatina/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Histonas/metabolismo , Cromossomo X/metabolismo , Adenosina Trifosfatases/química , Adenosina Trifosfatases/metabolismo , Sequência de Aminoácidos , Animais , Linhagem Celular , Cromatina/química , Homólogo 5 da Proteína Cromobox , Proteínas Cromossômicas não Histona/química , Células HEK293 , Histonas/química , Humanos , Lisina/análise , Camundongos , Modelos Moleculares , Dados de Sequência Molecular , Mapas de Interação de Proteínas , Multimerização Proteica , Estrutura Terciária de Proteína , Alinhamento de SequênciaRESUMO
Histone acetyl transferases (HATs) play distinct roles in many cellular processes and are frequently misregulated in cancers. Here, we study the regulatory potential of MYST1-(MOF)-containing MSL and NSL complexes in mouse embryonic stem cells (ESCs) and neuronal progenitors. We find that both complexes influence transcription by targeting promoters and TSS-distal enhancers. In contrast to flies, the MSL complex is not exclusively enriched on the X chromosome, yet it is crucial for mammalian X chromosome regulation as it specifically regulates Tsix, the major repressor of Xist lncRNA. MSL depletion leads to decreased Tsix expression, reduced REX1 recruitment, and consequently, enhanced accumulation of Xist and variable numbers of inactivated X chromosomes during early differentiation. The NSL complex provides additional, Tsix-independent repression of Xist by maintaining pluripotency. MSL and NSL complexes therefore act synergistically by using distinct pathways to ensure a fail-safe mechanism for the repression of X inactivation in ESCs.DOI: http://dx.doi.org/10.7554/eLife.02024.001.
Assuntos
Células-Tronco Embrionárias/citologia , Histona Acetiltransferases/metabolismo , RNA Longo não Codificante/metabolismo , Animais , Diferenciação Celular , Cromatina/metabolismo , Células-Tronco Embrionárias/metabolismo , Camundongos , Ligação Proteica , RNA Longo não Codificante/genética , Inativação do Cromossomo XRESUMO
The Arabidopsis gene DDM1 is required to maintain DNA methylation levels and is responsible for transposon and transgene silencing. However, rather than encoding a DNA methyltransferase, DDM1 has similarity to the SWI/SNF family of adenosine triphosphate-dependent chromatin remodeling genes, suggesting an indirect role in DNA methylation. Here we show that DDM1 is also required to maintain histone H3 methylation patterns. In wild-type heterochromatin, transposons and silent genes are associated with histone H3 methylated at lysine 9, whereas known genes are preferentially associated with methylated lysine 4. In ddm1 heterochromatin, DNA methylation is lost, and methylation of lysine 9 is largely replaced by methylation of lysine 4. Because DNA methylation has recently been shown to depend on histone H3 lysine 9 methylation, our results suggest that transposon methylation may be guided by histone H3 methylation in plant genomes. This would account for the epigenetic inheritance of hypomethylated DNA once histone H3 methylation patterns are altered.