Iris Cheung

Developmental regulation and individual differences of neuronal H3K4me3 epigenomes in the prefrontal cortex

Little is known about the regulation of neuronal and other cell-type specific epigenomes from the brain. Here, we map the genome-wide distribution of trimethylated histone H3K4 (H3K4me3), a mark associated with transcriptional regulation, in neuronal and nonneuronal nuclei collected from prefrontal cortex (PFC) of 11 individuals ranging in age from 0.5 to 69 years. Massively parallel sequencing identified 12,732–19,704 H3K4me3 enriched regions (peaks), the majority located proximal to (within 2 kb of) the transcription start site (TSS) of annotated genes. These included peaks shared by neurons in comparison with three control (lymphocyte) cell types, as well as peaks specific to individual subjects. We identified 6,213 genes that show highly enriched H3K4me3 in neurons versus control. At least 1,370 loci, including annotated genes and novel transcripts, were selectively tagged with H3K4me3 in neuronal but not in nonneuronal PFC chromatin. Our results reveal age-correlated neuronal epigenome reorganization, including decreased H3K4me3 at approximately 600 genes (many function in developmental processes) during the first year after birth. In comparison, the epigenome of aging (>60 years) PFC neurons showed less extensive changes, including increased H3K4me3 at 100 genes. These findings demonstrate that H3K4me3 in human PFC is highly regulated in a cell type- and subject-specific manner and highlight the importance of early childhood for developmentally regulated chromatin remodeling in prefrontal neurons.

Epigenetic signatures of autism: trimethylated H3K4 landscapes in prefrontal neurons.

CONTEXT Neuronal dysfunction in cerebral cortex and other brain regions could contribute to the cognitive and behavioral defects in autism. OBJECTIVE To characterize epigenetic signatures of autism in prefrontal cortex neurons. DESIGN We performed fluorescence-activated sorting and separation of neuronal and nonneuronal nuclei from postmortem prefrontal cortex, digested the chromatin with micrococcal nuclease, and deeply sequenced the DNA from the mononucleosomes with trimethylated H3K4 (H3K4me3), a histone mark associated with transcriptional regulation. Approximately 15 billion base pairs of H3K4me3-enriched sequences were collected from 32 brains. SETTING Academic medical center. PARTICIPANTS A total of 16 subjects diagnosed as having autism and 16 control subjects ranging in age from 0.5 to 70 years. MAIN OUTCOME MEASURES Identification of genomic loci showing autism-associated H3K4me3 changes in prefrontal cortex neurons. RESULTS Subjects with autism showed no evidence for generalized disruption of the developmentally regulated remodeling of the H3K4me3 landscape that defines normal prefrontal cortex neurons in early infancy. However, excess spreading of H3K4me3 from the transcription start sites into downstream gene bodies and upstream promoters was observed specifically in neuronal chromatin from 4 of 16 autism cases but not in controls. Variable subsets of autism cases exhibit altered H3K4me3 peaks at numerous genes regulating neuronal connectivity, social behaviors, and cognition, often in conjunction with altered expression of the corresponding transcripts. Autism-associated H3K4me3 peaks were significantly enriched in genes and loci implicated in neurodevelopmental diseases. CONCLUSIONS Prefrontal cortex neurons from subjects with autism show changes in chromatin structures at hundreds of loci genome-wide, revealing considerable overlap between genetic and epigenetic risk maps of developmental brain disorders.

Human-Specific Histone Methylation Signatures at Transcription Start Sites in Prefrontal Neurons

Mapping histone methylation landscapes in neurons from human, chimpanzee, and macaque brains reveals coordinated, human-specific epigenetic regulation at hundreds of regulatory sequences.

Coordinated cell type-specific epigenetic remodeling in prefrontal cortex begins before birth and continues into early adulthood.

Development of prefrontal and other higher-order association cortices is associated with widespread changes in the cortical transcriptome, particularly during the transitions from prenatal to postnatal development, and from early infancy to later stages of childhood and early adulthood. However, the timing and longitudinal trajectories of neuronal gene expression programs during these periods remain unclear in part because of confounding effects of concomitantly occurring shifts in neuron-to-glia ratios. Here, we used cell type–specific chromatin sorting techniques for genome-wide profiling of a histone mark associated with transcriptional regulation—H3 with trimethylated lysine 4 (H3K4me3)—in neuronal chromatin from 31 subjects from the late gestational period to 80 years of age. H3K4me3 landscapes of prefrontal neurons were developmentally regulated at 1,157 loci, including 768 loci that were proximal to transcription start sites. Multiple algorithms consistently revealed that the overwhelming majority and perhaps all of developmentally regulated H3K4me3 peaks were on a unidirectional trajectory defined by either rapid gain or loss of histone methylation during the late prenatal period and the first year after birth, followed by similar changes but with progressively slower kinetics during early and later childhood and only minimal changes later in life. Developmentally downregulated H3K4me3 peaks in prefrontal neurons were enriched for Paired box (Pax) and multiple Signal Transducer and Activator of Transcription (STAT) motifs, which are known to promote glial differentiation. In contrast, H3K4me3 peaks subject to a progressive increase in maturing prefrontal neurons were enriched for activating protein-1 (AP-1) recognition elements that are commonly associated with activity-dependent regulation of neuronal gene expression. We uncovered a developmental program governing the remodeling of neuronal histone methylation landscapes in the prefrontal cortex from the late prenatal period to early adolescence, which is linked to cis-regulatory sequences around transcription start sites.

Neuronal Kmt2a/Mll1 Histone Methyltransferase Is Essential for Prefrontal Synaptic Plasticity and Working Memory

Neuronal histone H3-lysine 4 methylation landscapes are defined by sharp peaks at gene promoters and other cis-regulatory sequences, but molecular and cellular phenotypes after neuron-specific deletion of H3K4 methyl-regulators remain largely unexplored. We report that neuronal ablation of the H3K4-specific methyltransferase, Kmt2a/Mixed-lineage leukemia 1 (Mll1), in mouse postnatal forebrain and adult prefrontal cortex (PFC) is associated with increased anxiety and robust cognitive deficits without locomotor dysfunction. In contrast, only mild behavioral phenotypes were observed after ablation of the Mll1 ortholog Kmt2b/Mll2 in PFC. Impaired working memory after Kmt2a/Mll1 ablation in PFC neurons was associated with loss of training-induced transient waves of Arc immediate early gene expression critical for synaptic plasticity. Medial prefrontal layer V pyramidal neurons, a major output relay of the cortex, demonstrated severely impaired synaptic facilitation and temporal summation, two forms of short-term plasticity essential for working memory. Chromatin immunoprecipitation followed by deep sequencing in Mll1-deficient cortical neurons revealed downregulated expression and loss of the transcriptional mark, trimethyl-H3K4, at <50 loci, including the homeodomain transcription factor Meis2. Small RNA-mediated Meis2 knockdown in PFC was associated with working memory defects similar to those elicited by Mll1 deletion. Therefore, mature prefrontal neurons critically depend on maintenance of Mll1-regulated H3K4 methylation at a subset of genes with an essential role in cognition and emotion.

Epigenetic dysregulation of hairy and enhancer of split 4 (HES4) is associated with striatal degeneration in postmortem Huntington brains

To investigate epigenetic contributions to Huntingtons disease (HD) pathogenesis, we carried out genome-wide mapping of the transcriptional mark, trimethyl-histone H3-lysine 4 (H3K4me3) in neuronal nuclei extracted from prefrontal cortex of HD cases and controls using chromatin immunoprecipitation followed by deep-sequencing. Neuron-specific mapping of the genome-wide distribution of H3K4me3 revealed 136 differentially enriched loci associated with genes implicated in neuronal development and neurodegeneration, including GPR3, TMEM106B, PDIA6 and the Notch signaling genes hairy and enhancer of split 4 (HES4) and JAGGED2, supporting the view that the neuronal epigenome is affected in HD. Importantly, loss of H3K4me3 at CpG-rich sequences on the HES4 promoter was associated with excessive DNA methylation, reduced binding of nuclear proteins to the methylated region and altered expression of HES4 and HES4 targeted genes MASH1 and P21 involved in striatal development. Moreover, hypermethylation of HES4 promoter sequences was strikingly correlated with measures of striatal degeneration and age-of-onset in a cohort of 25 HD brains (r = 0.56, P = 0.006). Lastly, shRNA knockdown of HES4 in human neuroblastoma cells altered MASH1 and P21 mRNA expression and markedly increased mutated HTT-induced aggregates and cell death. These findings, taken together, suggest that epigenetic dysregulation of HES4 could play a critical role in modifying HD disease pathogenesis and severity.

A simple method for improving the specificity of anti-methyl histone antibodies

Antibodies differentiating between the mono-, di- and trimethylated forms of specific histone lysine residues are a critical tool in epigenome research, but show variable specificity, potentially limiting comparisons across studies and between samples. Using trimethyl histone H3 lysine 4 (H3K4me3)—a mark enriched at transcription start sites (TSS) of active genes—as an example, we describe how simple co-incubation with synthetic peptide of the K4me2 modification leads to increased specificity for K4me3 and a much sharper peak distribution proximal to TSS following chromatin immunoprecipitation and massively parallel sequencing (ChIP-Seq).

Posttranslational Histone Modifications and the Neurobiology of Psychosis

Schizophrenia and related major psychiatric disease is typically defined by the conspicuous absence of a defining neuropathology and a lack of straightforward identifiable genetic factors in the majority of affected individuals. On the other hand, there is increasing evidence that a distinct set of RNAs, many of which encode proteins of critical importance for myelin regulation and oligodendrocyte function, or GABAergic inhibitory and glutamatergic excitatory neurotransmission are expressed at altered levels in diseased brain. This chapter explores the mechanisms by which epigenetic regulators of gene expression, including covalent histone modifications, could contribute to dysregulation of gene expression in schizophrenia. There is also discussion on the methodological and scientific limitations of histone-focused approaches, as it pertains to the human (postmortem) brain, as well as brief remarks on the topic of epigenetic heritability of chromatin structures potentially altered in schizophrenia. The authors predict that the study of histone modifications, both at defined candidate gene loci and genome-wide, will become an important tool in the investigation of gene expression abnormalities and potential epigenetic dysregulation in the brains of subjects on the psychosis spectrum.