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Division of labor among H3K4 Methyltransferases Define Distinct Facets of Homeostatic Plasticity

ABSTRACT: Histone H3 lysine 4 methylaton (H3K4me), a hallmark of transcriptionally engaged chromatin, is installed by the lysine methyltransferases 2 (KMT2) family of six enzymes in mammals. The six enzymes appear to have arisen from gene duplication of the ancient three enzymes found in the fruit fly. Heterozygous mutations in any of the six enzymes result in monogenic neurodevelopmental disorders, indicating nonredundant yet poorly understood roles of KMT2 family enzymes in neurodevelopment. Recent evidence suggests that histone methyltransferase activity may not be central to KMT2 functions; however, the enzymatic activity is evolutionary conserved, implicating the presence of selective pressure to maintain the catalytic activity. Here, we show that H3K4 methylation is dynamically regulated during prolonged alteration of neuronal activity. The perturbation of H3K4me by the H3.3K4M mutant blocks synaptic scaling, a form of homeostatic plasticity that buffers the impact of prolonged reductions or increases in network activity. Unexpectedly, we found that the six individual enzymes are all necessary for synaptic scaling and that the roles of KMT2 enzymes segregate into evolutionary-defined subfamilies; KMT2A and KMT2B (fly-Trx homologs) for synaptic downscaling, KMT2C and KMT2D (Trr homologs) for upscaling, and KMT2F and KMT2G (dSet homologs) for both directions. Selective blocking of KMT2A enzymatic activity by a small molecule and targeted disruption of the enzymatic domain both blocked the synaptic downscaling and interfered with the activity-dependent transcriptional program. Furthermore, our study revealed specific phases of synaptic downscaling, i.e., induction and maintenance, in which KMT2A and KMT2B play distinct roles. These results suggest that mammalian brains have co-opted intricate H3K4me installation to achieve stability of the expanding neuronal circuits.

ORGANISM(S): Mus musculus

PROVIDER: GSE239471 | GEO | 2024/08/01

REPOSITORIES: GEO

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Project description:Methylation of histone H3 lysine 4 (H3K4me) at actively expressed, cell type-specific genes is established during development by the Trithorax group of epigenetic regulators. In mammals, the Trithorax family includes KMT2A-D (MLL1-4), a family of SET domain proteins that function in large complexes to impart mono-, di-, and trimethylation at H3K4. Individual KMT2s and their co-factors are essential for embryonic development and the establishment of correct gene expression patterns, presumably by demarcating the active and accessible regions of the genome in a cell specific and heritable manner. Despite the importance of H3K4me marks in development, little is known about the importance of histone methylation in maintaining gene expression patterns in fully differentiated and non-dividing cell types. In this report, we utilized an inducible cardiac-specific Cre driver to delete the PTIP protein, a key component of a H3K4me complex, and ask whether this activity is still required to maintain the phenotype of terminally differentiated cardiomyocytes. Our results demonstrate that reducing the H3K4me3 marks is sufficient to alter gene expression patterns and significantly augment systolic heart function. These results clearly show that maintenance of H3K4me3 marks is necessary for the stability of the transcriptional program in differentiated cells. The array we performed allowed us to identify genes that are regulated by PTIP and histone methylation. 8-week-old littermate mice on a mixed C57B6 and B6129 background were utilized. Three mice were on a background with a PTIP floxed allele and a wild type PTIP allele (PTIP+1, PTIP+2, PTIP+3). Three mice had a transgene that expresses a modified estrogen receptor -Cre recombinase fusion protein under the control of a cardiac-specific driver (alpha myosin heavy chain, Jackson Lab stock #005650) and a floxed PTIP allele and a null PTIP (PTIPKO1, PTIPKO2, PTIPKO3). Both groups of mice were injected with tamoxifen at 8 weeks of age. Tamoxifen deletes the floxed PTIP allele in the PTIPKO mice. 5 days after tamoxifen injection, RNA was harvested from left ventricle (LV) apices in both groups. RNA was then sent to the University of Michigan microarray facility core for analysis.

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Division of labor among H3K4 Methyltransferases Define Distinct Facets of Homeostatic Plasticity

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