Enzymes catalyzing CpG methylation in DNA, including DNMT1 and DNMT3A/B, are indispensable for mammalian tissue development and homeostasis 1-4. They are also implicated in human developmental disorders and cancers 5-8 , supporting a critical role of DNA methylation during cell fate specification and maintenance. Recent studies suggest that histone posttranslational modifications (PTMs) are involved in specifying patterns of DNMT localization and DNA methylation at promoters and actively transcribed gene bodies 9-11. However, mechanisms governing the establishment and maintenance of intergenic DNA methylation remain poorly understood. Germline mutations in DNMT3A define Tatton-Brown-Rahman syndrome (TBRS), a

Mutations in epigenetic pathways are common oncogenic drivers. Histones, the fundamental substrate for chromatin-modifying and remodeling enzymes, are mutated in tumors including in gliomas, sarcomas, head and neck cancers, and carcinosarcomas. Classical 'oncohistone' mutations occur in the N-terminal tail of histone H3 and impact the function of Polycomb Repressor Complexes 1 and 2. However, the prevalence and function of histone mutations in additional tumor contexts is unknown. Here we show that somatic histone mutations conservatively occur in ~ 4% of tumors of diverse types and in critical regions of histone proteins. Mutations occur in all four core histones, in both the N-terminal tails and globular histone fold domains, and at or near residues that harbor important post-translational modifications. Many globular domain mutations are either homologous to yeast mutants that abrogate the need for SWI/SNF function, occur in the key regulatory 'acidic patch' of histone H2A and H2B, or are predicted to disrupt the H2B-H4 interface. The histone mutation dataset (https://bit.ly/2GXH5Ve) and the hypotheses presented herein on the impact of the mutations on important chromatin functions should serve as a resource and starting point for the chromatin and cancer biology fields in exploring an expanding role of histone mutations in cancer.

Determination of the molecular properties of genetically targeted cell types has led to fundamental insights into mouse brain function and dysfunction. Here, we report an efficient strategy for precise exploration of gene expression and epigenetic events in specific cell types in a range of species, including postmortem human brain. We demonstrate that classically defined, homologous neuronal and glial cell types differ between rodent and human by the expression of hundreds of orthologous, cell specific genes. Confirmation that these genes are differentially active was obtained using epigenetic mapping and immunofluorescence localization. Studies of sixteen human postmortem brains revealed gender specific transcriptional differences, cell-specific molecular responses to aging, and the induction of a shared, robust response to an unknown external event evident in three donor samples. Our data establish a comprehensive approach for analysis of molecular events associated with specific circuits and cell types in a wide variety of human conditions.

Myt1 and Myt1l (Myelin transcription factor 1, and Myt1-like) are members of a small family of closely related zinc finger transcription factors, characterized by two clusters of C2HC zinc fingers. Both are widely expressed during early embryogenesis, but are largely restricted to expression within the brain in the adult. Myt1l, as part of a three transcription factor mix, can reprogram fibroblasts to neurons and plays a role in maintaining neuronal identity. Previous analyses have indicated roles in both transcriptional activation and repression and suggested that Myt1 and Myt1l may have opposing functions in gene expression. We show that when targeted to DNA via multiple copies of the consensus Myt1/Myt1l binding site Myt1 represses transcription, whereas Myt1l activates. By targeting via a heterologous DNA binding domain we mapped an activation function in Myt1l to an amino-terminal region that is poorly conserved in Myt1. However, genome wide analyses of the effects of Myt1 and Myt1l expression in a glioblastoma cell line suggest that the two proteins have largely similar effects on endogenous gene expression. Transcriptional repression is likely mediated by binding to DNA via the known consensus site, whereas this site is not associated with the transcriptional start sites of genes with higher expression in the presence of Myt1 or Myt1l. This work suggests that these two proteins function similarly, despite differences observed in analyses based on synthetic reporter constructs.

SummaryDetermination of the molecular properties of genetically targeted cell types has led to fundamental insights into mouse brain function and dysfunction. Here, we report an efficient strategy for precise exploration of gene expression events in specific cell types in a broad range of species, including postmortem human brain. We demonstrate that classically defined, homologous neuronal and glial cell types differ between rodent and human by the expression of hundreds of orthologous, cell specific genes. Confirmation that these genes are differentially active was obtained using epigenetic mapping and immunofluorescence localization. Studies of sixteen human postmortem brains revealed cell-specific molecular responses to aging, and the induction of a shared, robust response to an unknown external event experienced by three donors. Our data establish a comprehensive approach for analysis of unique molecular events associated with specific circuits and cell types in a wide variety of human conditions.

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