DNMT1 modulates interneuron morphology by regulatingPak6expression through crosstalk with histone modifications

Abstract

Epigenetic mechanisms of gene regulation, including DNA methylation and histone modifications, call increasing attention in the context of development and human health. Thereby, interactions between DNA methylating enzymes and histone modifications tremendously multiply the spectrum of potential regulatory functions. Epigenetic networks are critically involved in the establishment and functionality of neuronal circuits that are composed of gamma-aminobutyric acid (GABA)-positive inhibitory interneurons and excitatory principal neurons in the cerebral cortex. We recently reported a crucial role of the DNA methyltransferase 1 (DNMT1) during the migration of immature POA-derived cortical interneurons by promoting the migratory morphology through repression of Pak6. However, the DNMT1-dependent regulation of Pak6 expression appeared to occur independently of direct DNA methylation. Here, we show that in addition to its DNA methylating activity, DNMT1 can act on gene transcription by modulating permissive H3K4 and repressive H3K27 trimethylation in developing inhibitory interneurons, similar to what was found in other cell types. In particular, the transcriptional control of Pak6, interactions of DNMT1 with the Polycomb-repressor complex 2 (PCR2) core enzyme EZH2, mediating repressive H3K27 trimethylations at regulatory regions of the Pak6 gene locus. Similar to what was observed upon Dnmt1 depletion, inhibition of EZH2 caused elevated Pak6 expression levels accompanied by increased morphological complexity, which was rescued by siRNA-mediated downregulation of Pak6 expression. Together, our data emphasise the relevance of DNMT1-dependent crosstalk with histone tail methylation for transcriptional control of genes like Pak6 required for proper cortical interneuron migration.

Neuronal Lhx1 expression is regulated by DNMT1-dependent modulation of histone marks

“…In agreement with the expression and DNA methylation analysis of POA-derived embryonic interneurons, elevated levels of Lhx1 expression were also detected upon Dnmt1 siRNA application in Neuro2a (N2a) cells, a cell culture model already applied in a previous study [12]. Of note, this increase in Lhx1 expression was not observed upon treatment with RG108, an inhibitor of DNA methylation (Figure 1(d)), which even leads to a significant decrease putatively by eliciting secondary effects.…”

“…We have recently reported that the DNA methyltransferase 1 (DNMT1) orchestrates the post-mitotic maturation of POA-derived cortical interneurons by promoting their migratory morphology and survival in part through the modulation of Pak6 expression [27]. Of note, we found that Pak6 transcription is not regulated by DNMT1-dependent DNA methylation [12,27], but non-canonically through interactions of DNMT1 with histone methylating enzymes [12].…”

“…In addition to its DNA methylating activity, we have recently reported that non-canonical functions of DNMT1, such as a crosstalk with histone-modifying enzymes, are involved in the transcriptional regulation in developing interneurons [12]. In detail, Pak6 expression was found to be controlled through direct or indirect interactions of DNMT1 with EZH2, the core enzyme of the polycomb-repressor complex 2 (PRC2), catalysing repressive trimethylations at H3K27 [30,31].…”

“…Apart from this, DNA methylation can instruct histone-modifying complexes (HMCs) and vice versa [5][6][7][8]. In addition, DNMTs act on histone modifications by transcriptional control over genes encoding for proteins implicated in HMCs or by interacting with protein complexes independent of their DNA methylating activity [9][10][11][12]. This diversity of actions requires detailed investigations to decipher the functional implications of distinct epigenetic mechanisms in directing cell-and stage-specific differentiation and maturation programmes, and to reveal causes for dysfunctions in related diseases.…”

DNA Methylation-Dependent Dysregulation of GABAergic Interneuron Functionality in Neuropsychiatric Diseases

“…Moreover, it should be kept in mind that DNMT1 was described to act non-canonically on gene expression by interactions with histone modifiers (Symmank and Zimmer, 2017;Symmank et al, 2018). DNMTs and DNA methylation interfere at different levels with histone modifications, which likewise modulate the specificity of transcriptional changes.…”