Identification of a transcriptional signature found in multiple models of ASD and related disorders

Histone variant H2BE enhances chromatin accessibility in neurons to promote synaptic gene expression and long-term memory

Regulation of histone proteins affects gene expression through multiple mechanisms including exchange with histone variants. However, widely expressed variants of H2B remain elusive. Recent findings link histone variants to neurological disorders, yet few are well studied in the brain. We applied new tools including novel antibodies, biochemical assays, and sequencing approaches to reveal broad expression of the H2B variant H2BE, and defined its role in regulating chromatin structure, neuronal transcription, and mouse behavior. We find that H2BE is enriched at promoters and a single unique amino acid allows it to dramatically enhance chromatin accessibility. Lastly, we show that H2BE is critical for synaptic gene expression and long-term memory. Together, these data reveal a novel mechanism linking histone variants to chromatin regulation, neuronal function, and memory. This work further identifies the first widely expressed H2B variant and uncovers a single histone amino acid with profound effects on genomic structure.

Cell consequences of loss of function of the epigenetic factor EHMT1

EHMT1 is an epigenetic factor with histone methyltransferase activity that appears mutated in Kleefstra syndrome, a neurodevelopmental genetic disorder characterized by developmental delay, intellectual disability, and autistic-like features. Despite recent progress in the study of the function of this gene and the molecular etiology of the disease, our knowledge of how EHMT1 haploinsufficiency causes Kleefstra syndrome is still very limited. Here, we show that EHMT1 depletion in RPE1 cells leads to alterations in the morphology and distribution of different subcellular structures, such as the Golgi apparatus, the lysosomes and different cell adhesion components. EHMT1 downregulation also increases centriolar satellites detection, which may indicate a role for EHMT1 in centrosome functioning. Furthermore, the migration process is also altered in EHMT1 depleted cells, which show reduced migration capacity. We consider that the described phenotypes could open new possibilities for understanding the functional impact of EHMT1 haploinsufficiency in Kleefstra syndrome, helping to elucidate the link between epigenetic regulation and the underlying cellular mechanisms that result in this neurodevelopmental disorder. This knowledge could be relevant not only for the treatment of this syndrome, but also for other neurodevelopmental conditions that could share similar deregulated cellular pathways.

Modulation of chromatin architecture influences the neuronal nucleus through activity-regulated gene expression

The disruption of chromatin-regulating genes is associated with many neurocognitive syndromes. While most of these genes are ubiquitously expressed across various cell-types, many chromatin regulators act upon activity regulated genes (ARGs) that play central roles in synaptic development and plasticity. Recent literature suggests a link between ARG expression disruption in neurons with the human phenotypes observed in various neurocognitive syndromes. Advances in chromatin biology have demonstrated how chromatin structure, from nucleosome occupancy to higher-order structures such as topologically associated domains, impacts the kinetics of transcription. This review discusses the dynamics of these various levels of chromatin structure and their influence on the expression of ARGs.

Age-differential sexual dimorphisms in CHD8-S62X-mutant mouse synapses and transcriptomes

Chd8^+/N2373K mice with a human C-terminal-truncating mutation (N2373K) display autistic-like behaviors in juvenile and adult males but not in females. In contrast, Chd8^+/S62X mice with a human N-terminal-truncating mutation (S62X) display behavioral deficits in juvenile males (not females) and adult males and females, indicative of age-differential sexually dimorphic behaviors. Excitatory synaptic transmission is suppressed and enhanced in male and female Chd8^+/S62X juveniles, respectively, but similarly enhanced in adult male and female mutants. ASD-like transcriptomic changes are stronger in newborn and juvenile (but not adult) Chd8^+/S62X males but in newborn and adult (not juvenile) Chd8^+/S62X females. These results point to age-differential sexual dimorphisms in Chd8^+/S62X mice at synaptic and transcriptomic levels, in addition to the behavioral level.