Neuronal enhancers fine-tune adaptive circuit plasticity

The evolving neurobiology of early-life stress

Because early-life stress is common and constitutes a strong risk factor for cognitive and mental health disorders, it has been the focus of a multitude of studies in humans and experimental models. Yet, we have an incomplete understanding of what is perceived as stressful by the developing brain, what aspects of stress influence brain maturation, what developmental ages are particularly vulnerable to stress, which molecules mediate the effects of stress on brain operations, and how transient stressful experiences can lead to enduring emotional and cognitive dysfunctions. Here, we discuss these themes, highlight the challenges and progress in resolving them, and propose new concepts and avenues for future research.

Blueprints for healing: central nervous system regeneration in zebrafish and neonatal mice

In adult mammals, including humans, neurons, and axons in the brain and spinal cord are inherently incapable of regenerating after injury. Studies of animals with innate capacity for regeneration are providing valuable insights into the mechanisms driving tissue healing. The aim of this review is to summarize recent data on regeneration mechanisms in the brain and spinal cord of zebrafish and neonatal mice. We infer that elucidating these mechanisms and understanding how and why they are lost in adult mammals will contribute to the development of strategies to promote central nervous system regeneration.

Chromatin regulation of neuronal activity-dependent gene programs in circuit formation and plasticity

Neuronal activity-dependent transcription is crucial for the development and plasticity of neuronal circuits. At the chromatin level, the induction of neuronal activity-regulated genes is orchestrated through various mechanisms, including the deposition of histone modifications at regulatory elements, the binding of transcriptional activators and repressors, chromatin remodeling, and the control of 3D genome architecture. Here, we review our current understanding of how chromatin mechanisms regulate temporally distinct transcriptional waves following neuronal stimulation and allow neurons to mount cell type-specific and stimulus-specific transcriptional responses. We also highlight a specific epigenetic mechanism in developing neurons that maintains immediate early genes (IEGs) in an inactive though poised state, while simultaneously preparing them for rapid activation in response to sensory stimulation. We discuss how chromatin regulation mechanisms play a crucial role in controlling activity-regulated gene expression, enabling the implementation of precise gene expression programs during different stages of neural circuit development and plasticity.

Early-life stress sensitizes response to future stress: Evidence and mechanisms

Early-life stress sensitizes individuals to additional stressors and increases lifetime risk for mood and anxiety disorders. Research in both human populations and rodent models of early-life stress have sought to determine how different types of stressors contribute to vulnerability, and whether there are developmental sensitive periods for such effects. Although differences in the type and timing of rodent early-life stress paradigms have led to differences in specific behavioral outcomes, this complexity is present among humans as well. Robust rodent research now shows how early-life stress increases sensitivity to future stressors at behavioral, neural circuit, and molecular levels. These recent discoveries are laying the foundation for translation to more effective interventions relevant for those who experienced childhood stress and trauma.

Histone variant H2BE controls activity-dependent gene expression and homeostatic scaling

A cell's ability to respond and adapt to environmental stimuli relies in part on transcriptional programs controlled by histone proteins. Histones affect transcription through numerous mechanisms including through replacement with variant forms that carry out specific functions. We recently identified the first widely expressed H2B histone variant, H2BE and found that it promotes transcription and is critical for neuronal function and long-term memory. However, how H2BE is regulated by extracellular stimuli and whether it controls activity-dependent transcription and cellular plasticity remain unknown. We used CUT&Tag and RNA-sequencing of primary neurons, single-nucleus sequencing of cortical tissue, and multielectrode array recordings to interrogate the expression of H2BE in response to stimuli and the role of H2BE in activity-dependent gene expression and plasticity. We find that unlike Further, we show that neurons lacking H2BE are unable to mount proper long-term activity-dependent transcriptional responses both in cultured neurons and in animal models. Lastly, we demonstrate that H2BE knockout neurons fail to undergo the electrophysiological changes associated with homeostatic plasticity in neurons after long-term stimulation. In summary, these data demonstrate that H2BE expression is inversely correlated to activity and necessary for long-term activity-dependent responses, revealing the first instance of a histone variant involved in the homeostatic plasticity response in neurons.