CBP histone acetyltransferase activity regulates embryonic neural differentiation in the normal and Rubinstein-Taybi syndrome brain

iPSC-derived neurons of CREBBP- and EP300-mutated Rubinstein-Taybi syndrome patients show morphological alterations and hypoexcitability

Rubinstein-Taybi syndrome (RSTS) is a rare neurodevelopmental disorder characterized by distinctive facial features, growth retardation, broad thumbs and toes and mild to severe intellectual disability, caused by heterozygous mutations in either CREBBP or EP300 genes, encoding the homologous CBP and p300 lysine-acetyltransferases and transcriptional coactivators. No RSTS in vitro induced Pluripotent Stem Cell (iPSC)-neuronal model is available yet to achieve mechanistic insights on cognitive impairment of RSTS patients. We established iPSC-derived neurons (i-neurons) from peripheral blood cells of three CREBBP- and two EP300-mutated patients displaying different levels of intellectual disability, and four unaffected controls. Pan neuronal and cortical-specific markers were expressed by all patients' i-neurons. Altered morphology of patients' differentiating neurons, showing reduced branch length and increased branch number, and hypoexcitability of differentiated neurons emerged as potential disease biomarkers. Anomalous neuronal morphology and reduced excitability varied across different RSTS patients' i-neurons. Further studies are needed to validate these markers and assess whether they reflect cognitive and behavioural impairment of the donor patients.

Epigenetics and epitranscriptomics in temporal patterning of cortical neural progenitor competence

Yoon et al. review epigenetic and epitranscriptomic mechanisms that regulate the lineage specification of neural progenitor cells in the developing brain.

During embryonic brain development, neural progenitor/stem cells (NPCs) sequentially give rise to different subtypes of neurons and glia via a highly orchestrated process. To accomplish the ordered generation of distinct progenies, NPCs go through multistep transitions of their developmental competence. The molecular mechanisms driving precise temporal coordination of these transitions remains enigmatic. Epigenetic regulation, including changes in chromatin structures, DNA methylation, and histone modifications, has been extensively investigated in the context of cortical neurogenesis. Recent studies of chemical modifications on RNA, termed epitranscriptomics, have also revealed their critical roles in neural development. In this review, we discuss advances in understanding molecular regulation of the sequential lineage specification of NPCs in the embryonic mammalian brain with a focus on epigenetic and epitranscriptomic mechanisms. In particular, the discovery of lineage-specific gene transcripts undergoing rapid turnover in NPCs suggests that NPC developmental fate competence is determined much earlier, before the final cell division, and is more tightly controlled than previously appreciated. We discuss how multiple regulatory systems work in harmony to coordinate NPC behavior and summarize recent findings in the context of a model of epigenetic and transcriptional prepatterning to explain NPC developmental competence.

Selective alteration of adult hippocampal neurogenesis and impaired spatial pattern separation performance in the RSK2-deficient mouse model of Coffin-Lowry syndrome

Adult neurogenesis is involved in certain hippocampus-dependent cognitive functions and is linked to psychiatric diseases including intellectual disabilities. The Coffin-Lowry syndrome (CLS) is a developmental disorder caused by mutations in the Rsk2 gene and characterized by intellectual disabilities associated with growth retardation. How RSK2-deficiency leads to cognitive dysfunctions in CLS is however poorly understood. Here, using Rsk2 Knock-Out mice, we characterized the impact of RSK2 deficiency on adult hippocampal neurogenesis in vivo. We report that the absence of RSK2 does not affect basal proliferation, differentiation and survival of dentate gyrus adult-born neurons but alters the maturation progression of young immature newborn neurons. Moreover, when RSK2-deficient mice were submitted to spatial learning, in contrast to wild-type mice, proliferation of adult generated neurons was decreased and no pro-survival effect of learning was observed. Thus, learning failed to recruit a selective population of young newborn neurons in association with deficient long-term memory recall. Given the proposed role of the dentate gyrus and of adult-generated newborn neurons in hippocampal-dependent pattern separation function, we explored this function in a delayed non-matching to place task and in an object-place pattern separation task and report severe deficits in spatial pattern separation in Rsk2-KO mice. Together, this study reveals a previously unknown role for RSK2 in the early stages of maturation and learning-dependent involvement of adult-born dentate gyrus neurons. These alterations associated with a deficit in the ability of RSK2-deficient mice to finely discriminate relatively similar spatial configurations, may contribute to cognitive dysfunction in CLS.

Epigenetic modifiers promote mitochondrial biogenesis and oxidative metabolism leading to enhanced differentiation of neuroprogenitor cells

During neural development, epigenetic modulation of chromatin acetylation is part of a dynamic, sequential and critical process to steer the fate of multipotent neural progenitors toward a specific lineage. Pan-HDAC inhibitors (HDCis) trigger neuronal differentiation by generating an “acetylation” signature and promoting the expression of neurogenic bHLH transcription factors. Our studies and others have revealed a link between neuronal differentiation and increase of mitochondrial mass. However, the neuronal regulation of mitochondrial biogenesis has remained largely unexplored. Here, we show that the HDACi, sodium butyrate (NaBt), promotes mitochondrial biogenesis via the NRF-1/Tfam axis in embryonic hippocampal progenitor cells and neuroprogenitor-like PC12-NeuroD6 cells, thereby enhancing their neuronal differentiation competency. Increased mitochondrial DNA replication by several pan-HDACis indicates a common mechanism by which they regulate mitochondrial biogenesis. NaBt also induces coordinates mitochondrial ultrastructural changes and enhanced OXPHOS metabolism, thereby increasing key mitochondrial bioenergetics parameters in neural progenitor cells. NaBt also endows the neuronal cells with increased mitochondrial spare capacity to confer resistance to oxidative stress associated with neuronal differentiation. We demonstrate that mitochondrial biogenesis is under HDAC-mediated epigenetic regulation, the timing of which is consistent with its integrative role during neuronal differentiation. Thus, our findings add a new facet to our mechanistic understanding of how pan-HDACis induce differentiation of neuronal progenitor cells. Our results reveal the concept that epigenetic modulation of the mitochondrial pool prior to neurotrophic signaling dictates the efficiency of initiation of neuronal differentiation during the transition from progenitor to differentiating neuronal cells. The histone acetyltransferase CREB-binding protein plays a key role in regulating the mitochondrial biomass. By ChIP-seq analysis, we show that NaBt confers an H3K27ac epigenetic signature in several interconnected nodes of nuclear genes vital for neuronal differentiation and mitochondrial reprogramming. Collectively, our study reports a novel developmental epigenetic layer that couples mitochondrial biogenesis to neuronal differentiation.

N6-methyladenosine RNA modification regulates embryonic neural stem cell self-renewal through histone modifications

Internal N6-methyladenosine (m6A) modification is widespread in messenger RNAs (mRNAs) and is catalyzed by heterodimers of methyltransferase-like protein 3 (Mettl3) and Mettl14. To understand the role of m6A in development, we deleted Mettl14 in embryonic neural stem cells (NSCs) in a mouse model. Phenotypically, NSCs lacking Mettl14 displayed markedly decreased proliferation and premature differentiation, suggesting that m6A modification enhances NSC self-renewal. Decreases in the NSC pool led to a decreased number of late-born neurons during cortical neurogenesis. Mechanistically, we discovered a genome-wide increase in specific histone modifications in Mettl14 knockout versus control NSCs. These changes correlated with altered gene expression and observed cellular phenotypes, suggesting functional significance of altered histone modifications in knockout cells. Finally, we found that m6A regulates histone modification in part by destabilizing transcripts that encode histone-modifying enzymes. Our results suggest an essential role for m6A in development and reveal m6A-regulated histone modifications as a previously unknown mechanism of gene regulation in mammalian cells.

A Translational Repression Complex in Developing Mammalian Neural Stem Cells that Regulates Neuronal Specification

The mechanisms instructing genesis of neuronal subtypes from mammalian neural precursors are not well understood. To address this issue, we have characterized the transcriptional landscape of radial glial precursors (RPs) in the embryonic murine cortex. We show that individual RPs express mRNA, but not protein, for transcriptional specifiers of both deep and superficial layer cortical neurons. Some of these mRNAs, including the superficial versus deep layer neuron transcriptional regulators Brn1 and Tle4, are translationally repressed by their association with the RNA-binding protein Pumilio2 (Pum2) and the 4E-T protein. Disruption of these repressive complexes in RPs mid-neurogenesis by knocking down 4E-T or Pum2 causes aberrant co-expression of deep layer neuron specification proteins in newborn superficial layer neurons. Thus, cortical RPs are transcriptionally primed to generate diverse types of neurons, and a Pum2/4E-T complex represses translation of some of these neuronal identity mRNAs to ensure appropriate temporal specification of daughter neurons.

Benign and malignant tumors in Rubinstein-Taybi syndrome

Rubinstein–Taybi syndrome (RSTS) is a multiple congenital anomalies syndrome associated with mutations in CREBBP (70%) and EP300 (5–10%). Previous reports have suggested an increased incidence of specific benign and possibly also malignant tumors. We identified all known individuals diagnosed with RSTS in the Netherlands until 2015 (n = 87) and studied the incidence and character of neoplastic tumors in relation to their CREBBP/EP300 alterations. The population–based Dutch RSTS data are compared to similar data of the Dutch general population and to an overview of case reports and series of all RSTS individuals with tumors reported in the literature to date. Using the Nationwide Network and Registry of Histopathology and Cytopathology in the Netherlands (PALGA Foundation), 35 benign and malignant tumors were observed in 26/87 individuals. Meningiomas and pilomatricomas were the most frequent benign tumors and their incidence was significantly elevated in comparison to the general Dutch population. Five malignant tumors were observed in four persons with RSTS (medulloblastoma; diffuse large‐cell B‐cell lymphoma; breast cancer; non‐small cell lung carcinoma; colon carcinoma). No clear genotype–phenotype correlation became evident. The Dutch population‐based data and reported case studies underscore the increased incidence of meningiomas and pilomatricomas in individuals with RSTS. There is no supporting evidence for an increased risk for malignant tumors in individuals with RSTS, however, due to the small numbers this risk may not be fully dismissed.

Language and Cognitive Impairment Associated with a Novel p.Cys63Arg Change in the MED13L Transcriptional Regulator

Mutations in the MED13L gene, which encodes a subunit of a transcriptional regulatory complex, result in a complex phenotype entailing physical and cognitive anomalies. Deep language impairment has been reported in affected individuals, mostly in patients with copy number variations. We report on a child with a nonsynonymous p.Cys63Arg change in MED13L (chr12:116675396A>G, GRCh37) who exhibits profound language impairment in the expressive domain, cognitive delay, behavioral disturbances, and an autism-like phenotype. Because of the brain areas in which MED13L is expressed and because of the functional links between MED13L and the products of selected candidate genes for cognitive disorders involving language deficits, the proband's linguistic phenotype may result from changes in a functional network important for language development and evolution.

The aPKC-CBP Pathway Regulates Post-stroke Neurovascular Remodeling and Functional Recovery

Epigenetic modifications have emerged as attractive molecular substrates that integrate extrinsic changes into the determination of cell identity. Since stroke-related brain damage releases micro-environmental cues, we examined the role of a signaling-induced epigenetic pathway, an atypical protein kinase C (aPKC)-mediated phosphorylation of CREB-binding protein (CBP), in post-stroke neurovascular remodeling. Using a knockin mouse strain (CbpS436A) where the aPKC-CBP pathway was defective, we show that disruption of the aPKC-CBP pathway in a murine focal ischemic stroke model increases the reprogramming efficiency of ischemia-activated pericytes (i-pericytes) to neural precursors. As a consequence of enhanced cellular reprogramming, CbpS436A mice show an increased transient population of locally derived neural precursors after stroke, while displaying a reduced number of i-pericytes, impaired vascular remodeling, and perturbed motor recovery during the chronic phase of stroke. Together, this study elucidates the role of the aPKC-CBP pathway in modulating neurovascular remodeling and functional recovery following focal ischemic stroke.

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CbpS436A increases the reprogramming efficiency of i-pericytes to NPCs in culture

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CbpS436A increases the number of locally derived NPCs from i-pericyte in vivo

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CbpS436A shows impaired vascular remodeling and functional recovery after stroke

Electromagnetic Fields for the Regulation of Neural Stem Cells

Localized magnetic fields (MFs) could easily penetrate the scalp, skull, and meninges, thus inducing an electrical current in both the central and peripheral nervous systems, which is primarily used in transcranial magnetic stimulation (TMS) for inducing specific effects on different regions or cells that play roles in various brain activities. Studies of repetitive transcranial magnetic stimulation (rTMS) have led to novel attractive therapeutic approaches. Neural stem cells (NSCs) in adult human brain are able to self-renew and possess multidifferential ability to maintain homeostasis and repair damage after acute central nervous system. In the present review, we summarized the electrical activity of NSCs and the fundamental mechanism of electromagnetic fields and their effects on regulating NSC proliferation, differentiation, migration, and maturation. Although it was authorized for the rTMS use in resistant depression patients by US FDA, there are still unveiling mechanism and limitations for rTMS in clinical applications of acute central nervous system injury, especially on NSC regulation as a rehabilitation strategy. More in-depth studies should be performed to provide detailed parameters and mechanisms of rTMS in further studies, making it a powerful tool to treat people who are surviving with acute central nervous system injuries.

Atypical PKC and Notch Inhibition Differentially Modulate Cortical Interneuron Subclass Fate from Embryonic Stem Cells

Recent studies indicate that the location of neurogenesis within the medial ganglionic eminence (MGE) critically influences the fate determination of cortical interneuron subgroups, with parvalbumin (Pv) interneurons originating from subventricular zone divisions and somatostatin (Sst) interneurons primarily arising from apical divisions. The aPKC-CBP and Notch signaling pathways regulate the transition from apical to basal progenitor and their differentiation into post-mitotic neurons. We find that aPKC inhibition enhances intermediate neurogenesis from stem cell-derived MGE progenitors, resulting in a markedly increased ratio of Pv- to Sst-expressing interneurons. Conversely, inhibition of Notch signaling enriches for Sst subtypes at the expense of Pv fates. These findings confirm that the mode of neurogenesis influences the fate of MGE-derived interneurons and provide a means of further enrichment for the generation of specific interneuron subgroups from pluripotent stem cells.

Stress and the Emerging Roles of Chromatin Remodeling in Signal Integration and Stable Transmission of Reversible Phenotypes

The influence of early life experience and degree of parental-infant attachment on emotional development in children and adolescents has been comprehensively studied. Structural and mechanistic insight into the biological foundation and maintenance of mammalian defensive systems (metabolic, immune, nervous and behavioral) is slowly advancing through the emerging field of developmental molecular (epi)genetics. Initial evidence revealed that differential nurture early in life generates stable differences in offspring hypothalamic-pituitary-adrenal (HPA) regulation, in part, through chromatin remodeling and changes in DNA methylation of specific genes expressed in the brain, revealing physical, biochemical and molecular paths for the epidemiological concept of gene-environment interactions. Herein, a primary molecular mechanism underpinning the early developmental programming and lifelong maintenance of defensive (emotional) responses in the offspring is the alteration of chromatin domains of specific genomic regions from a condensed state (heterochromatin) to a transcriptionally accessible state (euchromatin). Conversely, DNA methylation promotes the formation of heterochromatin, which is essential for gene silencing, genomic integrity and chromosome segregation. Therefore, inter-individual differences in chromatin modifications and DNA methylation marks hold great potential for assessing the impact of both early life experience and effectiveness of intervention programs—from guided psychosocial strategies focused on changing behavior to pharmacological treatments that target chromatin remodeling and DNA methylation enzymes to dietary approaches that alter cellular pools of metabolic intermediates and methyl donors to affect nutrient bioavailability and metabolism. In this review article, we discuss the potential molecular mechanism(s) of gene regulation associated with chromatin modeling and programming of endocrine (e.g., HPA and metabolic or cardiovascular) and behavioral (e.g., fearfulness, vigilance) responses to stress, including alterations in DNA methylation and the role of DNA repair machinery. From parental history (e.g., drugs, housing, illness, nutrition, socialization) to maternal-offspring exchanges of nutrition, microbiota, antibodies and stimulation, the nature of nurture provides not only mechanistic insight into how experiences propagate from external to internal variables, but also identifies a composite therapeutic target, chromatin modeling, for gestational/prenatal stress, adolescent anxiety/depression and adult-onset neuropsychiatric disease.

An Evolutionarily Conserved SoxB-Hdac2 Crosstalk Regulates Neurogenesis in a Cnidarian

SoxB transcription factors and histone deacetylases (HDACs) are each major players in the regulation of neurogenesis, but a functional link between them has not been previously demonstrated. Here, we show that SoxB2 and Hdac2 act together to regulate neurogenesis in the cnidarian Hydractinia echinata during tissue homeostasis and head regeneration. We find that misexpression of SoxB genes modifies the number of neural cells in all life stages and interferes with head regeneration. Hdac2 was co-expressed with SoxB2, and its downregulation phenocopied SoxB2 knockdown. We also show that SoxB2 and Hdac2 promote each other's transcript levels, but Hdac2 counteracts this amplification cycle by deacetylating and destabilizing SoxB2 protein. Finally, we present evidence for conservation of these interactions in human neural progenitors. We hypothesize that crosstalk between SoxB transcription factors and Hdac2 is an ancient feature of metazoan neurogenesis and functions to stabilize the correct levels of these multifunctional proteins.

Histone acetylation in neuronal (dys)function

Cognitive functions require the expression of an appropriate pattern of genes in response to environmental stimuli. Over the last years, many studies have accumulated knowledge towards the understanding of molecular mechanisms that regulate neuronal gene expression. Epigenetic modifications have been shown to play an important role in numerous neuronal functions, from synaptic plasticity to learning and memory. In particular, histone acetylation is a central player in these processes. In this review, we present the molecular mechanisms of histone acetylation and summarize the data underlying the relevance of histone acetylation in cognitive functions in normal and pathological conditions. In the last part, we discuss the different mechanisms underlying the dysregulation of histone acetylation associated with neurological disorders, with a particular focus on environmental causes (stress, drugs, or infectious agents) that are linked to impaired histone acetylation.

Lysine Acetylation and Deacetylation in Brain Development and Neuropathies

Embryonic development is critical for the final functionality and maintenance of the adult brain. Brain development is tightly regulated by intracellular and extracellular signaling. Lysine acetylation and deacetylation are posttranslational modifications that are able to link extracellular signals to intracellular responses. A wealth of evidence indicates that lysine acetylation and deacetylation are critical for brain development and functionality. Indeed, mutations of the enzymes and cofactors responsible for these processes are often associated with neurodevelopmental and psychiatric disorders. Lysine acetylation and deacetylation are involved in all levels of brain development, starting from neuroprogenitor survival and proliferation, cell fate decisions, neuronal maturation, migration, and synaptogenesis, as well as differentiation and maturation of astrocytes and oligodendrocytes, to the establishment of neuronal circuits. Hence, fluctuations in the balance between lysine acetylation and deacetylation contribute to the final shape and performance of the brain. In this review, we summarize the current basic knowledge on the specific roles of lysine acetyltransferase (KAT) and lysine deacetylase (KDAC) complexes in brain development and the different neurodevelopmental disorders that are associated with dysfunctional lysine (de)acetylation machineries.

Post‑translational modification of CREB‑1 decreases collagen I expression by inhibiting the TGF‑β1 signaling pathway in rat hepatic stellate cells

Liver fibrosis is a reversible wound‑healing response to liver damage. Following liver injury, activated hepatic stellate cells (HSCs) cause excessive deposition of collagen and other components of the extracellular matrix, which may eventually impair liver function. Transforming growth factor‑β1 (TGF‑β1) is critical for the development of liver fibrosis, and acts by activating HSCs, stimulating matrix deposition and inducing other profibrotic responses. Certain studies have demonstrated that the transcription factor, cyclic adenosine monophosphate (cAMP)‑response element binding protein‑1 (CREB‑1) is important in the inhibition of fibrosis; however, the underlying mechanism remains to be elucidated. The present study hypothesized that CREB‑1 inhibits fibrosis via blocking the TGF‑β1 signaling pathway in HSCs. Treatment with the cAMP‑elevating agent, forskolin stimulated CREB‑1 phosphorylation and transcription activation in HSCs. In addition, treatment with the histone deacetylase inhibitor, trichostatin A extended CREB‑1 phosphorylation. The present study used a pRSV‑CREB‑1 expression vector to upregulate CREB‑1 gene expression. The results indicated that activated CREB‑1 reduced TGF‑β1‑stimulated expression of collagen I, activated Smad2/3 and upregulated expression of Smad7. In addition, activated CREB‑1 attenuated the activation of extracellular signal‑regulated kinase 1/2 induced by TGF‑β1, expression of Ras homolog gene family, member A (RhoA) and Rho‑associated coiled‑coil containing protein kinase 1. Thus, post‑translational modification of CREB‑1 inhibited the profibrotic effects of TGF‑β1 in HSCs via Smad‑dependent and ‑independent signaling pathways.

Tunable regulation of CREB DNA binding activity couples genotoxic stress response and metabolism

cAMP response element binding protein (CREB) is a key regulator of glucose metabolism and synaptic plasticity that is canonically regulated through recruitment of transcriptional coactivators. Here we show that phosphorylation of CREB on a conserved cluster of Ser residues (the ATM/CK cluster) by the DNA damage-activated protein kinase ataxia-telangiectasia-mutated (ATM) and casein kinase1 (CK1) and casein kinase2 (CK2) positively and negatively regulates CREB-mediated transcription in a signal dependent manner. In response to genotoxic stress, phosphorylation of the ATM/CK cluster inhibited CREB-mediated gene expression, DNA binding activity and chromatin occupancy proportional to the number of modified Ser residues. Paradoxically, substoichiometric, ATM-independent, phosphorylation of the ATM/CK cluster potentiated bursts in CREB-mediated transcription by promoting recruitment of the CREB coactivator, cAMP-regulated transcriptional coactivators (CRTC2). Livers from mice expressing a non-phosphorylatable CREB allele failed to attenuate gluconeogenic genes in response to DNA damage or fully activate the same genes in response to glucagon. We propose that phosphorylation-dependent regulation of DNA binding activity evolved as a tunable mechanism to control CREB transcriptional output and promote metabolic homeostasis in response to rapidly changing environmental conditions.

The aPKC-CBP Pathway Regulates Adult Hippocampal Neurogenesis in an Age-Dependent Manner

While epigenetic modifications have emerged as attractive substrates to integrate environmental changes into the determination of cell identity and function, specific signals that directly activate these epigenetic modifications remain unknown. Here, we examine the role of atypical protein kinase C (aPKC)-mediated Ser436 phosphorylation of CBP, a histone acetyltransferase, in adult hippocampal neurogenesis and memory. Using a knockin mouse strain (CbpS436A) in which the aPKC-CBP pathway is deficient, we observe impaired hippocampal neuronal differentiation, maturation, and memory and diminished binding of CBP to CREB in 6-month-old CbpS436A mice, but not at 3 months of age. Importantly, elevation of CREB activity rescues these deficits, and CREB activity is reduced whereas aPKC activity is increased in the murine hippocampus as they age from 3 to 6 months regardless of genotype. Thus, the aPKC-CBP pathway is a homeostatic compensatory mechanism that modulates hippocampal neurogenesis and memory in an age-dependent manner in response to reduced CREB activity.

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The aPKC-CBP pathway maintains mature adult hippocampal neuronal differentiation

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The aPKC-CBP pathway is required for hippocampal-dependent memory in mature adult

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The aPKC-CBP pathway is required for CBP binding to CREB in mature adult hippocampi

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Increased CREB activity rescues the deficits due to the deficient aPKC-CBP pathway

CBP/p300 acetyltransferase activity in hematologic malignancies

CREB binding protein (CBP) and p300 are critical regulators of hematopoiesis through both their transcriptional coactivator and acetyltransferase activities. Loss or mutation of CBP/p300 results in hematologic deficiencies in proliferation and differentiation as well as disruption of hematopoietic stem cell renewal and the microenvironment. Aberrant lysine acetylation mediated by CBP/p300 has recently been implicated in the genesis of multiple hematologic cancers. Understanding the effects of disrupting the acetyltransferase activity of CBP/p300 could pave the way for new therapeutic approaches to treat patients with these diseases.

Chemical Modulation of Cell Fate in Stem Cell Therapeutics and Regenerative Medicine

Regenerative medicine aims to repair and regenerate injured tissues and restore their impaired functions. Recent developments in stem cell biology have attracted significant interest in their applications in regenerative medicine. Chemical approaches using small molecules have yielded exciting results in induction and differentiation of pluripotent stem cells, lineage conversion of somatic cells, and ex vivo as well as in vivo modulation of adult stem cells. In this review, we discuss recent progress, new insights, and future challenges of the chemical approaches in stem cell biology and regenerative medicine.

Hdac3 Interaction with p300 Histone Acetyltransferase Regulates the Oligodendrocyte and Astrocyte Lineage Fate Switch

Establishment and maintenance of CNS glial cell identity ensures proper brain development and function, yet the epigenetic mechanisms underlying glial fate control remain poorly understood. Here, we show that the histone deacetylase Hdac3 controls oligodendrocyte-specification gene Olig2 expression and functions as a molecular switch for oligodendrocyte and astrocyte lineage determination. Hdac3 ablation leads to a significant increase of astrocytes with a concomitant loss of oligodendrocytes. Lineage tracing indicates that the ectopic astrocytes originate from oligodendrocyte progenitors. Genome-wide occupancy analysis reveals that Hdac3 interacts with p300 to activate oligodendroglial lineage-specific genes, while suppressing astroglial differentiation genes including NFIA. Furthermore, we find that Hdac3 modulates the acetylation state of Stat3 and competes with Stat3 for p300 binding to antagonize astrogliogenesis. Thus, our data suggest that Hdac3 cooperates with p300 to prime and maintain oligodendrocyte identity while inhibiting NFIA and Stat3-mediated astrogliogenesis, and thereby regulates phenotypic commitment at the point of oligodendrocyte-astrocytic fate decision.

Thyroid Hormone Signaling in Oligodendrocytes: from Extracellular Transport to Intracellular Signal

Thyroid hormone plays an important role in central nervous system (CNS) development, including the myelination of variable axonal calibers. It is well-established that thyroid hormone is required for the terminal differentiation of oligodendrocyte precursor cells (OPCs) into myelinating oligodendrocytes by inducing rapid cell-cycle arrest and constant transcription of pro-differentiation genes. This is well supported by the hypomyelinating phenotypes exhibited by patients with congenital hypothyroidism, cretinism. During development, myelinating oligodendrocytes only appear after the formation of neural circuits, indicating that the timing of oligodendrocyte differentiation is important. Since fetal and post-natal serum thyroid hormone levels peak at the stage of active myelination, it is suspected that the timing of oligodendrocyte development is finely controlled by thyroid hormone. The essential machinery for thyroid hormone signaling such as deiodinase activity (utilized by cells to auto-regulate the level of thyroid hormone), and nuclear thyroid hormone receptors (for gene transcription) are expressed on oligodendrocytes. In this review, we discuss the known and potential thyroid hormone signaling pathways that may regulate oligodendrocyte development and CNS myelination. Moreover, we evaluate the potential of targeting thyroid hormone signaling for white matter injury or disease.

The role of nuclear PKMζ in memory maintenance

Recently, protein kinase M ζ (PKMζ) has emerged as an important player for maintaining memory. It has been reported that PKMζ regulates the trafficking of GluA2 in postsynaptic membranes to maintain memory. However, there has been no study on PKMζ outside the synaptic region regarding memory maintenance. Here, we found that PKMζ is transported to the nucleus in a neural activity-dependent manner. Moreover, we found that PKMζ phosphorylates CREB-binding protein (CBP) at serine residues and that PKMζ inhibition reduces the acetylation of histone H2B and H3. Finally, we showed that the amnesic effect of PKMζ inhibition can be rescued by enhancing histone acetylation level. These results suggest the possibility that nuclear PKMζ has a crucial role in memory maintenance.

The world of protein acetylation

Acetylation is one of the major post-translational protein modifications in the cell, with manifold effects on the protein level as well as on the metabolome level. The acetyl group, donated by the metabolite acetyl-coenzyme A, can be co- or post-translationally attached to either the α-amino group of the N-terminus of proteins or to the ε-amino group of lysine residues. These reactions are catalyzed by various N-terminal and lysine acetyltransferases. In case of lysine acetylation, the reaction is enzymatically reversible via tightly regulated and metabolism-dependent mechanisms. The interplay between acetylation and deacetylation is crucial for many important cellular processes. In recent years, our understanding of protein acetylation has increased significantly by global proteomics analyses and in depth functional studies. This review gives a general overview of protein acetylation and the respective acetyltransferases, and focuses on the regulation of metabolic processes and physiological consequences that come along with protein acetylation.

Presymptomatic Alterations in Amino Acid Metabolism and DNA Methylation in the Cerebellum of a Murine Model of Niemann-Pick Type C Disease

The fatal neurodegenerative disorder Niemann-Pick type C (NPC) is caused in most cases by mutations in NPC1, which encodes the late endosomal NPC1 protein. Loss of NPC1 disrupts cholesterol trafficking from late endosomes to the endoplasmic reticulum and plasma membrane, causing cholesterol accumulation in late endosomes/lysosomes. Neurons are particularly vulnerable to this cholesterol trafficking defect, but the pathogenic mechanisms through which NPC1 deficiency causes neuronal dysfunction remain largely unknown. Herein, we have investigated amino acid metabolism in cerebella of NPC1-deficient mice at different stages of NPC disease. Imbalances in amino acid metabolism were evident from increased branched chain amino acid and asparagine levels and altered expression of key enzymes of glutamine/glutamate metabolism in presymptomatic and early symptomatic NPC1-deficient cerebellum. Increased levels of several amino acid intermediates of one-carbon metabolism indicated disturbances in folate and methylation pathways. Alterations in DNA methylation were apparent in decreased expression of DNA methyltransferase 3a and methyl-5'-cytosine-phosphodiester-guanine-domain binding proteins, reduced 5-methylcytosine immunoreactivity in the molecular and Purkinje cell layers, demethylation of genome-wide repetitive LINE-1 elements, and hypermethylation in specific promoter regions of single-copy genes in NPC1-deficient cerebellum at early stages of the disease. Alterations in amino acid metabolism and epigenetic changes in the cerebellum at presymptomatic stages of NPC disease represent previously unrecognized mechanisms of NPC pathogenesis.

A Smaug2-Based Translational Repression Complex Determines the Balance between Precursor Maintenance versus Differentiation during Mammalian Neurogenesis

Here, we have asked about post-transcriptional mechanisms regulating murine developmental neurogenesis, focusing upon the RNA-binding proteins Smaug2 and Nanos1. We identify, in embryonic neural precursors of the murine cortex, a Smaug2 protein/nanos1 mRNA complex that is present in cytoplasmic granules with the translational repression proteins Dcp1 and 4E-T. We show that Smaug2 inhibits and Nanos1 promotes neurogenesis, with Smaug2 knockdown enhancing neurogenesis and depleting precursors, and Nanos1 knockdown inhibiting neurogenesis and maintaining precursors. Moreover, we show that Smaug2 likely regulates neurogenesis by silencing nanos1 mRNA. Specifically, Smaug2 knockdown inappropriately increases Nanos1 protein, and the Smaug2 knockdown-mediated neurogenesis is rescued by preventing this increase. Thus, Smaug2 and Nanos1 function as a bimodal translational repression switch to control neurogenesis, with Smaug2 acting in transcriptionally primed precursors to silence mRNAs important for neurogenesis, including nanos1 mRNA, and Nanos1 acting during the transition to neurons to repress the precursor state.

SIGNIFICANCE STATEMENT

The mechanisms instructing neural stem cells to generate the appropriate progeny are still poorly understood. Here, we show that the RNA-binding proteins Smaug2 and Nanos1 are critical regulators of this balance and provide evidence supporting the idea that neural precursors are transcriptionally primed to generate neurons but translational regulation maintains these precursors in a stem cell state until the appropriate developmental time.

[Epigenetic regulations and cerebral plasticity: towards new therapeutic options in neurodegenerative diseases?]

Although revealed in the 1950's, epigenetics is still a fast-growing field. Its delineations continuously evolve and become clarified. In particular, "neuroepigenetics", a notion that encompasses epigenetic regulations associated with neuronal processes, appears very promising. Indeed, the challenge to be undertaken in this sub-field is double. On the one hand, it should bring molecular comprehension of specific neuronal processes, some of them falling within the long term regulations, such as learning and memory. On the other hand, it could bring therapeutic options for brain diseases, e.g. neurodegenerative diseases such as Alzheimer's or Huntington's diseases.

Post-Translational Modifications of Histones in Vertebrate Neurogenesis

The process of neurogenesis, through which the entire nervous system of an organism is formed, has attracted immense scientific attention for decades. How can a single neural stem cell give rise to astrocytes, oligodendrocytes, and neurons? Furthermore, how is a neuron led to choose between the hundreds of different neuronal subtypes that the vertebrate CNS contains? Traditionally, niche signals and transcription factors have been on the spotlight. Recent research is increasingly demonstrating that the answer may partially lie in epigenetic regulation of gene expression. In this article, we comprehensively review the role of post-translational histone modifications in neurogenesis in both the embryonic and adult CNS.

Exome sequencing reveals a high genetic heterogeneity on familial Hirschsprung disease

Hirschsprung disease (HSCR; OMIM 142623) is a developmental disorder characterized by aganglionosis along variable lengths of the distal gastrointestinal tract, which results in intestinal obstruction. Interactions among known HSCR genes and/or unknown disease susceptibility loci lead to variable severity of phenotype. Neither linkage nor genome-wide association studies have efficiently contributed to completely dissect the genetic pathways underlying this complex genetic disorder. We have performed whole exome sequencing of 16 HSCR patients from 8 unrelated families with SOLID platform. Variants shared by affected relatives were validated by Sanger sequencing. We searched for genes recurrently mutated across families. Only variations in the FAT3 gene were significantly enriched in five families. Within-family analysis identified compound heterozygotes for AHNAK and several genes (N = 23) with heterozygous variants that co-segregated with the phenotype. Network and pathway analyses facilitated the discovery of polygenic inheritance involving FAT3, HSCR known genes and their gene partners. Altogether, our approach has facilitated the detection of more than one damaging variant in biologically plausible genes that could jointly contribute to the phenotype. Our data may contribute to the understanding of the complex interactions that occur during enteric nervous system development and the etiopathology of familial HSCR.

Brain size regulations by cbp haploinsufficiency evaluated by in-vivo MRI based volumetry

The Rubinstein-Taybi Syndrome (RSTS) is a congenital disease that affects brain development causing severe cognitive deficits. In most cases the disease is associated with dominant mutations in the gene encoding the CREB binding protein (CBP). In this work, we present the first quantitative analysis of brain abnormalities in a mouse model of RSTS using magnetic resonance imaging (MRI) and two novel self-developed automated algorithms for image volumetric analysis. Our results quantitatively confirm key syndromic features observed in RSTS patients, such as reductions in brain size (−16.31%, p < 0.05), white matter volume (−16.00%, p < 0.05), and corpus callosum (−12.40%, p < 0.05). Furthermore, they provide new insight into the developmental origin of the disease. By comparing brain tissues in a region by region basis between cbp^+/− and cbp^+/+ littermates, we found that cbp haploinsufficiency is specifically associated with significant reductions in prosencephalic tissue, such us in the olfactory bulb and neocortex, whereas regions evolved from the embryonic rhombencephalon were spared. Despite the large volume reductions, the proportion between gray-, white-matter and cerebrospinal fluid were conserved, suggesting a role of CBP in brain size regulation. The commonalities with holoprosencephaly and arhinencephaly conditions suggest the inclusion of RSTS in the family of neuronal migration disorders.

Protein kinase C coordinates histone H3 phosphorylation and acetylation

The re-assembly of chromatin following DNA replication is a critical event in the maintenance of genome integrity. Histone H3 acetylation at K56 and phosphorylation at T45 are two important chromatin modifications that accompany chromatin assembly. Here we have identified the protein kinase Pkc1 as a key regulator that coordinates the deposition of these modifications in S. cerevisiae under conditions of replicative stress. Pkc1 phosphorylates the histone acetyl transferase Rtt109 and promotes its ability to acetylate H3K56. Our data also reveal novel cross-talk between two different histone modifications as Pkc1 also enhances H3T45 phosphorylation and this modification is required for H3K56 acetylation. Our data therefore uncover an important role for Pkc1 in coordinating the deposition of two different histone modifications that are important for chromatin assembly.

DOI:http://dx.doi.org/10.7554/eLife.09886.001

Prior to cell division, DNA must be copied so that each new cell gets a complete copy of the cell’s genetic instructions. But DNA is so long that it is stored in a heavily compacted form in the nucleus of the cell, with the strands of DNA coiled around several proteins called histones. Before the DNA is copied, it must be unfurled. Then each new copy of DNA must be repackaged to fit compactly inside the nucleus of each new cell.

If errors occur in the process of copying DNA, it can lead to genetic mutations that may cause diseases like cancer. To prevent this, cells have mechanisms to identify errors and correct them before the DNA is repackaged. This requires a pause to allow the repairs to occur before the DNA recoils. However, it is not completely clear how this process is controlled.

Now, Darieva et al. show that an enzyme called protein kinase C (or Pkc1 for short) is essential to repackaging DNA after the errors are corrected. Several experiments showed that Pkc1 plays an important role when cells were exposed to stressful conditions that potentially cause errors in DNA copying. Specifically, Pkc1 helps prepare the third histone protein (histone H3) so that DNA can recoil around it. Pkc1 waits until the stressful conditions have passed and the DNA has been repaired to make the necessary changes.

Once the stress has passed, Pkc1 adds a phosphate to another enzyme called Rtt109 that prepares the histone. The Pkc1 simultaneously contributes to another necessary change to histone H3. These new details about DNA repackaging may help researchers understand how cells protect against DNA copying errors, and how this process goes wrong in cancer.

DOI:http://dx.doi.org/10.7554/eLife.09886.002

Neural and behavioral epigenetics; what it is, and what is hype

The ability to examine epigenetic mechanisms in the brain has become readily available over the last 20 years. This has led to an explosion of research and interest in neural and behavioral epigenetics. Of particular interest to researchers, and indeed the lay public, is the possibility that epigenetic processes, such as changes in DNA-methylation and histone modification, may provide a biochemical record of environmental effects. This has led to some fascinating insights into how molecular changes in the brain can control behavior. However, some of this research has also attracted controversy and, as is dealt with here, some overblown claims. This latter problem is partly linked to the shifting sands of what is defined as 'epigenetics'. In this review, I provide an overview of what exactly epigenetics is, and what is hype, with the aim of opening up a debate as to how this exciting field moves forward.

Ultra-Rare Syndromes: The Example of Rubinstein-Taybi Syndrome

Rubinstein-Taybi syndrome (RSTS) is a rare, congenital, plurimalformative, and neurodevelopmental disorder. Clinical diagnosis can be complicated by the heterogeneous clinical presentation and the lack of a consensus list of diagnostic criteria, and it is confirmed by molecular tests in approximately 55 to 78% of cases. The etiology is partially known with mutations in two functionally related genes: CREBBP and EP300. Notwithstanding the knowledge on clinical, genetic, and allelic heterogeneity, no clear genotype-phenotype correlation has yet been established. Standardized guidelines for the management of pediatric patients are available and therapy for RSTS patients is currently only symptomatic. In this article, several clinic and genetic aspects of RSTS are critically reviewed.

Epigenetic mechanisms: A possible link between autism spectrum disorders and fetal alcohol spectrum disorders

The etiology of autism spectrum disorders (ASDs) still remains unclear and seems to involve a considerable overlap between polygenic, epigenetic and environmental factors. We have summarized the current understanding of the interplay between gene expression dysregulation via epigenetic modifications and the potential epigenetic impact of environmental factors in neurodevelopmental deficits. Furthermore, we discuss the scientific controversies of the relationship between prenatal exposure to alcohol and alcohol-induced epigenetic dysregulations, and gene expression alterations which are associated with disrupted neural plasticity and causal pathways for ASDs. The review of the literature suggests that a better understanding of developmental epigenetics should contribute to furthering our comprehension of the etiology and pathogenesis of ASDs and fetal alcohol spectrum disorders.

Epigenetic factors in intellectual disability: the Rubinstein-Taybi syndrome as a paradigm of neurodevelopmental disorder with epigenetic origin

The number of genetic syndromes associated with intellectual disability that are caused by mutations in genes encoding chromatin-modifying enzymes has sharply risen in the last decade. We discuss here a neurodevelopmental disorder, the Rubinstein-Taybi syndrome (RSTS), originated by mutations in the genes encoding the lysine acetyltransferases CBP and p300. We first describe clinical and genetic aspects of the syndrome to later focus on the insight provided by the research in animal models of this disease. These studies have not only clarified the molecular etiology of RSTS and helped to dissect the developmental and adult components of the syndrome but also contributed to outline some important connections between epigenetics and cognition. We finally discuss how this body of research has opened new venues for the therapeutic intervention of this currently untreatable disease and present some of the outstanding questions in the field. We believe that the progress in the understanding of this rare disorder also has important implications for other intellectual disability disorders that share an epigenetic origin.

Activating Endogenous Neural Precursor Cells Using Metformin Leads to Neural Repair and Functional Recovery in a Model of Childhood Brain Injury

The development of cell replacement strategies to repair the injured brain has gained considerable attention, with a particular interest in mobilizing endogenous neural stem and progenitor cells (known as neural precursor cells [NPCs]) to promote brain repair. Recent work demonstrated metformin, a drug used to manage type II diabetes, promotes neurogenesis. We sought to determine its role in neural repair following brain injury. We find that metformin administration activates endogenous NPCs, expanding the size of the NPC pool and promoting NPC migration and differentiation in the injured neonatal brain in a hypoxia-ischemia (H/I) injury model. Importantly, metformin treatment following H/I restores sensory-motor function. Lineage tracking reveals that metformin treatment following H/I causes an increase in the absolute number of subependyma-derived NPCs relative to untreated H/I controls in areas associated with sensory-motor function. Hence, activation of endogenous NPCs is a promising target for therapeutic intervention in childhood brain injury models.

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Metformin activates endogenous NPCs in the neonatal brain

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Metformin increases the absolute number of NPCs after neonatal brain injury

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Sensory-motor functional recovery occurs following metformin treatment post-injury

Epigenetic Control of Stem Cell Potential during Homeostasis, Aging, and Disease

Stem cell decline is an important cellular driver of aging-associated pathophysiology in multiple tissues. Epigenetic regulation is central to establishing and maintaining stem cell function, and emerging evidence indicates that epigenetic dysregulation contributes to the altered potential of stem cells during aging. Unlike terminally differentiated cells, the impact of epigenetic dysregulation in stem cells is propagated beyond self; alterations can be heritably transmitted to differentiated progeny, in addition to being perpetuated and amplified within the stem cell pool through self-renewal divisions. This Review focuses on recent studies examining epigenetic regulation of tissue-specific stem cells in homeostasis, aging, and aging-related disease.

Role of nucleosome remodeling in neurodevelopmental and intellectual disability disorders

It is becoming increasingly important to understand how epigenetic mechanisms control gene expression during neurodevelopment. Two epigenetic mechanisms that have received considerable attention are DNA methylation and histone acetylation. Human exome sequencing and genome-wide association studies have linked several neurobiological disorders to genes whose products actively regulate DNA methylation and histone acetylation. More recently, a third major epigenetic mechanism, nucleosome remodeling, has been implicated in human developmental and intellectual disability (ID) disorders. Nucleosome remodeling is driven primarily through nucleosome remodeling complexes with specialized ATP-dependent enzymes. These enzymes directly interact with DNA or chromatin structure, as well as histone subunits, to restructure the shape and organization of nucleosome positioning to ultimately regulate gene expression. Of particular interest is the neuron-specific Brg1/hBrm Associated Factor (nBAF) complex. Mutations in nBAF subunit genes have so far been linked to Coffin-Siris syndrome (CSS), Nicolaides-Baraitser syndrome (NBS), schizophrenia, and Autism Spectrum Disorder (ASD). Together, these human developmental and ID disorders are powerful examples of the impact of epigenetic modulation on gene expression. This review focuses on the new and emerging role of nucleosome remodeling in neurodevelopmental and ID disorders and whether nucleosome remodeling affects gene expression required for cognition independently of its role in regulating gene expression required for development.

Borna disease virus phosphoprotein modulates epigenetic signaling in neurons to control viral replication

Understanding the modalities of interaction of neurotropic viruses with their target cells represents a major challenge that may improve our knowledge of many human neurological disorders for which viral origin is suspected. Borna disease virus (BDV) represents an ideal model to analyze the molecular mechanisms of viral persistence in neurons and its consequences for neuronal homeostasis. It is now established that BDV ensures its long-term maintenance in infected cells through a stable interaction of viral components with the host cell chromatin, in particular, with core histones. This has led to our hypothesis that such an interaction may trigger epigenetic changes in the host cell. Here, we focused on histone acetylation, which plays key roles in epigenetic regulation of gene expression, notably for neurons. We performed a comparative analysis of histone acetylation patterns of neurons infected or not infected by BDV, which revealed that infection decreases histone acetylation on selected lysine residues. We showed that the BDV phosphoprotein (P) is responsible for these perturbations, even when it is expressed alone independently of the viral context, and that this action depends on its phosphorylation by protein kinase C. We also demonstrated that BDV P inhibits cellular histone acetyltransferase activities. Finally, by pharmacologically manipulating cellular acetylation levels, we observed that inhibiting cellular acetyl transferases reduces viral replication in cell culture. Our findings reveal that manipulation of cellular epigenetics by BDV could be a means to modulate viral replication and thus illustrate a fascinating example of virus-host cell interaction.

IMPORTANCE

Persistent DNA viruses often subvert the mechanisms that regulate cellular chromatin dynamics, thereby benefitting from the resulting epigenetic changes to create a favorable milieu for their latent and persistent states. Here, we reasoned that Borna disease virus (BDV), the only RNA virus known to durably persist in the nucleus of infected cells, notably neurons, might employ a similar mechanism. In this study, we uncovered a novel modality of virus-cell interaction in which BDV phosphoprotein inhibits cellular histone acetylation by interfering with histone acetyltransferase activities. Manipulation of cellular histone acetylation is accompanied by a modulation of viral replication, revealing a perfect adaptation of this "ancient" virus to its host that may favor neuronal persistence and limit cellular damage.

Ankrd11 is a chromatin regulator involved in autism that is essential for neural development

Ankrd11 is a potential chromatin regulator implicated in neural development and autism spectrum disorder (ASD) with no known function in the brain. Here, we show that knockdown of Ankrd11 in developing murine or human cortical neural precursors caused decreased proliferation, reduced neurogenesis, and aberrant neuronal positioning. Similar cellular phenotypes and aberrant ASD-like behaviors were observed in Yoda mice carrying a point mutation in the Ankrd11 HDAC-binding domain. Consistent with a role for Ankrd11 in histone acetylation, Ankrd11 was associated with chromatin and colocalized with HDAC3, and expression and histone acetylation of Ankrd11 target genes were altered in Yoda neural precursors. Moreover, the Ankrd11 knockdown-mediated decrease in precursor proliferation was rescued by inhibiting histone acetyltransferase activity or expressing HDAC3. Thus, Ankrd11 is a crucial chromatin regulator that controls histone acetylation and gene expression during neural development, thereby providing a likely explanation for its association with cognitive dysfunction and ASD.

Modulation of neurogenesis by targeting epigenetic enzymes using small molecules: an overview

Neurogenesis consists of a plethora of complex cellular processes including neural stem cell (NSC) proliferation, migration, maturation or differentiation to neurons, and finally integration into the pre-existing neural circuits in the brain, which are temporally regulated and coordinated sequentially. Mammalian neurogenesis begins during embryonic development and continues in postnatal brain (adult neurogenesis). It is now evident that adult neurogenesis is driven by extracellular and intracellular signaling pathways, where epigenetic modifications like reversible histone acetylation, methylation, as well as DNA methylation play a vital role. Epigenetic regulation of gene expression during neural development is governed mainly by histone acetyltransferases (HATs), histone methyltransferase (HMTs), DNA methyltransferases (DNMTs), and also the enzymes for reversal, like histone deacetylases (HDACs), and many of these have also been shown to be involved in the regulation of adult neurogenesis. The contribution of these epigenetic marks to neurogenesis is increasingly being recognized, through knockout studies and small molecule modulator based studies. These small molecules are directly involved in regeneration and repair of neurons, and not only have applications from a therapeutic point of view, but also provide a tool to study the process of neurogenesis itself. In the present Review, we will focus on small molecules that act predominantly on epigenetic enzymes to enhance neurogenesis and neuroprotection and discuss the mechanism and recent advancements in their synthesis, targeting, and biology.

Regulation of proliferation and histone acetylation in embryonic neural precursors by CREB/CREM signaling

The transcription factor CREB (cAMP-response element binding protein) regulates differentiation, migration, survival and activity-dependent gene expression in the developing and mature nervous system. However, its specific role in the proliferation of embryonic neural progenitors is still not completely understood. Here we investigated how CREB regulates proliferation of mouse embryonic neural progenitors by a conditional mutant lacking Creb gene in neural progenitors. In parallel, we explored possible compensatory effects by the genetic ablation of another member of the same gene family, the cAMP-responsive element modulator (Crem). We show that CREB loss differentially impaired the proliferation, clonogenic potential and self-renewal of precursors derived from the ganglionic eminence (GE), in comparison to those derived from the cortex. This phenotype was associated with a specific reduction of histone acetylation in the GE of CREB mutant mice, and this reduction was rescued in vivo by inhibition of histone deacetylation. These observations indicate that the impaired proliferation could be caused by a reduced acetyltransferase activity in Creb conditional knock-out mice. These findings support a crucial role of CREB in controlling embryonic neurogenesis and propose a novel mechanism by which CREB regulates embryonic neural development.

Globularity and language-readiness: generating new predictions by expanding the set of genes of interest

This study builds on the hypothesis put forth in Boeckx and Benítez-Burraco (2014), according to which the developmental changes expressed at the levels of brain morphology and neural connectivity that resulted in a more globular braincase in our species were crucial to understand the origins of our language-ready brain. Specifically, this paper explores the links between two well-known 'language-related' genes like FOXP2 and ROBO1 implicated in vocal learning and the initial set of genes of interest put forth in Boeckx and Benítez-Burraco (2014), with RUNX2 as focal point. Relying on the existing literature, we uncover potential molecular links that could be of interest to future experimental inquiries into the biological foundations of language and the testing of our initial hypothesis. Our discussion could also be relevant for clinical linguistics and for the interpretation of results from paleogenomics.

Reinstatement of long-term memory following erasure of its behavioral and synaptic expression in Aplysia

Long-term memory (LTM) is believed to be stored in the brain as changes in synaptic connections. Here, we show that LTM storage and synaptic change can be dissociated. Cocultures of Aplysia sensory and motor neurons were trained with spaced pulses of serotonin, which induces long-term facilitation. Serotonin (5HT) triggered growth of new presynaptic varicosities, a synaptic mechanism of long-term sensitization. Following 5HT training, two antimnemonic treatments-reconsolidation blockade and inhibition of PKM--caused the number of presynaptic varicosities to revert to the original, pretraining value. Surprisingly, the final synaptic structure was not achieved by targeted retraction of the 5HT-induced varicosities but, rather, by an apparently arbitrary retraction of both 5HT-induced and original synapses. In addition, we find evidence that the LTM for sensitization persists covertly after its apparent elimination by the same antimnemonic treatments that erase learning-related synaptic growth. These results challenge the idea that stable synapses store long-term memories.