The growth factor EPIREGULIN promotes basal progenitor cell proliferation in the developing neocortex.

Neocortex expansion during evolution is linked to higher numbers of neurons, which are thought to result from increased proliferative capacity and neurogenic potential of basal progenitor cells during development. Here, we show that EREG, encoding the growth factor EPIREGULIN, is expressed in the human developing neocortex and in gorilla cerebral organoids, but not in the mouse neocortex. Addition of EPIREGULIN to the mouse neocortex increases proliferation of basal progenitor cells, whereas EREG ablation in human cortical organoids reduces proliferation in the subventricular zone. Treatment of cortical organoids with EPIREGULIN promotes a further increase in proliferation of gorilla but not of human basal progenitor cells. EPIREGULIN competes with the epidermal growth factor (EGF) to promote proliferation, and inhibition of the EGF receptor abrogates the EPIREGULIN-mediated increase in basal progenitor cells. Finally, we identify putative cis-regulatory elements that may contribute to the observed inter-species differences in EREG expression. Our findings suggest that species-specific regulation of EPIREGULIN expression may contribute to the increased neocortex size of primates by providing a tunable pro-proliferative signal to basal progenitor cells in the subventricular zone.

Widespread loss of the silencing epigenetic mark H3K9me3 in astrocytes and neurons along with hippocampal-dependent cognitive impairment in C9orf72 BAC transgenic mice.

BACKGROUND: Hexanucleotide repeat expansions of the G4C2 motif in a non-coding region of the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Tissues from C9ALS/FTD patients and from mouse models of ALS show RNA foci, dipeptide-repeat proteins, and notably, widespread alterations in the transcriptome. Epigenetic processes regulate gene expression without changing DNA sequences and therefore could account for the altered transcriptome profiles in C9ALS/FTD; here, we explore whether the critical repressive marks H3K9me2 and H3K9me3 are altered in a recently developed C9ALS/FTD BAC mouse model (C9BAC). RESULTS: Chromocenters that constitute pericentric constitutive heterochromatin were visualized as DAPI- or Nucblue-dense foci in nuclei. Cultured C9BAC astrocytes exhibited a reduced staining signal for H3K9me3 (but not for H3K9me2) at chromocenters that was accompanied by a marked decline in the global nuclear level of this mark. Similar depletion of H3K9me3 at chromocenters was detected in astrocytes and neurons of the spinal cord, motor cortex, and hippocampus of C9BAC mice. The alterations of H3K9me3 in the hippocampus of C9BAC mice led us to identify previously undetected neuronal loss in CA1, CA3, and dentate gyrus, as well as hippocampal-dependent cognitive deficits. CONCLUSIONS: Our data indicate that a loss of the repressive mark H3K9me3 in astrocytes and neurons in the central nervous system of C9BAC mice represents a signature during neurodegeneration and memory deficit of C9ALS/FTD.

Chronic Fluoxetine Treatment Induces Maturation-Compatible Changes in the Dendritic Arbor and in Synaptic Responses in the Auditory Cortex.

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) used to treat mood and anxiety disorders. Chronic treatment with this antidepressant drug is thought to favor functional recovery by promoting structural and molecular changes in several forebrain areas. At the synaptic level, chronic fluoxetine induces an increased size and density of dendritic spines and an increased ratio of GluN2A over GluN2B N-methyl-D-aspartate (NMDA) receptor subunits. The "maturation"-promoting molecular changes observed after chronic fluoxetine should also induce structural remodeling of the neuronal dendritic arbor and changes in the synaptic responses. We treated adult rats with fluoxetine (0.7 mg/kg i.p. for 28 days) and performed a morphometric analysis using Golgi stain in limbic and nonlimbic cortical areas. Then, we focused especially on the auditory cortex, where we evaluated the dendritic morphology of pyramidal neurons using a 3-dimensional reconstruction of neurons expressing mRFP after in utero electroporation. With both methodologies, a shortening and decreased complexity of the dendritic arbors was observed, which is compatible with an increased GluN2A over GluN2B ratio. Recordings of extracellular excitatory postsynaptic potentials in the auditory cortex revealed an increased synaptic response after fluoxetine and were consistent with an enrichment of GluN2A-containing NMDA receptors. Our results confirm that fluoxetine favors maturation and refinement of extensive cortical networks, including the auditory cortex. The fluoxetine-induced receptor switch may decrease GluN2B-dependent toxicity and thus could be applied in the future to treat neurodegenerative brain disorders characterized by glutamate toxicity and/or by an aberrant network connectivity.

Epigenetic editing of the Dlg4/PSD95 gene improves cognition in aged and Alzheimer's disease mice.

The Dlg4 gene encodes for post-synaptic density protein 95 (PSD95), a major synaptic protein that clusters glutamate receptors and is critical for plasticity. PSD95 levels are diminished in ageing and neurodegenerative disorders, including Alzheimer's disease and Huntington's disease. The epigenetic mechanisms that (dys)regulate transcription of Dlg4/PSD95, or other plasticity genes, are largely unknown, limiting the development of targeted epigenome therapy. We analysed the Dlg4/PSD95 epigenetic landscape in hippocampal tissue and designed a Dlg4/PSD95 gene-targeting strategy: a Dlg4/PSD95 zinc finger DNA-binding domain was engineered and fused to effector domains to either repress (G9a, Suvdel76, SKD) or activate (VP64) transcription, generating artificial transcription factors or epigenetic editors (methylating H3K9). These epi-editors altered critical histone marks and subsequently Dlg4/PSD95 expression, which, importantly, impacted several hippocampal neuron plasticity processes. Intriguingly, transduction of the artificial transcription factor PSD95-VP64 rescued memory deficits in aged and Alzheimer's disease mice. Conclusively, this work validates PSD95 as a key player in memory and establishes epigenetic editing as a potential therapy to treat human neurological disorders.