MeCP2:multifaceted roles in gene regulation and neural development

Methyl-CpG-binding protein 2 （MeCP2） is a classic methylated-DNA-binding protein, dysfunctions of which lead to various neurodevelopmental disorders such as Rett syndrome and autism spectrum disorder. Initially recognized as a transcriptional repressor, MeCP2 has been studied extensively and its functions have been expanded dramatically in the past two decades. Recently, it was found to be involved in gene regulation at the post-transcriptional level. MeCP2 represses nuclear microRNA processing by interacting directly with the Drosha/DGCR8 complex. In addition to its multifaceted functions, MeCP2 is remarkably modulated by post- translational modifications such as phosphorylation, SUMOylation, and acetylation, providing more regulatory dimensions to its functions. The role of MeCP2 in the central nervous system has been studied extensively, from neurons to glia. Future investigations combining molecular, cellular, and physiological methods are necessary for defining the roles of MeCP2 in the brain and developing efficient treatments for MeCP2-related brain disorders.

Induction of core symptoms of autism spectrum disorder by in vivo CRISPR/Cas9-based gene editing in the brain of adolescent rhesus monkeys

Although CRISPR/Cas9-mediated gene editing is widely applied to mimic human disorders,whether acute manipulation of disease-causing genes in the brain leads to behavioral abnormalities in non-human primates remains to be determined.Here we induced genetic mutations in MECP2,a critical gene linked to Rett syndrome(RTT)and autism spectrum disorders(ASD),in the hippocampus(DG and CA1–4)of adolescent rhesus monkeys(Macaca mulatta)in vivo via adeno-associated virus(AAV)-delivered Staphylococcus aureus Cas9 with small guide RNAs(sg RNAs)targeting MECP2.In comparison to monkeys injected with AAV-Sa Cas9 alone(n=4),numerous autistic-like behavioral abnormalities were identified in the AAV-Sa Cas9-sg MECP2-injected monkeys(n=7),including social interaction deficits,abnormal sleep patterns,insensitivity to aversive stimuli,abnormal hand motions,and defective social reward behaviors.Furthermore,some aspects of ASD and RTT,such as stereotypic behaviors,did not appear in the MECP2 gene-edited monkeys,suggesting that different brain areas likely contribute to distinct ASD symptoms.This study showed that acute manipulation of disease-causing genes via in vivo gene editing directly led to behavioral changes in adolescent primates,paving the way for the rapid generation of genetically engineered non-human primate models for neurobiological studies and therapeutic development.

Reversal of Social Recognition Deficit in Adult Mice with MECP2 Duplication via Normalization of MeCP2 in the Medial Prefrontal Cortex

Methyl-CpG binding protein 2(MeCP2) is a basic nuclear protein involved in the regulation of gene expression and microRNA processing.Duplication of MECP2-containing genomic segments causes MECP2 duplication syndrome,a severe neurodevelopmental disorder characterized by intellectual disability,motor dysfunction,heightened anxiety,epilepsy,autistic phenotypes,and early death.Reversal of the abnormal phenotypes in adult mice with MECP2 duplication(MECP2-TG) by normalizing the MeCP2 levels across the whole brain has been demonstrated.However,whether different brain areas or neural circuits contribute to different aspects of the behavioral deficits is still unknown.Here,we found that MECP2-TG mice showed a significant social recognition deficit,and were prone to display aversive-like behaviors,including heightened anxiety-like behaviors and a fear generalization phenotype.In addition,reduced locomotor activity was observed in MECP2-TG mice.However,appetitive behaviors and learning and memory were comparable in MECP2-TG and wild-type mice.Functional magnetic resonance imaging illustrated that the differences between MECP2-TG and wild-type mice were mainly concentrated in brain areas regulating emotion and social behaviors.We used the CRISPR-Cas9 method to restore normal MeCP2 levels in the medial prefrontal cortex(mPFC) and bed nuclei of the stria terminalis(BST) of adult MECP2-TG mice,and found that normalization of MeCP2 levels in the mPFC but not in the BST reversed the social recognition deficit.These data indicate that the mPFC is responsible for the social recognition deficit in the transgenic mice,and provide new insight into potential therapies for MECP2 duplication syndrome.

Visualization and correction of social abnormalities-associated neural ensembles in adult MECP2 duplication mice

Duplications of MECP2-containing genomic segments led to severe autistic symptoms in male. Transgenic mice overexpressing the human MECP2 gene exhibit autistic-like behaviors. Neural circuits underlying social defects in MECP2 transgenic(MECP2-TG) mice remain unknown. To observe neural activity of MECP2-TG mice in vivo, we performed calcium imaging by implantation of microendoscope in the hippocampal CA1 regions of MECP2-TG and wild type(WT) mice. We identified neurons whose activities were tightly associated with social interaction, which activity patterns were compromised in MECP2-TG mice. Strikingly, we rescued the social-related neural activity in CA1 and social defects in MECP2-TG mice by deleting the human MECP2 transgene using the CRISPR/Cas9 method during adulthood.Our data points to the neural circuitry responsible for social interactions and provides potential therapeutic targets for autism in adulthood.

Role of the PTEN signaling pathway in autism spectrum disorder

Autism is an etiologically heterogeneous group of neurodevelopmental disorders,diagnosed mostly by the clinical behavioral phenotypes.The concept that the tumor-related gene PTEN plays a critical role in autism spectrum disorder has emerged over the last decade.In this review,we focus on the essential role of the PTEN signaling pathway in neuronal differentiation and the formation of neural circuitry,as well as genetic mouse models with Pten manipulations.Particularly,accumulated data suggest that the effect of PTEN on neural stem-cell development contributes significantly to the pathophysiology of autism spectrum disorders.

Autism-related protein MeCP2 regulates FGF13 expression and emotional behaviors

Methyl-CpG binding protein 2 （MeCP2） has a crucial role in transcriptional regulation and neural development （Ausi6 et al., 2014）. Loss of function mutations of MECP2 in human lead to Rett syndrome （RTT）, a severe neurodevelopmental disorders （Amir et al., 1999）, whereas individuals with the chromosomal duplications containing the MECP2 locus showed severe autism-like symptoms （Ramocki et al., 2009）.

Identification of the Genetic Cause for Childhood Disintegrative Disorder by Whole-Exome Sequencing

Dear Editor,Childhood Disintegrative Disorder（CDD）,also known as Heller’s syndrome and disintegrative psychosis,is a rare progressive neurological disorder,characterized by a late onset（[2 years of age）and regression of language,social

Long non-coding RNA tagging and expression manipulation via CRISPR/Cas9-mediated targeted insertion

Dear Editor, Long non-coding RNAs （IncRNAs）, defined as RNA transcripts longer than 200 nucleotides without the protein-coding ability （Carninci et al., 2005）, share many features with protein-coding messenger RNAs （mRNAs） such as polyadenylated 5＇ ends and multi-exonic structures （Guttman et al., 2010）. Though expression levels are less abundant, IncRNAs outnumber mRNAs with more diverse regulatory functions （Quinn and Chang, 2016）. They may serve as decoys, sponges, signals or scaffolds in regulating chromatin conformation, nuclear organization, gene expression, and protein activity in cis or trans manner （Ulitsky and Bartel, 2013; Quinn and Chang, 2016）. LncRNAs are involved in various physiological processes and their lossor gain-offunction mutations have been implicated in the pathogenesis of human diseases （Wapinski and Chang, 2011）.