The expression of methyl CpG binding factor MeCP2 correlates with cellular differentiation in the developing rat brain and in cultured cells

Mutations in the MeCP2 gene cause Rett syndrome, a neurologic condition affecting primarily young girls. To gain insight into the normal function of MeCP2, we examined its temporal and spatial expression patterns, and immunoreactive prevalence, during late embryonic and perinatal brain development. MeCP2 mRNA was detected in most regions of the developing rat brain by the late embryonic stage. Regions displaying the strongest mRNA expression include the hippocampus, cortex, and cerebellum, and moderate expression was observed in most other brain regions. At the protein level, MeCP2 was strongly expressed in adult forebrain neurons, but was not detected in astrocytes. The nonubiquitous expression of MeCP2 was also observed in the embryonic cortex, as about one-third of acutely dissociated embryonic day 14 neuroepithelial cells failed to stain with MeCP2. To test whether MeCP2 expression correlates with neuronal differentiation, colocalization of MeCP2 expression with either the precursor cell marker nestin or the young neuronal marker beta-III tubulin was examined in the same acutely dissociated cortical cells. Although strong MeCP2 expression was detected in approximately 75% of beta-III tubulin-positive cells, only about 25% of nestin-positive precursor cells were MeCP2 positive. Further support for a correlation of MeCP2 expression with cell differentiation was observed in culture, where Western blot analysis during the in vitro differentiation of PC12, NG108-15, and SH-SY5Y cells revealed that MeCP2 levels increased as the cells acquired a more differentiated phenotype. This increase was associated with differentiation, as MeCP2 expression levels did not vary within different phases of the cell cycle. Taken together, these data support a role for MeCP2 in the establishment and/or maintenance of neuronal maturity.     

MeCP2在Rett综合征中的调控机制

Rett综合征(Rett syndrome, RTT)是一种X连锁的神经发育障碍性遗传病, 是导致女性严重智力障碍的主要原因之一。编码甲基化CpG结合蛋白2(Methyl-CpG-binding protein 2, MeCP2)基因突变是RTT主要的遗传病理学改变, MeCP2作为转录抑制因子调控基因表达。在RTT发病机制中, 由于缺乏MeCP2与甲基化DNA的正确结合, 阻碍了它对下游靶基因表达的正常调控, 最终导致脑功能障碍。目前, 对MeCP2在脑发育过程中的作用以及如何导致RTT的发生, 其机制尚不清楚。文章从MECP2基因和MeCP2蛋白两个方面, 对基因结构、蛋白质功能以及在分子水平上的调控机制进行了综述, 以期为RTT的发病机制研究提供新思路。     

Reduced MeCP2 Expression is Frequent in Autism Frontal Cortex and Correlates with Aberrant MECP2 Promoter Methylation

Mutations in MECP2, encoding methyl CpG binding protein 2 (MeCP2), cause most cases of Rett syndrome (RTT), an X-linked neurodevelopmental disorder. Both RTT and autism are “pervasive developmental disorders” and share a loss of social, cognitive and language skills and a gain in repetitive stereotyped behavior, following apparently normal perinatal development. Although MECP2 coding mutations are a rare cause of autism, MeCP2 expression defects were previously found in autism brain. To further study the role of MeCP2 in autism spectrum disorders (ASDs), we determined the frequency of MeCP2 expression defects in brain samples from autism and other ASDs. We also tested the hypotheses that MECP2 promoter mutations or aberrant promoter methylation correlate with reduced expression in cases of idiopathic autism. MeCP2 immunofluorescence in autism and other neurodevelopmental disorders was quantified by laser scanning cytometry and compared with control postmortem cerebral cortex samples on a large tissue microarray. A significant reduction in MeCP2 expression compared to age-matched controls was found in 11/14 autism (79%), 9/9 RTT (100%), 4/4 Angelman syndrome (100%), 3/4 Prader-Willi syndrome (75%), 3/5 Down syndrome (60%), and 2/2 attention deficit hyperactivity disorder (100%) frontal cortex samples. One autism female was heterozygous for a rare MECP2 promoter variant that correlated with reduced MeCP2 expression. A more frequent occurrence was significantly increased MECP2 promoter methylation in autism male frontal cortex compared to controls. Furthermore, percent promoter methylation of MECP2 significantly correlated with reduced MeCP2 protein expression. These results suggest that both genetic and epigenetic defects lead to reduced MeCP2 expression and may be important in the complex etiology of autism.     

Multiple epigenetic biomarkers for evaluation of students' academic performance

Several reports have shown that methyl CpG‐binding protein 2 (MeCP2), brain‐derived neurotrophic factor (BDNF), phospho‐cAMP response element‐binding protein (p‐CREB) and microRNAs may be important in regulating academic performance because of their roles in neuropsychiatry and cognitive diseases. The first goal of this study was to explore the associations among MeCP2, BDNF, CREB and academic performance. This study also examined the pathway responsible for the effects of MeCP2, BDNF, p‐CREB and microRNAs on academic performance. Scores from the basic competency test, an annual national competitive entrance examination, were used to evaluate academic performance. Subjects' plasma RNA was extracted and analyzed. This study determined that participants in the higher academic performance group had a significant difference in MECP2 mRNA expression compared with the lower academic performance group. We then used neuronal human derived neuroblastoma cell line (SH‐SY5Y) cells with inducible MeCP2 expression from a second copy of the gene as a gain‐of‐function model and found that MeCP2 overexpression positively affected p‐CREB and BDNF expression initially. After negative feedback, the p‐CREB and BDNF levels subsequently decreased. In the neuronal phenotype examination, we found a significant reduction in total outgrowth and branches in MeCP2‐induced cells compared with noninduced cells. This work describes pathways that may be responsible for the effects of MeCP2, BDNF, p‐CREB and microRNAs on academic performance. These results may shed light on the development of promising clinical treatment strategies in the area of neuropsychological adjustment.     

MeCP2 inhibits proliferation and migration of breast cancer via suppression of epithelial‐mesenchymal transition

Methyl‐CpG‐binding protein 2 (MeCP2) is an important epigenetic regulator for normal neuronal maturation and brain glial cell function. Additionally, MeCP2 is also involved in a variety of cancers, such as breast, prostate, lung, liver and colorectal. However, whether MeCP2 contributes to the progression of breast cancer remains unknown. In the present study, we investigated the role of MeCP2 in cell proliferation, migration and invasion in vitro. We found that knockdown of MeCP2 inhibited expression of epithelial‐mesenchymal transition (EMT)‐related markers in breast cancer cell lines. In conclusion, our study suggests that MeCP2 inhibits proliferation and invasion through suppression of the EMT pathway in breast cancer.     

MeCP2 interacts with chromosomal microRNAs in brain

Although methyl CpG binding domain protein-2 (MeCP2) is commonly understood to function as a silencing factor at methylated DNA sequences, recent studies also show that MeCP2 can bind unmethylated sequences and coordinate gene activation. MeCP2 displays broad binding patterns throughout the genome, with high expression levels similar to histone H1 in neurons. Despite its significant presence in the brain, only subtle gene expression changes occur in the absence of MeCP2. This may reflect a more complex regulatory mechanism of MeCP2 to complement chromatin binding. Using an RNA immunoprecipitation of native chromatin technique, we identify MeCP2 interacting microRNAs in mouse primary cortical neurons. In addition, comparison with mRNA sequencing data from Mecp2-null mice suggests that differentially expressed genes may indeed be targeted by MeCP2-interacting microRNAs. These findings highlight the MeCP2 interaction with microRNAs that may modulate its binding with chromatin and regulate gene expression.     

Sex Difference in Mecp2 Expression During a Critical Period of Rat Brain Development

Pervasive developmental disorder is a classification covering five related conditions including the neurodevelopmental disorder Rett syndrome (RTT) and autism. Of these five conditions, only RTT has a known genetic cause, with mutations in Methyl-CpG-binding protein 2 (MeCP2), a global repressor of gene expression, responsible for the majority of RTT cases. However, recent evidence indicates that reduced MeCP2 expression or activity is also found in autism and other disorders with overlapping phenotypes. Considering the sex difference in autism diagnosis, with males diagnosed four times more often than females, we questioned if a sex difference existed in the expression of MeCP2, in particular within the amygdala, a region that develops atypically in autism. We found that male rats express significantly less mecp2 mRNA and protein than females within the amygdala, as well as the ventromedial hypothalamus (VMH), but not within the preoptic area (POA) on post-natal day 1 (PN1). At PN10 these differences were gone; however, on this day males had more mecp2 mRNA than females within the POA. The transient sex difference of mecp2 expression during the steroid-sensitive period of brain development suggests that mecp2 may participate in normal sexual differentiation of the rat brain. Considering the strong link between MeCP2 and neurodevelopmental disorders, the lower levels of mecp2 expression in males may also underlie a biological risk for mecp2-related neural disorders.     

Genome-wide activity-dependent MeCP2 phosphorylation regulates nervous system development and function

Autism spectrum disorders such as Rett syndrome (RTT) have been hypothesized to arise from defects in experience-dependent synapse maturation. RTT is caused by mutations in MECP2, a nuclear protein that becomes phosphorylated at S421 in response to neuronal activation. We show here that disruption of MeCP2 S421 phosphorylation in?vivo results in defects in synapse development and behavior, implicating activity-dependent regulation of MeCP2 in brain development and RTT. We investigated the mechanism by which S421 phosphorylation regulates MeCP2 function and show by chromatin immunoprecipitation-sequencing that this modification occurs on MeCP2 bound across the genome. The phosphorylation of MeCP2 S421 appears not to regulate the expression of specific genes; rather, MeCP2 functions as a histone-like factor whose phosphorylation may facilitate a genome-wide response of chromatin to neuronal activity during nervous system development. We propose that RTT results in part from a loss of this experience-dependent chromatin remodeling.     

Methyl CpG-binding protein isoform MeCP2_e2 is dispensable for Rett syndrome phenotypes but essential for embryo viability and placenta development

Methyl CpG-binding protein 2 gene (MeCP2) mutations are implicated in Rett syndrome (RTT), one of the common causes of female mental retardation. Two MeCP2 isoforms have been reported: MeCP2_e2 (splicing of all four exons) and MeCP2_e1 (alternative splicing of exons 1, 3, and 4). Their relative expression levels vary among tissues, with MeCP2_e1 being more dominant in adult brain, whereas MeCP2_e2 is expressed more abundantly in placenta, liver, and skeletal muscle. In this study, we performed specific disruption of the MeCP2_e2-defining exon 2 using the Cre-loxP system and examined the consequences of selective loss of MeCP2_e2 function in vivo. We performed behavior evaluation, gene expression analysis, using RT-PCR and real-time quantitative PCR, and histological analysis. We demonstrate that selective deletion of MeCP2_e2 does not result in RTT-associated neurological phenotypes but confers a survival disadvantage to embryos carrying a MeCP2_e2 null allele of maternal origin. In addition, we reveal a specific requirement for MeCP2_e2 function in extraembryonic tissue, where selective loss of MeCP2_e2 results in placenta defects and up-regulation of peg-1, as determined by the parental origin of the mutant allele. Taken together, our findings suggest a novel role for MeCP2 in normal placenta development and illustrate how paternal X chromosome inactivation in extraembryonic tissues confers a survival disadvantage for carriers of a mutant maternal MeCP2_e2 allele. Moreover, our findings provide an explanation for the absence of reports on MeCP2_e2-specific exon 2 mutations in RTT. MeCP2_e2 mutations in humans may result in a phenotype that evades a diagnosis of RTT.