Melatonin modifies SOX2^+ cell proliferation in dentate gyrus and modulates SIRT1 and MECP2 in long-term sleep deprivation

Melatonin is a pleiotropic molecule that,after a short-term sleep deprivation,promotes the proliferation of neural stem cells in the adult hippocampus.However,this effect has not been observed in long-term sleep deprivation.The precise mechanism exerted by melatonin on the modulation of neural stem cells is not entirely elucidated,but evidence indicates that epigenetic regulators may be involved in this process.In this study,we investigated the effect of melatonin treatment during a 96-hour sleep deprivation and analyzed the expression of epigenetic modulators predicted by computational text mining and keyword clusterization.Our results showed that the administration of melatonin under sleep-deprived conditions increased the MECP2 expression and reduced the SIRT1 expression in the dentate gyrus.We observed that let-7 b,mir-132,and mir-124 were highly expressed in the dentate gyrus after melatonin administration,but they were not modified by sleep deprivation.In addition,we found more Sox2^+/5-bromo-2’-deoxyuridine(BrdU)^+cells in the subgranular zone of the sleep-deprived group treated with melatonin than in the untreated group.These findings may support the notion that melatonin modifies the expression of epigenetic mediators that,in turn,regulate the proliferation of neural progenitor cells in the adult dentate gyrus under long-term sleep-deprived conditions.All procedures performed in this study were approved by the Animal Ethics Committee of the University of Guadalajara,Mexico(approval No.CI-16610)on January 2,2016.

Methyl-CpG binding proteins in the nervous system

Classical methyl-CpG binding proteins contain the conserved DNA binding motif methyl-cytosine binding domain(MBD), which preferentially binds to methylated CpG dinucleotides. These proteins serve as transcriptional repressors,mediating gene silencing via DNA cytosine methylation. Mutations in methyl-CpG binding protein 2 (MeCP2) have beenlinked to the human mental retardation disorder Rett syndrome, suggesting an important role for methyl-CpG bindingproteins in brain development and function. This mini-review summarizes the recent advances in studying the diversefunctions of MeCP2 as a prototype for other methyl-CpG binding proteins in the development and function of thevertebrate nervous system.

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）.

MeCP2 deficiency promotes cell reprogramming by stimulating IGF1/AKT/mTOR signaling and activating ribosomal protein-mediated ceil cycle gene translation

The generation of induced pturipotent stem cells (iPSCs)offers a great opportunity in research and regenerative medicine.The current poor efficiency and incomplete mechanistic understanding of the reprogramming process hamper the clinical application of iPSCs. MeCP2 connects histone modification and DNA methyiation,which are key changes of somatic cell reprogramming.However,the rote of MeCP2 in celt reprogramming has not been examined.In this study,we found that MeCP2 deficiency enhanced reprogramming efficiency and stimulated cell proliferation through regulating cell cycle protein expression in the earLy stage of reprogramming.MeCP2 deficiency enhanced the expression of ribosomal protein genes,thereby enhancing reprogramming efficiency through promoting the translation of ceLl cycle genes.In the end,MeCP2 deficiency stimulated IGF1/AKT/mTOR signaling and activated ribosomal protein gene expression.Taken together,our data indicate that MeCP2 deficiency promoted cell reprogramming through stimulating IGF1/AKT/mTOR signaling and activating ribosomal protein-mediated cell cycle gene translation in the early stage of reprogramming.

Structural investigation of Rett-inducing MeCP2 mutations

X-ray structure of methyl-CpG binding domain(MBD)of MeCP2,an intrinsically disordered protein(IDP)involved in Rett syndrome,offers a rational basis for defining the spatial distribution for most of the sites where mutations responsible of Rett syndrome,RTT,occur.We have ascribed pathogenicity for mutations of amino acids bearing positively charged side chains,all located at the protein-DNA interface,as positive charge removal cause reduction of the MeCP2-DNA adduct lifetime.Pathogenicity of the frequent proline replacements,outside the DNA contact moiety of MBD,can be attributed to the role of this amino acid for maintaining both unfolded states for unbound MeCP2 and,at the same time,to favor some higher conformational order for stabilizing structural determinants required by protein activity.These hypotheses can be extended to transcription repressor domain,TRD,the other MeCP2-DNA interaction site and,in general,to all the IDP that interact with nucleic acids.

Epigenetic regulation of neuronal dendrite and dendritic spine development

Dendrites and the dendritic spines of neurons play key roles in the connectivity of the brain and have been recognized as the locus of long-term synaptic plasticity,which is correlated with learning and memory.The development of dendrites and spines in the mammalian central nervous system is a complex process that requires specific molecular events over a period of time.It has been shown that specific molecules are needed not only at the spine’s point of contact,but also at a distance,providing signals that initiate a cascade of events leading to synapse formation.The specific molecules that act to signal neuronal differentiation,dendritic morphology,and synaptogenesis are tightly regulated by genetic and epigenetic programs.It has been shown that the dendritic spine structure and distribution are altered in many diseases,including many forms of mental retardation(MR),and can also be potentiated by neuronal activities and an enriched environment.Because dendritic spine pathologies are found in many types of MR,it has been proposed that an inability to form normal spines leads to the cognitive and motor deficits that are characteristic of MR.Epigenetic mechanisms,including DNA methylation,chromatin remodeling,and the noncoding RNA-mediated process,have profound regulatory roles in mammalian gene expression.The study of epigenetics focuses on cellular effects that result in a heritable pattern of gene expression without changes to genomic encoding.Despite extensive efforts to understand the molecular regulation of dendrite and spine development,epigenetic mechanisms have only recently been considered.In this review,we will focus on epigenetic mechanisms that regulate the development and maturation of dendrites and spines.We will discuss how epigenetic alterations could result in spine abnormalities that lead to MR,such as is seen in fragile X and Rett syndromes.We will also discuss both general methodology and recent technological advances in the study of neuronal dendrites and spines.