Chromatin remodeling in development and disease: focus on CHD7

Loss of the chromatin remodeler CHD7 impacts glial cells and myelination in the mouse cochlear spiral ganglion

CHARGE syndrome is a multiple anomaly developmental disorder characterized by a variety of sensory deficits, including sensorineural hearing loss of unknown etiology. Most cases of CHARGE are caused by heterozygous pathogenic variants in CHD7, the gene encoding Chromodomain DNA-binding Protein 7 (CHD7), a chromatin remodeler important for the development of neurons and glial cells. Previous studies in the Chd7^Gt/+ mouse model of CHARGE syndrome showed substantial neuron loss in the early stages of the developing inner ear that are compensated for by mid-gestation. In this study, we sought to determine if early developmental delays caused by Chd7 haploinsufficiency affect neurons, glial cells, and inner hair cell innervation in the mature cochlea. Analysis of auditory brainstem response recordings in Chd7^Gt/+ adult animals showed elevated thresholds at 4 kHz and 16 kHz, but no differences in ABR Wave I peak latency or amplitude compared to wild type controls. Proportions of neurons in the Chd7^Gt/+ adult spiral ganglion and densities of nerve projections from the spiral ganglion to the organ of Corti were not significantly different from wild type controls. Inner hair cell synapse formation also appeared unaffected in mature Chd7^Gt/+ cochleae. However, histological analysis of adult Chd7^Gt/+ cochleae revealed diminished satellite glial cells and hypermyelinated Type I spiral ganglion axons. We characterized the expression of CHD7 in developing inner ear glia and found CHD7 to be expressed during a tight window of inner ear development at the Schwann cell precursor stage at E9.5. While cochlear neurons appear to differentiate normally in the setting of Chd7 haploinsufficiency, our results suggest an important role for CHD7 in glial cells in the inner ear. This study highlights the dynamic nature of CHD7 activity during inner ear development in mice and contributes to understanding CHARGE syndrome pathology.

Eyes on CHARGE syndrome: Roles of CHD7 in ocular development

The development of the vertebrate visual system involves complex morphogenetic interactions of cells derived from multiple embryonic lineages. Disruptions in this process are associated with structural birth defects such as microphthalmia, anophthalmia, and coloboma (collectively referred to as MAC), and inherited retinal degenerative diseases such as retinitis pigmentosa and allied dystrophies. MAC and retinal degeneration are also observed in systemic congenital malformation syndromes. One important example is CHARGE syndrome, a genetic disorder characterized by coloboma, heart defects, choanal atresia, growth retardation, genital abnormalities, and ear abnormalities. Mutations in the gene encoding Chromodomain helicase DNA binding protein 7 (CHD7) cause the majority of CHARGE syndrome cases. However, the pathogenetic mechanisms that connect loss of CHD7 to the ocular complications observed in CHARGE syndrome have not been identified. In this review, we provide a general overview of ocular development and congenital disorders affecting the eye. This is followed by a comprehensive description of CHARGE syndrome, including discussion of the spectrum of ocular defects that have been described in this disorder. In addition, we discuss the current knowledge of CHD7 function and focus on its contributions to the development of ocular structures. Finally, we discuss outstanding gaps in our knowledge of the role of CHD7 in eye formation, and propose avenues of investigation to further our understanding of how CHD7 activity regulates ocular and retinal development.

Classification of CHD7 Rare Variants in Chinese Congenital Hypogonadotropic Hypogonadism Patients and Analysis of Their Clinical Characteristics

Purpose:CHD7 rare variants can cause congenital hypogonadotropic hypogonadism (CHH) and CHARGE syndrome. We aimed to summarize the genotype and phenotype characteristics of CHH patients with CHD7 rare variants.

Methods: Rare sequencing variants (RSVs) were detected by Sanger sequencing in a series of 327 CHH patients and were interpreted and grouped according to the American College of Medical Genetics and Genomics (ACMG) guideline. Detailed phenotyping and genotype-phenotype correlation were analyzed.

Results: The RSV detection rate was 11.01% (36/327) in the CHH patients. We identified 30 RSVs and 19 of them were novel. Following ACMG criteria, three variants were pathogenic (P), 4 were likely pathogenic (LP), 3 were of uncertain significance with paradoxical evidence (US1), and 20 were of uncertain significance without enough evidence (US2). All patients (4/4, 100%) with P or LP variants manifested extragonadal symptoms.

Conclusion: Addition of 19 novel CHD7 variants expanded the spectrum of variants, and pathogenic or likely pathogenic RSVs were more likely to cause syndromic CHH. For CHH patients carrying CHD7 RSVs, detailed genotyping and phenotyping can facilitate clinical diagnosis and therapy.

Genetic Variability of the Functional Domains of Chromodomains Helicase DNA-Binding (CHD) Proteins

In the past few years, there has been an increasing neuroscientific interest in understanding the function of mammalian chromodomains helicase DNA-binding (CHD) proteins due to their association with severe developmental syndromes. Mammalian CHDs include nine members (CHD1 to CHD9), grouped into subfamilies according to the presence of specific functional domains, generally highly conserved in evolutionary terms. Mutations affecting these domains hold great potential to disrupt protein function, leading to meaningful pathogenic scenarios, such as embryonic defects incompatible with life. Here, we analysed the evolution of CHD proteins by performing a comparative study of the functional domains of CHD proteins between orthologous and paralogous protein sequences. Our findings show that the highest degree of inter-species conservation was observed at Group II (CHD3, CHD4, and CHD5) and that most of the pathological variations documented in humans involve amino acid residues that are conserved not only between species but also between paralogs. The parallel analysis of both orthologous and paralogous proteins, in cases where gene duplications have occurred, provided extra information showing patterns of flexibility as well as interchangeability between amino acid positions. This added complexity needs to be considered when the impact of novel mutations is assessed in terms of evolutionary conservation.

Chromatin remodeling in oligodendrogenesis

Oligodendrocytes are one type of glial cells responsible for myelination and providing trophic support for axons in the central nervous system of vertebrates. Thanks to myelin, the speed of electrical-signal conduction increases several hundred-fold because myelin serves as a kind of electrical insulator of nerve f ibers and allows for quick saltatory conduction of action potentials through Ranvier nodes, which are devoid of myelin. Given that different parts of the central nervous system are myelinated at different stages of development and most regions contain both myelinated and unmyelinated axons, it is obvious that very precise mechanisms must exist to control the myelination of individual axons. As they go through the stages of specif ication and differentiation – from multipotent neuronal cells in the ventricular zone of the neural tube to mature myelinating oligodendrocytes as well as during migration along blood vessels to their destination – cells undergo dramatic changes in the pattern of gene expression. These changes require precisely spatially and temporally coordinated interactions of various transcription factors and epigenetic events that determine the regulatory landscape of chromatin. Chromatin remodeling substantially affects transcriptional activity of genes. The main component of chromatin is the nucleosome, which, in addition to the structural function, performs a regulatory one and serves as a general repressor of genes. Changes in the type, position, and local density of nucleosomes require the action of specialized ATPdependent chromatin-remodeling complexes, which use the energy of ATP hydrolysis for their activity. Mutations in the genes encoding proteins of the remodeling complexes are often accompanied by serious disorders at early stages of embryogenesis and are frequently identif ied in various cancers. According to the domain arrangement of the ATP-hydrolyzing subunit, most of the identif ied ATP-dependent chromatin-remodeling complexes are classif ied into four subfamilies: SWI/SNF, CHD, INO80/SWR, and ISWI. In this review, we discuss the roles of these subunits of the different subfamilies at different stages of oligodendrogenesis

Modeling human congenital disorders with neural crest developmental defects using patient-derived induced pluripotent stem cells

The neural crest is said to be the fourth germ layer in addition to the ectoderm, mesoderm and endoderm because of its ability to differentiate into a variety of cells that contribute to the various tissues of the vertebrate body. Neural crest cells (NCCs) can be divided into three functional groups: cranial NCCs, cardiac NCCs and trunk NCCs. Defects related to NCCs can contribute to a broad spectrum of syndromes known as neurocristopathies. Studies on the neural crest have been carried out using animal models such as Xenopus, chicks, and mice. However, the precise control of human NCC development has not been elucidated in detail due to species differences. Using induced pluripotent stem cell (iPSC) technology, we developed an in vitro disease model of neurocristopathy by inducing the differentiation of patient-derived iPSCs into NCCs and/or neural crest derivatives. It is now possible to address complicated questions regarding the pathogenetic mechanisms of neurocristopathies by characterizing cellular biological features and transcriptomes and by transplanting patient-derived NCCs in vivo. Here, we provide some examples that elucidate the pathophysiology of neurocristopathies using disease modeling via iPSCs.

Chromatin remodeller CHD7 is required for GABAergic neuron development by promoting PAQR3 expression

Mutations in the chromatin remodeller‐coding gene CHD7 cause CHARGE syndrome (CS). CS features include moderate to severe neurological and behavioural problems, clinically characterized by intellectual disability, attention‐deficit/hyperactivity disorder and autism spectrum disorder. To investigate the poorly characterized neurobiological role of CHD7, we here generate a zebrafish chd7^−/− model. chd7^−/− mutants have less GABAergic neurons and exhibit a hyperactivity behavioural phenotype. The GABAergic neuron defect is at least in part due to downregulation of the CHD7 direct target gene paqr3b, and subsequent upregulation of MAPK/ERK signalling, which is also dysregulated in CHD7 mutant human cells. Through a phenotype‐based screen in chd7^−/− zebrafish and Caenorhabditis elegans, we show that the small molecule ephedrine restores normal levels of MAPK/ERK signalling and improves both GABAergic defects and behavioural anomalies. We conclude that chd7 promotes paqr3b expression and that this is required for normal GABAergic network development. This work provides insight into the neuropathogenesis associated with CHD7 deficiency and identifies a promising compound for further preclinical studies.

Semaphorin Regulation by the Chromatin Remodeler CHD7: An Emerging Genetic Interaction Shaping Neural Cells and Neural Crest in Development and Cancer

CHD7 is a chromatin remodeler protein that controls gene expression via the formation of multi-protein complexes with specific transcription factors. During development, CHD7 controls several differentiation programs, mainly by acting on neural progenitors and neural crest (NC) cells. Thus, its roles range from the central nervous system to the peripheral nervous system and the organs colonized by NC cells, including the heart. Accordingly, mutated CHD7 is linked to CHARGE syndrome, which is characterized by several neuronal dysfunctions and by malformations of NC-derived/populated organs. Altered CHD7 has also been associated with different neoplastic transformations. Interestingly, recent evidence revealed that semaphorins, a class of molecules involved in developmental and pathological processes similar to those controlled by CHD7, are regulated by CHD7 in a context-specific manner. In this article, we will review the recent insights that support the existence of genetic interactions between these pathways, both during developmental processes and cancer progression.

Convergent epigenetic regulation of glial plasticity in myelin repair and brain tumorigenesis: A focus on histone modifying enzymes

Brain regeneration and tumorigenesis are complex processes involving in changes in chromatin structure to regulate cellular states at the molecular and genomic level. The modulation of chromatin structure dynamics is critical for maintaining progenitor cell plasticity, growth and differentiation. Oligodendrocyte precursor cells (OPC) can be differentiated into mature oligodendrocytes, which produce myelin sheathes to permit saltatory nerve conduction. OPCs and their primitive progenitors such as pri-OPC or pre-OPC are highly adaptive and plastic during injury repair or brain tumor formation. Recent studies indicate that chromatin modifications and epigenetic homeostasis through histone modifying enzymes shape genomic regulatory landscape conducive to OPC fate specification, lineage differentiation, maintenance of myelin sheaths, as well as brain tumorigenesis. Thus, histone modifications can be convergent mechanisms in regulating OPC plasticity and malignant transformation. In this review, we will focus on the impact of histone modifying enzymes in modulating OPC plasticity during normal development, myelin regeneration and tumorigenesis.

Epigenetic regulation of oligodendrocyte myelination in developmental disorders and neurodegenerative diseases

Oligodendrocytes are the critical cell types giving rise to the myelin nerve sheath enabling efficient nerve transmission in the central nervous system (CNS). Oligodendrocyte precursor cells differentiate into mature oligodendrocytes and are maintained throughout life. Deficits in the generation, proliferation, or differentiation of these cells or their maintenance have been linked to neurological disorders ranging from developmental disorders to neurodegenerative diseases and limit repair after CNS injury. Understanding the regulation of these processes is critical for achieving proper myelination during development, preventing disease, or recovering from injury. Many of the key factors underlying these processes are epigenetic regulators that enable the fine tuning or reprogramming of gene expression during development and regeneration in response to changes in the local microenvironment. These include chromatin remodelers, histone-modifying enzymes, covalent modifiers of DNA methylation, and RNA modification-mediated mechanisms. In this review, we will discuss the key components in each of these classes which are responsible for generating and maintaining oligodendrocyte myelination as well as potential targeted approaches to stimulate the regenerative program in developmental disorders and neurodegenerative diseases.

Chromatin modification and epigenetic control in functional nerve regeneration

The repair and functional recovery of the nervous system is a highly regulated process that requires the coordination of many different components including the proper myelination of regenerated axons. Dysmyelination and remyelination failures after injury result in defective nerve conduction, impairing normal nervous system functions. There are many convergent regulatory networks and signaling mechanisms between development and regeneration. For instance, the regulatory mechanisms required for oligodendrocyte lineage progression could potentially play fundamental roles in myelin repair. In recent years, epigenetic chromatin modifications have been implicated in CNS myelination and functional nerve restoration. The pro-regenerative transcriptional program is likely silenced or repressed in adult neural cells including neurons and myelinating cells in the central and peripheral nervous systems limiting the capacity for repair after injury. In this review, we will discuss the roles of epigenetic mechanisms, including histone modifications, chromatin remodeling, and DNA methylation, in the maintenance and establishment of the myelination program during normal oligodendrocyte development and regeneration. We also discuss how these epigenetic processes impact myelination and axonal regeneration, and facilitate the improvement of current preclinical therapeutics for functional nerve regeneration in neurodegenerative disorders or after injury.

Epigenetic modifications associated with pathophysiological effects of lead exposure

Lead (Pb) exposure during different stages of development has demonstrated dose, duration, sex, and tissue-specific pathophysiological outcomes due to altered epigenetic regulation via (a) DNA methylation, (b) histone modifications, (c) miRNAs, and (d) chromatin accessibility. Pb-induced alteration of epigenetic regulation causes neurotoxic and extra-neurotoxic pathophysiological outcomes. Neurotoxic effects of Pb include dysfunction of memory and learning, behavioral disorder, attention deficit hyperactivity disorder, autism spectrum disorder, aging, Alzheimer's disease, tauopathy, and neurodegeneration. Extra-neurotoxic effects of Pb include altered body weight, metabolic disorder, cardiovascular disorders, hematopoietic disorder, and reproductive impairment. Pb exposure either early in life or at any stage of development results in undesirable pathophysiological outcomes that tends to sustain and maintain for a lifetime.

CHD7 promotes glioblastoma cell motility and invasiveness through transcriptional modulation of an invasion signature

Chromatin remodeler proteins exert an important function in promoting dynamic modifications in the chromatin architecture, performing a central role in regulating gene transcription. Deregulation of these molecular machines may lead to striking perturbations in normal cell function. The CHD7 gene is a member of the chromodomain helicase DNA-binding family and, when mutated, has been shown to be the cause of the CHARGE syndrome, a severe developmental human disorder. Moreover, CHD7 has been described to be essential for neural stem cells and it is also highly expressed or mutated in a number of human cancers. However, its potential role in glioblastoma has not yet been tested. Here, we show that CHD7 is up-regulated in human glioma tissues and we demonstrate that CHD7 knockout (KO) in LN-229 glioblastoma cells suppresses anchorage-independent growth and spheroid invasion in vitro. Additionally, CHD7 KO impairs tumor growth and increases overall survival in an orthotopic mouse xenograft model. Conversely, ectopic overexpression of CHD7 in LN-428 and A172 glioblastoma cell lines increases cell motility and invasiveness in vitro and promotes LN-428 tumor growth in vivo. Finally, RNA-seq analysis revealed that CHD7 modulates a specific transcriptional signature of invasion-related target genes. Further studies should explore clinical-translational implications for glioblastoma treatment.

Epigenetic modifications-insight into oligodendrocyte lineage progression, regeneration, and disease

Myelination by oligodendrocytes in the central nervous system permits high-fidelity saltatory conduction from neuronal cell bodies to axon terminals. Dysmyelinating and demyelinating disorders impair normal nervous system functions. Consequently, an understanding of oligodendrocyte differentiation that moves beyond the genetic code into the field of epigenetics is essential. Chromatin reprogramming is critical for steering stage-specific differentiation processes during oligodendrocyte development. Fine temporal control of chromatin remodeling through ATP-dependent chromatin remodelers and sequential histone modifiers shapes a chromatin regulatory landscape conducive to oligodendrocyte fate specification, lineage differentiation, and maintenance of cell identity. In this Review, we will focus on the biological functions of ATP-dependent chromatin remodelers and histone deacetylases in myelinating oligodendrocyte development and implications for myelin regeneration in neurodegenerative diseases.

CHARGE syndrome modeling using patient-iPSCs reveals defective migration of neural crest cells harboring CHD7 mutations

CHARGE syndrome is caused by heterozygous mutations in the chromatin remodeler, CHD7, and is characterized by a set of malformations that, on clinical grounds, were historically postulated to arise from defects in neural crest formation during embryogenesis. To better delineate neural crest defects in CHARGE syndrome, we generated induced pluripotent stem cells (iPSCs) from two patients with typical syndrome manifestations, and characterized neural crest cells differentiated in vitro from these iPSCs (iPSC-NCCs). We found that expression of genes associated with cell migration was altered in CHARGE iPSC-NCCs compared to control iPSC-NCCs. Consistently, CHARGE iPSC-NCCs showed defective delamination, migration and motility in vitro, and their transplantation in ovo revealed overall defective migratory activity in the chick embryo. These results support the historical inference that CHARGE syndrome patients exhibit defects in neural crest migration, and provide the first successful application of patient-derived iPSCs in modeling craniofacial disorders.

CHARGE syndrome is a disease in which organs including the heart, eyes and ears may not develop properly. The cells that form the tissues affected by CHARGE syndrome develop in embryos from precursor cells called neural crest cells. Individuals with CHARGE syndrome also have mutations in a gene called CHD7. However, it is difficult to examine how CHD7 mutations affect neural crest cells in embryos.

In recent years, cell reprogramming techniques have made it possible to create induced pluripotent stem cells (iPSCs) from the specialized somatic cells found in the human body. These iPSCs can be developed into many different cell types, including neural crest cells.

Okuno et al. created iPSCs from the skin cells of people with CHARGE syndrome, developed these cells into neural crest cells, and compared them with neural crest cells that were developed from the skin cells of people without CHARGE syndrome. The neural crest cells developed from people with CHARGE syndrome showed multiple abnormalities. For example, they were not able to move around correctly. This is an important observation because neural crest cells must move through tissues to form the various organs affected by CHARGE syndrome.

Okuno et al. also observed changes in the activity of many genes other than CHD7 in the neural crest cells developed from CHARGE patients. Further research is now needed to find out which genes are the most important for restoring the normal activity of neural crest cells.

CHARGE and Kabuki Syndromes: Gene-Specific DNA Methylation Signatures Identify Epigenetic Mechanisms Linking These Clinically Overlapping Conditions

Epigenetic dysregulation has emerged as a recurring mechanism in the etiology of neurodevelopmental disorders. Two such disorders, CHARGE and Kabuki syndromes, result from loss of function mutations in chromodomain helicase DNA-binding protein 7 (CHD7^LOF) and lysine (K) methyltransferase 2D (KMT2D^LOF), respectively. Although these two syndromes are clinically distinct, there is significant phenotypic overlap. We therefore expected that epigenetically driven developmental pathways regulated by CHD7 and KMT2D would overlap and that DNA methylation (DNAm) alterations downstream of the mutations in these genes would identify common target genes, elucidating a mechanistic link between these two conditions, as well as specific target genes for each disorder. Genome-wide DNAm profiles in individuals with CHARGE and Kabuki syndromes with CHD7^LOF or KMT2D^LOF identified distinct sets of DNAm differences in each of the disorders, which were used to generate two unique, highly specific and sensitive DNAm signatures. These DNAm signatures were able to differentiate pathogenic mutations in these two genes from controls and from each other. Analysis of the DNAm targets in each gene-specific signature identified both common gene targets, including homeobox A5 (HOXA5), which could account for some of the clinical overlap in CHARGE and Kabuki syndromes, as well as distinct gene targets. Our findings demonstrate how characterization of the epigenome can contribute to our understanding of disease pathophysiology for epigenetic disorders, paving the way for explorations of novel therapeutics.

Epigenetics and inheritance of phenotype variation in livestock

Epigenetic inheritance plays a crucial role in many biological processes, such as gene expression in early embryo development, imprinting and the silencing of transposons. It has recently been established that epigenetic effects can be inherited from one generation to the next. Here, we review examples of epigenetic mechanisms governing animal phenotype and behaviour, and we discuss the importance of these findings in respect to animal studies, and livestock in general. Epigenetic parameters orchestrating transgenerational effects, as well as heritable disorders, and the often-overlooked areas of livestock immunity and stress, are also discussed. We highlight the importance of nutrition and how it is linked to epigenetic alteration. Finally, we describe how our understanding of epigenetics is underpinning the latest cancer research and how this can be translated into directed efforts to improve animal health and welfare.

Epigenetics and inheritance of phenotype variation in livestock

Epigenetic inheritance plays a crucial role in many biological processes, such as gene expression in early embryo development, imprinting and the silencing of transposons. It has recently been established that epigenetic effects can be inherited from one generation to the next. Here, we review examples of epigenetic mechanisms governing animal phenotype and behaviour, and we discuss the importance of these findings in respect to animal studies, and livestock in general. Epigenetic parameters orchestrating transgenerational effects, as well as heritable disorders, and the often-overlooked areas of livestock immunity and stress, are also discussed. We highlight the importance of nutrition and how it is linked to epigenetic alteration. Finally, we describe how our understanding of epigenetics is underpinning the latest cancer research and how this can be translated into directed efforts to improve animal health and welfare.

Chromatin remodelers: We are the drivers!!

Chromatin is a highly dynamic structure that imparts structural organization to the genome and regulates the gene expression underneath. The decade long research in deciphering the significance of epigenetics in maintaining cellular integrity has embarked the focus on chromatin remodeling enzymes. These drivers have been categorized as readers, writers and erasers with each having significance of their own. Largely, on the basis of structure, ATP dependent chromatin remodelers have been grouped into 4 families; SWI/SNF, ISWI, IN080 and CHD. It is still unclear to what degree these enzymes are swayed by local DNA sequences when shifting a nucleosome to different positions. The ability of regulating active and repressive transcriptional state via open and close chromatin architecture has been well studied however, the significance of chromatin remodelers in regulating transcription at each step i.e. initiation, elongation and termination require further attention. The authors have highlighted the significance and role of different chromatin remodelers in transcription, DNA repair and histone variant deposition.

Chd7 cooperates with Sox10 and regulates the onset of CNS myelination and remyelination

Mutations in CHD7, encoding ATP-dependent chromodomain-helicase-DNA-binding protein 7, in CHARGE syndrome leads to multiple congenital anomalies including craniofacial malformations, neurological dysfunction and growth delay. Currently, mechanisms underlying the CNS phenotypes remain poorly understood. Here, we show that Chd7 is a direct transcriptional target of oligodendrogenesis-promoting factors Olig2 and Smarca4/Brg1, and is required for proper onset of CNS myelination and remyelination. Genome-occupancy analyses, coupled with transcriptome profiling, reveal that Chd7 interacts with Sox10 and targets the enhancers of key myelinogenic genes, and identify novel Chd7 targets including bone formation regulators Osterix/Sp7 and Creb3l2, which are also critical for oligodendrocyte maturation. Thus, Chd7 coordinates with Sox10 to regulate the initiation of myelinogenesis and acts as a molecular nexus of regulatory networks that account for the development of a seemingly diverse array of lineages including oligodendrocytes and osteoblasts, pointing to the hitherto previously uncharacterized Chd7 functions in white matter pathogenesis in CHARGE syndrome.

Architects of the genome: CHD dysfunction in cancer, developmental disorders and neurological syndromes

Chromatin is vital to normal cells, and its deregulation contributes to a spectrum of human ailments. An emerging concept is that aberrant chromatin regulation culminates in gene expression programs that set the stage for the seemingly diverse pathologies of cancer, developmental disorders and neurological syndromes. However, the mechanisms responsible for such common etiology have been elusive. Recent evidence has implicated lesions affecting chromatin-remodeling proteins in cancer, developmental disorders and neurological syndromes, suggesting a common source for these different pathologies. Here, we focus on the chromodomain helicase DNA binding chromatin-remodeling family and the recent evidence for its deregulation in diverse pathological conditions, providing a new perspective on the underlying mechanisms and their implications for these prevalent human diseases.

Roles of chromatin remodelers in maintenance mechanisms of multipotency of mouse trunk neural crest cells in the formation of neural crest-derived stem cells

We analyzed roles of two chromatin remodelers, Chromodomain Helicase DNA-binding protein 7 (CHD7) and SWItch/Sucrose NonFermentable-B (SWI/SNF-B), and Bone Morphogenetic Protein (BMP)/Wnt signaling in the maintenance of the multipotency of mouse trunk neural crest cells, leading to the formation of mouse neural crest-derived stem cells (mouse NCSCs). CHD7 was expressed in the undifferentiated neural crest cells and in the dorsal root ganglia (DRG) and sciatic nerve, typical tissues containing NCSCs. BMP/Wnt signaling stimulated the expression of CHD7 and participated in maintaining the multipotency of neural crest cells. Furthermore, the promotion of CHD7 expression maintained the multipotency of these cells. The inhibition of CHD7 and SWI/SNF-B expression significantly suppressed the maintenance of the multipotency of these cells. In addition, BMP/Wnt treatment promoted CHD7 expression and caused the increase of the percentage of multipotent cells in DRG. Thus, the present data suggest that the chromatin remodelers as well as BMP/Wnt signaling play essential roles in the maintenance of the multipotency of mouse trunk neural crest cells and in the formation of mouse NCSCs.

The Cardiac Phenotype in Patients With a CHD7 Mutation

Background—

Loss-of-function mutations in CHD7 cause Coloboma, Heart Disease, Atresia of Choanae, Retardation of Growth and/or Development, Genital Hypoplasia, and Ear Abnormalities With or Without Deafness (CHARGE) syndrome, a variable combination of multiple congenital malformations including heart defects. Heart defects are reported in 70% to 92% of patients with a CHD7 mutation, but most studies are small and do not provide a detailed classification of the defects. We present the first, detailed, descriptive study on the cardiac phenotype of 299 patients with a CHD7 mutation and discuss the role of CHD7 in cardiac development.

Methods and Results—

We collected information on congenital heart defects in 299 patients with a pathogenic CHD7 mutation, of whom 220 (74%) had a congenital heart defect. Detailed information on the heart defects was available for 202 of these patients. We classified the heart defects based on embryonic cardiac development and compared the distribution to 1007 equally classified nonsyndromic heart defects of patients registered by EUROCAT, a European Registry of Congenital Anomalies. Heart defects are highly variable in patients with CHD7 mutations, but atrioventricular septal defects and conotruncal heart defects are over-represented. Sex did not have an effect on the presence of heart defects, but truncating CHD7 mutations resulted in a heart defect significantly more often than missense or splice-site mutations (χ 2 , P <0.001).

Conclusions—

CHD7 plays an important role in cardiac development, given that we found a wide range of heart defects in 74% of a large cohort of patients with a CHD7 mutation. Conotruncal defects and atrioventricular septal defects are over-represented in patients with CHD7 mutations compared with patients with nonsyndromic heart defects.

Chd7 plays a critical role in controlling left-right symmetry during zebrafish somitogenesis

Somitogenesis is a complex process during early vertebrate development involving interactions between many factors to form a bilateral somite series. A role for chromatin remodelers in somitogenesis has not yet been demonstrated. Here, we investigate the function of chromodomain helicase DNA binding protein 7 (chd7) during zebrafish somitogenesis. We show that Chd7 deficiency leads to asymmetric segmentation of the presomitic mesoderm (PSM), as revealed by expression of the somitogenesis genes, cdx1a, dlc, her7, mespa, and ripply1. Moreover, we show that abrogation of Chd7 results in the loss of asymmetric expression of spaw in the lateral plate mesoderm, which is consistent with more general laterality defects. Based on the observation that insufficient Chd7 leads to left-right asymmetry defects during PSM segmentation, and because CHD7 has been linked to human spinal deformities, we suggest that zebrafish chd7 morphants may be a good in vivo model to examine the pathophysiology of these diseases.

Mature middle and inner ears express Chd7 and exhibit distinctive pathologies in a mouse model of CHARGE syndrome

Heterozygous mutations in the gene encoding chromodomain-DNA-binding-protein 7 (CHD7) cause CHARGE syndrome, a multiple anomaly condition which includes vestibular dysfunction and hearing loss. Mice with heterozygous Chd7 mutations exhibit semicircular canal dysgenesis and abnormal inner ear neurogenesis, and are an excellent model of CHARGE syndrome. Here we characterized Chd7 expression in mature middle and inner ears, analyzed morphological features of mutant ears and tested whether Chd7 mutant mice have altered responses to noise exposure and correlated those responses to inner and middle ear structure. We found that Chd7 is highly expressed in mature inner and outer hair cells, spiral ganglion neurons, vestibular sensory epithelia and middle ear ossicles. There were no obvious defects in individual hair cell morphology by prestin immunostaining or scanning electron microscopy, and cochlear innervation appeared normal in Chd7(Gt)(/+) mice. Hearing thresholds by auditory brainstem response (ABR) testing were elevated at 4 and 16 kHz in Chd7(Gt)(/+) mice, and there were reduced distortion product otoacoustic emissions (DPOAE). Exposure of Chd7(Gt)(/+) mice to broadband noise resulted in variable degrees of hair cell loss which inversely correlated with severity of stapedial defects. The degrees of hair cell loss and threshold shifts after noise exposure were more severe in wild type mice than in mutants. Together, these data indicate that Chd7(Gt)(/+) mice have combined conductive and sensorineural hearing loss, correlating with changes in both middle and inner ears.

Voluntary wheel running reverses age-induced changes in hippocampal gene expression

Normal aging alters expression of numerous genes within the brain. Some of these transcription changes likely contribute to age-associated cognitive decline, reduced neural plasticity, and the higher incidence of neuropathology. Identifying factors that modulate brain aging is crucial for improving quality of life. One promising intervention to counteract negative effects of aging is aerobic exercise. Aged subjects that exercise show enhanced cognitive performance and increased hippocampal neurogenesis and synaptic plasticity. Currently, the mechanisms behind the anti-aging effects of exercise are not understood. The present study conducted a microarray on whole hippocampal samples from adult (3.5-month-old) and aged (18-month-old) male BALB/c mice that were individually housed with or without running wheels for 8 weeks. Results showed that aging altered genes related to chromatin remodeling, cell growth, immune activity, and synapse organization compared to adult mice. Exercise was found to modulate many of the genes altered by aging, but in the opposite direction. For example, wheel running increased expression of genes related to cell growth and attenuated expression of genes involved in immune function and chromatin remodeling. Collectively, findings show that even late-onset exercise may attenuate age-related changes in gene expression and identifies possible pathways through which exercise may exert its beneficial effects.

Epigenetic regulation in neural crest development

The neural crest (NC) is a multipotent, migratory cell population that arises from the developing dorsal neural fold of vertebrate embryos. Once their fates are specified, neural crest cells (NCCs) migrate along defined routes and differentiate into a variety of tissues, including bone and cartilage of the craniofacial skeleton, peripheral neurons, glia, pigment cells, endocrine cells, and mesenchymal precursor cells (Santagati and Rijli,2003; Dupin et al.,2006; Hall,2009). Abnormal development of NCCs causes a number of human diseases, including ear abnormalities (including deafness), heart anomalies, neuroblastomas, and mandibulofacial dysostosis (Hall,2009). For more than a century, NCCs have attracted the attention of geneticists and developmental biologists for their stem cell-like properties, including self-renewal and multipotent differentiation potential. However, we have only begun to understand the underlying mechanisms responsible for their formation and behavior. Recent studies have demonstrated that epigenetic regulation plays important roles in NC development. In this review, we focused on some of the most recent findings on chromatin-mediated mechanisms for vertebrate NCC development.