Study of smell and reproductive organs in a mouse model for CHARGE syndrome

Morphological and sensorimotor phenotypes in a zebrafish CHARGE syndrome model are domain-dependent

CHARGE syndrome is a heterogeneous disorder characterized by a spectrum of defects affecting multiple tissues and behavioral difficulties such as autism, attention-deficit/hyperactivity disorder, obsessive-compulsive disorder, anxiety, and sensory deficits. Most CHARGE cases arise from de novo, loss-of-function mutations in chromodomain-helicase-DNA-binding-protein-7 (CHD7). CHD7 is required for processes such as neuronal differentiation and neural crest cell migration, but how CHD7 affects neural circuit function to regulate behavior is unclear. To investigate the pathophysiology of behavioral symptoms in CHARGE, we established a mutant chd7 zebrafish line that recapitulates multiple CHARGE phenotypes including ear, cardiac, and craniofacial defects. Using a panel of behavioral assays, we found that chd7 mutants have specific auditory and visual behavior deficits that are independent of defects in sensory structures. Mauthner cell-dependent short-latency acoustic startle responses are normal in chd7 mutants, while Mauthner-independent long-latency responses are reduced. Responses to sudden decreases in light are also reduced in mutants, while responses to sudden increases in light are normal, suggesting that the retinal OFF pathway may be affected. Furthermore, by analyzing multiple chd7 alleles we observed that the penetrance of morphological and behavioral phenotypes is influenced by genetic background but that it also depends on the mutation location, with a chromodomain mutation causing the highest penetrance. This pattern is consistent with analysis of a CHARGE patient dataset in which symptom penetrance was highest in subjects with mutations in the CHD7 chromodomains. These results provide new insight into the heterogeneity of CHARGE and will inform future work to define CHD7-dependent neurobehavioral mechanisms.

Combined pituitary hormone deficiency harboring CHD7 gene missense mutation without CHARGE syndrome: a case report

BACKGROUND

Heterozygous loss-of-function mutations in the chromodomain helicase DNA-binding protein 7 (CHD7) gene cause CHARGE syndrome characterized by various congenital anomalies. A majority of patients with CHARGE syndrome present with congenital hypogonadotropic hypogonadism (HH), and combined pituitary hormone deficiency (CPHD) can also be present. Whereas CHD7 mutations have been identified in some patients with isolated HH without a diagnosis of CHARGE syndrome, it remains unclear whether CHD7 mutations can be identified in patients with CPHD who do not fulfill the criteria for CHARGE syndrome.

CASE PRESENTATION

A 33-year-old woman was admitted to our hospital. She had primary amenorrhea and was at Tanner stage 2 for both pubic hair and breast development. She was diagnosed with CPHD (HH, growth hormone deficiency, and central hypothyroidism), and a heterozygous rare missense mutation (c.6745G > A, p.Asp2249Asn) in the CHD7 gene was identified. Our conservation analysis and numerous in silico analyses suggested that this mutation had pathogenic potential. She had mild intellectual disability, a minor feature of CHARGE syndrome, but did not fulfill the criteria for CHARGE syndrome.

CONCLUSIONS

We report a rare case of CPHD harboring CHD7 mutation without CHARGE syndrome. This case provides valuable insights into phenotypes caused by CHD7 mutations. CHD7 mutations can have a continuous phenotypic spectrum depending on the severity of hypopituitarism and CHARGE features. Therefore, we would like to propose a novel concept of CHD7-associated syndrome.

Hypothalamic GnRH expression and pulsatility depends on a balance of prolactin receptors in the plains vizcacha, Lagostomus maximus

In mammals, gestation is considered a physiological hyperprolactinemia status. Prolactin (PRL) is one of the modulators of gonadotropin-releasing hormone (GnRH) neurons function. The South American plains vizcacha (Lagostomus maximus) is a unique model to study the regulation of hypothalamic GnRH neurons by direct and indirect steroid-dependent pathways. The aim was to characterize the hypothalamic expression of endocrine markers in vizcacha during gestation as well as their response to experimental induced hyperprolactinemia. The possible involvement of PRL regulatory pathways on GnRH in the context of hypothalamic and pituitary reactivation in mid-gestating vizcachas was discussed. Using two in vivo approaches, we determined changes in the hypothalamic expression and distribution of prolactin receptor (PRLR), tyrosine hydroxylase (TH), and dopamine type 2 receptor. A significant increment in the number of tuberoinfundibular dopaminergic (TIDA) neurons was determined in the arcuate nucleus from early to term pregnancy. On the other hand, at preoptic area, the number of both TH+PRLR+ and GnRH+PRLR+ double-labeled neurons significantly decreased at mid-pregnancy probably allowing the recovery of GnRH expression indicating that both types of neurons may represent the key points of PRL indirect and direct pathways modulating GnRH. Moreover, in a model of induced hyperprolactinemic vizcachas, the inhibitory effect of PRL on GnRH at both expression and delivery levels were confirmed. These results suggest the concomitant participation of both PRL regulatory pathways on GnRH modulation and pinpoint the key role of PRL on GnRH expression enabling the recovery of the hypothalamic activity during the gestation in this species.

Characterization of Two Mouse Chd7 Heterozygous Loss-of-Function Models Shows Dysgenesis of the Corpus Callosum and Previously Unreported Features of CHARGE Syndrome

CHARGE syndrome is a rare congenital disorder frequently caused by mutations in the chromodomain helicase DNA-binding protein-7 CHD7. Here, we developed and systematically characterized two genetic mouse models with identical, heterozygous loss-of-function mutation of the Chd7 gene engineered on inbred and outbred genetic backgrounds. We found that both models showed consistent phenotypes with the core clinical manifestations seen in CHARGE syndrome, but the phenotypes in the inbred Chd7 model were more severe, sometimes having reduced penetrance and included dysgenesis of the corpus callosum, hypoplasia of the hippocampus, abnormal retrosplenial granular cortex, ventriculomegaly, hyperactivity, growth delays, impaired grip strength and repetitive behaviors. Interestingly, we also identified previously unreported features including reduced levels of basal insulin and reduced blood lipids. We suggest that the phenotypic variation reported in individuals diagnosed with CHARGE syndrome is likely due to the genetic background and modifiers. Finally, our study provides a valuable resource, making it possible for mouse biologists interested in Chd7 to make informed choices on which mouse model they should use to study phenotypes of interest and investigate in more depth the underlying cellular and molecular mechanisms.

CHARGE syndrome-associated proteins FAM172A and CHD7 influence male sex determination and differentiation through transcriptional and alternative splicing mechanisms

To gain further insight into chromatin‐mediated regulation of mammalian sex determination, we analyzed the role of the CHARGE syndrome‐associated proteins FAM172A and CHD7. This study is based on our prior discoveries that a subset of corresponding mutant mice display complete male‐to‐female sex reversal, and that both of these proteins regulate co‐transcriptional alternative splicing in neural crest cells. Here, we report that FAM172A and CHD7 are present in the developing gonads when sex determination normally occurs in mice. The interactome of FAM172A in pre‐Sertoli cells again suggests a role at the chromatin‐spliceosome interface, like in neural crest cells. Accordingly, analysis of Fam172a‐mutant pre‐Sertoli cells revealed transcriptional and splicing dysregulation of hundreds of genes. Many of these genes are similarly affected in Chd7‐mutant pre‐Sertoli cells, including several known key regulators of sex determination and subsequent formation of testis cords. Among them, we notably identified Sry as a direct transcriptional target and WNT pathway‐associated Lef1 and Tcf7l2 as direct splicing targets. The identified molecular defects are also associated with the abnormal morphology of seminiferous tubules in mutant postnatal testes. Altogether, our results thus identify FAM172A and CHD7 as new players in the regulation of male sex determination and differentiation in mice, and further highlight the importance of chromatin‐mediated regulatory mechanisms in these processes.

The Differential Roles for Neurodevelopmental and Neuroendocrine Genes in Shaping GnRH Neuron Physiology and Deficiency

Gonadotropin releasing hormone (GnRH) neurons are hypothalamic neuroendocrine cells that control sexual reproduction. During embryonic development, GnRH neurons migrate from the nose to the hypothalamus, where they receive inputs from several afferent neurons, following the axonal scaffold patterned by nasal nerves. Each step of GnRH neuron development depends on the orchestrated action of several molecules exerting specific biological functions. Mutations in genes encoding for these essential molecules may cause Congenital Hypogonadotropic Hypogonadism (CHH), a rare disorder characterized by GnRH deficiency, delayed puberty and infertility. Depending on their action in the GnRH neuronal system, CHH causative genes can be divided into neurodevelopmental and neuroendocrine genes. The CHH genetic complexity, combined with multiple inheritance patterns, results in an extreme phenotypic variability of CHH patients. In this review, we aim at providing a comprehensive and updated description of the genes thus far associated with CHH, by dissecting their biological relevance in the GnRH system and their functional relevance underlying CHH pathogenesis.

Folic Acid Fortification Prevents Morphological and Behavioral Consequences of X-Ray Exposure During Neurulation

Previous studies suggested a causal link between pre-natal exposure to ionizing radiation and birth defects such as microphthalmos and exencephaly. In mice, these defects arise primarily after high-dose X-irradiation during early neurulation. However, the impact of sublethal (low) X-ray doses during this early developmental time window on adult behavior and morphology of central nervous system structures is not known. In addition, the efficacy of folic acid (FA) in preventing radiation-induced birth defects and persistent radiation-induced anomalies has remained unexplored. To assess the efficacy of FA in preventing radiation-induced defects, pregnant C57BL6/J mice were X-irradiated at embryonic day (E)7.5 and were fed FA-fortified food. FA partially prevented radiation-induced (1.0 Gy) anophthalmos, exencephaly and gastroschisis at E18, and reduced the number of pre-natal deaths, fetal weight loss and defects in the cervical vertebrae resulting from irradiation. Furthermore, FA food fortification counteracted radiation-induced impairments in vision and olfaction, which were evidenced after exposure to doses ≥0.1 Gy. These findings coincided with the observation of a reduction in thickness of the retinal ganglion cell and nerve fiber layer, and a decreased axial length of the eye following exposure to 0.5 Gy. Finally, MRI studies revealed a volumetric decrease of the hippocampus, striatum, thalamus, midbrain and pons following 0.5 Gy irradiation, which could be partially ameliorated after FA food fortification. Altogether, our study is the first to offer detailed insights into the long-term consequences of X-ray exposure during neurulation, and supports the use of FA as a radioprotectant and antiteratogen to counter the detrimental effects of X-ray exposure during this crucial period of gestation.

Development of the human olfactory system

This chapter focuses on the development of the human olfactory system. In this system, function does not require full neuroanatomical maturity. Thus, discrimination of odorous molecules, including a number within the mother's diet, occurs in amniotic fluid after 28-30 weeks of gestation, at which time the olfactory bulbs are identifiable by MRI. Hypoplasia/aplasia of the bulbs is documented in the third trimester and postnatally. Interestingly, olfactory axons project from the nasal epithelium to the telencephalon before formation of the olfactory bulbs and lack a peripheral ganglion, but the synaptic glomeruli of the future olfactory bulb serves this function. Histologic lamination of the olfactory bulb is present by 14 weeks, but maturation remains incomplete at term for neuronal differentiation, synaptogenesis, myelination, and persistence of the normal transitory fetal ventricular recess. Myelination occurs postnatally. Although olfaction is the only sensory system without direct thalamic projections, the olfactory bulb and anterior olfactory nucleus are, in effect, thalamic surrogates. For example, many dendro-dendritic synapses occur within the bulb between GABAergic granular neurons and periglomerular neurons. Moreover, bulbar synaptic glomeruli are analogous to peripheral ganglia of other sensory cranial nerves. The olfactory tract contains much gray as well as white matter. The olfactory epithelium and bulb both incorporate progenitor cells at all ages. Diverse malformations of the olfactory bulb can be detected by clinical examination, imaging, and neuropathology; indeed, olfactory reflexes of the neonate can be reliably tested. We recommend that such testing be routine in the neonatal neurologic examination, especially in children with brain malformations, endocrinopathies, chromosomopathies, genetic/metabolic disorders, and perinatal hypoxic/ischemic encephalopathy.

Transcriptional and Epigenetic Control of Mammalian Olfactory Epithelium Development

The postnatal mammalian olfactory epithelium (OE) represents a major aspect of the peripheral olfactory system. It is a pseudostratified tissue that originates from the olfactory placode and is composed of diverse cells, some of which are specialized receptor neurons capable of transducing odorant stimuli to afford the perception of smell (olfaction). The OE is known to offer a tractable miniature model for studying the systematic generation of neurons and glia that typify neural tissue development. During OE development, stem/progenitor cells that will become olfactory sensory neurons and/or non-neuronal cell types display fine spatiotemporal expression of neuronal and non-neuronal genes that ensures their proper proliferation, differentiation, survival, and regeneration. Many factors, including transcription and epigenetic factors, have been identified as key regulators of the expression of such requisite genes to permit normal OE morphogenesis. Typically, specific interactive regulatory networks established between transcription and epigenetic factors/cofactors orchestrate histogenesis in the embryonic and adult OE. Hence, investigation of these regulatory networks critical for OE development promises to disclose strategies that may be employed in manipulating the stepwise transition of olfactory precursor cells to become fully differentiated and functional neuronal and non-neuronal cell types. Such strategies potentially offer formidable means of replacing injured or degenerated neural cells as therapeutics for nervous system perturbations. This review recapitulates the developmental cellular diversity of the olfactory neuroepithelium and discusses findings on how the precise and cooperative molecular control by transcriptional and epigenetic machinery is indispensable for OE ontogeny.

Dysregulation of cotranscriptional alternative splicing underlies CHARGE syndrome

CHARGE syndrome-which stands for coloboma of the eye, heart defects, atresia of choanae, retardation of growth/development, genital abnormalities, and ear anomalies-is a severe developmental disorder with wide phenotypic variability, caused mainly by mutations in CHD7 (chromodomain helicase DNA-binding protein 7), known to encode a chromatin remodeler. The genetic lesions responsible for CHD7 mutation-negative cases are unknown, at least in part because the pathogenic mechanisms underlying CHARGE syndrome remain poorly defined. Here, we report the characterization of a mouse model for CHD7 mutation-negative cases of CHARGE syndrome generated by insertional mutagenesis of Fam172a (family with sequence similarity 172, member A). We show that Fam172a plays a key role in the regulation of cotranscriptional alternative splicing, notably by interacting with Ago2 (Argonaute-2) and Chd7. Validation studies in a human cohort allow us to propose that dysregulation of cotranscriptional alternative splicing is a unifying pathogenic mechanism for both CHD7 mutation-positive and CHD7 mutation-negative cases. We also present evidence that such splicing defects can be corrected in vitro by acute rapamycin treatment.

New insights and advances in CHARGE syndrome: Diagnosis, etiologies, treatments, and research discoveries

CHARGE syndrome is a multiple congenital anomaly condition caused, in a majority of individuals, by loss of function pathogenic variants in the gene CHD7. In this special issue of the American Journal of Medical Genetics part C, authors of eleven manuscripts describe specific organ system features of CHARGE syndrome, with a focus on recent developments in diagnosis, etiologies, and treatments. Since 2004, when CHD7 was identified as the major causative gene in CHARGE, several animal models (mice, zebrafish, flies, and frog) and cell-based systems have been developed to explore the underlying pathophysiology of this condition. In this article, we summarize those advances, highlight opportunities for new discoveries, and encourage readers to explore specific organ systems in more detail in each individual article. We hope the excitement around innovative research and development in CHARGE syndrome will encourage others to join this effort, and will stimulate other investigators and professionals to engage with individuals diagnosed as having CHARGE syndrome, their families, and their care providers.

Reproductive endocrine phenotypes relating to CHD7 mutations in humans

Mutations in the gene CHD7 cause CHARGE syndrome, a rare multi-organ syndromic disorder. Gonadal defects are common in individuals with CHARGE syndrome (seen in ∼60-80% of cases) and represent the letter "G" in the CHARGE syndrome acronym. The gonadal defect in CHARGE syndrome results from congenital deficiency of the hypothalamic hormone Gonadotropin-releasing hormone (GnRH), which manifests clinically as pubertal failure and infertility, and biochemically as hypogonadotropic hypogonadism (low sex steroid hormone levels with inappropriately normal or low gonadotropin levels). In addition to the gonadal endocrine abnormalities, in a small minority of individuals with CHARGE, additional endocrine defects including growth hormone deficiency, multiple pituitary hormone deficits and primary hypothyroidism may also be seen. CHD7 mutations disrupt the targeting of olfactory axons and the migration of GnRH-synthesizing neurons during embryonic development, resulting in congenital idiopathic hypogonadotropic hypogonadism (IHH) and anosmia (or hyposmia), two features that define human Kallmann syndrome. Since Kallmann syndrome is one of the constituent phenotypes within CHARGE, recent studies have investigated the role of CHD7 mutations in individuals with IHH and established that deleterious missense mutations in CHD7 are associated with Kallmann syndrome as well as normosmic form of IHH. These missense mutations affect the ATPase and nucleosome remodeling activities of the CHD7 protein. These observations suggest that CHD7 protein function is critical for the ontogeny of GnRH neurons and neuroendocrine regulation of GnRH secretion.

The terminal nerve plays a prominent role in GnRH-1 neuronal migration independent from proper olfactory and vomeronasal connections to the olfactory bulbs

Gonadotropin-releasing hormone-1 (GnRH-1) neurons (GnRH-1 ns) migrate from the developing olfactory pit into the hypothalamus during embryonic development. Migration of the GnRH-1 neurons is required for mammalian reproduction as these cells control release of gonadotropins from the anterior pituitary gland. Disturbances in GnRH-1 ns migration, GnRH-1 synthesis, secretion or signaling lead to varying degrees of hypogonadotropic hypogonadism (HH), which impairs pubertal onset and fertility. HH associated with congenital olfactory defects is clinically defined as Kallmann Syndrome (KS). The association of olfactory defects with HH in KS suggested a potential direct relationship between defective olfactory axonal routing, lack of olfactory bulbs (OBs) and aberrant GnRH-1 ns migration. However, it has never been experimentally proven that the formation of axonal connections of the olfactory/vomeronasal neurons to their functional targets are necessary for the migration of GnRH-1 ns to the hypothalamus. Loss-of-function of the Arx-1 homeobox gene leads to the lack of proper formation of the OBs with abnormal axonal termination of olfactory sensory neurons ( Yoshihara et al., 2005). Our data prove that correct development of the OBs and axonal connection of the olfactory/vomeronasal sensory neurons to the forebrain are not required for GnRH-1 ns migration, and suggest that the terminal nerve, which forms the GnRH-1 migratory scaffold, follows different guidance cues and differs in gene expression from olfactory/vomeronasal sensory neurons.

Summary: Our work reveals that correct olfactory bulb development is not required for GnRH-1 neuronal migration. This study challenges the idea that GnRH-1 neuronal migration to the hypothalamus relies on correct routing of the olfactory and vomeronasal neurons and supports the existence of the TN in mammals.

Versatile Roles of the Chromatin Remodeler CHD7 during Brain Development and Disease

CHD7 (Chromo-Helicase-DNA binding protein 7) protein is an ATP-dependent chromatin remodeler. Heterozygous mutation of the CHD7 gene causes a severe congenital disease known as CHARGE syndrome. Most CHARGE syndrome patients have brain structural anomalies, implicating an important role of CHD7 during brain development. In this review, we summarize studies dissecting developmental functions of CHD7 in the brain and discuss pathogenic mechanisms behind neurodevelopmental defects caused by mutation of CHD7. As we discussed, CHD7 protein exhibits a remarkably specific and dynamic expression pattern in the brain. Studies in human and animal models have revealed that CHD7 is involved in multiple developmental lineages and processes in the brain. Mechanistically, CHD7 is essential for neural differentiation due to its transcriptional regulation in progenitor cells.

Olfactory Development, Part 2: Neuroanatomic Maturation and Dysgeneses

Olfactory axons project from nasal epithelium to the primitive telencephalon before olfactory bulbs form. Olfactory bulb neurons do not differentiate in situ but arrive via the rostral migratory stream. Synaptic glomeruli and concentric laminar architecture are unlike other cortices. Fetal olfactory maturation of neuronal differentiation, synaptogenesis, and myelination remains incomplete at term and have a protracted course of postnatal development. The olfactory ventricular recess involutes postnatally but dilates in congenital hydrocephalus. Olfactory bulb, tract and epithelium are repositories of progenitor stem cells in fetal and adult life. Diverse malformations of the olfactory bulb can be diagnosed by clinical examination, imaging, and neuropathologically. Cellular markers of neuronal differentiation and synaptogenesis demonstrate immaturity of the olfactory system at birth, previously believed by histology alone to occur early in fetal life. Immaturity does not preclude function.

The Chromodomain Helicase DNA-Binding Chromatin Remodelers: Family Traits that Protect from and Promote Cancer

A plethora of mutations in chromatin regulators in diverse human cancers is emerging, attesting to the pivotal role of chromatin dynamics in tumorigenesis. A recurrent theme is inactivation of the chromodomain helicase DNA-binding (CHD) family of proteins-ATP-dependent chromatin remodelers that govern the cellular machinery's access to DNA, thereby controlling fundamental processes, including transcription, proliferation, and DNA damage repair. This review highlights what is currently known about how genetic and epigenetic perturbation of CHD proteins and the pathways that they regulate set the stage for cancer, providing new insight for designing more effective anti-cancer therapies.

The chromatin remodeling factor CHD7 controls cerebellar development by regulating reelin expression

The mechanisms underlying the neurodevelopmental deficits associated with CHARGE syndrome, which include cerebellar hypoplasia, developmental delay, coordination problems, and autistic features, have not been identified. CHARGE syndrome has been associated with mutations in the gene encoding the ATP-dependent chromatin remodeler CHD7. CHD7 is expressed in neural stem and progenitor cells, but its role in neurogenesis during brain development remains unknown. Here we have shown that deletion of Chd7 from cerebellar granule cell progenitors (GCps) results in reduced GCp proliferation, cerebellar hypoplasia, developmental delay, and motor deficits in mice. Genome-wide expression profiling revealed downregulated expression of the gene encoding the glycoprotein reelin (Reln) in Chd7-deficient GCps. Recessive RELN mutations have been associated with severe cerebellar hypoplasia in humans. We found molecular and genetic evidence that reductions in Reln expression contribute to GCp proliferative defects and cerebellar hypoplasia in GCp-specific Chd7 mouse mutants. Finally, we showed that CHD7 is necessary for maintaining an open, accessible chromatin state at the Reln locus. Taken together, this study shows that Reln gene expression is regulated by chromatin remodeling, identifies CHD7 as a previously unrecognized upstream regulator of Reln, and provides direct in vivo evidence that a mammalian CHD protein can control brain development by modulating chromatin accessibility in neuronal progenitors.

CHD7 promotes proliferation of neural stem cells mediated by MIF

Macrophage migration inhibitory factor (MIF) plays an important role in supporting the proliferation and/or survival of murine neural stem/progenitor cells (NSPCs); however, the downstream effectors of this factor remain unknown. Here, we show that MIF increases the expression of Pax6 and Chd7 in NSPCs in vitro. During neural development, the chromatin remodeling factor Chd7 (chromatin helicase-DNA-binding protein 7) is expressed in the ventricular zone of the telencephalon of mouse brain at embryonic day 14.5, as well as in cultured NSPCs. Retroviral overexpression of Pax6 in NSPCs increased Chd7 gene expression. Lentivirally-expressed Chd7 shRNA suppressed cell proliferation and neurosphere formation, and inhibited neurogenesis in vitro, while decreasing gene expression of Hes5 and N-myc. In addition, CHD7 overexpression increased cell proliferation in human embryonic stem cell-derived NSPCs (ES-NSPCs). In Chd7 mutant fetal mouse brains, there were fewer intermediate progenitor cells (IPCs) compared to wildtype littermates, indicating that Chd7 contributes to neurogenesis in the early developmental mouse brain. Furthermore, in silico database analysis showed that, among members of the CHD family, CHD7 is highly expressed in human gliomas. Interestingly, high levels of CHD7 gene expression in human glioma initiating cells (GICs) compared to normal astrocytes were revealed and gene silencing of CHD7 decreased GIC proliferation. Collectively, our data demonstrate that CHD7 is an important factor in the proliferation and stemness maintenance of NSPCs, and CHD7 is a promising therapeutic target for the treatment of gliomas.

A role for TENM1 mutations in congenital general anosmia

Congenital general anosmia (CGA) is a neurological disorder entailing a complete innate inability to sense odors. While the mechanisms underlying vertebrate olfaction have been studied in detail, there are still gaps in our understanding of the molecular genetic basis of innate olfactory disorders. Applying whole-exome sequencing to a family multiply affected with CGA, we identified three members with a rare X-linked missense mutation in the TENM1 (teneurin 1) gene (ENST00000422452:c.C4829T). In Drosophila melanogaster, TENM1 functions in synaptic-partner-matching between axons of olfactory sensory neurons and target projection neurons and is involved in synapse organization in the olfactory system. We used CRISPR-Cas9 system to generate a Tenm1 disrupted mouse model. Tenm1(-/-) and point-mutated Tenm1(A) (/A) adult mice were shown to have an altered ability to locate a buried food pellet. Tenm1(A) (/A) mice also displayed an altered ability to sense aversive odors. Results of our study, that describes a new Tenm1 mouse, agree with the hypothesis that TENM1 has a role in olfaction. However, additional studies should be done in larger CGA cohorts, to provide statistical evidence that loss-of-function mutations in TENM1 can solely cause the disease in our and other CGA cases.

Maturation and Dysgenesis of the Human Olfactory Bulb

The olfactory bulb with its unique architecture was studied for neuronal maturation in human fetuses. Neuroblasts stream into the olfactory bulb from the rostral telencephalon and secondarily migrate radially. The transitory olfactory ventricular recess regresses postnatally. Olfactory is the only sensory system without thalamic projections but incorporates intrinsic thalamic equivalents. The bulb is a repository of progenitor cells. Maturation of the bulb and tract was studied in 18 normal human fetuses of 16-41 weeks gestation; mid-gestational twins with hydrocephalus; 7 arrhinencephaly/holoprosencephaly; 2 olfactory dysgeneses. Multiple immunoreactivities were performed. Synaptophysin around mitral neurons, in a few synaptic glomeruli and concentric lamination of the outer granular layer, was seen at 16 weeks. Outer granular neurons exhibited NeuN at 16 weeks, only 2/3 were reactive at term. Concentric alternating sheets of granular neurons and their dendrodendritic synapses are seen during maturation. Calretinin reactivity is seen in neurons and neurites, primary olfactory nerve axons, periglomerular cells and neuroepithelial cells surrounding the ventricular recess; reactivity occurs later in synaptic glomeruli than with synaptophysin; not all glomeruli are strongly reactive even at term. Nestin- and vimentin-reactive bipolar progenitor cells were demonstrated at all ages and extend into the olfactory tract. Myelin is demonstrated by Luxol fast blue (LFB) only postnatally. In hydrocephalus, the olfactory recess is dilated. Mitral cell dispersion, disrupted glomeruli, heterotopia and maturational delay are seen in some dysgeneses. Malformations exhibit unique findings. Fusion of hypoplastic bulbs can occur. Abnormal architecture is seen in hemimegalencephaly. More documentation of olfactory dysgenesis is needed in other major brain malformations.

Dysfunctional SEMA3E signaling underlies gonadotropin-releasing hormone neuron deficiency in Kallmann syndrome

Individuals with an inherited deficiency in gonadotropin-releasing hormone (GnRH) have impaired sexual reproduction. Previous genetic linkage studies and sequencing of plausible gene candidates have identified mutations associated with inherited GnRH deficiency, but the small number of affected families and limited success in validating candidates have impeded genetic diagnoses for most patients. Using a combination of exome sequencing and computational modeling, we have identified a shared point mutation in semaphorin 3E (SEMA3E) in 2 brothers with Kallmann syndrome (KS), which causes inherited GnRH deficiency. Recombinant wild-type SEMA3E protected maturing GnRH neurons from cell death by triggering a plexin D1-dependent (PLXND1-dependent) activation of PI3K-mediated survival signaling. In contrast, recombinant SEMA3E carrying the KS-associated mutation did not protect GnRH neurons from death. In murine models, lack of either SEMA3E or PLXND1 increased apoptosis of GnRH neurons in the developing brain, reducing innervation of the adult median eminence by GnRH-positive neurites. GnRH neuron deficiency in male mice was accompanied by impaired testes growth, a characteristic feature of KS. Together, these results identify SEMA3E as an essential gene for GnRH neuron development, uncover a neurotrophic function for SEMA3E in the developing brain, and elucidate SEMA3E/PLXND1/PI3K signaling as a mechanism that prevents GnRH neuron deficiency.

Chromodomain helicase DNA-binding proteins in stem cells and human developmental diseases

Dynamic regulation of gene expression is vital for proper cellular development and maintenance of differentiated states. Over the past 20 years, chromatin remodeling and epigenetic modifications of histones have emerged as key controllers of rapid reversible changes in gene expression. Mutations in genes encoding enzymes that modify chromatin have also been identified in a variety of human neurodevelopmental disorders, ranging from isolated intellectual disability and autism spectrum disorder to multiple congenital anomaly conditions that affect major organ systems and cause severe morbidity and mortality. In this study, we review recent evidence that chromodomain helicase DNA-binding (CHD) proteins regulate stem cell proliferation, fate, and differentiation in a wide variety of tissues and organs. We also highlight known roles of CHD proteins in human developmental diseases and present current unanswered questions about the pleiotropic effects of CHD protein complexes, their genetic targets, nucleosome sliding functions, and enzymatic effects in cells and tissues.

Functionally compromised CHD7 alleles in patients with isolated GnRH deficiency

Inactivating mutations in chromodomain helicase DNA binding protein 7 (CHD7) cause CHARGE syndrome, a severe multiorgan system disorder of which Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) is a minor feature. Recent reports have described predominantly missense CHD7 alleles in IGD patients, but it is unclear if these alleles are relevant to causality or overall genetic burden of Kallmann syndrome (KS) and normosmic form of IGD. To address this question, we sequenced CHD7 in 783 well-phenotyped IGD patients lacking full CHARGE features; we identified nonsynonymous rare sequence variants in 5.2% of the IGD cohort (73% missense and 27% splice variants). Functional analyses in zebrafish using a surrogate otolith assay of a representative set of these CHD7 alleles showed that rare sequence variants observed in controls showed no altered function. In contrast, 75% of the IGD-associated alleles were deleterious and resulted in both KS and normosmic IGD. In two families, pathogenic mutations in CHD7 coexisted with mutations in other known IGD genes. Taken together, our data suggest that rare deleterious CHD7 alleles contribute to the mutational burden of patients with both KS and normosmic forms of IGD in the absence of full CHARGE syndrome. These findings (i) implicate a unique role or preferential sensitivity for CHD7 in the ontogeny of GnRH neurons, (ii) reiterate the emerging genetic complexity of this family of IGD disorders, and (iii) demonstrate how the coordinated use of well-phenotyped cohorts, families, and functional studies can inform genetic architecture and provide insights into the developmental biology of cellular systems.

The chromatin remodeling protein CHD7, mutated in CHARGE syndrome, is necessary for proper craniofacial and tracheal development

BACKGROUND

Heterozygous mutations in the chromatin remodeling gene CHD7 cause CHARGE syndrome, a developmental disorder with variable craniofacial dysmorphisms and respiratory difficulties. The molecular etiologies of these malformations are not well understood. Homozygous Chd7 null mice die by E11, whereas Chd7(Gt/+) heterozygous null mice are a viable and excellent model of CHARGE. We explored skeletal phenotypes in Chd7(Gt/+) and Chd7 conditional knockout mice, using Foxg1-Cre to delete Chd7 (Foxg1-CKO) in the developing eye, ear, nose, pharyngeal pouch, forebrain, and gut and Wnt1-Cre (Wnt1-CKO) to delete Chd7 in migrating neural crest cells.

RESULTS

Foxg1-CKO mice exhibited postnatal respiratory distress and death, dysplasia of the eye, concha, and frontal bone, hypoplastic maxillary shelves and nasal epithelia, and reduced tracheal rings. Wnt1-CKO mice exhibited frontal and occipital bone dysplasia, hypoplasia of the maxillary shelves and mandible, and cleft palate. In contrast, heterozygous Chd7(Gt/+) mice had apparently normal skeletal development.

CONCLUSIONS

Conditional deletion of Chd7 in ectodermal and endodermal derivatives (Foxg1-Cre) or migrating neural crest cells (Wnt1-Cre) results in varied and more severe craniofacial defects than in Chd7(Gt/+) mice. These studies indicate that CHD7 has an important, dosage-dependent role in development of several different craniofacial tissues.

CHD7 and retinoic acid signaling cooperate to regulate neural stem cell and inner ear development in mouse models of CHARGE syndrome

CHARGE syndrome is a multiple congenital anomaly disorder that leads to life-threatening birth defects, such as choanal atresia and cardiac malformations as well as multiple sensory impairments, that affect hearing, vision, olfaction and balance. CHARGE is caused by heterozygous mutations in CHD7, which encodes an ATP-dependent chromatin remodeling enzyme. Identification of the mechanisms underlying neurological and sensory defects in CHARGE is a first step toward developing treatments for CHARGE individuals. Here, we used mouse models of Chd7 deficiency to explore the function of CHD7 in the development of the subventricular zone (SVZ) neural stem cell niche and inner ear, structures that are important for olfactory bulb neurogenesis and hearing and balance, respectively. We found that loss of Chd7 results in cell-autonomous proliferative, neurogenic and self-renewal defects in the perinatal and mature mouse SVZ stem cell niche. Modulation of retinoic acid (RA) signaling prevented in vivo inner ear and in vitro neural stem cell defects caused by Chd7 deficiency. Our findings demonstrate critical, cooperative roles for RA and CHD7 in SVZ neural stem cell function and inner ear development, suggesting that altered RA signaling may be an effective method for treating Chd7 deficiency.

More Clinical Overlap between 22q11.2 Deletion Syndrome and CHARGE Syndrome than Often Anticipated

CHARGE (coloboma, heart defects, atresia of choanae, retardation of growth and development, genital hypoplasia, and ear abnormalities) and 22q11.2 deletion syndromes are variable, congenital malformation syndromes that show considerable phenotypic overlap. We further explored this clinical overlap and proposed recommendations for the genetic diagnosis of both syndromes. We described 2 patients clinically diagnosed with CHARGE syndrome, who were found to carry a 22q11.2 deletion, and searched the literature for more cases. In addition, we screened our cohort of CHD7 mutation carriers (n = 802) for typical 22q11.2 deletion features and studied CHD7 in 20 patients with phenotypically 22q11.2 deletion syndrome but without haploinsufficiency of TBX1. In total, we identified 5 patients with a clinical diagnosis of CHARGE syndrome and a proven 22q11.2 deletion. Typical 22q11.2 deletion features were found in 30 patients (30/802, 3.7%) of our CHD7 mutation-positive cohort. We found truncating CHD7 mutations in 5/20 patients with phenotypically 22q11.2 deletion syndrome. Differentiating between CHARGE and 22q11.2 deletion syndromes can be challenging. CHD7 and TBX1 probably share a molecular pathway or have common target genes in affected organs. We strongly recommend performing CHD7 analysis in patients with a 22q11.2 deletion phenotype without TBX1 haploinsufficiency and conversely, performing a genome-wide array in CHARGE syndrome patients without a CHD7 mutation.

Identification and characterization of FAM124B as a novel component of a CHD7 and CHD8 containing complex

Background

Mutations in the chromodomain helicase DNA binding protein 7 gene (CHD7) lead to CHARGE syndrome, an autosomal dominant multiple malformation disorder. Proteins involved in chromatin remodeling typically act in multiprotein complexes. We previously demonstrated that a part of human CHD7 interacts with a part of human CHD8, another chromodomain helicase DNA binding protein presumably being involved in the pathogenesis of neurodevelopmental (NDD) and autism spectrum disorders (ASD). Because identification of novel CHD7 and CHD8 interacting partners will provide further insights into the pathogenesis of CHARGE syndrome and ASD/NDD, we searched for additional associated polypeptides using the method of stable isotope labeling by amino acids in cell culture (SILAC) in combination with mass spectrometry.

Principle findings

The hitherto uncharacterized FAM124B (Family with sequence similarity 124B) was identified as a potential interaction partner of both CHD7 and CHD8. We confirmed the result by co-immunoprecipitation studies and showed a direct binding to the CHD8 part by direct yeast two hybrid experiments. Furthermore, we characterized FAM124B as a mainly nuclear localized protein with a widespread expression in embryonic and adult mouse tissues.

Conclusion

Our results demonstrate that FAM124B is a potential interacting partner of a CHD7 and CHD8 containing complex. From the overlapping expression pattern between Chd7 and Fam124B at murine embryonic day E12.5 and the high expression of Fam124B in the developing mouse brain, we conclude that Fam124B is a novel protein possibly involved in the pathogenesis of CHARGE syndrome and neurodevelopmental disorders.

Chromatin remodeling by the CHD7 protein is impaired by mutations that cause human developmental disorders

Mutations in the CHD7 gene cause human developmental disorders including CHARGE syndrome. Genetic studies in model organisms have further established CHD7 as a central regulator of vertebrate development. Functional analysis of the CHD7 protein has been hampered by its large size. We used a dual-tag system to purify intact recombinant CHD7 protein and found that it is an ATP-dependent nucleosome remodeling factor. Biochemical analyses indicate that CHD7 has characteristics distinct from SWI/SNF- and ISWI-type remodelers. Further investigations show that CHD7 patient mutations have consequences that range from subtle to complete inactivation of remodeling activity, and that mutations leading to protein truncations upstream of amino acid 1899 of CHD7 are likely to cause a hypomorphic phenotype for remodeling. We propose that nucleosome remodeling is a key function for CHD7 during developmental processes and provide a molecular basis for predicting the impact of disease mutations on that function.

Otitis media in a new mouse model for CHARGE syndrome with a deletion in the Chd7 gene

Otitis media is a middle ear disease common in children under three years old. Otitis media can occur in normal individuals with no other symptoms or syndromes, but it is often seen in individuals clinically diagnosed with genetic diseases such as CHARGE syndrome, a complex genetic disease caused by mutation in the Chd7 gene and characterized by multiple birth defects. Although otitis media is common in human CHARGE syndrome patients, it has not been reported in mouse models of CHARGE syndrome. In this study, we report a mouse model with a spontaneous deletion mutation in the Chd7 gene and with chronic otitis media of early onset age accompanied by hearing loss. These mice also exhibit morphological alteration in the Eustachian tubes, dysregulation of epithelial proliferation, and decreased density of middle ear cilia. Gene expression profiling revealed up-regulation of Muc5ac, Muc5b and Tgf-β1 transcripts, the products of which are involved in mucin production and TGF pathway regulation. This is the first mouse model of CHARGE syndrome reported to show otitis media with effusion and it will be valuable for studying the etiology of otitis media and other symptoms in CHARGE syndrome.

Uncovering novel reproductive defects in neurokinin B receptor null mice: closing the gap between mice and men

Patients bearing mutations in TAC3 and TACR3 (which encode neurokinin B and its receptor, respectively) have sexual infantilism and infertility due to GnRH deficiency. In contrast, Tacr3(-/-) mice have previously been reported to be fertile. Because of this apparent phenotypic discordance between mice and men bearing disabling mutations in Tacr3/TACR3, Tacr3 null mice were phenotyped with close attention to pubertal development, estrous cyclicity, and fertility. Tacr3(-/-) mice demonstrated normal timing of preputial separation and day of first estrus, markers of sexual maturation. However, at postnatal d 60, Tacr3(-/-) males had significantly smaller testes and lower FSH levels than their wild-type littermates. Tacr3(-/-) females had lower uterine weights and abnormal estrous cyclicity. Approximately half of Tacr3(-/-) females had no detectable corpora lutea on ovarian histology at postnatal d 60. Despite this apparent ovulatory defect, all Tacr3(-/-) females achieved fertility when mated. However, Tacr3(-/-) females were subfertile, having both reduced numbers of litters and pups per litter. The subfertility of these animals was not due to a primary ovarian defect, because they demonstrated a robust response to exogenous gonadotropins. Thus, although capable of fertility, Tacr3-deficient mice have central reproductive defects. The remarkable ability of acyclic female Tacr3 null mice to achieve fertility is reminiscent of the reversal of hypogonadotropic hypogonadism seen in a high proportion of human patients bearing mutations in TACR3. Tacr3 mice are a useful model to examine the mechanisms by which neurokinin B signaling modulates GnRH release.

The role of CHD7 and the newly identified WDR11 gene in patients with idiopathic hypogonadotropic hypogonadism and Kallmann syndrome

Mutations in the chromodomain helicase DNA binding protein-7 (CHD7) cause CHARGE syndrome, which includes eye coloboma, heart malformations, atresia of the choanae, retardation of growth/development, genital anomalies, and ear abnormalities. CHARGE syndrome is usually sporadic, but is also autosomal dominant. CHD7 encodes a large protein that participates in chromatin remodeling and transcription. Findings from studies of mouse models employing ENU-mutagenesis or gene-trap methods recapitulate human CHARGE syndrome. CHARGE patients may manifest anosmia and/or hypogonadism, features that overlap with idiopathic hypogonadotropic hypogonadism (IHH) and Kallmann syndrome (KS). Similarly, IHH/KS patients may also display partial CHARGE features. Therefore, it has been hypothesized that IHH/KS represents a milder allelic variant of CHARGE syndrome, which has been supported by the identification of heterozygous CHD7 mutations in both normosmic IHH and KS. Developmental expression within the hypothalamus and the presence of human mutations indicate that CHD7 has an important role in puberty and reproduction. In addition, WDR11 was recently identified by positional cloning; and mutations in were identified in IHH/KS patients, suggesting a role for this gene in normal puberty.

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.

Reproductive dysfunction and decreased GnRH neurogenesis in a mouse model of CHARGE syndrome

CHARGE is a multiple congenital anomaly disorder and a common cause of pubertal defects, olfactory dysfunction, growth delays, deaf-blindness, balance disorders and congenital heart malformations. Mutations in CHD7, the gene encoding chromodomain helicase DNA binding protein 7, are present in 60-80% of individuals with the CHARGE syndrome. Mutations in CHD7 have also been reported in the Kallmann syndrome (olfactory dysfunction, delayed puberty and hypogonadotropic hypogonadism). CHD7 is a positive regulator of neural stem cell proliferation and olfactory sensory neuron formation in the olfactory epithelium, suggesting that the loss of CHD7 might also disrupt development of other neural populations. Here we report that female Chd7(Gt/+) mice have delays in vaginal opening and estrus onset, and erratic estrus cycles. Chd7(Gt/+) mice also have decreased circulating levels of luteinizing hormone and follicle-stimulating hormone but apparently normal responsiveness to gonadotropin-releasing hormone (GnRH) agonist and antagonist treatment. GnRH neurons in the adult Chd7(Gt/+) hypothalamus and embryonic nasal region are diminished, and there is decreased cellular proliferation in the embryonic olfactory placode. Expression levels of GnRH1 and Otx2 in the hypothalamus and GnRHR in the pituitary are significantly reduced in adult Chd7(Gt/+) mice. Additionally, Chd7 mutant embryos have CHD7 dosage-dependent reductions in expression levels of Fgfr1, Bmp4 and Otx2 in the olfactory placode. Together, these data suggest that CHD7 has critical roles in the development and maintenance of GnRH neurons for regulating puberty and reproduction.

A missense mutation in Fgfr1 causes ear and skull defects in hush puppy mice

The hush puppy mouse mutant has been shown previously to have skull and outer, middle, and inner ear defects, and an increase in hearing threshold. The fibroblast growth factor receptor 1 (Fgfr1) gene is located in the region of chromosome 8 containing the mutation. Sequencing of the gene in hush puppy heterozygotes revealed a missense mutation in the kinase domain of the protein (W691R). Homozygotes were found to die during development, at approximately embryonic day 8.5, and displayed a phenotype similar to null mutants. Reverse transcription PCR indicated a decrease in Fgfr1 transcript in heterozygotes and homozygotes. Generation of a construct containing the mutation allowed the function of the mutated receptor to be studied. Immunocytochemistry showed that the mutant receptor protein was present at the cell membrane, suggesting normal expression and trafficking. Measurements of changes in intracellular calcium concentration showed that the mutated receptor could not activate the IP₃ pathway, in contrast to the wild-type receptor, nor could it initiate activation of the Ras/MAP kinase pathway. Thus, the hush puppy mutation in fibroblast growth factor receptor 1 appears to cause a loss of receptor function. The mutant protein appears to have a dominant negative effect, which could be due to it dimerising with the wild-type protein and inhibiting its activity, thus further reducing the levels of functional protein. A dominant modifier, Mhspy, which reduces the effect of the hush puppy mutation on pinna and stapes development, has been mapped to the distal end of chromosome 7 and may show imprinting.

Anosmia predicts hypogonadotropic hypogonadism in CHARGE syndrome

OBJECTIVE

To test the hypothesis that a smell test could predict the occurrence of hypogonadotropic hypogonadism (HH) in patients with CHARGE syndrome, which is a variable combination of ocular coloboma, heart defects, choanal atresia, retardation of growth/development, genital hypoplasia, and ear anomalies or hearing loss caused by mutations in the CHD7 (chromodomain helicase DNA binding protein 7) gene.

STUDY DESIGN

We performed endocrine studies and smell testing (University of Pennsylvania Smell Identification Test) in 35 adolescent patients with molecularly confirmed CHARGE syndrome.

RESULTS

Complete data on smell and puberty were available for 15 patients; 11 patients had both anosmia and HH, whereas 4 patients had normosmia/hyposmia and spontaneous puberty. In addition, 7 boys were highly suspected of having HH (they were too young for definite HH diagnosis, but all had cryptorchidism, micropenis, or both) and had anosmia. The type of CHD7 mutation could not predict HH because a father and daughter with the same CHD7 mutation were discordant for HH and anosmia.

CONCLUSION

Anosmia and HH were highly correlated in our cohort, and therefore smell testing seems to be an attractive method for predicting the occurrence of HH in patients with CHARGE syndrome. The use of this test could prevent delay of hormonal pubertal induction, resulting in an age-appropriate puberty.

CHD7 functions in the nucleolus as a positive regulator of ribosomal RNA biogenesis

De novo mutation of the gene encoding chromodomain helicase DNA-binding protein 7 (CHD7) is the primary cause of CHARGE syndrome, a complex developmental disorder characterized by the co-occurrence of a specific set of birth defects. Recent studies indicate that CHD7 functions as a transcriptional regulator in the nucleoplasm. Here, we report based on immunofluorescence and western blotting of subcellular fractions that CHD7 is also constitutively localized to the nucleolus, the site of rRNA transcription. Standard chromatin immunoprecipitation (ChIP) assays indicate that CHD7 physically associates with rDNA, a result that is also observable upon alignment of whole-genome CHD7 ChIP coupled with massively parallel DNA sequencing data to the rDNA reference sequence. ChIP-chop analyses demonstrate that CHD7 specifically associates with hypomethylated, active rDNA, suggesting a role as a positive regulator of rRNA synthesis. Consistent with this hypothesis, siRNA-mediated depletion of CHD7 results in hypermethylation of the rDNA promoter and a concomitant reduction of 45S pre-rRNA levels. Accordingly, cells overexpressing CHD7 show increased levels of 45S pre-rRNA compared with control cells. Depletion of CHD7 also reduced cell proliferation and protein synthesis. Lastly, compared with wild-type ES cells, the levels of 45S pre-rRNA are reduced in both Chd7(+/-) and Chd7(-/-) mouse ES cells, as well as in Chd7(-/-) whole mouse embryos and multiple tissues dissected from Chd7(+/-) embryos. Together with previously published studies, these results indicate that CHD7 dually functions as a regulator of both nucleoplasmic and nucleolar genes and provide a novel avenue for investigation into the pathogenesis of CHARGE syndrome.

Molecular and phenotypic aspects of CHD7 mutation in CHARGE syndrome

CHARGE syndrome [coloboma of the eye, heart defects, atresia of the choanae, retardation of growth and/or development, genital and/or urinary abnormalities, and ear abnormalities (including deafness)] is a genetic disorder characterized by a specific and a recognizable pattern of anomalies. De novo mutations in the gene encoding chromodomain helicase DNA binding protein 7 (CHD7) are the major cause of CHARGE syndrome. Here, we review the clinical features of 379 CHARGE patients who tested positive or negative for mutations in CHD7. We found that CHARGE individuals with CHD7 mutations more commonly have ocular colobomas, temporal bone anomalies (semicircular canal hypoplasia/dysplasia), and facial nerve paralysis compared with mutation negative individuals. We also highlight recent genetic and genomic studies that have provided functional insights into CHD7 and the pathogenesis of CHARGE syndrome.

Chromodomain proteins in development: lessons from CHARGE syndrome

In humans, heterozygous mutations in the adenosine triphosphate-dependent chromatin remodeling gene CHD7 cause CHARGE syndrome, a common cause of deaf-blindness, balance disorders, congenital heart malformations, and olfactory dysfunction with an estimated incidence of approximately 1 in 10,000 newborns. The clinical features of CHARGE in humans and mice are highly variable and incompletely penetrant, and most mutations appear to result in haploinsufficiency of functional CHD7 protein. Mice with heterozygous loss of function mutations in Chd7 are a good model for CHARGE syndrome, and analyses of mouse mutant phenotypes have begun to clarify a role for CHD7 during development and into adulthood. Chd7 heterozygous mutant mice have postnatal delayed growth, inner ear malformations, anosmia/hyposmia, and craniofacial defects, and Chd7 homozygous mutants are embryonic lethal. A central question in developmental biology is how chromodomain proteins like CHD7 regulate important developmental processes, and whether they directly activate or repress downstream gene transcription or act more globally to alter chromatin structure and/or function. CHD7 is expressed in a wide variety of tissues during development, suggesting that it has tissue-specific and developmental stage-specific roles. Here, we review recent and ongoing analyses of CHD7 function in mouse models and cell-based systems. These studies explore tissue-specific effects of CHD7 deficiency, known CHD7 interacting proteins, and downstream target sites for CHD7 binding. CHD7 is emerging as a critical regulator of important developmental processes in organs affected by human CHARGE syndrome.