A 22q13.1 duplication in mosaicism including SOX10.

Waardenburg syndrome (WS) is characterized by the association of sensorineural hearing loss and pigmentation abnormalities. Among the four types, WS Type 2 (WS2) is the only one without a remarkable distinguishing feature. Here, we report a patient initially diagnosed with WS2 who exhibits a 446 kb mosaic duplication in chromosome 22q13.1, encompassing SOX10, and detected using whole genome sequencing in a trio. The patient, a 46,XY boy, presents with profound bilateral sensorineural hearing loss, right heterochromia iridium, left bright blue iris, and skin-depigmented areas in the abdomen and limbs. Vestibular and imaging tests are normal, without inner ear or olfactory bulb malformations. Bilateral cochlear implantation did not prevent language and speech delays. Moderate congenital chronic constipation and neurodevelopmental difficulties were also present. Given the few genes included in this duplicated region (only one OMIM gene with dominant inheritance), this report provides further delineation of the phenotype related to duplications encompassing the entire SOX10 gene.

SOX10: 20 years of phenotypic plurality and current understanding of its developmental function.

SOX10 belongs to a family of 20 SRY (sex-determining region Y)-related high mobility group box-containing (SOX) proteins, most of which contribute to cell type specification and differentiation of various lineages. The first clue that SOX10 is essential for development, especially in the neural crest, came with the discovery that heterozygous mutations occurring within and around SOX10 cause Waardenburg syndrome type 4. Since then, heterozygous mutations have been reported in Waardenburg syndrome type 2 (Waardenburg syndrome type without Hirschsprung disease), PCWH or PCW (peripheral demyelinating neuropathy, central dysmyelination, Waardenburg syndrome, with or without Hirschsprung disease), intestinal manifestations beyond Hirschsprung (ie, chronic intestinal pseudo-obstruction), Kallmann syndrome and cancer. All of these diseases are consistent with the regulatory role of SOX10 in various neural crest derivatives (melanocytes, the enteric nervous system, Schwann cells and olfactory ensheathing cells) and extraneural crest tissues (inner ear, oligodendrocytes). The recent evolution of medical practice in constitutional genetics has led to the identification of SOX10 variants in atypical contexts, such as isolated hearing loss or neurodevelopmental disorders, making them more difficult to classify in the absence of both a typical phenotype and specific expertise. Here, we report novel mutations and review those that have already been published and their functional consequences, along with current understanding of SOX10 function in the affected cell types identified through in vivo and in vitro models. We also discuss research options to increase our understanding of the origin of the observed phenotypic variability and improve the diagnosis and medical care of affected patients.

Dysregulation of the NRG1/ERBB pathway causes a developmental disorder with gastrointestinal dysmotility in humans.

Hirschsprung disease (HSCR) is the most frequent developmental anomaly of the enteric nervous system, with an incidence of 1 in 5000 live births. Chronic intestinal pseudo-obstruction (CIPO) is less frequent and classified as neurogenic or myogenic. Isolated HSCR has an oligogenic inheritance with RET as the major disease-causing gene, while CIPO is genetically heterogeneous, caused by mutations in smooth muscle-specific genes. Here, we describe a series of patients with developmental disorders including gastrointestinal dysmotility, and investigate the underlying molecular bases. Trio-exome sequencing led to the identification of biallelic variants in ERBB3 and ERBB2 in 8 individuals variably associating HSCR, CIPO, peripheral neuropathy, and arthrogryposis. Thorough gut histology revealed aganglionosis, hypoganglionosis, and intestinal smooth muscle abnormalities. The cell type-specific ErbB3 and ErbB2 function was further analyzed in mouse single-cell RNA sequencing data and in a conditional ErbB3-deficient mouse model, revealing a primary role for ERBB3 in enteric progenitors. The consequences of the identified variants were evaluated using quantitative real-time PCR (RT-qPCR) on patient-derived fibroblasts or immunoblot assays on Neuro-2a cells overexpressing WT or mutant proteins, revealing either decreased expression or altered phosphorylation of the mutant receptors. Our results demonstrate that dysregulation of ERBB3 or ERBB2 leads to a broad spectrum of developmental anomalies, including intestinal dysmotility.

Generation of an iPSC line (IMAGINi022-A) from a patient carrying a SOX10 missense mutation and presenting with deafness, depigmentation and progressive neurological impairment.

Mutations of SOX10 result in a broad range of phenotypes including Waardenburg syndrome (WS types 2 and 4) that can be found in association with peripheral demyelinating neuropathy and/or central dysmyelinating leukodystrophy. Here, we generated induced pluripotent stem cells (iPSCs) from a patient carrying a de novo heterozygous missense mutation in the SOX10 gene (MIM* 602229, NM006941.3c.523C > G; p.Pro175Ala) presenting with deafness, depigmentation and progressive neurological impairment. Cells were reprogrammed by non-integrative viral transduction from blood sample, have normal karyotype, express pluripotency markers and are able to differentiate into the three germ cell layers.

ADAR1 mediated regulation of neural crest derived melanocytes and Schwann cell development.

The neural crest gives rise to numerous cell types, dysfunction of which contributes to many disorders. Here, we report that adenosine deaminase acting on RNA (ADAR1), responsible for adenosine-to-inosine editing of RNA, is required for regulating the development of two neural crest derivatives: melanocytes and Schwann cells. Neural crest specific conditional deletion of Adar1 in mice leads to global depigmentation and absence of myelin from peripheral nerves, resulting from alterations in melanocyte survival and differentiation of Schwann cells, respectively. Upregulation of interferon stimulated genes precedes these defects, which are associated with the triggering of a signature resembling response to injury in peripheral nerves. Simultaneous extinction of MDA5, a key sensor of unedited RNA, rescues both melanocytes and myelin defects in vitro, suggesting that ADAR1 safeguards neural crest derivatives from aberrant MDA5-mediated interferon production. We thus extend the landscape of ADAR1 function to the fields of neural crest development and disease.

LKB1 specifies neural crest cell fates through pyruvate-alanine cycling.

Metabolic processes underlying the development of the neural crest, an embryonic population of multipotent migratory cells, are poorly understood. Here, we report that conditional ablation of the Lkb1 tumor suppressor kinase in mouse neural crest stem cells led to intestinal pseudo-obstruction and hind limb paralysis. This phenotype originated from a postnatal degeneration of the enteric nervous ganglia and from a defective differentiation of Schwann cells. Metabolomic profiling revealed that pyruvate-alanine conversion is enhanced in the absence of Lkb1. Mechanistically, inhibition of alanine transaminases restored glial differentiation in an mTOR-dependent manner, while increased alanine level directly inhibited the glial commitment of neural crest cells. Treatment with the metabolic modulator AICAR suppressed mTOR signaling and prevented Schwann cell and enteric defects of Lkb1 mutant mice. These data uncover a link between pyruvate-alanine cycling and the specification of glial cell fate with potential implications in the understanding of the molecular pathogenesis of neural crest diseases.

News from the endothelin-3/EDNRB signaling pathway: Role during enteric nervous system development and involvement in neural crest-associated disorders.

The endothelin system is a vertebrate-specific innovation with important roles in regulating the cardiovascular system and renal and pulmonary processes, as well as the development of the vertebrate-specific neural crest cell population and its derivatives. This system is comprised of three structurally similar 21-amino acid peptides that bind and activate two G-protein coupled receptors. In 1994, knockouts of the Edn3 and Ednrb genes revealed their crucial function during development of the enteric nervous system and melanocytes, two neural-crest derivatives. Since then, human and mouse genetics, combined with cellular and developmental studies, have helped to unravel the role of this signaling pathway during development and adulthood. In this review, we will summarize the known functions of the EDN3/EDNRB pathway during neural crest development, with a specific focus on recent scientific advances, and the enteric nervous system in normal and pathological conditions.

EDNRB mutations cause Waardenburg syndrome type II in the heterozygous state.

Waardenburg syndrome (WS) is a genetic disorder characterized by sensorineural hearing loss and pigmentation anomalies. The clinical definition of four WS types is based on additional features due to defects in structures mostly arising from the neural crest, with type I and type II being the most frequent. While type I is tightly associated to PAX3 mutations, WS type II (WS2) remains partly enigmatic with mutations in known genes (MITF, SOX10) accounting for only 30% of the cases. We performed exome sequencing in a WS2 index case and identified a heterozygous missense variation in EDNRB. Interestingly, homozygous (and very rare heterozygous) EDNRB mutations are already described in type IV WS (i.e., in association with Hirschsprung disease [HD]) and heterozygous mutations in isolated HD. Screening of a WS2 cohort led to the identification of an overall of six heterozygous EDNRB variations. Clinical phenotypes, pedigrees and molecular segregation investigations unraveled a dominant mode of inheritance with incomplete penetrance. In parallel, cellular and functional studies showed that each of the mutations impairs the subcellular localization of the receptor or induces a defective downstream signaling pathway. Based on our results, we now estimate EDNRB mutations to be responsible for 5%-6% of WS2.

Differentiation of Mouse Enteric Nervous System Progenitor Cells Is Controlled by Endothelin 3 and Requires Regulation of Ednrb by SOX10 and ZEB2.

BACKGROUND & AIMS: Maintenance and differentiation of progenitor cells in the developing enteric nervous system are controlled by molecules such as the signaling protein endothelin 3 (EDN3), its receptor (the endothelin receptor type B [EDNRB]), and the transcription factors SRY-box 10 (SOX10) and zinc finger E-box binding homeobox 2 (ZEB2). We used enteric progenitor cell (EPC) cultures and mice to study the roles of these proteins in enteric neurogenesis and their cross regulation. METHODS: We performed studies in mice with a Zeb2 loss-of-function mutation (Zeb2Δ) and mice carrying a spontaneous recessive mutation that prevents conversion of EDN3 to its active form (Edn3ls). EPC cultures issued from embryos that expressed only wild-type Zeb2 (Zeb2+/+ EPCs) or were heterozygous for the mutation (Zeb2Δ/+ EPCs) were exposed to EDN3; we analyzed the effects on cell differentiation using immunocytochemistry. In parallel, Edn3ls mice were crossed with Zeb2Δ/+mice; intestinal tissues were collected from embryos for immunohistochemical analyses. We investigated regulation of the EDNRB gene in transactivation and chromatin immunoprecipitation assays; results were validated in functional rescue experiments using transgenes expression in EPCs from retroviral vectors. RESULTS: Zeb2Δ/+ EPCs had increased neuronal differentiation compared to Zeb2+/+ cells. When exposed to EDN3, Zeb2+/+ EPCs continued expression of ZEB2 but did not undergo any neuronal differentiation. Incubation of Zeb2Δ/+ EPCs with EDN3, on the other hand, resulted in only partial inhibition of neuronal differentiation. This indicated that 2 copies of Zeb2 are required for EDN3 to prevent neuronal differentiation. Mice with combined mutations in Zeb2 and Edn3 (double mutants) had more severe enteric anomalies and increased neuronal differentiation compared to mice with mutations in either gene alone. The transcription factors SOX10 and ZEB2 directly activated the EDNRB promoter. Overexpression of EDNRB in Zeb2Δ/+ EPCs restored inhibition of neuronal differentiation, similar to incubation of Zeb2+/+ EPCs with EDN3. CONCLUSIONS: In studies of cultured EPCs and mice, we found that control of differentiation of mouse enteric nervous system progenitor cells by EDN3 requires regulation of Ednrb expression by SOX10 and ZEB2.

Endothelin-3 stimulates cell adhesion and cooperates with ß1-integrins during enteric nervous system ontogenesis.

Endothelin-3 (EDN3) and ß1-integrins are required for the colonization of the embryonic gut by enteric neural crest cells (ENCCs) to form the enteric nervous system (ENS). ß1-integrin-null ENCCs exhibit migratory defects in a region of the gut enriched in EDN3 and in specific extracellular matrix (ECM) proteins. We investigated the putative role of EDN3 on ENCC adhesion properties and its functional interaction with ß1-integrins during ENS development. We show that EDN3 stimulates ENCC adhesion to various ECM components in vitro. It induces rapid changes in ENCC shape and protrusion dynamics favouring sustained growth and stabilization of lamellipodia, a process coincident with the increase in the number of focal adhesions and activated ß1-integrins. In vivo studies and ex-vivo live imaging revealed that double mutants for Itgb1 and Edn3 displayed a more severe enteric phenotype than either of the single mutants demonstrated by alteration of the ENS network due to severe migratory defects of mutant ENCCs taking place early during the ENS development. Altogether, our results highlight the interplay between the EDN3 and ß1-integrin signalling pathways during ENS ontogenesis and the role of EDN3 in ENCC adhesion.

Mouse models of Hirschsprung disease and other developmental disorders of the enteric nervous system: Old and new players.

Hirschsprung disease (HSCR, intestinal aganglionosis) is a multigenic disorder with variable penetrance and severity that has a general population incidence of 1/5000 live births. Studies using animal models have contributed to our understanding of the developmental origins of HSCR and the genetic complexity of this disease. This review summarizes recent progress in understanding control of enteric nervous system (ENS) development through analyses in mouse models. An overview of signaling pathways that have long been known to control the migration, proliferation and differentiation of enteric neural progenitors into and along the developing gut is provided as a framework for the latest information on factors that influence enteric ganglia formation and maintenance. Newly identified genes and additional factors beyond discrete genes that contribute to ENS pathology including regulatory sequences, miRNAs and environmental factors are also introduced. Finally, because HSCR has become a paradigm for complex oligogenic diseases with non-Mendelian inheritance, the importance of gene interactions, modifier genes, and initial studies on genetic background effects are outlined.

White paper on guidelines concerning enteric nervous system stem cell therapy for enteric neuropathies.

Over the last 20 years, there has been increasing focus on the development of novel stem cell based therapies for the treatment of disorders and diseases affecting the enteric nervous system (ENS) of the gastrointestinal tract (so-called enteric neuropathies). Here, the idea is that ENS progenitor/stem cells could be transplanted into the gut wall to replace the damaged or absent neurons and glia of the ENS. This White Paper sets out experts' views on the commonly used methods and approaches to identify, isolate, purify, expand and optimize ENS stem cells, transplant them into the bowel, and assess transplant success, including restoration of gut function. We also highlight obstacles that must be overcome in order to progress from successful preclinical studies in animal models to ENS stem cell therapies in the clinic.

Subnuclear re-localization of SOX10 and p54NRB correlates with a unique neurological phenotype associated with SOX10 missense mutations.

SOX10 is a transcription factor with well-known functions in neural crest and oligodendrocyte development. Mutations in SOX10 were first associated with Waardenburg-Hirschsprung disease (WS4; deafness, pigmentation defects and intestinal aganglionosis). However, variable phenotypes that extend beyond the WS4 definition are now reported. The neurological phenotypes associated with some truncating mutations are suggested to be the result of escape from the nonsense-mediated mRNA decay pathway; but, to date, no mechanism has been suggested for missense mutations, of which approximately 20 have now been reported, with about half of the latter shown to be redistributed to nuclear bodies of undetermined nature and function in vitro. Here, we report that p54NRB, which plays a crucial role in the regulation of gene expression during many cellular processes including differentiation, interacts synergistically with SOX10 to regulate several target genes. Interestingly, this paraspeckle protein, as well as two other members of the Drosophila behavior human splicing (DBHS) protein family, co-localize with SOX10 mutants in nuclear bodies, suggesting the possible paraspeckle nature of these foci or re-localization of the DBHS members to other subnuclear compartments. Remarkably, the co-transfection of wild-type and mutant SOX10 constructs led to the sequestration of wild-type protein in mutant-induced foci. In contrast to mutants presenting with additional cytoplasmic re-localization, those exclusively found in the nucleus alter synergistic activity between SOX10 and p54NRB. We propose that such a dominant negative effect may contribute to or be at the origin of the unique progressive and severe neurological phenotype observed in affected patients.

Phenotypic similarities and differences in patients with a p.Met112Ile mutation in SOX10.

Waardenburg syndrome (WS) is characterized by an association of pigmentation abnormalities and sensorineural hearing loss. Four types, defined on clinical grounds, have been delineated, but this phenotypic classification correlates imperfectly with known molecular anomalies. SOX10 mutations have been found in patients with type II and type IV WS (i.e., with Hirschsprung disease), more complex syndromes, and partial forms of the disease. The phenotype induced by SOX10 mutations is highly variable and, except for the neurological forms of the disease, no genotype-phenotype correlation has been characterized to date. There is no mutation hotspot in SOX10 and most cases are sporadic, making it particularly difficult to correlate the phenotypic and genetic variability. This study reports on three independent families with SOX10 mutations predicted to result in the same missense mutation at the protein level (p.Met112Ile), offering a rare opportunity to improve our understanding of the mechanisms underlying phenotypic variability. The pigmentation defects of these patients are very similar, and the neurological symptoms showed a somewhat similar evolution over time, indicating a potential partial genotype-phenotype correlation. However, variability in gastrointestinal symptoms suggests that other genetic factors contribute to the expression of these phenotypes. No correlation between the rs2435357 polymorphism of RET and the expression of Hirschsprung disease was found. In addition, one of the patients has esophageal achalasia, which has rarely been described in WS.

An impairment of long distance SOX10 regulatory elements underlies isolated Hirschsprung disease.

A deletion encompassing several SOX10 enhancers was recently identified in a patient presenting with Waardenburg syndrome type 4 (WS4), which is defined as a combination of Hirschsprung disease (HSCR, intestinal aganglionosis) and WS (deafness and pigmentation defects). The expression patterns of some of the known SOX10 enhancers in animal models led to the speculation that endophenotypes of WS4 may be linked to mutations within some of these sequences. The present study investigated deletions and point mutations within four SOX10 enhancers in 144 unexplained isolated HSCR cases. One deletion and two point mutations affecting binding sites for known neural crest transcription factors were identified. In vitro functional analysis revealed that the first point mutation disrupts autoregulation by SOX10, whereas the second affects AP2a and SOX10 synergistic activity. The present findings suggest that the mutations within SOX10 enhancers contribute to isolated HSCR.

Loss-of-function mutations in SOX10 cause Kallmann syndrome with deafness.

Transcription factor SOX10 plays a role in the maintenance of progenitor cell multipotency, lineage specification, and cell differentiation and is a major actor in the development of the neural crest. It has been implicated in Waardenburg syndrome (WS), a rare disorder characterized by the association between pigmentation abnormalities and deafness, but SOX10 mutations cause a variable phenotype that spreads over the initial limits of the syndrome definition. On the basis of recent findings of olfactory-bulb agenesis in WS individuals, we suspected SOX10 was also involved in Kallmann syndrome (KS). KS is defined by the association between anosmia and hypogonadotropic hypogonadism due to incomplete migration of neuroendocrine gonadotropin-releasing hormone (GnRH) cells along the olfactory, vomeronasal, and terminal nerves. Mutations in any of the nine genes identified to date account for only 30% of the KS cases. KS can be either isolated or associated with a variety of other symptoms, including deafness. This study reports SOX10 loss-of-function mutations in approximately one-third of KS individuals with deafness, indicating a substantial involvement in this clinical condition. Study of SOX10-null mutant mice revealed a developmental role of SOX10 in a subpopulation of glial cells called olfactory ensheathing cells. These mice indeed showed an almost complete absence of these cells along the olfactory nerve pathway, as well as defasciculation and misrouting of the nerve fibers, impaired migration of GnRH cells, and disorganization of the olfactory nerve layer of the olfactory bulbs.

Chromosome 21 scan in Down syndrome reveals DSCAM as a predisposing locus in Hirschsprung disease.

Hirschsprung disease (HSCR) genetics is a paradigm for the study and understanding of multigenic disorders. Association between Down syndrome and HSCR suggests that genetic factors that predispose to HSCR map to chromosome 21. To identify these additional factors, we performed a dose-dependent association study on chromosome 21 in Down syndrome patients with HSCR. Assessing 10,895 SNPs in 26 Caucasian cases and their parents led to identify two associated SNPs (rs2837770 and rs8134673) at chromosome-wide level. Those SNPs, which were located in intron 3 of the DSCAM gene within a 19 kb-linkage disequilibrium block region were in complete association and are consistent with DSCAM expression during enteric nervous system development. We replicated the association of HSCR with this region in an independent sample of 220 non-syndromic HSCR Caucasian patients and their parents. At last, we provide the functional rationale to the involvement of DSCAM by network analysis and assessment of SOX10 regulation. Our results reveal the involvement of DSCAM as a HSCR susceptibility locus, both in Down syndrome and HSCR isolated cases. This study further ascertains the chromosome-scan dose-dependent methodology used herein as a mean to map the genetic bases of other sub-phenotypes both in Down syndrome and other aneuploidies.

The role of SOX10 during enteric nervous system development.

The SOX10 transcription factor is a characteristic marker for migratory multipotent neural crest (NC) progenitors as well as several of their differentiated derivatives. The involvement of SOX10 in Waardenburg-Hirschsprung disease (pigmentation defects, deafness and intestinal aganglionosis) and studies of mutant animal models have contributed significantly to the understanding of its function in neural crest cells (NCC) in general and in the melanocytes and enteric nervous system (ENS) in particular. Cell-based studies have further demonstrated the important roles of this transcription factor in maintaining the NC progenitor cell number and in determining glial cell fate. Phenotypic variability observed among patients presenting with SOX10 mutations is in agreement with molecular genetics and animal model studies, which revealed that SOX10 cooperates with different partner factors; a number of genetic modifiers of SOX10 have been identified. This study reviews the expression, regulation, and function of SOX10 in normal development of the ENS and in disease conditions, as well as the genetic and molecular interactions of SOX10 with other ENS genes/factors. We also discuss future research areas. Further understanding of SOX10 function will benefit from genomic and cell biological studies that integrate the cell-intrinsic molecular mechanisms and the interactions of the enteric NCC with the niche environment.

Sox10 and Itgb1 interaction in enteric neural crest cell migration.

SOX10 involvement in syndromic form of Hirschsprung disease (intestinal aganglionosis, HSCR) in humans as well as developmental defects in animal models highlight the importance of this transcription factor in control of the pool of enteric progenitors and their differentiation. Here, we characterized the role of SOX10 in cell migration and its interactions with ß1-integrins. To this end, we crossed the Sox10(lacZ/+) mice with the conditional Ht-PA::Cre; beta1(neo/+) and beta1(fl/fl) mice and compared the phenotype of embryos of different genotypes during enteric nervous system (ENS) development. The Sox10(lacZ/+); Ht-PA::Cre; beta1(neo/fl) double mutant embryos presented with increased intestinal aganglionosis length and more severe neuronal network disorganization compared to single mutants. These defects, detected by E11.5, are not compensated after birth, showing that a coordinated and balanced interaction between these two genes is required for normal ENS development. Use of video-microscopy revealed that defects observed result from reduced migration speed and altered directionality of enteric neural crest cells. Expression of ß1-integrins upon SOX10 overexpression or in Sox10(lacZ/+) mice was also analyzed. The modulation of SOX10 expression altered ß1-integrins, suggesting that SOX10 levels are critical for proper expression and function of this adhesion molecule. Together with previous studies, our results strongly indicate that SOX10 mediates ENCC adhesion and migration, and contribute to the understanding of the molecular and cellular basis of ENS defects observed both in mutant mouse models and in patients carrying SOX10 mutations.