Mutations in SIP1, encoding Smad interacting protein-1, cause a form of Hirschsprung disease

miR-200b regulates cell migration via Zeb family during mouse palate development

Palate development requires coordinating proper cellular and molecular events in palatogenesis, including the epithelial-mesenchymal transition (EMT), apoptosis, cell proliferation, and cell migration. Zeb1 and Zeb2 regulate epithelial cadherin (E-cadherin) and EMT during organogenesis. While microRNA 200b (miR-200b) is known to be a negative regulator of Zeb1 and Zeb2 in cancer progression, its regulatory effects on Zeb1 and Zeb2 in palatogenesis have not yet been clarified. The aim of this study is to investigate the relationship between the regulators of palatal development, specifically, miR-200b and the Zeb family. Expression of both Zeb1 and Zeb2 was detected in the mesenchyme of the mouse palate, while miR-200b was expressed in the medial edge epithelium. After contact with the palatal shelves, miR-200b was expressed in the palatal epithelial lining and epithelial island around the fusion region but not in the palatal mesenchyme. The function of miR-200b was examined by overexpression via a lentiviral vector in the palatal shelves. Ectopic expression of miR-200b resulted in suppression of the Zeb family, upregulation of E-cadherin, and changes in cell migration and palatal fusion. These results suggest that miR-200b plays crucial roles in cell migration and palatal fusion by regulating Zeb1 and Zeb2 as a noncoding RNA during palate development.

Genetics of human enteric neuropathies

Knowledge of molecular mechanisms that underlie development of the enteric nervous system has greatly expanded in recent decades. Enteric neuropathies related to aberrant genetic development are thus becoming increasingly recognized. There has been no recent review of these often highly morbid disorders. This review highlights advances in knowledge of the molecular pathogenesis of these disorders from a clinical perspective. It includes diseases characterized by an infantile aganglionic Hirschsprung phenotype and those in which structural abnormalities are less pronounced. The implications for diagnosis, screening and possible reparative approaches are presented.

The behavioral phenotype of Mowat-Wilson syndrome

Mowat-Wilson syndrome (MWS) is caused by a heterozygous mutation or deletion of the ZEB2 gene. It is characterized by a distinctive facial appearance in association with intellectual disability (ID) and variable other features including agenesis of the corpus callosum, seizures, congenital heart defects, microcephaly, short stature, hypotonia, and Hirschsprung disease. The current study investigated the behavioral phenotype of MWS. Parents and carers of 61 individuals with MWS completed the Developmental Behavior Checklist. Data were compared with those for individuals selected from an epidemiological sample of people with ID from other causes. The behaviors associated with MWS included a high rate of oral behaviors, an increased rate of repetitive behaviors, and an under-reaction to pain. Other aspects of the MWS behavioral phenotype are suggestive of a happy affect and sociable demeanor. Despite this, those with MWS displayed similarly high levels of behavioral problems as those with intellectual disabilities from other causes, with over 30% showing clinically significant levels of behavioral or emotional disturbance. These findings have the potential to expand our knowledge of the role of the ZEB2 gene during neurodevelopment. Furthermore, they are a foundation for informing interventions and management options to enhance the independence and quality of life for persons with MWS.

Downregulation of Notch-1/Jagged-2 in human colon tissues from Hirschsprung disease patients

PURPOSE

Recent studies have shown that the Notch pathways play important roles in the differentiation and development of neurons. Hirschsprung disease (HSCR) is characterized by the absence of intramural ganglion cells in the nerve plexuses of the distal gut. However, putative Notch function in enteric nervous system (ENS) development and the etiology of HSCR is unknown.

MATERIALS AND METHODS

The aganglionosis segments of 30 HSCR patients were introduced to investigate the expression pattern of Notch-1 and Jagged-2 using immunohistochemical staining, reverse transcriptase polymerase chain reaction (RT-PCR), and Western blot analysis.

RESULTS

Intensive Notch-1 and Jagged-2 staining was detected in the submucosal and the myenteric plexuses in normal or oligoganglionosis segments. Aganglionosis segments from HSCR patients contained no plexuses and thus not labeled with Notch-1 and Jagged-2. Western blot analysis revealed reduced Notch-1 and Jagged-2 protein levels, and RT-PCR revealed reduced Notch-1 and Jagged-2 mRNA in the aganglionosis segments of HSCR patients.

CONCLUSIONS

This study is the first illustration of Notch-1 and Jagged-2 expression in human tissues from non-cancerous disease and sets up the base for further investigations of Notch function in ENS development and intestinal motility.

Genetic interactions and modifier genes in Hirschsprung's disease

Hirschsprung’s disease is a congenital disorder that occurs in 1:5000 live births. It is characterised by an absence of enteric neurons along a variable region of the gastrointestinal tract. Hirschsprung’s disease is classified as a multigenic disorder, because the same phenotype is associated with mutations in multiple distinct genes. Furthermore, the genetics of Hirschsprung’s disease are highly complex and not strictly Mendelian. The phenotypic variability and incomplete penetrance observed in Hirschsprung’s disease also suggests the involvement of modifier genes. Here, we summarise the current knowledge of the genetics underlying Hirschsprung’s disease based on human and animal studies, focusing on the principal causative genes, their interactions, and the role of modifier genes.

Few Smad proteins and many Smad-interacting proteins yield multiple functions and action modes in TGFβ/BMP signaling in vivo

Signaling by the many ligands of the TGFβ family strongly converges towards only five receptor-activated, intracellular Smad proteins, which fall into two classes i.e. Smad2/3 and Smad1/5/8, respectively. These Smads bind to a surprisingly high number of Smad-interacting proteins (SIPs), many of which are transcription factors (TFs) that co-operate in Smad-controlled target gene transcription in a cell type and context specific manner. A combination of functional analyses in vivo as well as in cell cultures and biochemical studies has revealed the enormous versatility of the Smad proteins. Smads and their SIPs regulate diverse molecular and cellular processes and are also directly relevant to development and disease. In this survey, we selected appropriate examples on the BMP-Smads, with emphasis on Smad1 and Smad5, and on a number of SIPs, i.e. the CPSF subunit Smicl, Ttrap (Tdp2) and Sip1 (Zeb2, Zfhx1b) from our own research carried out in three different vertebrate models.

Copy number variants in candidate genes are genetic modifiers of Hirschsprung disease

Hirschsprung disease (HSCR) is a neurocristopathy characterized by absence of intramural ganglion cells along variable lengths of the gastrointestinal tract. The HSCR phenotype is highly variable with respect to gender, length of aganglionosis, familiality and the presence of additional anomalies. By molecular genetic analysis, a minimum of 11 neuro-developmental genes (RET, GDNF, NRTN, SOX10, EDNRB, EDN3, ECE1, ZFHX1B, PHOX2B, KIAA1279, TCF4) are known to harbor rare, high-penetrance mutations that confer a large risk to the bearer. In addition, two other genes (RET, NRG1) harbor common, low-penetrance polymorphisms that contribute only partially to risk and can act as genetic modifiers. To broaden this search, we examined whether a set of 67 proven and candidate HSCR genes harbored additional modifier alleles. In this pilot study, we utilized a custom-designed array CGH with ∼33,000 test probes at an average resolution of ∼185 bp to detect gene-sized or smaller copy number variants (CNVs) within these 67 genes in 18 heterogeneous HSCR patients. Using stringent criteria, we identified CNVs at three loci (MAPK10, ZFHX1B, SOX2) that are novel, involve regulatory and coding sequences of neuro-developmental genes, and show association with HSCR in combination with other congenital anomalies. Additional CNVs are observed under relaxed criteria. Our research suggests a role for CNVs in HSCR and, importantly, emphasizes the role of variation in regulatory sequences. A much larger study will be necessary both for replication and for identifying the full spectrum of small CNV effects.

Hepatocyte-derived Snail1 propagates liver fibrosis progression

Chronic exposure of the liver to hepatotoxic agents initiates an aberrant wound healing response marked by proinflammatory, as well as fibrotic, changes, leading to compromised organ structure and function. In a variety of pathological states, correlative links have been established between tissue fibrosis and the expression of transcription factors associated with the induction of epithelial-mesenchymal cell transition (EMT) programs similar to those engaged during development. However, the role played by endogenously derived, EMT-associated transcription factors in fibrotic states in vivo remains undefined. Using a mouse model of acute liver fibrosis, we demonstrate that hepatocytes upregulate the expression of the zinc finger transcriptional repressor, Snail1, during tissue remodeling. Hepatocyte-specific ablation of Snail1 demonstrates that this transcription factor plays a key role in liver fibrosis progression in vivo by triggering the proximal genetic programs that control multiple aspects of fibrogenesis, ranging from growth factor expression and extracellular matrix biosynthesis to the ensuing chronic inflammatory responses that characterize this class of pathological disorders.

Fine mapping of the NRG1 Hirschsprung's disease locus

The primary pathology of Hirschsprung's disease (HSCR, colon aganglionosis) is the absence of ganglia in variable lengths of the hindgut, resulting in functional obstruction. HSCR is attributed to a failure of migration of the enteric ganglion precursors along the developing gut. RET is a key regulator of the development of the enteric nervous system (ENS) and the major HSCR-causing gene. Yet the reduced penetrance of RET DNA HSCR-associated variants together with the phenotypic variability suggest the involvement of additional genes in the disease. Through a genome-wide association study, we uncovered a ∼350 kb HSCR-associated region encompassing part of the neuregulin-1 gene (NRG1). To identify the causal NRG1 variants contributing to HSCR, we genotyped 243 SNPs variants on 343 ethnic Chinese HSCR patients and 359 controls. Genotype analysis coupled with imputation narrowed down the HSCR-associated region to 21 kb, with four of the most associated SNPs (rs10088313, rs10094655, rs4624987, and rs3884552) mapping to the NRG1 promoter. We investigated whether there was correlation between the genotype at the rs10088313 locus and the amount of NRG1 expressed in human gut tissues (40 patients and 21 controls) and found differences in expression as a function of genotype. We also found significant differences in NRG1 expression levels between diseased and control individuals bearing the same rs10088313 risk genotype. This indicates that the effects of NRG1 common variants are likely to depend on other alleles or epigenetic factors present in the patients and would account for the variability in the genetic predisposition to HSCR.

Bone morphogenetic proteins regulate enteric gliogenesis by modulating ErbB3 signaling

The neural crest-derived cell population that colonizes the bowel (ENCDC) contains proliferating neural/glial progenitors. We tested the hypothesis that bone morphogenetic proteins (BMPs 2 and 4), which are known to promote enteric neuronal differentiation at the expense of proliferation, function similarly in gliogenesis. Enteric gliogenesis was analyzed in mice that overexpress the BMP antagonist, noggin, or BMP4 in the primordial ENS. Noggin-induced loss-of-function decreased, while BMP4-induced gain-of-function increased the glial density and glia/neuron ratio. When added to immunoisolated ENCDC, BMPs provoked nuclear translocation of phosphorylated SMAD proteins and enhanced both glial differentiation and expression of the neuregulin receptor ErbB3. ErbB3 transcripts were detected in E12 rat gut, before glial markers are expressed; moreover, expression of the ErbB3 ligand, glial growth factor 2 (GGF2) escalated rapidly after its first detection at E14. ErbB3-immunoreactive cells were located in the ENS of fetal and adult mice. GGF2 stimulated gliogenesis and proliferation and inhibited glial cell derived neurotrophic factor (GDNF)-promoted neurogenesis. Enhanced glial apoptosis occurred following GGF2 withdrawal; BMPs intensified this GGF2-dependence and reduced GGF2-stimulated proliferation. These observations support the hypotheses that BMPs are required for enteric gliogenesis and act by promoting responsiveness of ENCDC to ErbB3 ligands such as GGF2.

Analyses of PRMT1 proteins in human colon tissues from Hirschsprung disease patients

BACKGROUND

Protein arginine methyltransferase 1 (PRMT1) catalyzes the majority of arginine methylation in cells and plays important roles in the differentiation and development of neurons. It is also implicated in the regulation of nitric oxide synthetase (NOS). Hirschsprung disease (HSCR) is characterized by the absence of intramural ganglion cells in the nerve plexuses of the distal gut.

METHODS

Western blot analyses revealed reduced PRMT1 protein levels in the aganglionosis segments of HSCR patients. Immunohistochemistry detected PRMT1 expression in the colonic mucosa, the enteric nervous system (ENS) and endothelial cells. Specific and strong PRMT1 expression in neuron cell bodies of the plexus was demonstrated by immunofluorescent double-labeling with neuron-specific marker HuC/D.

KEY RESULTS

In the mucosa, PRMT1 was detected at all crypt cells. Intensive PRMT1 staining was detected in the submucosal and the myenteric plexuses in normal or oligoganglionosis segments. Aganglionosis segments from HSCR patients contain no plexuses, and thus not labeled with PRMT1. The phenomenon is specific to the megacolon of HSCR as strong PRMT1 staining was observed in plexuses of the rectal ectasia segments (dilated rectum and distal sigmoid not related with aganglionosis) from anorectal malformation patients. Furthermore, PRMT1 was also present in the same neuronal cells expressing neuronal NOS in the plexuses.

CONCLUSIONS & INFERENCES

We suggest that PRMT1 can be a useful marker for HSCR. This study is the first illustration of PRMT1 protein expression in human tissues from non-cancerous disease and set up the base for further investigations of PRMT1 function in ENS development and intestinal motility.

Severe clinical course of Hirschsprung disease in a Mowat-Wilson syndrome patient

We present a clinical case of a female infant with multiple anomalies and distinctive facial features, with an exceptionally severe clinical course of Hirschsprung disease. The girl was also diagnosed with Mowat-Wilson syndrome, confirmed by molecular analysis as a heterozygous deletion of the ZEB2 gene. Moreover, molecular karyotyping revealed a deletion involving further genes (KYNU, ARHGAP15, and GTDC1).

Genetics of Hirschsprung disease and anorectal malformations

Hirschsprung disease (HD) and anorectal malformations (ARMs) result from alterations in hindgut development. It has long been recognized that both recur in families and thus result, at least in part, from genetic factors. Progress in the understanding of the genetic basis of HD has been made by the application of findings from genetic animal models of altered enteric nervous system development to human beings. Several genes have been shown to be important for human enteric nervous system development, and current work is progressing to identify genetic interactions that may explain the variable phenotype of HD. By contrast, understanding of the genetic factors underlying ARMs is much less developed. We and others have shown that genetic factors play an important role in the pathogenesis of ARMs, and many mouse genetic models suggest molecular pathways that may be altered in ARMs.

A survey of well conserved families of C2H2 zinc-finger genes in Daphnia

Background

A recent comparative genomic analysis tentatively identified roughly 40 orthologous groups of C2H2 Zinc-finger proteins that are well conserved in "bilaterians" (i.e. worms, flies, and humans). Here we extend that analysis to include a second arthropod genome from the crustacean, Daphnia pulex.

Results

Most of the 40 orthologous groups of C2H2 zinc-finger proteins are represented by just one or two proteins within each of the previously surveyed species. Likewise, Daphnia were found to possess a similar number of orthologs for all of these small orthology groups. In contrast, the number of Sp/KLF homologs tends to be greater and to vary between species. Like the corresponding mammalian Sp/KLF proteins, most of the Drosophila and Daphnia homologs can be placed into one of three sub-groups: Class I-III. Daphnia were found to have three Class I proteins that roughly correspond to their Drosophila counterparts, dSP1, btd, CG5669, and three Class II proteins that roughly correspond to Luna, CG12029, CG9895. However, Daphnia have four additional KLF-Class II proteins that are most similar to the vertebrate KLF1/2/4 proteins, a subset not found in Drosophila. Two of these four proteins are encoded by genes linked in tandem. Daphnia also have three KLF-Class III members, one more than Drosophila. One of these is a likely Bteb2 homolog, while the other two correspond to Cabot and KLF13, a vertebrate homolog of Cabot.

Conclusion

Consistent with their likely roles as fundamental determinants of bilaterian form and function, most of the 40 groups of C2H2 zinc-finger proteins are conserved in kind and number in Daphnia. However, the KLF family includes several additional genes that are most similar to genes present in vertebrates but missing in Drosophila.

Fine mapping of the 9q31 Hirschsprung's disease locus

Hirschsprung’s disease (HSCR) is a congenital disorder characterised by the absence of ganglia along variable lengths of the intestine. The RET gene is the major HSCR gene. Reduced penetrance of RET mutations and phenotypic variability suggest the involvement of additional modifying genes in the disease. A RET-dependent modifier locus was mapped to 9q31 in families bearing no coding sequence (CDS) RET mutations. Yet, the 9q31 causative locus is to be identified. To fine-map the 9q31 region, we genotyped 301 tag-SNPs spanning 7 Mb on 137 HSCR Dutch trios. This revealed two HSCR-associated regions that were further investigated in 173 Chinese HSCR patients and 436 controls using the genotype data obtained from a genome-wide association study recently conducted. Within one of the two identified regions SVEP1 SNPs were found associated with Dutch HSCR patients in the absence of RET mutations. This ratifies the reported linkage to the 9q31 region in HSCR families with no RET CDS mutations. However, this finding could not be replicated. In Chinese, HSCR was found associated with IKBKAP. In contrast, this association was stronger in patients carrying RET CDS mutations with p = 5.10 × 10⁻⁶ [OR = 3.32 (1.99, 5.59)] after replication. The HSCR-association found for IKBKAP in Chinese suggests population specificity and implies that RET mutation carriers may have an additional risk. Our finding is supported by the role of IKBKAP in the development of the nervous system.

Genetic interaction between Sox10 and Zfhx1b during enteric nervous system development

The involvement of SOX10 and ZFHX1B in Waardenburg-Hirschsprung disease (hypopigmentation, deafness, and absence of enteric ganglia) and Mowat-Wilson syndrome (mental retardation, facial dysmorphy and variable congenital malformations including Hirschsprung disease) respectively, highlighted the importance of both transcription factors during enteric nervous system (ENS) development. The expression and function of SOX10 are now well established, but those of ZFHX1B remain elusive. Here we describe the expression profile of Zfhx1b and its genetic interactions with Sox10 during mouse ENS development. Through phenotype analysis of Sox10;Zfhx1b double mutants, we show that a coordinated and balanced interaction between these two genes is required for normal ENS development. Double mutants present with more severe ENS defects due to decreased proliferation of enteric progenitors and increased neuronal differentiation from E11.5 onwards. Thus, joint activity between these two transcription factors is crucial for proper ENS development and our results contribute to the understanding of the molecular basis of ENS defects observed both in mutant mouse models and in patients carrying SOX10 and ZFHX1B mutations.

[Mowat-Wilson syndrome--a case report]

INTRODUCTION

Mowat-Wilson syndrome (MWS) is characterised by severe mental retardation and multiple congenital anomalies. Key features for diagnosis are specific facial dysmorphism with uplifted ear lobes and Hirschsprung's disease. Ganglionic disorders of the colon, both the number of ganglion cells and the length of the aganglionic segment vary significantly in these patients. The disease is caused by ZFHX1B gene mutation. The management of MWS is symptomatic.

CASE OUTLINE

We report a four-year-old boy with mental retardation, specific facial dysmorphy and multiple anomalies. During prenatal follow-up intrauterine growth retardation was revealed. Karyotype was normal. Clinical findings showed that growth and mental retardation, gastrointestinal disturbance and heart defect were predominant. A gastrostoma was inserted. Hypoganglionosis of the colon caused severe obstipation. He had a severe stenosis of the pulmonary artery and was a candidate for cardiac surgery. There were several attempts to establish diagnosis, but so far, without results

CONCLUSION

Hirschsprung's disease/hypoganglionosis of the colon associated with other congenital anomalies or mental retardation require evaluation for dysmorphic syndromes. One of them is MWS, presented in this report.

Genetic basis of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder characterized by the absence of ganglion cells in the lower digestive tract. Aganglionosis is attributed to a disorder of the enteric nervous system (ENS) whereby ganglion cells fail to innervate the lower gastrointestinal tract during embryonic development. HSCR is a complex disease that results from the interaction of several genes and manifests with low, sex-dependent penetrance and variability in the length of the aganglionic segment. The genetic complexity observed in HSCR can be conceptually understood in light of the molecular and cellular events that take place during the ENS development. DNA alterations in any of the genes involved in the ENS development may interfere with the colonization process, and represent a primary etiology for HSCR. This review will focus on the genes known to be involved in HSCR pathology, how they interact, and on how technology advances are being employed to uncover the pathological processes underlying this disease.

Regulation of Epithelial-Mesenchymal Transition in Palatal Fusion

During palatal fusion, the midline epithelial seam between the palatal shelves degrades to achieve mesenchymal confluence. Morphological and molecular evidence support the theory that the epithelial-mesenchymal transition is one mechanism that regulates palatal fusion. It appears that transforming growth factor (TGF)-β signaling plays a role in palatal EMT. TGFβ3 is the main inducer in palatal fusion and activates both Smad-dependent and -independent signaling pathways, including the key EMT transcription factors, Lef1, Twist, and Snail1, in the MEE prior to the palatal EMT program. The roles and interactions among these transcription factors will be discussed.

Balanced translocations in mental retardation

Over the past few decades, the knowledge on genetic defects causing mental retardation has dramatically increased. In this review, we discuss the importance of balanced chromosomal translocations in the identification of genes responsible for mental retardation. We present a database-search guided overview of balanced translocations identified in patients with mental retardation. We divide those in four categories: (1) balanced translocations that helped to identify a causative gene within a contiguous gene syndrome, (2) balanced translocations that led to the identification of a mental retardation gene confirmed by independent methods, (3) balanced translocations disrupting candidate genes that have not been confirmed by independent methods and (4) balanced translocations not reported to disrupt protein coding sequences. It can safely be concluded that balanced translocations have been instrumental in the identification of multiple genes that are involved in mental retardation. In addition, many more candidate genes were identified with a suspected but (as yet?) unconfirmed role in mental retardation. Some balanced translocations do not disrupt a protein coding gene and it can be speculated that in the light of recent findings concerning ncRNA's and ultra-conserved regions, such findings are worth further investigation as these potentially may lead us to the discovery of novel disease mechanisms.

Outcomes of Hirschsprung's disease associated with Mowat-Wilson syndrome

PURPOSE

Mowat-Wilson syndrome (MWS) is a developmental disorder presenting with mental retardation, delayed motor development, and a wide spectrum of clinical features. Hirschsprung's disease (HD) is associated in almost 50% of cases. This report aims to analyze the course of HD and to evaluate the clinical outcomes of these patients.

PATIENTS AND METHODS

Between 1997 and 2007, 110 patients presenting with HD were diagnosed and managed in our institution. Five of them presented the association of HD and MWS. Their records were reviewed retrospectively.

RESULTS

All of the 5 patients have a genetic disorder specific of MWS (nonsense mutation or deletion on SIP1 gene, locus 2q22). Two patients underwent transanal endorectal pull-through procedure for classic rectosigmoid HD. Three patients were operated on for total colonic aganglionosis using Duhamel procedure. The median follow-up was 4 (range, 0.3-7) years. Only one patient is doing well (rectosigmoid HD). Two patients have a stoma diversion for severe motility disorders. Of the 3 total colonic aganglionosis, one still has repeated episodes of obstruction requiring total parenteral nutrition (TPN). The 2 others still have repeated episodes of enterocolitis. All patients required a prolonged TPN (32.5 months in average).

CONCLUSION

Hirschsprung's disease associated with MWS is a severe condition. Even in case of short segment HD, patients can present motility disorder requiring a prolonged TPN. Physician and surgeon should be aware about the evolution of this rare condition.

Polymorphisms in the genes encoding the 4 RET ligands, GDNF, NTN, ARTN, PSPN, and susceptibility to Hirschsprung disease

PURPOSE

Hirschsprung disease (HSCR) is a developmental disorder caused by a failure of neural crest cells to migrate, proliferate, and/or differentiate during the enteric nervous system development. It presents a multifactorial, nonmendelian pattern of inheritance, with several genes playing some role in its pathogenesis. Its major susceptibility gene is the RET protooncogene, which encodes a receptor tyrosine kinase activating several key signaling pathways in the enteric nervous system development. Given the pivotal role of RET in HSCR, the genes encoding their ligands (GDNF, NRTN, ARTN, and PSPN) are also good candidates for the disease.

METHODS

We have performed a case-control study using Taqman technology to evaluate 10 polymorphisms within these genes, as well as haplotypes comprising them, as susceptibility factors for HSCR.

RESULTS

No differences were found in the allelic frequencies of the variants or in the haplotype distribution between patients and controls. In addition, no particular association was detected of the variants/haplotypes to any demographic/clinical parameters within the group of patients.

CONCLUSION

These data would be consistent with the lack of association between these polymorphisms and HSCR, although they do not permit to completely discard a possible role of other variants within these genes in the disease. Moreover, because the gene-by-gene approach does not take into account the polygenic nature of HSCR disease, it would be interesting to investigate sets of variants in many other different susceptibility loci described for HSCR, which may permit to consider possible interactions among susceptibility genes.

Zebrafish sip1a and sip1b are essential for normal axial and neural patterning

Smad-interacting protein-1 (SIP1) has been implicated in the development of Mowat-Wilson syndrome whose patients exhibit Hirschsprung disease, an aganglionosis of the large intestine, as well as other phenotypes. We have identified and cloned two sip1 orthologues in zebrafish. Both sip1 orthologues are expressed maternally and have dynamic zygotic expression patterns that are temporally and spatially distinct. We have investigated the function of both orthologues using translation and splice-blocking morpholino antisense oligonucleotides. Knockdown of the orthologues causes axial and neural patterning defects consistent with the previously described function of SIP1 as an inhibitor of BMP signaling. In addition, knockdown of both genes leads to a significant reduction/loss of the post-otic cranial neural crest. This results in a subsequent absence of neural crest precursors in the posterior pharyngeal arches and a loss of enteric precursors in the intestine.

Mowat-Wilson syndrome: an underdiagnosed syndrome?

Mowat-Wilson syndrome (MWS) is an autosomal dominant developmental disorder with mental retardation and variable multiple congenital abnormalities due to mutations of the ZEB2 (ZFHX1B) gene at 2q22. MWS was first described in 1998 and the causative gene was delineated in 2001. Since then, 115 different mutations of ZEB2 have been published in association with this syndrome in 161 individuals. However, recent reports suggest that due to the variability of the congenital abnormalities, this syndrome may still be underdiagnosed. We report two unrelated patients with MWS where the clinical diagnosis was established only after finding of disruption of the ZEB2 gene by a balanced translocation breakpoint and an interstitial microdeletion, respectively.

Mowat-Wilson syndrome affecting 3 siblings

We herein report 3 cases of Mowat-Wilson syndrome, characterized by distinct facial features, severe psychomotor retardation, and epilepsy, recurring in 3 siblings from the same parents. The proband was a 15-month-old boy, the youngest of 3 children (2 elder sisters), who was referred to our hospital for the treatment of severe seizures. The clinical features and course of these 3 siblings were compatible with those of previously reported Mowat-Wilson syndrome patients, and all siblings had the same E87X nonsense mutation in ZFHX1B, whereas their mother did not show the mutation. Because Mowat-Wilson syndrome has been caused by de novo mutation in ZFHX1B, germ-line mosaicism should be considered if recurrence in siblings is observed.

deltaEF1 and SIP1 are differentially expressed and have overlapping activities during Xenopus embryogenesis

The zinc finger/homeo-domain transcription factor (zfh x 1) family in vertebrates consists of two members, deltaEF1 and SIP1. They have been proposed to display antagonistic activities in the interpretation of Smad-dependent TGFbeta signaling during mesoderm formation. We cloned Xenopus deltaEF1 cDNA, analyzed the expression profile of the gene, and compared the inducing and interacting properties of the protein to that of XSIP1. Whereas XSIP1 RNA is selectively expressed in the early developing nervous system, we show that XdeltaEF1 gene transcription is only activated during neurulation and that its expression is restricted to the paraxial mesoderm. From early tail bud stage, XdeltaEF1 and XSIP1 are coexpressed in migratory cranial neural crest, in the retina, and in the neural tube. Overproduction of XdeltaEF1 in RNA-injected embryos, like that of XSIP1, reduced the expression of BMP-dependent genes but only XSIP1 has the ability to induce neural markers. We find that XdeltaEF1 and XSIP1 can both form complexes, although with different efficiency, with Smad3, with the coactivators p300 and pCAF, and with the corepressor CtBP1. Together, these results indicate that deltaEF1 and SIP1 do not function as antagonists during Xenopus early embryogenesis but do display different repression efficiencies and interaction properties.

Mowat-Wilson syndrome

Mowat-Wilson syndrome (MWS) is a multiple congenital anomaly syndrome characterized by a distinct facial phenotype (high forehead, frontal bossing, large eyebrows, medially flaring and sparse in the middle part, hypertelorism, deep set but large eyes, large and uplifted ear lobes, with a central depression, saddle nose with prominent rounded nasal tip, prominent columella, open mouth, with M-shaped upper lip, frequent smiling, and a prominent but narrow and triangular pointed chin), moderate-to-severe intellectual deficiency, epilepsy and variable congenital malformations including Hirschsprung disease (HSCR), genitourinary anomalies (in particular hypospadias in males), congenital heart defects, agenesis of the corpus callosum and eye anomalies. The prevalence of MWS is currently unknown, but 171 patients have been reported so far. It seems probable that MWS is under-diagnosed, particularly in patients without HSCR. MWS is caused by heterozygous mutations or deletions in the Zinc finger E-box-binding homeobox 2 gene, ZEB2, previously called ZFHX1B (SIP1). To date, over 100 deletions/mutations have been reported in patients with a typical phenotype; they are frequently whole gene deletions or truncating mutations, suggesting that haploinsufficiency is the main pathological mechanism. Studies of genotype-phenotype analysis show that facial gestalt and delayed psychomotor development are constant clinical features, while the frequent and severe congenital malformations are variable. In a small number of patients, unusual mutations can lead to an atypical phenotype. The facial phenotype is particularly important for the initial clinical diagnosis and provides the hallmark warranting ZEB2 mutational analysis, even in the absence of HSCR. The majority of MWS cases reported so far were sporadic, therefore the recurrence risk is low. Nevertheless, rare cases of sibling recurrence have been observed. Congenital malformations and seizures require precocious clinical investigation with intervention of several specialists (including neonatologists and pediatricians). Psychomotor development is delayed in all patients, therefore rehabilitation (physical therapy, psychomotor and speech therapy) should be started as soon as possible.

Signaling by small GTPases in the immune system

The Ras superfamily consists of over 50 low-molecular-weight proteins that cycle between an inactive guanosine diphosphate-bound state and an active guanosine triphosphate (GTP)-bound state. They are involved in a variety of signal transduction pathways that regulate cell growth, intracellular trafficking, cell migration, and apoptosis. Several methods have been devised to measure the activation state of Ras proteins, defined as the percent of Ras molecules in the active GTP-bound state. We have previously developed a quantitative biochemical method that can be applied to animal and human tissues and have used it to measure the activation state of Ras, Rap1, Rheb, and Rho proteins in cultured cells and in animal and human tumors. Ras, Rac, and Rho all play roles in regulating the functions of T and B lymphocytes and dendritic cells, and these proteins are clearly important in maintaining normal immune system function.

Neural crest and the development of the enteric nervous system

The formation of the enteric nervous system (ENS) is a particularly interesting example of the migratory ability of the neural crest and of the complexity of structures to which neural crest cells contribute. The distance that neural crest cells migrate to colonize the entire length of the gastrointestinal tract exceeds that of any other neural crest cell population. Furthermore, this migration takes a long time--over 25% of the gestation period for mice and around 3 weeks in humans. After colonizing the gut, neural crest-derived cells within the gut wall then differentiate into glial cells plus many different types of neurons, and generate the most complex part of the peripheral nervous system.

miR-200b mediates post-transcriptional repression of ZFHX1B

MicroRNAs have important functions during animal development and homeostasis through post-transcriptional regulation of their cognate mRNA targets. ZFHX1B is a transcriptional repressor involved in the TGFbeta signaling pathway and in processes of epithelial to mesenchymal transition via regulation of E-cadherin. We show that Zfhx1b and miR-200b are regionally coexpressed in the adult mouse brain and that miR-200b represses the expression of Zfhx1b via multiple sequence elements present in the 3'-untranslated region. Overexpression of miR-200b leads to repression of endogenous ZFHX1B, and inhibition of miR-200b relieves the repression of ZFHX1B. In accordance with these findings, miR-200b regulates the activity of the E-cadherin promoter.

Smad-interacting protein-1 (Zfhx1b) acts upstream of Wnt signaling in the mouse hippocampus and controls its formation

Smad-interacting protein-1 (Sip1) [Zinc finger homeobox (Zfhx1b)] is a transcription factor implicated in the genesis of Mowat-Wilson syndrome in humans. Sip1 expression in the dorsal telencephalon of mouse embryos was documented from E12.5. We inactivated the gene specifically in cortical precursors. This resulted in the lack of the entire hippocampal formation. Sip1 mutant mice exhibited death of differentiating cells and decreased proliferation in the region of the prospective hippocampus and dentate gyrus. The expression of the Wnt antagonist Sfrp1 was ectopically activated, whereas the activity of the noncanonical Wnt effector, JNK, was down-regulated in the embryonic hippocampus of mutant mice. In cortical cells, Sip1 protein was detected on the promoter of Sfrp1 gene and both genes showed a mutually exclusive pattern of expression suggesting that Sfrp1 expression is negatively regulated by Sip1. Sip1 is therefore essential to the development of the hippocampus and dentate gyrus, and is able to modulate Wnt signaling in these regions.

Enteric nervous system development and Hirschsprung's disease: advances in genetic and stem cell studies

The enteric nervous system (ENS) has been explored by developmental neurobiologists and medical researchers for decades. Whereas developmental biologists have been unravelling the molecular mechanisms underlying the migration, proliferation and differentiation of the neural crest derivatives that give rise to the ENS, human geneticists have been uncovering the genetic basis for diseases of the ENS, notably Hirschsprung's disease. Here we discuss the exciting recent advances, including novel transgenic and genetic tools, a broadening range of model organisms, and the pursuit of ENS stem cells as a therapeutic tool, that are bringing these fields closer together.

miR-200b mediates post-transcriptional repression of ZFHX1B

MicroRNAs have important functions during animal development and homeostasis through post-transcriptional regulation of their cognate mRNA targets. ZFHX1B is a transcriptional repressor involved in the TGFbeta signaling pathway and in processes of epithelial to mesenchymal transition via regulation of E-cadherin. We show that Zfhx1b and miR-200b are regionally coexpressed in the adult mouse brain and that miR-200b represses the expression of Zfhx1b via multiple sequence elements present in the 3'-untranslated region. Overexpression of miR-200b leads to repression of endogenous ZFHX1B, and inhibition of miR-200b relieves the repression of ZFHX1B. In accordance with these findings, miR-200b regulates the activity of the E-cadherin promoter.

Symptomatology, pathophysiology, diagnostic work-up, and treatment of Hirschsprung disease in infancy and childhood

In the majority of infants and children with constipation, no obvious cause can be identified. A rare cause of constipation is Hirschsprung disease (HD). HD is characterized by the absence of ganglion cells from the anorectum for a variable length up to the duodenum. The extent of the aganglionic segment varies, but in most patients the lesion does not extend beyond the rectum and sigmoid colon. This review focuses on the passage of meconium, the recognition of HD, and new insights in its pathophysiology and genetics. The authors also provide a summary of the diagnostic evaluation and treatment of HD in infancy and childhood.

Neural crest-specific removal of Zfhx1b in mouse leads to a wide range of neurocristopathies reminiscent of Mowat-Wilson syndrome

Mowat-Wilson syndrome is a recently delineated autosomal dominant developmental anomaly, whereby heterozygous mutations in the ZFHX1B gene cause mental retardation, delayed motor development, epilepsy and a wide spectrum of clinically heterogeneous features, suggestive of neurocristopathies at the cephalic, cardiac and vagal levels. However, our understanding of the etiology of this condition at the cellular level remains vague. This study presents the Zfhx1b protein expression domain in mouse embryos and correlates this with a novel mouse model involving a conditional mutation in the Zfhx1b gene in neural crest precursor cells. These mutant mice display craniofacial and gastrointestinal malformations that show resemblance to those found in human patients with Mowat-Wilson syndrome. In addition to these clinically recognized alterations, we document developmental defects in the heart, melanoblasts and sympathetic and parasympathetic anlagen. The latter observations in our mouse model for Mowat-Wilson suggest a hitherto unknown role for Zfhx1b in the development of these particular neural crest derivatives, which is a set of observations that should be acknowledged in the clinical management of this genetic disorder.

ZFHX1B mutations in patients with Mowat-Wilson syndrome

Mowat-Wilson syndrome (MWS) is a recently delineated mental retardation (MR)-multiple congenital anomaly syndrome, characterized by typical facies, severe MR, epilepsy, and variable congenital malformations, including Hirschsprung disease (HSCR), genital anomalies, congenital heart disease (CHD), and agenesis of the corpus callosum (ACC). It is caused by de novo heterozygous mutations or deletions of the ZFHX1B gene located at 2q22. ZFHX1B encodes Smad-interacting protein-1 (SMADIP1 or SIP1), a transcriptional corepressor involved in the transforming growth factor-beta signaling pathway. It is a highly evolutionarily conserved gene, widely expressed in embryological development. Over 100 mutations have been described in patients with clinically typical MWS, who almost always have whole gene deletions or truncating mutations (nonsense or frameshift) of ZFHX1B, suggesting that haploinsufficiency is the basis of MWS pathology. No obvious genotype-phenotype correlation could be identified so far, but atypical phenotypes have been reported with missense or splice mutations in the ZFHX1B gene. In this work we describe 40 novel mutations and we summarize the various mutational reports published since the identification of the causative gene.

Haploinsufficiency of TCF4 causes syndromal mental retardation with intermittent hyperventilation (Pitt-Hopkins syndrome)

Pitt-Hopkins syndrome is a rarely reported syndrome of so-far-unknown etiology characterized by mental retardation, wide mouth, and intermittent hyperventilation. By molecular karyotyping with GeneChip Human Mapping 100K SNP arrays, we detected a 1.2-Mb deletion on 18q21.2 in one patient. Sequencing of the TCF4 transcription factor gene, which is contained in the deletion region, in 30 patients with significant phenotypic overlap revealed heterozygous stop, splice, and missense mutations in five further patients with severe mental retardation and remarkable facial resemblance. Thus, we establish the Pitt-Hopkins syndrome as a distinct but probably heterogeneous entity caused by autosomal dominant de novo mutations in TCF4. Because of its phenotypic overlap, Pitt-Hopkins syndrome evolves as an important differential diagnosis to Angelman and Rett syndromes. Both null and missense mutations impaired the interaction of TCF4 with ASCL1 from the PHOX-RET pathway in transactivating an E box-containing reporter construct; therefore, hyperventilation and Hirschsprung disease in patients with Pitt-Hopkins syndrome might be explained by altered development of noradrenergic derivatives.

CHD4/Mi-2beta activity is required for the positioning of the mesoderm/neuroectoderm boundary in Xenopus

Experiments in Xenopus have illustrated the importance of extracellular morphogens for embryonic gene regulation in vertebrates. Much less is known about how induction leads to the correct positioning of boundaries; for example, between germ layers. Here we report that the neuroectoderm/mesoderm boundary is controlled by the chromatin remodeling ATPase CHD4/Mi-2beta. Gain and loss of CHD4 function experiments shifted this boundary along the animal-vegetal axis at gastrulation, leading to excess mesoderm formation at the expense of neuroectoderm, or vice versa. This phenotype results from specific alterations in gene transcription, notably of the neural-promoting gene Sip1 and the mesodermal regulatory gene Xbra. We show that CHD4 suppresses Sip1 transcription by direct binding to the 5' end of the Sip1 gene body. Furthermore, we demonstrate that CHD4 and Sip1 expression levels determine the "ON" threshold for Nodal-dependent but not for eFGF-dependent induction of Xbra transcription. The CHD4/Sip1 epistasis thus constitutes a regulatory module, which balances mesoderm and neuroectoderm formation.

XSip1 neuralizing activity involves the co-repressor CtBP and occurs through BMP dependent and independent mechanisms

The DNA-binding transcription factor Smad-interacting protein-1 (Sip1) (also named Zfhx1b/ZEB2) plays essential roles in vertebrate embryogenesis. In Xenopus, XSip1 is essential at the gastrula stage for neural tissue formation, but the precise molecular mechanisms that underlie this process have not been fully identified yet. Here we show that XSip1 functions as a transcriptional repressor during neural induction. We observed that constitutive activation of BMP signaling prevents neural induction by XSip1 but not the inhibition of several epidermal genes. We provide evidence that XSip1 binds directly to the BMP4 proximal promoter and modulates its activity. Finally, by deletion and mutational analysis, we show that XSip1 possesses multiple repression domains and that CtBPs contribute to its repression activity. Consistent with this, interference with XCtBP function reduced XSip1 neuralizing activity. These results suggest that Sip1 acts in neural tissue formation through direct repression of BMP4 but that BMP-independent mechanisms are involved as well. Our data also provide the first demonstration of the importance of CtBP binding in Sip1 transcriptional activity in vivo.

A 6Mb deletion in band 2q22 due to a complex chromosome rearrangement associated with severe psychomotor retardation, microcephaly and distinctive dysmorphic facial features

High-resolution analyses of complex chromosome rearrangements (CCR) have demonstrated in individuals with abnormal phenotypes that not all seemingly balanced CCRs based on G-banding are completely balanced at breakpoint level. Here we report on an apparently balanced de novo CCR involving chromosomes 2, 3 and 5 present in a 6-month-old girl. She was referred for genetic evaluation because of severe psychomotor retardation, distinctive dysmorphic features and microcephaly. A 1Mb resolution array-CGH analysis of DNA from the patient revealed a deletion of about 6Mb for chromosome 2. FISH analysis showed that the deletion interval found in band 2q22 mapped at the translocation breakpoint, and that the ZFHX1B gene, which is known to be involved in the Mowat-Wilson syndrome, is located within the deletion interval. To our knowledge this is the first case of a complex chromosomal rearrangement associated with Mowat-Wilson syndrome. Our data illustrate the important role for high-resolution investigation of apparently balanced chromosome rearrangements in patients with unexplained psychomotor retardation and/or other clinical features, and should contribute to our understanding of the mechanisms involved in chromosome rearrangement.

A complex additive model of inheritance for Hirschsprung disease is supported by both RET mutations and predisposing RET haplotypes

PURPOSE

The RET proto-oncogene is considered to be the major susceptibility gene involved in Hirschsprung disease. Traditional RET germline mutations account for a small subset of Hirschsprung disease patients, but several studies have shown that there is a specific haplotype of RET associated with the sporadic forms of Hirschsprung disease. We have investigated for RET germline mutations and analyzed the RET haplotypic distribution in carriers versus noncarriers of RET germline mutations.

METHODS

We have screened the coding region of RET in 106 Spanish Hirschsprung disease patients using dHPLC technology. Statistical comparisons of the distribution of RET haplotypes between sporadic patients with and without a RET germline mutation were performed.

RESULTS

Nine novel germline mutations and one previously described were identified. A significant over-transmission of the "Hirschsprung disease haplotype" was detected when comparing transmitted versus nontransmitted alleles in the group of Hirschsprung disease triads without mutation. However, no distortion of the transmission of alleles was found in the group of mutated families.

CONCLUSIONS

These results would be concordant with a complex additive model of inheritance. The whole findings seem to suggest that low-penetrance mutations would be necessary but not sufficient and the additional presence of the "Hirschsprung disease haplotype" could contribute to the manifestation of the disease.

Comorbidity, hospitalization, and medication use and their influence on mental and motor development of young infants with Down syndrome

OBJECTIVE

Young infants with Down syndrome have an increased occurrence of several well-known medical conditions such as congenital heart and gastrointestinal disease. The aim of this study was to establish consequences like hospitalization and medication use rates and to determine their possible influence on early neurodevelopment.

PATIENTS AND METHODS

This study compared 2 years of thyroxine treatment with placebo in 196 neonates with Down syndrome who were included in a previously reported randomized clinical trial. Parents were interviewed about comorbidity, hospitalization, and medication use at random assignment and regularly thereafter. Data were cross-checked with discharge letters when available. The influence of comorbidity on neurodevelopment at 2 years old (Bayley Scales of Infant Development II) was determined by stepwise multiple linear-regression analysis.

RESULTS

Before trial entry, 163 infants with Down syndrome had been admitted to hospital for an average of 14.01 days, whereas during the trial, 95 of 181 infants who completed the trial were hospitalized for an average 19.75 days. Main hospitalization reasons during the trial were lung/airway and congenital heart and gastrointestinal disease. The 48 infants operated on for heart or gastrointestinal disease accounted for 1401 of the total number of 1876 hospital admission days during the trial and for 33 of 62 admissions for lung/airway infection. During their second year of life, approximately 60% of the infants were prescribed drugs, mostly antibiotics and pulmonary. Regression analysis showed infantile spasms, "other" central nervous system disease, and gastrointestinal disease necessitating surgery to be associated with greater developmental age delays at 24 months old (mental: 6.87, 3.52, and 1.69 months; and motor: 3.59, 2.54, and 1.68 months, respectively).

CONCLUSIONS

Hospital admission and medication use rates in young infants with Down syndrome are still very high, mainly because of congenital heart and gastrointestinal disease and acquired respiratory disease. Central nervous system disease and gastrointestinal disease necessitating surgery were independently associated with a worse developmental outcome.

Functional conservation of zinc-finger homeodomain gene zfh1/SIP1 in Drosophila heart development

Comparative genetic studies of diverse animal model systems have revealed that similar developmental mechanisms operate across the Metazoa. In many cases, the genes from one organism can functionally replace homologues in other phyla, a result consistent with a high degree of evolutionarily conserved gene function. We investigated functional conservation among the Drosophila zinc-finger homeodomain protein 1 (zfh1) and its mouse functional homologue Smad-interacting protein 1 (SIP1). Northern blot analyses of SIP1 expression patterns detected three novel variants (8.3, 2.7, and 1.9 kb) in addition to the previously described 5.3 kb SIP1 transcript. The two shorter novel SIP1 transcripts were encountered only in developing embryos and both lacked zinc-finger clusters or homeodomain regions. The SIP1 transcripts showed complex embryonic expression patterns consistent with that observed for Drosophila zfh1. They were highly expressed in the developing nervous systems and in a number of mesoderm-derived tissues including lungs, heart, developing myotomes, skeletal muscle, and visceral smooth muscle. The expression of the mammalian 5.3 kb SIP1 transcript in Drosophila zfh1 null mutant embryos completely restored normal heart development in the fly, demonstrating their functional equivalence in cardiogenic pathways. Our present data, together with the previously described heart defects associated with both SIP1 and Drosophila zfh1 mutations, solidify the conclusion that the zfh1 family members participate in an evolutionary conserved program of metazoan cardiogenesis.

RET receptor signaling: dysfunction in thyroid cancer and Hirschsprung's disease

Gain-of-function mutations within the receptor tyrosine kinase gene RET cause inherited and non-inherited thyroid cancer. Somatic gene rearrangements of RET have been found in papillary thyroid carcinoma and germline point mutations in multiple endocrine neoplasia (MEN) types 2A and 2B and familial medullary thyroid carcinoma (FMTC). Conversely, loss-of-function mutations are responsible for the development of Hirschsprung's disease, a congenital malformation of the enteric nervous system. Comparison between normal RET signaling activated by the RET ligand glial cell line-derived neurotrophic factor (GDNF) and abnormal RET signaling caused by various mutations has led to a deeper understanding of disease mechanisms. The focus of the present review is on recent progress in the study of RET signaling dysfunction in human diseases.