Disruption of the temporally regulated cloaca endodermal ß-catenin signaling causes anorectal malformations.

The cloaca is temporally formed and eventually divided by the urorectal septum (URS) during urogenital and anorectal organ development. Although congenital malformations, such as anorectal malformations (ARMs), are frequently observed during this process, the underlying pathogenic mechanisms remain unclear. ß-Catenin is a critical component of canonical Wnt signaling and is essential for the regulation of cell differentiation and morphogenesis during embryogenesis. The expression of ß-catenin is observed in endodermal epithelia, including URS epithelia. We modulated the ß-catenin gene conditionally in endodermal epithelia by utilizing tamoxifen-inducible Cre driver line (Shh(CreERT2)). Both ß-catenin loss- and gain-of-function (LOF and GOF) mutants displayed abnormal clefts in the perineal region and hypoplastic elongation of the URS. The mutants also displayed reduced cell proliferation in the URS mesenchyme. In addition, the ß-catenin GOF mutants displayed reduced apoptosis and subsequently increased apoptosis in the URS epithelium. This instability possibly resulted in reduced expression levels of differentiation markers, such as keratin 1 and filaggrin, in the perineal epithelia. The expression of bone morphogenetic protein (Bmp) genes, such as Bmp4 and Bmp7, was also ectopically induced in the epithelia of the URS in the ß-catenin GOF mutants. The expression of the Msx2 gene and phosphorylated-Smad1/5/8, possible readouts of Bmp signaling, was also increased in the mutants. Moreover, we introduced an additional mutation for a Bmp receptor gene: BmprIA. The Shh(CreERT2/+); ß-catenin(flox(ex3)/+); BmprIA(flox/-) mutants displayed partial restoration of URS elongation compared with the ß-catenin GOF mutants. These results indicate that some ARM phenotypes in the ß-catenin GOF mutants were caused by abnormal Bmp signaling. The current analysis revealed the close relation of endodermal ß-catenin signaling to the ARM phenotypes. These results are considered to shed light on the pathogenic mechanisms of human ARMs.

Dysregulation of Wnt inhibitory factor 1 (Wif1) expression resulted in aberrant Wnt-ß-catenin signaling and cell death of the cloaca endoderm, and anorectal malformations.

In mammalian urorectal development, the urorectal septum (urs) descends from the ventral body wall to the cloaca membrane (cm) to partition the cloaca into urogenital sinus and rectum. Defective urs growth results in human congenital anorectal malformations (ARMs), and their pathogenic mechanisms are unclear. Recent studies only focused on the importance of urs mesenchyme proliferation, which is induced by endoderm-derived Sonic Hedgehog (Shh). Here, we showed that the programmed cell death of the apical urs and proximal cm endoderm is particularly crucial for the growth of urs during septation. The apoptotic endoderm was closely associated with the tempo-spatial expression of Wnt inhibitory factor 1 (Wif1), which is an inhibitor of Wnt-ß-catenin signaling. In Wif1(lacZ/lacZ) mutant mice and cultured urorectum with exogenous Wif1, cloaca septation was defective with undescended urs and hypospadias-like phenotypes, and such septation defects were also observed in Shh(-/-) mutants and in endodermal ß-catenin gain-of-function (GOF) mutants. In addition, Wif1 and Shh were expressed in a complementary manner in the cloaca endoderm, and Wif1 was ectopically expressed in the urs and cm associated with excessive endodermal apoptosis and septation defects in Shh(-/-) mutants. Furthermore, apoptotic cells were markedly reduced in the endodermal ß-catenin GOF mutant embryos, which counteracted the inhibitory effects of Wif1. Taken altogether, these data suggest that regulated expression of Wif1 is critical for the growth of the urs during cloaca septation. Hence, Wif1 governs cell apoptosis of urs endoderm by repressing ß-catenin signal, which may facilitate the protrusion of the underlying proliferating mesenchymal cells towards the cm for cloaca septation. Dysregulation of this endodermal Shh-Wif1-ß-catenin signaling axis contributes to ARM pathogenesis.

Perturbation of Hoxb5 signaling in vagal and trunk neural crest cells causes apoptosis and neurocristopathies in mice.

Neural crest cells (NCCs) migrate from different regions along the anterior-posterior axis of the neural tube (NT) to form different structures. Defective NCC development causes congenital neurocristopathies affecting multiple NCC-derived tissues in human. Perturbed Hoxb5 signaling in vagal NCC causes enteric nervous system (ENS) defects. This study aims to further investigate if perturbed Hoxb5 signaling in trunk NCC contributes to defects of other NCC-derived tissues besides the ENS. We perturbed Hoxb5 signaling in NCC from the entire NT, and investigated its impact in the development of tissues derived from these cells in mice. Perturbation of Hoxb5 signaling in these NCC resulted in Sox9 downregulation, NCC apoptosis, hypoplastic sympathetic and dorsal root ganglia, hypopigmentation and ENS defects. Mutant mice with NCC-specific Sox9 deletion also displayed some of these phenotypes. In vitro and in vivo assays indicated that the Sox9 promoter was bound and trans-activated by Hoxb5. In ovo studies further revealed that Sox9 alleviated apoptosis induced by perturbed Hoxb5 signaling, and Hoxb5 induced ectopic Sox9 expression in chick NT. This study demonstrates that Hoxb5 regulates Sox9 expression in NCC and disruption of this signaling causes Sox9 downregulation, NCC apoptosis and multiple NCC-developmental defects. Phenotypes such as ENS deficiency, hypopigmentation and some of the neurological defects are reported in patients with Hirschsprung disease (HSCR). Whether dysregulation of Hoxb5 signaling and early depletion of NCC contribute to ENS defect and other neurocristopathies in HSCR patients deserves further investigation.

Correlation between genetic variations in Hox clusters and Hirschsprung's disease.

Interactions between migrating neural crest cells and the environment of the gut are crucial for the development of the enteric nervous system (ENS). A key signalling mediator is the RET-receptor-tyrosine-kinase which, when defective, causes Hirschprung's disease (HSCR, colon aganglionosis). RET mutations alone cannot account for the variable HSCR phenotype, invoking interactions with as yet unknown, and probably inter-related, loci involved in ENS development. Homeobox (HOX) genes have a major role in gut development as depicted by the enteric Hox code. We investigated whether DNA alterations in HOX genes, either alone or in combination with RET, are implicated in HSCR. Genotyping effort was minimized by applying the HapMap data on Han Chinese from Beijing (CHB). 194 HSCR patients and 168 controls were genotyped using Sequenom technology for 72 tag, single nucleotide polymorphisms (SNPs) distributed along the HOX clusters. The HapMap frequencies were compared to those in our population and standard statistics were used for frequency comparisons. The multifactor-dimensionality-reduction method was used for multilocus analysis, in which RET promoter SNP genotypes were included. Genetic interactions were found between two HOX loci (5'-HOXA13 and 3'UTR-HOXB7) and the RET loci tested. Minor allele frequencies (MAF) of the SNPs tested in our sample were not significantly different from those reported by HapMap when the sample sizes of the populations compared were considered. This is the first evaluation of the HOX genes in HSCR and the first application of HapMap data in a Chinese population. The interacting HOX loci may affect the penetrance of the RET risk allele. HapMap data for the CHB population correlated well with the general Chinese population.

Depletion of intestinal resident macrophages prevents ischaemia reperfusion injury in gut.

BACKGROUND AND AIMS: The cellular and molecular events involved in ischaemia reperfusion (IR) injury are complex and not fully understood. Previous studies have implicated polymorphonuclear neutrophils (PMN) as major inflammatory cells in IR injury. However, anti-PMN antiserum treatment offers only limited protection, indicating that other inflammatory cells are involved. We have therefore investigated the contribution of resident macrophages in IR injury using an IR gut injury model. METHODS: DA rats were divided into sham operation and IR groups. The superior mesenteric artery was clamped for 30, 45, or 60 minutes (ischaemia) followed by 60 minutes of reperfusion. IR injuries were evaluated by histological staining. Expression of early growth response factor 1 (Egr-1), myeloperoxidase (MPO), and proinflammatory cytokines was analysed by immunohistochemistry, reverse transcription-polymerase chain reaction, and western blotting analysis. The specific role of macrophages in IR gut injury was also evaluated in resident macrophage depleted rats. RESULTS: Mucosal sloughing and villi destruction were seen in 45/60 minute and 60/60 minute IR guts. PMN infiltration at the damaged mucosal area was undetectable in 45/60 minute and 60/60 minute IR guts. PMN were localised around the capillaries at the base of the crypts in 60/60 minute IR gut. Obvious PMN infiltration was only observed in damaged villi after three hours of reperfusion. Elevated nuclear Egr-1 immunostaining was localised in resident macrophages at the damaged villi before histological appearance of mucosal damage. Furthermore, resident macrophages at the damaged site expressed MPO. Protein levels of the proinflammatory cytokines RANTES and MCP-1 were increased in IR gut. Depletion of resident macrophages by dichloromethylene bisphosphonate significantly reduced mucosal damage in rat guts after IR. CONCLUSION: Our findings indicate that resident macrophages play a role in early mucosal damage in IR gut injury. Therefore, macrophages should be treated as a prime target for therapeutic intervention for IR damage.

Esophageal atresia and achalasialike esophageal dysmotility.

A 14-year-old boy presented with regurgitation, malnutrition, and chronic lung insufficiency with a history of successful repair of esophageal atresia and tracheoesophageal fistula in the newborn period. Barium swallow and manometry results showed achalasia. Hellar operation with antireflux procedure resulted in complete symptomatic relief. Histology and immunohistochemistry including PGP9.5, MAP5, cKit, and nNOS of myotomy specimen showed intact innervation. Although esophageal dysmotility after esophageal atresia repair usually is caused by gastroesophageal reflux and incoordination of peristalsis, the possibility of achalasia should also be considered, because a casual relationship between esophageal atresia and achalasia may exist.

Embryonic development of the ganglion plexuses and the concentric layer structure of human gut: a topographical study.

In this study, we performed a detailed topographical study on the development of ganglion plexuses and the smooth muscle layers of human embryonic and fetal gut. Neuron and glia differentiation was investigated with anti-PGP9.5 and anti-S100 antibodies respectively. The differentiation of smooth muscle and interstitial cells of Cajal (ICC) was studied with anti-smooth muscle alpha-actin and anti-C-Kit antibodies respectively. By week 7, rostro-caudal neural crest cell (NCC) colonization of the gut was complete, and NCCs have differentiated into neurons and glia. At the foregut, neurons and glia were aggregated into ganglion plexus in the myenteric region, and the longitudinal and circular muscle layers have started to differentiate; however, neurons and glia were not found in the submucosa. At the hindgut, neurons and glia were dispersed within the mesenchyme. Myenteric plexus, longitudinal and circular muscle layers formed along the entire gut by week 9. Scattered and individual neurons and glia, and small ganglion plexuses were detected in the foregut and midgut submucosa by week 12. Ganglion plexus was not seen in the hindgut submucosa until week 14. Muscularis mucosae was formed at the foregut and midgut by week 12 but was only discernible at the hindgut 2 weeks later. As the gut wall developed, ganglion plexus increased in size with more neurons and glia, and the formation of intra-plexus nerve fascicle. ICCs were localized in the ganglion plexus as early as week 7. ICCs were initially dispersed in the plexus and were preferentially localized at the periphery of the plexus by week 20. The specification of the annular layers of human embryonic and fetal gut follows a strict spatio-temporal pattern in a rostro-caudal and centripetal manner suggesting that interaction between (1) homotypic and/or heterotypic cells; and (2) cells and the extracellular matrix is critical for the embryonic development of the gut mesenchyme and the enteric nervous system.

Is there a role for the IHH gene in Hirschsprung's disease?

Hirschsprung disease (HSCR) is characterized by the absence of ganglion cells along a variable length of the intestine. HSCR has a complex genetic aetiology with 50% of the patients unexplained by mutations in the major HSCR genes. The Ihh gene is involved in the development of the enteric nervous system (ENS) and Ihh mutant mice present with a phenotype reminiscent of HSCR. The requirement of Ihh signalling for the proper development of the ENS, together with the evidence presented by the Ihh murine model, prompted us to investigate the involvement of the human IHH gene in HSCR. Sequence analysis revealed seven single nucleotide polymorphisms, six of which were new. Allele and haplotype frequencies were compared between cases and controls, and, among the cases, between genders, between different phenotypes, and between patients with different mutation status in the main HSCR genes. Despite the involvement of IHH in the development of the ENS, IHH is not a major gene in HSCR. Nevertheless, as the manifestation of the HSCR phenotype is genetic background dependent, polymorphic loci should be tested simultaneously to characterize gene-gene interaction. The involvement of IHH in other intestinal anomalies should be investigated.

Deficient motor innervation of the sphincter mechanism in fetal rats with anorectal malformation: a quantitative study by fluorogold retrograde tracing.

BACKGROUND/PURPOSE: Deficiency of motoneuron innervation to the sphincter mechanism has been described in patients with anorectal malformation. Whether this event is primary or secondary remains unclear. METHODS: The authors quantified the motoneuron innervation of the sphincter mechanism by Fluorogold (FG) retrograde tracing experiment in fetal rats with anorectal malformation. Anorectal malformation was induced in rat fetuses by ethylenethiourea (ETU). Serial longitudinal sections encompassing the whole width of lumbosacral spinal cord were examined. The number of FG-labelled motoneurons were scored and compared between male fetuses with or without malformation in the ETU-fed group and normal controls. RESULTS: The number of FG-labelled motoneurons in the fetuses without defect, with imperforate anus (IA), with neural tube anomalies (NTA), with combined IA and NTA, and normal controls were determined to be (mean +/- SEM) 109.13 +/- 37.88, 55.05 +/- 25.85, 48.20 +/- 30.34, 54.43 +/- 28.55, and 135.22 +/- 28.78, respectively. FG-labelled motoneurons in the fetuses with IA, NTA, and combined IA and NTA are significantly fewer than that in fetuses without defects (P <.05) and in normal controls (P <.005). CONCLUSIONS: These findings suggest that defective motoneuron innervation to the sphincter mechanism is a primary anomaly that coexists with the alimentary tract anomaly in anorectal malformation during fetal development. The intrinsic neural deficiency is an important factor likely to contribute to poor postoperative anorectal function despite surgical correction of anorectal malformation.

Association study of PHOX2B as a candidate gene for Hirschsprung's disease.

BACKGROUND: Hirschsprung's disease (HSCR) is a congenital disorder characterised by an absence of ganglion cells in the nerve plexuses of the lower digestive tract. Manifestation of the disease has been linked to mutations in genes that encode the crucial signals for the development of the enteric nervous system-the RET and EDNRB signalling pathways. The Phox2b gene is involved in neurogenesis and regulates Ret expression in mice, in which disruption of the Phox2b results in a HSCR-like phenotype. AIMS: To investigate the contribution of PHOX2B to the HSCR phenotype. METHODS: Using polymerase chain reaction amplification and direct sequencing, we screened PHOX2B coding regions and intron/exon boundaries for mutations and polymorphisms in 91 patients with HSCR and 71 ethnically matched controls. Seventy five HSCR patients with no RET mutations were independently considered. Haplotype and genotype frequencies were compared using the standard case control statistic. RESULTS: Sequence analysis revealed three new polymorphisms: two novel single nucleotide polymorphisms (A-->G(1364); A-->C(2607)) and a 15 base pair deletion (DEL(2609)). Statistically significant differences were found for A-->G(1364). Genotypes comprising allele G were underrepresented in patients (19% v 36%; chi(2)=9.30; p=0.0095 and 22% v 36%; chi(2)=7.38; p=0.024 for patients with no RET mutations). Pairwise linkage disequilibrium (LD) analysis revealed no LD between physically close polymorphisms indicating a hot spot for recombination in exon 3. CONCLUSION: The PHOX2B A-->G(1364) polymorphism is associated with HSCR. Whether it directly contributes to disease susceptibility or represents a marker for a locus in LD with PHOX2B needs further investigation. Our findings are in accordance with the involvement of PHOX2B in the signalling pathways governing the development of enteric neurones.