Neural crest development. Do developing enteric neurons need endothelins?

Skip segment Hirschsprung's disease: a systematic review

PURPOSE

Hirschsprung's disease is characterised by the congenital absence of ganglion cells beginning in the distal rectum and extending proximally for varying distances. 'Zonal aganglionosis' is a phenomenon involving a zone of aganglionosis occurring within normally innervated intestine. 'Skip segment' Hirschsprung's disease (SSHD) involves a 'skip area' of normally ganglionated intestine, surrounded proximally and distally by aganglionosis. While Hirschsprung's disease is believed to be the result of incomplete craniocaudal migration of neural crest-derived cells, the occurrence of SSHD has no clear embryological explanation. The aim of this study was to perform a systematic review of SSHD, reported in the literature between 1954 and 2009, in order to determine the clinical characteristics of this rare entity and its significance.

METHODS

The first reported case of SSHD was published in 1954. A systematic review of SSHD cases in the literature, from 1954 to 2009, was carried out using the electronic database 'Pubmed'. Detailed information was recorded regarding the age, gender, presenting symptoms and location of the skip segment in each patient.

RESULTS

24 cases of SSHD have been reported in the literature to date. 18/24 (75%) of these cases were males and 6/24 (25%) were females. Of these, 22/24 (92%) were cases of total colonic aganglionosis (TCA), and 2/24 (8%) were rectosigmoid Hirschsprung's disease. Of the 22 TCA cases, 9 (41%) had a skip segment in the transverse colon, 6 (27%) in the ascending colon, 2 (9%) in the caecum and 5 (23%) had multiple skip segments. In both rectosigmoid Hirschsprung's disease cases, the skip segment was in the sigmoid colon. Overall, the length of the skip segment was variable, with the entire transverse colon ganglionated in some cases.

CONCLUSION

SSHD occurs predominantly in patients with TCA. The existence of a skip area of normally innervated colon in TCA may influence surgical management, enabling surgeons to preserve and use the ganglionated skip area during pull-through operations.

Isolation and propagation of enteric neural crest progenitor cells from mouse embryonic stem cells and embryos

Neural crest is a source of diverse cell types, including the peripheral nervous system. The transcription factor Sox10 is expressed throughout early neural crest. We exploited Sox10 reporter and selection markers created by homologous recombination to investigate the generation, maintenance and expansion of neural crest progenitors. Sox10-GFP-positive cells are produced transiently from mouse embryonic stem (ES) cells by treatment with retinoic acid in combination with Fgf8b and the cytokine leukaemia inhibitory factor (Lif). We found that expression of Sox10 can be maintained using noggin, Wnt3a, Lif and endothelin (NWLE). ES cell-derived Sox10-GFP-positive cells cultured in NWLE exhibit molecular markers of neural crest progenitors. They differentiate into peripheral neurons in vitro and are able to colonise the enteric network in organotypic gut cultures. Neural crest cells purified from embryos using the Sox10 reporter also survive in NWLE, but progressively succumb to differentiation. We therefore applied selection to eliminate differentiating cells. Sox10-selected cells could be clonally expanded, cryopreserved, and multiplied for over 50 days in adherent culture. They remained neurogenic in vitro and in foetal gut grafts. Generation of neural crest from mouse ES cells opens a new route to the identification and validation of determination factors. Furthermore, the ability to propagate undifferentiated progenitors creates an opportunity for experimental dissection of the stimuli and molecular circu that govern neural crest lineage progression. Finally, the demonstration of robust enteric neurogenesis provides a system for investigating and modelling cell therapeutic approaches to neurocristopathies such as Hirschsprung's disease.

Endothelial cells promote migration and proliferation of enteric neural crest cells via beta1 integrin signaling

Enteric neural crest-derived cells (ENCCs) migrate along the intestine to form a highly organized network of ganglia that comprises the enteric nervous system (ENS). The signals driving the migration and patterning of these cells are largely unknown. Examining the spatiotemporal development of the intestinal neurovasculature in avian embryos, we find endothelial cells (ECs) present in the gut prior to the arrival of migrating ENCCs. These ECs are patterned in concentric rings that are predictive of the positioning of later arriving crest-derived cells, leading us to hypothesize that blood vessels may serve as a substrate to guide ENCC migration. Immunohistochemistry at multiple stages during ENS development reveals that ENCCs are positioned adjacent to vessels as they colonize the gut. A similar close anatomic relationship between vessels and enteric neurons was observed in zebrafish larvae. When EC development is inhibited in cultured avian intestine, ENCC migration is arrested and distal aganglionosis results, suggesting that ENCCs require the presence of vessels to colonize the gut. Neural tube and avian midgut were explanted onto a variety of substrates, including components of the extracellular matrix and various cell types, such as fibroblasts, smooth muscle cells, and endothelial cells. We find that crest-derived cells from both the neural tube and the midgut migrate avidly onto cultured endothelial cells. This EC-induced migration is inhibited by the presence of CSAT antibody, which blocks binding to beta1 integrins expressed on the surface of crest-derived cells. These results demonstrate that ECs provide a substrate for the migration of ENCCs via an interaction between beta1 integrins on the ENCC surface and extracellular matrix proteins expressed by the intestinal vasculature. These interactions may play an important role in guiding migration and patterning in the developing ENS.

Disturbances of colonic motility in mouse models of Hirschsprung's disease

Mutations in genes encoding members of the GDNF and endothelin-3 (Et-3) signaling pathways can cause Hirschsprung's disease, a congenital condition associated with an absence of enteric neurons in the distal gut. GDNF signals through Ret, a receptor tyrosine kinase, and Et-3 signals through endothelin receptor B (Ednrb). The effects of Gdnf, Ret, and ET-3 haploinsufficiency and a null mutation in ET-3 on spontaneous motility patterns in adult and developing mice were investigated. Video recordings were used to construct spatiotemporal maps of spontaneous contractile patterns in colon from postnatal and adult mice in vitro. In Ret(+/-) and ET-3(+/-) mice, which have normal numbers of enteric neurons, colonic migrating motor complexes (CMMCs) displayed similar properties under control conditions and following inhibition of nitric oxide synthase (NOS) activity to wild-type mice. In the colon of Gdnf(+/-) mice and in the ganglionic region of ET-3(-/-) mice, there was a 50-60% reduction in myenteric neuron number. In Gdnf(+/-) mice, CMMCs were present, but abnormal, and the proportion of myenteric neurons containing NOS was not different from that of wild-type mice. In the ganglionic region of postnatal ET-3(-/-) mice, CMMCs were absent, and the proportion of myenteric neurons containing NOS was over 100% higher than in wild-type mice. Thus impairments in spontaneous motility patterns in the colon of Gdnf(+/-) mice and in the ganglionic region of ET-3(-/-) mice are correlated with a reduction in myenteric neuron density.

Pharmacological characterization of endothelin receptors-mediated contraction in the mouse isolated proximal and distal colon

The study investigated the role of endothelin (ET) and the ET receptor subtypes ET(A) and ET(B) in mediating longitudinal contraction in the mouse proximal and distal colon. Cumulative concentration-response curves to a range of ET agonists (ET-1, ET-2, ET-3, (Ala(1,3,11,13)) ET and IRL 1620) were established by administering concentrations ranging from 0.01 nM to 0.3 microM. Concentration-response curves to ET-1, which exhibits a high affinity for both ET(A) and ET(B) receptor subtypes, were also established in the presence of the ET(A) antagonist BMS 182874 and the ET(B) antagonist IRL1038. The addition of the selective ET(A) receptor antagonist BMS 182874 caused a rightward shift of the concentration-response curve to ET-1 in both sections of the colon. The ET(B) receptor antagonist IRL1038 (0.3-1 microM) did not significantly effect the response to ET-1 in the proximal colon but caused a significant decrease in response towards higher concentrations ranges (>or=3 nM) in the distal colon. A comparison of the concentration-response curves to ET-1, ET-2 and ET-3 showed a rank order of potency ET-1>or=ET-2>>ET-3 in the proximal colon and ET-1>or=ET-2>or=ET-3 in the distal colon. The selective ET(B) receptor agonists, (Ala(1,3,11,13)) ET and IRL 1620 did not produce any response in the proximal sections of the colon but produced a smaller contraction in the distal segments. The data indicate that ET can contract the proximal tissues of the mouse colon predominantly via ET(A) receptors and in the distal tissues via ET(A) and ET(B) receptors.

Increased O2*- production and upregulation of ETB receptors by sympathetic neurons in DOCA-salt hypertensive rats

Superoxide anion (O2*-) production is elevated in the vasculature of hypertensive animals but it is not known if O2*- production is also elevated in the sympathetic nervous system. We measured O2*- levels in prevertebral sympathetic ganglia of deoxycorticosterone acetate (DOCA)-salt hypertensive rats using the dihydroethidine (DHE) fluorescence method. O2*- was elevated in ganglia from DOCA-salt rats compared with normotensive sham rats. Treatment of ganglia with endothelin (ET)-1 (3x10(-8) mol/L) resulted in a 200% increase in fluorescence intensity in neurons, which was attenuated by the ET(B) receptor antagonist BQ788 (10(-7) mol/L). ET-1 also increased the O2*- induced fluorescence in dissociated sympathetic neurons and PC-12 cells via activation of ET(B) receptors, but not ET(A) receptors. To evaluate whether elevated ET-1 levels in the ganglia might contribute to the elevated O2*- found in ganglia we measured the amount of ET-1 using an ELISA assay. ET-1 levels in sham rat celiac ganglia were 695.6+/-40.9 picogram per gram; they were not different than ET-1 levels in ganglia from DOCA-salt rats. We then compared ET(B) receptor levels in ganglia from sham and DOCA-salt animals. ET(B) receptor mRNA levels were 32% higher and ET(B) receptor protein levels were 20% higher in celiac ganglia from DOCA-salt rats than from sham rats separately. In conclusion, O2*- is elevated in prevertebral sympathetic ganglia in DOCA-salt hypertension, and ET-1 is a potent stimulus for the elevation of O2*- levels in sympathetic ganglia, an effect that may be mediated by the upregulation of ET(B) receptors.

An endothelin-converting enzyme homologue in the locust, Locusta migratoria: functional activity, molecular cloning and tissue distribution

Endothelin-converting enzyme is the key enzyme in the process of endothelin production. Endothelin is a peptide that plays an important role in vasoconstriction and the development of neural crest-derived cells in vertebrates. Activity assays performed on membrane extracts from Locusta migratoria brain revealed the existence of a protease activity responsible for the formation of mature endothelin-1 from its precursor, big endothelin. Cloning experiments led to a cDNA sequence (Lom ECE) with an open reading frame of 727 amino acid residues displaying all the characteristic ECE features. A comparison of ECE activity levels among different tissues of the locust showed a high enzyme activity in the gonads and midgut. RT-PCR experiments showed a wide tissue distribution of Lom ECE mRNA, with transcription being most abundant in brain tissue.

Gdnf haploinsufficiency causes Hirschsprung-like intestinal obstruction and early-onset lethality in mice

Hirschsprung disease (HSCR) is a common congenital disorder that results in intestinal obstruction and lethality, as a result of defective innervation of the gastrointestinal (GI) tract. Despite its congenital origin, the molecular etiology of HSCR remains elusive for >70% of patients. Although mutations in the c-RET receptor gene are frequently detected in patients with HSCR, mutations in the gene encoding its ligand (glial cell line-derived neurotrophic factor [GDNF]), are rarely found. In an effort to establish a possible link between human HSCR and mutations affecting the Gdnf locus, we studied a large population of mice heterozygous for a Gdnf null mutation. This Gdnf(+/-) mutant cohort recapitulates complex features characteristic of HSCR, including dominant inheritance, incomplete penetrance, and variable severity of symptoms. The lack of one functioning Gdnf allele causes a spectrum of defects in gastrointestinal motility and predisposes the mutant mice to HSCR-like phenotypes. As many as one in five Gdnf(+/-) mutant mice die shortly after birth. Using a transgenic marking strategy, we identified hypoganglionosis of the gastrointestinal tract as a developmental defect that renders the mutant mice susceptible to clinical symptoms of HSCR. Our findings offer a plausible way to link an array of seemingly disparate features characteristic of a complex disease to a much more narrowly defined genetic cause. These findings may have general implications for the genetic analysis of cause and effect in complex human diseases.

Decreased wild-type full-length Et-A and -B receptors in neuroblastoma and Ewing sarcoma cells

BACKGROUND

Endothelins and their receptors, Et-A and Et-B, play an essential role in differentiation and migration of neural crest cells. Expression of endothelin receptors has been examined in neuroblastoma and Ewing sarcoma cell lines.

PROCEDURE

RNA was amplified for Et-A and Et-B by RT-PCR. Amplified products were cloned into the expression vector pLNCX, which was used to transfect CHO cells. Binding characteristics of transfected CHO cells were examined.

RESULTS

Full-length Et-A mRNA was identified in all cell lines, in addition to a truncated Et-A product. CHO cells expressing full-length Et-A bound to endothelin, but cells expressing truncated Et-A did not. Full length Et-B mRNA was not detected, but two smaller molecular weight products were amplified. These are as yet uncharacterised.

CONCLUSIONS

These results suggest that endothelins and their receptors may be important in the development and biology of neuroblastoma and Ewing sarcoma.

The endothelin system in normal human colon

Endothelin (ET)-1 is a potent vasoconstrictor and mitogenic peptide that has a variety of biological effects in noncardiovascular tissues. The precise cellular distribution of the ET-1 system in the wall of the normal human colon was studied to identify the physiological role of ET in the gut. In situ hybridization revealed ET-converting enzyme-1 (ECE-1) mRNA in all vessels, the colon epithelium, and macrophages. Prepro-ET-1 (PPET-1) mRNA had a similar distribution except for a scattered signal in mucosal microvessels. ET(A) and ET(B) receptor mRNAs were mainly in the lamina propria, pericryptal myofibroblasts, microvessels, and mononuclear cells, with ET(A) mRNA more abundant than ET(B) mRNA. (125)I-ET-1 binding showed ET(B) along the crypts and in nerve fibers descending from the ganglionic plexus that contained PPET-1, ECE-1, and ET(B) transcripts, whereas glia contained ET(A) receptors. The finding of the entire ET system in the normal mucosa suggests its implication in some characteristic functions of the colon and its secretion as both a neuroactive and a vasoactive peptide.

Development of the mammalian enteric nervous system

The mammalian enteric nervous system is derived from neural crest cells which invade the foregut and hindgut mesenchyme. It has been established that signalling molecules produced by the mesenchyme of the gut wall play a critical role in the development of the mammalian enteric nervous system. Recent studies have characterised further the role of such molecules and have identified novel extracellular and intracellular signals that are critical for enteric ganglia formation.

Cellular distribution of endothelin-converting enzyme-1 in human tissues

Endothelin-converting enzyme-1 (ECE-1) is the key enzyme of endothelin biosynthesis, catalyzing the final processing step. As shown by the targeted disruption of the ECE-1 gene, mature endothelins must be produced at specific sites for normal embryonic development. Therefore, it is important to know the exact pattern of ECE-1 gene expression. In this study we investigated the cellular distribution of ECE-1 in a variety of human tissues by in situ hybridization and immunohistochemistry. Widespread expression of the ECE-1 gene was noted, with a similar distribution pattern for mRNA and protein in normal human tissues, suggesting a major biological role for ECE-1. ECE-1 levels were particularly high in the cardiovascular, reproductive, and endocrine systems. There was strong and consistent labeling for ECE-1 in the vascular endothelial cells of all organs examined and in various nonvascular cells, especially some glandular cells. A large amount of ECE-1 protein and mRNA was detected in the Leydig cells of the testis and in the granulosa and theca cells of the ovary. In the adrenal gland, ECE-1 was detected in the cortex and medulla, with the strongest labeling in the zona glomerulosa. Therefore, ECE-1 may be involved in other systems, such as the regulation of hormone secretion, rather than exclusively generating ET-1 from its precursor. These results point out the potential side effects of ECE-1 inhibitors that are currently under development for treatment of cardiovascular diseases. (J Histochem Cytochem 47:447-461, 1999)

GDNF and ET-3 differentially modulate the numbers of avian enteric neural crest cells and enteric neurons in vitro

Vagal (hindbrain) neural crest cells migrate rostrocaudally in the gut to establish the enteric nervous system. Glial-derived neurotrophic factor (GDNF) and its receptor(s), and endothelin-3 (ET-3) and its receptor, are crucial for enteric nervous system development. Mutations interrupting either of these signaling pathways cause aganglionosis in the gut, termed Hirschsprung's disease in humans. However, the precise functions of GDNF and ET-3 in enteric neurogenesis are still unknown. We isolated precursor cells of the enteric nervous system from the vagal level neural crest of E1.7 quail embryos prior to entry into the gut and from the developing midgut at stages corresponding to migrating (E4.7) and longer resident differentiating cells (E7) using HNK-1 immunoaffinity and magnetic beads. These cells were tested for their response to GDNF and ET-3 in culture. ET-3 and GDNF had little effect in vitro on the growth, survival, migration, or neurogenesis of E1.7 vagal neural crest cells. In contrast, GDNF increased the proliferation rate and numbers of enteric neural precursors isolated from the E4.7 and E7 gut. Also, many more neurons and neurites developed in cultures treated with GDNF, disproportionately greater than the effect on cell numbers. At high cell density and in the presence of serum, ET-3, and GDNF had an additive effect on proliferation of neuron precursor cells. In defined medium, or low cell density, ET-3 reduced cell proliferation, overriding the proliferative effect of GDNF. Regardless of the culture condition, the stimulatory effect of GDNF on neuron numbers was strikingly diminished by the simultaneous presence of ET-3. We propose first that GDNF promotes the proliferation in the migratory enteric neural precursor cell population once the cells have entered the gut and is especially crucial for the differentiation of these cells into nonmigrating, nonproliferating enteric neurons. Second, we suggest that ET-3 modulates the action of GDNF, inhibiting neuronal differentiation to maintain the precursor cell pool, so ensuring sufficient population numbers to construct the entire enteric nervous system. Third, we suggest that generalized defects in enteric neural precursor cell numbers and differentiation due to mutations in the ET-3 and GDNF systems are converted to distal gut neural deficiencies by the rostrocaudal migration pattern of the precursors. Fourth, we suggest that additional factors such as those found in serum and produced by the enteric neural cells themselves are likely also to be involved in enteric nervous system development and consequently in Hirschsprung's disease.

Sox10 mutation disrupts neural crest development in Dom Hirschsprung mouse model

Hirschsprung disease (HSCR, MIM #142623) is a multigenic neurocristopathy (neural crest disorder) characterized by absence of enteric ganglia in a variable portion of the distal colon. Subsets of HSCR individuals also present with neural crest-derived melanocyte deficiencies (Hirschsprung-Waardenburg, HSCR-WS, MIM #277580). Murine models have been instrumental in the identification and analysis of HSCR disease genes. These include mice with deficiencies of endothelin B receptor (Ednrb(s-l); refs 1,2) endothelin 3 (Edn3(ls): refs 1,3) the tyrosine kinase receptor cRet and glial-derived neurotrophic factor. Another mouse model of HSCR disease, Dom, arose spontaneously at the Jackson Laboratory. While Dom/+ heterozygous mice display regional deficiencies of neural crest-derived enteric ganglia in the distal colon, Dom/Dom homozygous animals are embryonic lethal. We have determined that premature termination of Sox10, a member of the SRY-like HMG box family of transcription factors, is responsible for absence of the neural crest derivatives in Dom mice. We demonstrate expression of Sox10 in normal neural crest cells, disrupted expression of both Sox10 and the HSCR disease gene Ednrb in Dom mutant embryos, and loss of neural crest derivatives due to apoptosis. Our studies suggest that Sox10 is essential for proper peripheral nervous system development. We propose SOX10 as a candidate disease gene for individuals with HSCR whose disease does not have an identified genetic origin.

Construction, expression and characterization of a soluble form of human endothelin-converting-enzyme-1

Endothelin-converting-enzyme-1 (ECE-1) belongs to the family of zinc metallopeptidases and is responsible for generating endothelin (ET) peptides from their inactive precursors the big endothelins (bigET). The enzyme is a type II integral membrane protein consisting of a short amino-terminal cytosolic domain of 56 amino acids, a single transmembrane domain and a large putative extracellular domain containing the catalytic site. Recombinant and native ECE-1 are expressed as a dimer. We have constructed a soluble form of ECE, named sECE*, by fusing the cleavable signal peptide of pro-opiomelanocortin in frame to the complete extracellular domain of human ECE-1. Stable expression of this construct in CHO cells resulted in the secretion of a fully active enzyme. In contrast to membrane-bound ECE, sECE* was expressed as a monomer, highly glycosylated, as assessed by gel filtration and Western blot. However, recombinant sECE* converted bigET-1 with similar specific activity as ECE-1a. This activity was completely inhibited by phosphoramidon, but not by thiorphan and captopril. sECE* was active in a broad range of pH, showing an optimum of 6.6-6.8 for bigET-1. Thus, the extracellular domain alone is sufficient for conferring full ECE-1 activity, inhibitors recognition and substrate specificity.