Acquisition of neuronal and glial markers by neural crest-derived cells in the mouse intestine

N-cadherin and β1-integrins cooperate during the development of the enteric nervous system

Cell adhesion controls various embryonic morphogenetic processes, including the development of the enteric nervous system (ENS). Ablation of β1-integrin (β1-/-) expression in enteric neural crest cells (ENCC) in mice leads to major alterations in the ENS structure caused by reduced migration and increased aggregation properties of ENCC during gut colonization, which gives rise to a Hirschsprung's disease-like phenotype. In the present study, we examined the role of N-cadherin in ENS development and the interplay with β1 integrins during this process. The Ht-PA-Cre mouse model was used to target gene disruption of N-cadherin and β1 integrin in migratory NCC and to produce single- and double-conditional mutants for these two types of adhesion receptors. Double mutation of N-cadherin and β1 integrin led to embryonic lethality with severe defects in ENS development. N-cadherin-null (Ncad-/-) ENCC exhibited a delayed colonization in the developing gut at E12.5, although this was to a lesser extent than in β1-/- mutants. This delay of Ncad-/- ENCC migration was recovered at later stages of development. The double Ncad-/-; β1-/- mutant ENCC failed to colonize the distal part of the gut and there was more severe aganglionosis in the proximal hindgut than in the single mutants for N-cadherin or β1-integrin. This was due to an altered speed of locomotion and directionality in the gut wall. The abnormal aggregation defect of ENCC and the disorganized ganglia network in the β1-/- mutant was not observed in the double mutant. This indicates that N-cadherin enhances the effect of the β1-integrin mutation and demonstrates cooperation between these two adhesion receptors during ENS ontogenesis. In conclusion, our data reveal that N-cadherin is not essential for ENS development but it does modulate the modes of ENCC migration and acts in concert with β1-integrin to control the proper development of the ENS.

The enteric nervous system

The enteric nervous system (ENS), the intrinsic innervation of the gastrointestinal tract, consists of numerous types of neurons, and glial cells, that are distributed in two intramuscular plexuses that extend along the entire length of the gut and control co-ordinated smooth muscle contractile activity and other gut functions. All enteric neurons and glia are derived from neural crest cells (NCC). Vagal (hindbrain) level NCC provide the majority of enteric precursors along the entire length of the gut, while a lesser contribution, that is restricted to the hindgut, arises from the sacral region of the neuraxis. After leaving the dorsal neural tube NCC undergo extensive migration, proliferation, survival and differentiation in order to form a functional ENS. This article reviews the molecular mechanisms underlying these key developmental processes and highlights the major groups of molecules that affect enteric NCC proliferation and survival (Ret/Gdnf and EdnrB/Et-3 pathways, Sox10 and Phox2b transcription factors), cell migration (Ret and EdnrB signalling, semaphorin 3A, cell adhesion molecules, Rho GTPases), and the development of enteric neuronal subtypes and morphologies (Mash1, Gdnf/neurturin, BMPs, Hand2, retinoic acid). Finally, looking to the future, we discuss the need to translate the wealth of data gleaned from animal studies to the clinical area and thus better understand, and develop treatments for, congenital human diseases affecting the ENS.

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.

Enteric nervous system specific deletion of Foxd3 disrupts glial cell differentiation and activates compensatory enteric progenitors

The enteric nervous system (ENS) arises from the coordinated migration, expansion and differentiation of vagal and sacral neural crest progenitor cells. During development, vagal neural crest cells enter the foregut and migrate in a rostro-to-caudal direction, colonizing the entire gastrointestinal tract and generating the majority of the ENS. Sacral neural crest contributes to a subset of enteric ganglia in the hindgut, colonizing the colon in a caudal-to-rostral wave. During this process, enteric neural crest-derived progenitors (ENPs) self-renew and begin expressing markers of neural and glial lineages as they populate the intestine. Our earlier work demonstrated that the transcription factor Foxd3 is required early in neural crest-derived progenitors for self-renewal, multipotency and establishment of multiple neural crest-derived cells and structures including the ENS. Here, we describe Foxd3 expression within the fetal and postnatal intestine: Foxd3 was strongly expressed in ENPs as they colonize the gastrointestinal tract and was progressively restricted to enteric glial cells. Using a novel Ednrb-iCre transgene to delete Foxd3 after vagal neural crest cells migrate into the midgut, we demonstrated a late temporal requirement for Foxd3 during ENS development. Lineage labeling of Ednrb-iCre expressing cells in Foxd3 mutant embryos revealed a reduction of ENPs throughout the gut and loss of Ednrb-iCre lineage cells in the distal colon. Although mutant mice were viable, defects in patterning and distribution of ENPs were associated with reduced proliferation and severe reduction of glial cells derived from the Ednrb-iCre lineage. Analyses of ENS-lineage and differentiation in mutant embryos suggested activation of a compensatory population of Foxd3-positive ENPs that did not express the Ednrb-iCre transgene. Our findings highlight the crucial roles played by Foxd3 during ENS development including progenitor proliferation, neural patterning, and glial differentiation and may help delineate distinct molecular programs controlling vagal versus sacral neural crest development.

Targeted deletion of Hand2 in enteric neural precursor cells affects its functions in neurogenesis, neurotransmitter specification and gangliogenesis, causing functional aganglionosis

Targeted deletion of the bHLH DNA-binding protein Hand2 in the neural crest, impacts development of the enteric nervous system (ENS), possibly by regulating the transition from neural precursor cell to neuron. We tested this hypothesis by targeting Hand2 deletion in nestin-expressing neural precursor (NEP) cells. The mutant mice showed abnormal ENS development, resulting in lethal neurogenic pseudo-obstruction. Neurogenesis of neurons derived from NEP cells identified a second nestin non-expressing neural precursor (NNEP) cell in the ENS. There was substantial compensation for the loss of neurons derived from the NEP pool by the NNEP pool but this was insufficient to abrogate the negative impact of Hand2 deletion. Hand2-mediated regulation of proliferation affected both neural precursor and neuron numbers. Differentiation of glial cells derived from the NEP cells was significantly decreased with no compensation from the NNEP pool of cells. Our data indicate differential developmental potential of NEPs and NNEPs; NNEPs preferentially differentiate as neurons, whereas NEPs give rise to both neurons and glial cells. Deletion of Hand2 also resulted in complete loss of NOS and VIP and a significant decrease in expression of choline acetyltransferase and calretinin, demonstrating a role for Hand2 in neurotransmitter specification and/or expression. Loss of Hand2 resulted in a marked disruption of the developing neural network, exemplified by lack of a myenteric plexus and extensive overgrowth of fibers. Thus, Hand2 is essential for neurogenesis, neurotransmitter specification and neural network patterning in the developing ENS.

Glial cells in the mouse enteric nervous system can undergo neurogenesis in response to injury

The enteric nervous system (ENS) in mammals forms from neural crest cells during embryogenesis and early postnatal life. Nevertheless, multipotent progenitors of the ENS can be identified in the adult intestine using clonal cultures and in vivo transplantation assays. The identity of these neurogenic precursors in the adult gut and their relationship to the embryonic progenitors of the ENS are currently unknown. Using genetic fate mapping, we here demonstrate that mouse neural crest cells marked by SRY box-containing gene 10 (Sox10) generate the neuronal and glial lineages of enteric ganglia. Most neurons originated from progenitors residing in the gut during mid-gestation. Afterward, enteric neurogenesis was reduced, and it ceased between 1 and 3 months of postnatal life. Sox10-expressing cells present in the myenteric plexus of adult mice expressed glial markers, and we found no evidence that these cells participated in neurogenesis under steady-state conditions. However, they retained neurogenic potential, as they were capable of generating neurons with characteristics of enteric neurons in culture. Furthermore, enteric glia gave rise to neurons in vivo in response to chemical injury to the enteric ganglia. Our results indicate that despite the absence of constitutive neurogenesis in the adult gut, enteric glia maintain limited neurogenic potential, which can be activated by tissue dissociation or injury.

Expression of PROKR1 and PROKR2 in human enteric neural precursor cells and identification of sequence variants suggest a role in HSCR

Background

The enteric nervous system (ENS) is entirely derived from neural crest and its normal development is regulated by specific molecular pathways. Failure in complete ENS formation results in aganglionic gut conditions such as Hirschsprung's disease (HSCR). Recently, PROKR1 expression has been demonstrated in mouse enteric neural crest derived cells and Prok-1 was shown to work coordinately with GDNF in the development of the ENS.

Principal Findings

In the present report, ENS progenitors were isolated and characterized from the ganglionic gut from children diagnosed with and without HSCR, and the expression of prokineticin receptors was examined. Immunocytochemical analysis of neurosphere-forming cells demonstrated that both PROKR1 and PROKR2 were present in human enteric neural crest cells. In addition, we also performed a mutational analysis of PROKR1, PROKR2, PROK1 and PROK2 genes in a cohort of HSCR patients, evaluating them for the first time as susceptibility genes for the disease. Several missense variants were detected, most of them affecting highly conserved amino acid residues of the protein and located in functional domains of both receptors, which suggests a possible deleterious effect in their biological function.

Conclusions

Our results suggest that not only PROKR1, but also PROKR2 might mediate a complementary signalling to the RET/GFRα1/GDNF pathway supporting proliferation/survival and differentiation of precursor cells during ENS development. These findings, together with the detection of sequence variants in PROKR1, PROK1 and PROKR2 genes associated to HSCR and, in some cases in combination with RET or GDNF mutations, provide the first evidence to consider them as susceptibility genes for HSCR.

On the role of differential adhesion in gangliogenesis in the enteric nervous system

A defining characteristic of the normal development of the enteric nervous system (ENS) is the existence of mesoscale patterned entities called ganglia. Ganglia are clusters of neurons with associated enteric neural crest (ENC) cells, which form in the simultaneously growing gut wall. At first the precursor ENC cells proliferate and gradually differentiate to produce the enteric neurons; these neurons form clusters with ENC scattered around and later lying on the periphery of neuronal clusters. By immunolabelling neural cell-cell adhesion molecules, we infer that the adhesive capacity of neurons is greater than that of ENC cells. Using a discrete mathematical model, we test the hypothesis that local rules governing differential adhesion of neuronal agents and ENC agents will produce clusters which emulate ganglia. The clusters are relatively stable, relatively uniform and small in size, of fairly uniform spacing, with a balance between the number of neuronal and ENC agents. These features are attained in both fixed and growing domains, reproducing respectively organotypic in vitro and in vivo observations. Various threshold criteria governing ENC agent proliferation and differentiation and neuronal agent inhibition of differentiation are important for sustaining these characteristics. This investigation suggests possible explanations for observations in normal and abnormal ENS development.

Isolation and live imaging of enteric progenitors based on Sox10-Histone2BVenus transgene expression

To facilitate dynamic imaging of neural crest (NC) lineages and discrimination of individual cells in the enteric nervous system (ENS) where close juxtaposition often complicates viewing, we generated a mouse BAC transgenic line that drives a Histone2BVenus (H2BVenus) reporter from Sox10 regulatory regions. This strategy does not alter the endogenous Sox10 locus and thus facilitates analysis of normal NC development. Our Sox10-H2BVenus BAC transgene exhibits temporal, spatial, and cell-type specific expression that reflects endogenous Sox10 patterns. Individual cells exhibiting nuclear-localized fluorescence of the H2BVenus reporter are readily visualized in both fixed and living tissue and are amenable to isolation by fluorescence activated cell sorting (FACS). FACS-isolated H2BVenus+ enteric NC-derived progenitors (ENPs) exhibit multipotency, readily form neurospheres, self-renew in vitro and express a variety of stem cell genes. Dynamic live imaging as H2BVenus+ ENPs migrate down the fetal gut reveals cell fragmentation suggesting that apoptosis occurs at a low frequency during normal development of the ENS. Confocal imaging both during population of the fetal intestine and in postnatal gut muscle strips revealed differential expression between individual cells consistent with down-regulation of the transgene as progression towards non-glial fates occurs. The expression of the Sox10-H2BVenus transgene in multiple regions of the peripheral nervous system will facilitate future studies of NC lineage segregation as this tool is expressed in early NC progenitors and maintained in enteric glia.

Prospective identification and isolation of enteric nervous system progenitors using Sox2

The capacity to identify and isolate lineage-specific progenitor cells from developing and mature tissues would enable the development of cell replacement therapies for disease treatment. The enteric nervous system (ENS) regulates important gut functions, including controlling peristaltic muscular contractions, and consists of interconnected ganglia containing neurons and glial cells. Hirschsprung's disease (HSCR), one of the most common and best understood diseases affecting the ENS, is characterized by absence of enteric ganglia from the distal gut due to defects in gut colonization by neural crest progenitor cells and is an excellent candidate for future cell replacement therapies. Our previous microarray experiments identified the neural progenitor and stem cell marker SRY-related homoebox transcription factor 2 (Sox2) as expressed in the embryonic ENS. We now show that Sox2 is expressed in the ENS from embryonic to adult stages and constitutes a novel marker of ENS progenitor cells and their glial cell derivatives. We also show that Sox2 expression overlaps significantly with SOX10, a well-established marker of ENS progenitors and enteric glial cells. We have developed a strategy to select cells expressing Sox2, by using G418 selection on cultured gut cells derived from Sox2^βgeo/+ mouse embryos, thus allowing substantial enrichment and expansion of neomycin-resistant Sox2-expressing cells. Sox2^βgeo cell cultures are enriched for ENS progenitors. Following transplantation into embryonic mouse gut, Sox2^βgeo cells migrate, differentiate, and colocalize with the endogenous ENS plexus. Our studies will facilitate development of cell replacement strategies in animal models, critical to develop human cell replacement therapies for HSCR. Stem Cells 2011;29:128–140

Evidence for neural progenitor cells in the human adult enteric nervous system

Putative neural stem cells have been identified within the enteric nervous system (ENS) of adult rodents and cultured from human myenteric plexus. We conducted studies to identify neural stem cells or progenitor cells within the submucosa of adult human ENS. Jejunum tissue was removed from adult human subjects undergoing gastric bypass surgery. The tissue was immunostained, and confocal images of ganglia in the submucosal plexus were collected to identify protein gene product 9.5 (PGP 9.5) - immunoractive neurons and neuronal progenitor cells that coexpress PGP 9.5 and nestin. In addition to PGP-9.5-positive/nestin-negative neuronal cells within ganglia, we observed two other types of cells: (1) cells in which PGP 9.5 and nestin were co-localized, (2) cells negative for both PGP 9.5 and nestin. These observations suggest that the latter two types of cells are related to a progenitor cell population and are consistent with the concept that the submucosa of human adult ENS contains stem cells capable of maintenance and repair within the peripheral nervous system.

Building stable chains with motile agents: Insights into the morphology of enteric neural crest cell migration

A defining characteristic of the normal development of the enteric nervous system (ENS) is the existence of an enteric neural crest (ENC) cell colonization wave, where the ENC cells form stable chains often associated with axons and near the vascular network. However, within this evolving neural network, the individual ENC cell elements constantly move, change direction and appear to act independently of neighbors. Three possible hypotheses are investigated. The simplest of these postulates that the ENS follows the vascular network as a template. We present evidence which does not support this hypothesis. Two viable alternatives are either that (i) the axons muster the ENC cells, providing the pattern for the chain migration or (ii) ENC cells form chains and the axons follow these paths. These two hypotheses are explored by developing a stochastic cellular automata model, where ENC agents follow simple rules, which reflect the underlying biology of movement, proliferation and differentiation. By simulating ENC precursors and the associated neurons and axons, two models with different fundamental mechanisms are developed. From local rules, a mesoscale network pattern with lacunae emerges, which can be analyzed quantitatively. Simulation and analysis establishes the parameters that affect the morphology of the resulting network. This investigation into the axon/ENC and ENC/ENC interplay suggests possible explanations for observations in mouse and avian embryos in normal and abnormal ENS development, as well as further experimentation.

Neural crest stem cell multipotency requires Foxd3 to maintain neural potential and repress mesenchymal fates

Neural crest (NC) progenitors generate a wide array of cell types, yet molecules controlling NC multipotency and self-renewal and factors mediating cell-intrinsic distinctions between multipotent versus fate-restricted progenitors are poorly understood. Our earlier work demonstrated that Foxd3 is required for maintenance of NC progenitors in the embryo. Here, we show that Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. Neural derivatives of NC were lost in Foxd3 mutant mouse embryos, whereas abnormally fated NC-derived vascular smooth muscle cells were ectopically located in the aorta. Cranial NC defects were associated with precocious differentiation towards osteoblast and chondrocyte cell fates, and individual mutant NC from different anteroposterior regions underwent fate changes, losing neural and increasing myofibroblast potential. Our results demonstrate that neural potential can be separated from NC multipotency by the action of a single gene, and establish novel parallels between NC and other progenitor populations that depend on this functionally conserved stem cell protein to regulate self-renewal and multipotency.

Dependence of serotonergic and other nonadrenergic enteric neurons on norepinephrine transporter expression

The norepinephrine transporter (NET), which is expressed on the plasma membranes of noradrenergic neurons, is important in terminating neurotransmission. The noradrenergic sympathetic neurons that innervate the bowel express NET, but they are extrinsic and their cell bodies are not components of the enteric nervous system (ENS). Subsets of neurons were nevertheless found in the murine ENS that express transcripts encoding NET, NET protein, and dopamine β-hydroxylase; these neurons lack tyrosine hydroxylase (TH) and thus are not catecholaminergic. Enteric NET expression, moreover, preceded the ingrowth of sympathetic axons during development and did not disappear when the gut was extrinsically denervated. Transiently catecholaminergic (TC), neural crest-derived precursors of enteric neurons expressed NET at embryonic day 10 (E10) and NET expression in the fetal gut peaked coincidentally with early neurogenesis at E12. Serotonergic neurons, which are born early from TC progenitors, were found to express NET in the adult ENS, as did also other early-born neurons containing calretinin or neuronal nitric oxide synthase (nNOS) immunoreactivities. NET was not expressed in TH-immunoreactive dopaminergic neurons, which are born perinatally. Genetic deletion of NET almost eliminated tryptophan hydroxylase 2 expression and significantly reduced the numbers of total, 5-HT- and calretinin-immunoreactive enteric neurons, without affecting the immunoreactivities of nNOS or TH. These observations indicate that TC precursors of subsets of noncatecholaminergic enteric neurons express NET that persists in the successors of these cells despite their loss of TH. NET expression is essential for development and/or survival of some (5-HT- and calretinin-expressing), but not all (nNOS-expressing), of these neurons.

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.

Gastroschisis in mice lacking aortic carboxypeptidase-like protein is associated with a defect in neuromuscular development of the eviscerated intestine

Mice lacking aortic carboxypeptidase-like protein (ACLP) exhibit a gastroschisis (GS) like abdominal wall defect. The objectives of this study were to evaluate the pathophysiological features of GS in ACLP mice and to characterize the neuromuscular development of the eviscerated intestine (EI). ACLP mice were created by heterozygous mating from previously generated mice with targeted disruption of ACLP. Specimens were processed for H&E, and immunohistochemistry for smooth muscle cells [SMC, alpha-smooth muscle actin (alpha-SMA) antibody], interstitial cells of Cajal (ICC, c-kit-antibody), neural crest cells (NCC, Hox-b5-antibody), and enteric neurons (EN, PGP9.5-, alpha-internexin, and synaptophysin antibody). From 47 fetuses genotyped, 13 (27.7%) were wild type, 20 (42.5%) were heterozygous, and 14 (29.8%) were ACLP homozygous. In GS mice, expression of c-kit, Hox-b5, PGP-9.5, alpha-internexin, and synaptophysin were almost completely absent and only faint alpha-SMA expression was seen in the EI. In contrast, c-kit, Hox-b5, PGP9.5, alpha-internexin, synaptophysin, and alpha-SMA expression in intra-abdominal intestine in GS fetuses was the same as control intestine. The defect observed in ACLP mice closely resembles GS. Absence of ICC, NCC, EN, and immature differentiation of SMC supports an associated defect in neuromuscular development that is restricted to the EI.

Glial cells revealed by GFAP immunoreactivity in fish gut

Glial fibrillary acidic protein (GFAP) is a commonly used marker to identify enteric glia in the mammalian gut. Little is however known about enteric glia in other vertebrates. The aim of the present study was to examine the distribution of GFAP immunoreactivity in adult and developing fish. In adult shorthorn sculpin (Myoxocephalus scorpius) and zebrafish (Danio rerio), GFAP immunoreactivity was seen in the myenteric plexus in all regions of the gut. Co-staining for the neuronal markers Hu C/D and acetylated tubulin showed that GFAP immunoreactivity was not associated with nerves. GFAP immunoreactivity was predominantly seen in processes with few glial cell bodies being demonstrated in adult fish. GFAP immunoreactivity was also found in the gut in larval zebrafish from 3 days post-fertilisation, i.e. at approximately the same time that differentiated enteric nerve cells first occur. Immunoreactivity was most prominent in areas with no or a low density of Hu-immunoreactive nerve cell bodies, indicating that the developing glia follows a different pattern from that of enteric neurons. The results suggest that GFAP can be used as a marker for enteric glia in fish, as in birds and mammals. The distribution of GFAP immunoreactivity implies that enteric glia are widespread in the fish gastrointestinal tract. Glia and neurons diverge early during development of the gastrointestinal tract.

Development of the autonomic nervous system: a comparative view

In this review we summarize current understanding of the development of autonomic neurons in vertebrates. The mechanisms controlling the development of sympathetic and enteric neurons have been studied in considerable detail in laboratory mammals, chick and zebrafish, and there are also limited data about the development of sympathetic and enteric neurons in amphibians. Little is known about the development of parasympathetic neurons apart from the ciliary ganglion in chicks. Although there are considerable gaps in our knowledge, some of the mechanisms controlling sympathetic and enteric neuron development appear to be conserved between mammals, avians and zebrafish. For example, some of the transcriptional regulators involved in the development of sympathetic neurons are conserved between mammals, avians and zebrafish, and the requirement for Ret signalling in the development of enteric neurons is conserved between mammals (including humans), avians and zebrafish. However, there are also differences between species in the migratory pathways followed by sympathetic and enteric neuron precursors and in the requirements for some signalling pathways.

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.

Expansion and differentiation of neural progenitors derived from the human adult enteric nervous system

BACKGROUND & AIMS

Neural stem and progenitor cells from the enteric nervous system have been proposed for use in cell-based therapies against specific neurogastrointestinal disorders. Recently, enteric neural progenitors were generated from human neonatal and early postnatal (until 5 years after birth) gastrointestinal tract tissues. We investigated the proliferation and differentiation of enteric nervous system progenitors isolated from human adult gastrointestinal tract.

METHODS

Human enteric spheroids were generated from adult small and large intestine tissues and then expanded and differentiated, depending on the applied cell culture conditions. For implantation studies, spheres were grafted into fetal slice cultures and embryonic aganglionic hindgut explants from mice. Differentiating enteric neural progenitors were characterized by 5-bromo-2-deoxyuridine labeling, in situ hybridization, immunocytochemistry, quantitative real-time polymerase chain reaction, and electrophysiological studies.

RESULTS

The yield of human neurosphere-like bodies was increased by culture in conditional medium derived from fetal mouse enteric progenitors. We were able to generate proliferating enterospheres from adult human small or large intestine tissues; these enterospheres could be subcultured and maintained for several weeks in vitro. Spheroid-derived cells could be differentiated into a variety of neuronal subtypes and glial cells with characteristics of the enteric nervous system. Experiments involving implantation into organotypic intestinal cultures showed the differentiation capacity of neural progenitors in a 3-dimensional environment.

CONCLUSIONS

It is feasible to isolate and expand enteric progenitor cells from human adult tissue. These findings offer new strategies for enteric stem cell research and future cell-based therapies.

Beta1 integrins are required for the invasion of the caecum and proximal hindgut by enteric neural crest cells

Integrins are the major adhesive receptors for extracellular matrix and have various roles in development. To determine their role in cell migration, the gene encoding the beta1 integrin subunit (Itgb1) was conditionally deleted in mouse neural crest cells just after their emigration from the neural tube. We previously identified a major defect in gut colonisation by conditional Itgb1-null enteric neural crest cells (ENCCs) resulting from their impaired migratory abilities and enhanced aggregation properties. Here, we show that the migration defect occurs primarily during the invasion of the caecum, when Itgb1-null ENCCs stop their normal progression before invading the caecum and proximal hindgut by becoming abnormally aggregated. We found that the caecum and proximal hindgut express high levels of fibronectin and tenascin-C, two well-known ligands of integrins. In vitro, tenascin-C and fibronectin have opposite effects on ENCCs, with tenascin-C decreasing migration and adhesion and fibronectin strongly promoting them. Itgb1-null ENCCs exhibited an enhanced response to the inhibitory effect of tenascin-C, whereas they were insensitive to the stimulatory effect of fibronectin. These findings suggest that beta1 integrins are required to overcome the tenascin-C-mediated inhibition of migration within the caecum and proximal hindgut and to enhance fibronectin-dependent migration in these regions.

Enteric nervous system development: Recent progress and future challenges

The enteric nervous system is the largest subdivision of the peripheral nervous system that plays a critical role in digestive functions. Despite considerable progress over the last 15 years in understanding the molecular and cellular mechanisms that control the development of the enteric nervous system, several questions remain unanswered. The present review will focus on recent progress on understanding the development of the mammalian enteric nervous system and highlight interesting directions of future research.

5-HT4 receptor-mediated neuroprotection and neurogenesis in the enteric nervous system of adult mice

Although the mature enteric nervous system (ENS) has been shown to retain stem cells, enteric neurogenesis has not previously been demonstrated in adults. The relative number of enteric neurons in wild-type (WT) mice and those lacking 5-HT(4) receptors [knock-out (KO)] was found to be similar at birth; however, the abundance of ENS neurons increased during the first 4 months after birth in WT but not KO littermates. Enteric neurons subsequently decreased in both WT and KO but at 12 months were significantly more numerous in WT. We tested the hypothesis that stimulation of the 5-HT(4) receptor promotes enteric neuron survival and/or neurogenesis. In vitro, 5-HT(4) agonists increased enteric neuronal development/survival, decreased apoptosis, and activated CREB (cAMP response element-binding protein). In vivo, in WT but not KO mice, 5-HT(4) agonists induced bromodeoxyuridine incorporation into cells that expressed markers of neurons (HuC/D, doublecortin), neural precursors (Sox10, nestin, Phox2b), or stem cells (Musashi-1). This is the first demonstration of adult enteric neurogenesis; our results suggest that 5-HT(4) receptors are required postnatally for ENS growth and maintenance.

Characterization of RAGE, HMGB1, and S100beta in inflammation-induced preterm birth and fetal tissue injury

Immune activation represents an adaptive reaction triggered by both noxious exogenous (microbes) and endogenous [high mobility group box-1 protein (HMGB1), S100 calcium binding proteins] inducers of inflammation. Cell stress or necrosis lead the release of HMGB1 and S100 proteins in the extracellular compartment where they act as damage-associated molecular pattern molecules (or alarmins) by engaging the receptor for advanced glycation end-products (RAGE). Although the biology of RAGE is dictated by the accumulation of damage-associated molecular pattern molecules at sites of tissue injury, the role of RAGE in mediating antenatal fetal injury remains unknown. First, we studied the relationships at birth between the intensity of human fetal inflammation and sRAGE (an endogenous RAGE antagonist), HMGB1, and S100beta protein. We found significantly lower sRAGE in human fetuses that mounted robust inflammatory responses. HMGB1 levels correlated significantly with levels of interleukin-6 and S100beta in fetal circulation. We then evaluated the levels and areas of tissue expression of RAGE, HMGB1, and S100beta in specific organs of mouse fetuses on E16. Using an animal model of endotoxin-induced fetal damage and preterm birth, we determined that inflammation induces a significant change in expression of RAGE and HMGB1, but not S100beta, at sites of tissue damage. Our findings indicate that RAGE and HMGB1 may be important mediators of cellular injury in fetuses delivered in the setting of inflammation-induced preterm birth.

ATP-dependent paracrine communication between enteric neurons and glia in a primary cell culture derived from embryonic mice

The importance of dynamic interactions between glia and neurons is increasingly recognized, both in the central and enteric nervous system. However, apart from their protective role, little is known about enteric neuro-glia interaction. The aim was to investigate neuro-glia intercellular communication in a mouse culture model using optical techniques. Complete embryonic (E13) guts were enzymatically dissociated, seeded on coverslips and studied with immunohistochemistry and Ca(2+)-imaging. Putative progenitor-like cells (expressing both PGP9.5 and S-100) differentiated over approximately 5 days into glia or neurons expressing typical cell-specific markers. The glia-neuron ratio could be manipulated by specific supplements (N2, G5). Neurons and glia were functionally identified both by their Ca(2+)-response to either depolarization (high K(+)) or lysophosphatidic acid and by the expression of typical markers. Neurons responded to ACh, DMPP, 5-HT, ATP and electrical stimulation, while glia responded to ATP and ADPbetas. Inhibition of glial responses by MRS2179 suggests involvement of P2Y1 receptors. Neuronal stimulation also caused delayed glial responses, which were reduced by suramin and by exogenous apyrases that catalyse nucleotide breakdown. Conversely, glial responses were enhanced by ARL-67156, an ecto-ATPase inhibitor. In this mouse enteric co-culture, functional glia and neurons can be easily monitored using optical techniques. Glial cells can be activated directly by ATP or ADPbetas. Activation of neuronal cells (DMPP, K(+)) causes secondary responses in glial cells, which can be modulated by tuning ATP and ADP breakdown. This strongly supports the involvement of paracrine purinergic communication between enteric neurons and glia.

Development of enteric neuron diversity

The mature enteric nervous system (ENS) is composed of many different neuron subtypes and enteric glia, which all arise from the neural crest. How this diversity is generated from neural crest-derived cells is a central question in neurogastroenterology, as defects in these processes are likely to underlie some paediatric motility disorders. Here we review the developmental appearance (the earliest age at which expression of specific markers can be localized) and birthdates (the age at which precursors exit the cell cycle) of different enteric neuron subtypes, and their projections to some targets. We then focus on what is known about the mechanisms underlying the generation of enteric neuron diversity and axon pathfinding. Finally, we review the development of the ENS in humans and the etiologies of a number of paediatric motility disorders.

Development of satellite glia in mouse sympathetic ganglia: GDNF and GFR alpha 1 are not essential

The phenotypic development of satellite cells in mouse sympathetic ganglia was examined by localizing the transcription factors, Sox10 and Phox2b, the neuronal marker, tyrosine hydroxylase (TH), and brain-derived fatty acid binding protein (B-FABP), which identifies glial precursors and mature glia. In E10.5 mice, most cells in the sympathetic chain expressed both Sox10 and Phox2b, with a minority of cells expressing Sox10 only or Phox2b only. In E11.5 mice, the majority of cells expressed Sox10 only or Phox2b only. B-FABP was colocalized with Sox10 in satellite glial precursors, which were located on the periphery of the ganglion. There was no overlap between B-FABP and Phox2b or B-FABP and TH. During subsequent development, the number of B-FABP+ cells increased and they became more common deep within the ganglion. In E12.5 and E18.5 mice, there was no overlap between Sox10 and Phox2b, and 98% of Sox10 cells were also B-FABP+. Satellite glial precursors in E11.5-E15.5 mice also expressed the GDNF-binding molecule, GFRalpha1. B-FABP immunoreactive cells did not express Ret or NCAM, two potential signaling molecules for GDNF/GFRalpha1. In E12.5 and E18.5 mice lacking GFRalpha1 or GDNF, the development of B-FABP immunoreactive satellite cells was normal, and hence neither GDNF or GFRalpha1 are essential for the development of satellite glia in sympathetic ganglia.

Notch signaling is required for the maintenance of enteric neural crest progenitors

Notch signaling is involved in neurogenesis, including that of the peripheral nervous system as derived from neural crest cells (NCCs). However,it remains unclear which step is regulated by this signaling. To address this question, we took advantage of the Cre-loxP system to specifically eliminate the protein O-fucosyltransferase 1 (Pofut1) gene, which is a core component of Notch signaling, in NCCs. NCC-specific Pofut1-knockout mice died within 1 day of birth, accompanied by a defect of enteric nervous system (ENS) development. These embryos showed a reduction in enteric neural crest cells (ENCCs) resulting from premature neurogenesis. We found that Sox10 expression, which is normally maintained in ENCC progenitors, was decreased in Pofut1-null ENCCs. By contrast,the number of ENCCs that expressed Mash1, a potent repressor of Sox10, was increased in the Pofut1-null mouse. Given that Mash1 is suppressed via the Notch signaling pathway, we propose a model in which ENCCs have a cell-autonomous differentiating program for neurons as reflected in the expression of Mash1, and in which Notch signaling is required for the maintenance of ENS progenitors by attenuating this cell-autonomous program via the suppression of Mash1.

An evolutionarily conserved intronic region controls the spatiotemporal expression of the transcription factor Sox10

Background

A major challenge lies in understanding the complexities of gene regulation. Mutation of the transcription factor SOX10 is associated with several human diseases. The disease phenotypes reflect the function of SOX10 in diverse tissues including the neural crest, central nervous system and otic vesicle. As expected, the SOX10 expression pattern is complex and highly dynamic, but little is known of the underlying mechanisms regulating its spatiotemporal pattern. SOX10 expression is highly conserved between all vertebrates characterised.

Results

We have combined in vivo testing of DNA fragments in zebrafish and computational comparative genomics to identify the first regulatory regions of the zebrafish sox10 gene. Both approaches converged on the 3' end of the conserved 1^st intron as being critical for spatial patterning of sox10 in the embryo. Importantly, we have defined a minimal region crucial for this function. We show that this region contains numerous binding sites for transcription factors known to be essential in early neural crest induction, including Tcf/Lef, Sox and FoxD3. We show that the identity and relative position of these binding sites are conserved between zebrafish and mammals. A further region, partially required for oligodendrocyte expression, lies in the 5' region of the same intron and contains a putative CSL binding site, consistent with a role for Notch signalling in sox10 regulation. Furthermore, we show that β-catenin, Notch signalling and Sox9 can induce ectopic sox10 expression in early embryos, consistent with regulatory roles predicted from our transgenic and computational results.

Conclusion

We have thus identified two major sites of sox10 regulation in vertebrates and provided evidence supporting a role for at least three factors in driving sox10 expression in neural crest, otic epithelium and oligodendrocyte domains.

Quantitative assessment of glial cells in the human and guinea pig enteric nervous system with an anti-Sox8/9/10 antibody

Quantitative changes of enteric glia (EGC) have been implicated in gastrointestinal disorders. To facilitate future studies of EGC in human pathology, we aimed to characterize thoroughly glial markers in the human enteric nervous system (ENS) and to compare EGC in man and guinea pig. Whole-mount preparations of the enteric nerve plexuses from human and guinea pig ileum and colon were labeled with antibodies against S100b, glial fibrillary acidic protein (GFAP), and p75NGFR and the transcription factors Sox8/9/10 and neuronally counterstained. Abundant immunoreactivity (IR) for S100b, GFAP, p75NGFR, and Sox8/9/10 was detected in EGC of all studied regions. Although the cytoplasmatic staining pattern of most markers did not permit glial quantification, the nuclear localization of Sox8/9/10-IR allowed to identify and count all EGC individually. In both man and guinea pig, myenteric ganglia were larger and contained more EGC and neurons than submucous ganglia. Furthermore, there were more EGC in the human than in the guinea pig myenteric plexus (MP), glial density was consistently higher in the human ENS, and the glia index (glia:neuron ratio) ranged from 1.3 to 1.9 and from 5.9 to 7.0 in the human submucous plexus (SMP) and MP, respectively, whereas, in guinea pig, the glia index was 0.8-1.0 in the SMP and 1.7 in the MP. The glia index was the most robust quantitative descriptor within one species. This is a comprehensive set of quantitative EGC measures in man and guinea pig that provides a basis for pathological assessment of glial proliferation and/or degeneration in the diseased gut.

A Histone2BCerulean BAC transgene identifies differential expression of Phox2b in migrating enteric neural crest derivatives and enteric glia

The mammalian enteric nervous system (ENS) derives from migratory enteric neural crest-derived cells (ENCC) that express the transcription factor Phox2b. Studies of these enteric progenitors have typically relied on immunohistochemical (IHC) detection. To circumvent complicating factors of IHC, we have generated a mouse BAC transgenic line that drives a Histone2BCerulean (H2BCFP) reporter from Phox2b regulatory regions. This construct does not alter the endogenous Phox2b locus and enables studies of normal neural crest (NC) derivatives. The Phox2b-H2BCFP transgene expresses the H2BCFP reporter in patterns that recapitulate expression of endogenous Phox2b. Our studies reveal Phox2b expression in mature enteric glia at levels below that of enteric neurons. Moreover, we also observe differential expression of the transgene reporter within the leading ENCC that traverse the gut. Our findings indicate that the wavefront of migrating enteric progenitors is not homogeneous, and suggest these cells may be fate-specified before expression of mature lineage markers appears.

Signals from the neural crest regulate beta-cell mass in the pancreas

Pancreatic islet cells and neurons share common functions and similar ontogenies, but originate in different germ layers. To determine whether ectoderm-derived cells contribute instructive signals to the developing endoderm-derived pancreas, we defined the chronology of migration and differentiation of neural crest cells in the pancreas, and tested their role in the development of the islets. The homeodomain transcription factor Phox2b marks the neural precursors from the neural crest that colonize the gut to form the enteric nervous system. In the embryonic mouse pancreas, we found Phox2b expressed briefly together with Sox10 along the epithelial-mesenchymal border at E12.5 in cells derived from the neural crest. Downregulation of Phox2b shortly thereafter was dependent upon Nkx2.2 expressed in the adjacent pancreatic epithelium. In Phox2b-/- embryos, neurons and glia did not develop in the pancreas, and Nkx2.2 expression was markedly upregulated in the epithelium. In addition, the number and replication rate of insulin-expressing beta-cells increased in the Phox2b-/-mice. We conclude that, during pancreatic development, Phox2b and Nkx2.2 form a non-cell-autonomous feedback loop that links the neural crest with the pancreatic epithelium, regulates the size of the beta-cell population, and thereby impacts insulin-secretory capacity and energy homeostasis.

Ret isoform function and marker gene expression in the enteric nervous system is conserved across diverse vertebrate species

The enteric nervous system (ENS) derives from migratory neural crest cells that colonize the developing gut tube, giving rise to an integrated network of neurons and glial cells, which together regulate important aspects of gut function, including coordinating the smooth muscle contractions of the gut wall. The absence of enteric neurons in portions of the gut (aganglionosis) is the defining feature of Hirschsprung's disease (HSCR) and has been replicated in a number of mouse models. Mutations in the RET tyrosine kinase account for over half of familial cases of HSCR and mice mutant for Ret exhibit aganglionosis. RET exists in two main isoforms, RET9 and RET51 and studies in mouse have shown that RET9 is sufficient to allow normal development of the ENS. In the last several years, zebrafish has emerged as a model of vertebrate ENS development, having been supported by a number of demonstrations of conservation of gene function between zebrafish, mouse and human. In this study we further analyse the potential similarities and differences between ENS development in zebrafish, mouse and human. We demonstrate that zebrafish Ret is required in a dose-dependent manner to regulate colonization of the gut by neural crest derivatives, as in human. Additionally, we show that as in mouse and human, zebrafish ret is produced as two isoforms, ret9 and ret51. Moreover, we show that, as in mouse, the Ret9 isoform is sufficient to support colonization of the gut by enteric neurons. Finally, we identify zebrafish orthologues of genes previously identified to be expressed in the mouse ENS and demonstrate that these genes are expressed in the developing zebrafish ENS, thereby identifying useful ENS markers in this model organism. These studies reveal that the similarities between gene expression and gene function across vertebrate species is more extensive than previously appreciated, thus supporting the use of zebrafish as a general model for vertebrate ENS development and the use of zebrafish genetic screens as a way to identify candidate genes mutated in HSCR cases.

Functional development of the enteric nervous system--from migration to motility

The enteric nervous system (ENS) consists of many different types of enteric neurones forming complex reflex circuits that underlie or regulate many gut functions. Studies of humans with Hirschsprung's disease (distal aganglionosis), and of animal models of Hirschsprung's disease, have led to the identification of many of the genetic, molecular and cellular mechanisms responsible for the colonization of the gut by enteric neurone precursors. However, later events in the ENS development are still poorly understood, including the development of functioning ENS circuits. This article is a personal view of the current state of play in our understanding of the ENS development and of the future of the field.

Neural progenitors from isolated postnatal rat myenteric ganglia: expansion as neurospheres and differentiation in vitro

Identification of the stem cell niche is crucial for understanding the factors that regulate these cells. Rodent enteric neural crest-derived stem cells have previously been isolated by flow cytometry and culture of cell suspensions from the outer smooth muscle layers or the entire gut wall from postnatal and adult animals. Such cell suspensions contain a mixture of cell types, including smooth muscle, fibroblasts and cells associated with the vasculature and extrinsic innervation. Thus these preparations may be contaminated by stem cells associated with extrinsic sensory and autonomic nerves and by other types of stem cell that reside in the gut. Here we describe a different approach, similar to that recently used for infant human gut, to obtain enteric ganglion-derived cells, with properties of neural progenitor cells, using isolated myenteric ganglia from postnatal rat ileum. Myenteric ganglia were separated from the gut wall, dispersed and resulting cell dissociates were plated in non-adherent culture conditions with EGF and FGF-2. Under these conditions neurosphere-like bodies (NLB) developed. Cells in NLB incorporated BrdU and expressed the stem cell marker nestin but not the pan-neuronal marker PGP 9.5. Upon growth factor withdrawal some BrdU-immunopositive cells assumed the morphology of neurons and expressed PGP 9.5; others were flattened and expressed the glial cell marker GFAP. This work therefore provides evidence that neural crest-derived progenitors in the postnatal rat gut are located in the myenteric plexus, and shows that these cells can be expanded and differentiated in NLB in vitro.

Conditional ablation of GFRalpha1 in postmigratory enteric neurons triggers unconventional neuronal death in the colon and causes a Hirschsprung's disease phenotype

The regulation of neuronal survival and death by neurotrophic factors plays a central role in the sculpting of the nervous system, but the identity of survival signals for developing enteric neurons remains obscure. We demonstrate here that conditional ablation of GFRalpha1, the high affinity receptor for GDNF, in mice during late gestation induces rapid and widespread neuronal death in the colon, leading to colon aganglionosis reminiscent of Hirschsprung's disease. Enteric neuron death induced by GFRalpha1 inactivation is not associated with the activation of common cell death executors, caspase-3 or -7, and lacks the morphological hallmarks of apoptosis, such as chromatin compaction and mitochondrial pathology. Consistent with these in vivo observations, neither caspase inhibition nor Bax deficiency blocks death of colon-derived enteric neurons induced by GDNF deprivation. This study reveals an essential role for GFRalpha1 in the survival of enteric neurons and suggests that caspase-independent death can be triggered by abolition of neurotrophic signals.

Expression of the Rai (Shc C) adaptor protein in the human enteric nervous system

The adaptor protein Rai (ShcC/N-Shc) is almost exclusively present in the nervous system, although little is documented about its expression in the gut and the enteric nervous system (ENS). As Rai is a physiological substrate of Ret, an important factor for the development of ENS, we have evaluated the expression of Rai in the ENS in various segments of the human gastrointestinal tract. The expression of Rai was assessed by immunohistochemistry in disease-free human gut samples (oesophagus, stomach, small bowel and colon) obtained from subjects undergoing surgical procedures. Rai was not expressed in the epithelia or lymphoid tissue, whereas a moderate level of expression was observed in the endothelial cells of blood vessels and on the outer membrane of smooth muscle cells in both the muscularis mucosae and the muscularis propria. In the ENS, strong positivity was observed only in enteric glial cells, overlapping with GFAP and S100. In conclusion, Rai is expressed in the human gut, especially in the enteric glial cells. We conclude that Rai may provide an additional marker for this cell type.

The receptor tyrosine kinase RET regulates hindgut colonization by sacral neural crest cells

The enteric nervous system (ENS) is formed from vagal and sacral neural crest cells (NCC). Vagal NCC give rise to most of the ENS along the entire gut, whereas the contribution of sacral NCC is mainly limited to the hindgut. This, and data from heterotopic quail-chick grafting studies, suggests that vagal and sacral NCC have intrinsic differences in their ability to colonize the gut, and/or to respond to signalling cues within the gut environment. To better understand the molecular basis of these differences, we studied the expression of genes known to be essential for ENS formation, in sacral NCC within the chick hindgut. Our results demonstrate that, as in vagal NCC, Sox10, EdnrB, and Ret are expressed in sacral NCC within the gut. Since we did not detect a qualitative difference in expression of these ENS genes we performed DNA microarray analysis of vagal and sacral NCC. Of 11 key ENS genes examined from the total data set, Ret was the only gene identified as being highly differentially expressed, with a fourfold increase in expression in vagal versus sacral NCC. We also found that over-expression of RET in sacral NCC increased their ENS developmental potential such that larger numbers of cells entered the gut earlier in development, thus promoting the fate of sacral NCC towards that of vagal NCC.

Enteric glial cells and their role in gastrointestinal motor abnormalities: Introducing the neuro-gliopathies

The role of enteric glial cells has somewhat changed from that of mere mechanical support elements, gluing together the various components of the enteric nervous system, to that of active participants in the complex interrelationships of the gut motor and inflammatory events. Due to their multiple functions, spanning from supporting elements in the myenteric plexuses to neurotransmitters, to neuronal homeostasis, to antigen presenting cells, this cell population has probably more intriguing abilities than previously thought. Recently, some evidence has been accumulating that shows how these cells may be involved in the pathophysiological aspects of some diseases. This review will deal with the properties of the enteric glial cells more strictly related to gastrointestinal motor function and the human pathological conditions in which these cells may play a role, suggesting the possibility of enteric neuro-gliopathies.

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.

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.

Enteric glial cells: new players in gastrointestinal motility?

The enteric glial cells, in addition to being support structures for the enteric nervous system, have many other additional roles, such as modulators for the homeostasis of enteric neurons, cells involved in enteric neurotransmission and antigen-presenting cells. Moreover, in the last years, data have been accumulating that demonstrate a possible active role of these cells in the pathophysiology of gastrointestinal motor activity. Thus, as also shown by recent evidence in both experimental animal models, and in some human diseases, alterations of enteric glial cells might have some role in the development of intestinal motor abnormalities.

Expression of the epithelial marker E-cadherin by thyroid C cells and their precursors during murine development

Studies of chick-quail chimeras have reported that avian ultimobranchial C cells originate from the neural crest. It has consequently been assumed, without much supporting evidence, that mammalian thyroid C cells also originate from the neural crest. To test this notion, we employed both Connexin43-lacZ and Wnt1-Cre/R26R transgenic mice, because their neural crest cells can be marked. We also examined the immunohistochemical expression of a number of markers that identify migratory or postmigratory neural crest cells, namely, TuJ1, neurofilament 160, nestin, P75NTR, and Sox10. Moreover, we examined the expression of E-cadherin, an epithelial cell marker. At embryonic day (E)10.5, the neural crest cells densely populated the pharyngeal arches but were not distributed in the pharyngeal pouches, including the fourth pouch. At E11.5, the ultimobranchial rudiment formed from the fourth pouch and was located close to the fourth arch artery. At E13.0, this organ came into contact with the thyroid lobe, and at E13.5, it fused with this lobe. However, the ultimobranchial body was not colonized by neural crest-derived cells at any of these developmental stages. Instead, all ultimobranchial cells, as well as the epithelium of the fourth pharyngeal pouch, were intensely immunoreactive for E-cadherin. Furthermore, confocal microscopy of newborn mouse thyroid glands revealed colocalization of calcitonin and E-cadherin in the C cells. The cells, however, were not marked in the Wnt-Cre/R26R mice. These results indicated that murine thyroid C cells are derived from the endodermal epithelial cells of the fourth pharyngeal pouch and do not originate from neural crest cells.

Hand2 is necessary for terminal differentiation of enteric neurons from crest-derived precursors but not for their migration into the gut or for formation of glia

Hand genes encode basic helix-loop-helix transcription factors that are expressed in the developing gut, where their function is unknown. We now report that enteric Hand2 expression is limited to crest-derived cells, whereas Hand1 expression is restricted to muscle and interstitial cells of Cajal. Hand2 is developmentally regulated and is intranuclear in precursors but cytoplasmic in neurons. Neurons develop in explants from wild-type but not Hand2(-/-) bowel, although, in both, crest-derived cells are present and glia arise. Similarly, small interfering RNA (siRNA) silencing of Hand2 in enteric crest-derived cells prevents neuronal development. Terminally differentiated enteric neurons do not develop after conditional inactivation of Hand2 in migrating crest-derived cells; nevertheless, conditional Hand2 inactivation does not prevent precursors from expressing early neural markers. We suggest that enteric neuronal development occurs in stages and that Hand2 expression is required for terminal differentiation but not for precursors to enter the neuronal lineage.

Pelvic plexus contributes ganglion cells to the hindgut enteric nervous system

The hindgut enteric nervous system (ENS) contains cells originating from vagal and sacral neural crest. In avians, the sacral crest gives rise to the nerve of Remak (NoR) and pelvic plexus. Whereas the NoR has been suggested to serve as the source of sacral crest-derived cells to the gut, the contribution of the pelvic ganglia is unknown. The purpose of this study was to test the hypothesis that the pelvic ganglia contribute ganglion cells to the hindgut ENS. We observed that the quail pelvic plexus develops from neural crest-derived cells that aggregate around the cloaca at embryonic day 5. Using chick-quail tissue recombinations, we found that hindgut grafts did not contain enteric ganglia unless the pelvic plexus was included. Neurofibers extended from the NoR into the intestine, but no ganglion cell contribution from the NoR was identified. These results demonstrate that the pelvic plexus, and not the NoR, serves as the staging area for sacral crest-derived cells to enter the avian hindgut, confirming the evolutionary conservation of this important embryologic process.

Biology of the adult enteric neural stem cell

An increasing body of evidence has accumulated in recent years supporting the existence of neural stem cells in the adult gut. There are at least three groups that have obtained them using different methodologies and have described them in vitro. There is a growing amount of knowledge on their biology, but many questions are yet unanswered. Among these questions is whether these cells are part of a permanent undifferentiated pool or are recruited in a regular basis; in addition, the factors and genes involved in their survival, proliferation, migration, and differentiation are largely unknown. Finally, with between 10 and 20% of adults suffering from diseases involving the enteric nervous system, most notably irritable bowel syndrome and gastroesophageal reflux, what is the possible role of enteric nervous stem cells in health and disease?

In vitro development of gut-like tissue demonstrating rhythmic contractions from embryonic mouse intestinal cells

The rhythmic motility of the intestine is regulated by the interstitial cells of Cajal (ICC) and the enteric nervous system. Rhythmic motility is considered to occur after the differentiation of mesenchymal progenitor cells into ICC during the late embryonic period. In this study, we successfully reconstructed a gut-like tissue demonstrating rhythmic contractions by culturing dispersed cells enzymatically isolated from the mouse intestine during the mid-embryonic period. These intestinal cells were reconstituted into a collagen gel at high density, made to proliferate considerably, and grew into a gut-like tissue after 1 week of culturing. The reconstituted tissue showed rhythmic contractions and stained positive for the specific marker proteins of neurones and ICC, PGP9.5 and c-Kit. The tissue also demonstrated network formation by developing nerve cells and ICC. Moreover, in the presence of nifedipine, c-Kit-immunopositive cells showed spontaneous Ca(2+) oscillation, which is considered to be coupled to the electrical activity that corresponds to slow waves. Therefore, this culture system may be of use in elucidating the developmental mechanisms of gastrointestinal motility.