Accumulation of components of basal laminae: association with the failure of neural crest cells to colonize the presumptive aganglionic bowel of ls/ls mutant mice

The impact of the recipient intestinal site on the differentiation of transplanted enteric neural crest cells

PURPOSE

It has long been established that the failure of enteric neural crest cells (ENCCs) to colonize the entire gut results in aganglionosis at the distal colon in Hirschsprung disease (HD). However, it is still unclear how the intestinal microenvironment of the distal aganglionic gut differs from that of the proximal ganglionic gut in HD versus normal gut. We have recently succeeded in transplanting ENCC into aganglionic gut in endothelin receptor B (Ednrb) knockout (KO) mice. to advance the development of cell therapy for HD, it is essential to determine if the transplanted ENCCs differentiate normally in aganglionic gut. Therefore, we designed this study to investigate the impact of the environment of the recipient intestinal tract, at various sites of aganglionic gut, on the differentiation of transplanted ENCCs.

METHODS

ENCCs were isolated from Sox10 Venus transgenic (Tg) mouse gut on embryonic day 18.5 (E18.5) and neurospheres (NS) were generated. Then, NS were transplanted into aganglionic KO and wildtype (WT) gut that had been transected just distal to the ENCC wavefront (KO-wf: n = 6, WT: n = 7), and into distal KO gut transected at a site equivalent to that of the WT (KO-d: n = 6) on E12.5. ENCC differentiation was evaluated using whole-mount immunohistochemistry with Tuj-1 (neuronal marker) and GFAP (glial marker) antibodies.

RESULTS

The transplanted ENCCs migrated to form the myenteric and submucosal plexus in all groups. The ratio of the area of Tuj-1-positive cells/GFAP-positive cells in migrated cells in the recipient gut was found to be significantly lower in KO-d compared to KO-wf and WT, while there was no significant difference between KO-wf and WT groups. This suggests that neuronal/glial differentiation was decreased in KO-d compared to that in KO-wf and WT groups.

CONCLUSION

Our study highlights the differences in ENCC differentiation depending on the site of transplantation. To further develop cell therapy for HD, it is important to consider the impact of the recipient intestinal environment on transplanted ENCCs.

Roles of Enteric Neural Stem Cell Niche and Enteric Nervous System Development in Hirschsprung Disease

The development of the enteric nervous system (ENS) is highly modulated by the synchronized interaction between the enteric neural crest cells (ENCCs) and the neural stem cell niche comprising the gut microenvironment. Genetic defects dysregulating the cellular behaviour(s) of the ENCCs result in incomplete innervation and hence ENS dysfunction. Hirschsprung disease (HSCR) is a rare complex neurocristopathy in which the enteric neural crest-derived cells fail to colonize the distal colon. In addition to ENS defects, increasing evidence suggests that HSCR patients may have intrinsic defects in the niche impairing the extracellular matrix (ECM)-cell interaction and/or dysregulating the cellular niche factors necessary for controlling stem cell behaviour. The niche defects in patients may compromise the regenerative capacity of the stem cell-based therapy and advocate for drug- and niche-based therapies as complementary therapeutic strategies to alleviate/enhance niche-cell interaction. Here, we provide a summary of the current understandings of the role of the enteric neural stem cell niche in modulating the development of the ENS and in the pathogenesis of HSCR. Deciphering the contribution of the niche to HSCR may provide important implications to the development of regenerative medicine for HSCR.

Diabetes-related intestinal region-specific thickening of ganglionic basement membrane and regionally decreased matrix metalloproteinase 9 expression in myenteric ganglia

BACKGROUND

The importance of the neuronal microenvironment has been recently highlighted in gut region-specific diabetic enteric neuropathy. Regionally distinct thickening of endothelial basement membrane (BM) of intestinal capillaries supplying the myenteric ganglia coincide with neuronal damage in different intestinal segments. Accelerated synthesis of matrix molecules and reduced degradation of matrix components may also contribute to the imbalance of extracellular matrix dynamics resulting in BM thickening. Among the matrix degrading proteinases, matrix metalloproteinase 9 (MMP9) and its tissue inhibitor (TIMP1) are essential in regulating extracellular matrix remodelling.

AIM

To evaluate the intestinal segment-specific effects of diabetes and insulin replacement on ganglionic BM thickness, MMP9 and TIMP1 expression.

METHODS

Ten weeks after the onset of hyperglycaemia gut segments were taken from the duodenum and ileum of streptozotocin-induced diabetic, insulin-treated diabetic and sex- and age-matched control rats. The thickness of BM surrounding myenteric ganglia was measured by electron microscopic morphometry. Whole-mount preparations of myenteric plexus were prepared from the different gut regions for MMP9/TIMP1 double-labelling fluorescent immunohistochemistry. Post-embedding immunogold electron microscopy was applied on ultrathin sections to evaluate the MMP9 and TIMP1 expression in myenteric ganglia and their microenvironment from different gut segments and conditions. The MMP9 and TIMP1 messenger ribonucleic acid (mRNA) level was measured by quantitative polymerase chain reaction.

RESULTS

Ten weeks after the onset of hyperglycaemia, the ganglionic BM was significantly thickened in the diabetic ileum, while it remained intact in the duodenum. The immediate insulin treatment prevented the diabetes-related thickening of the BM surrounding the ileal myenteric ganglia. Quantification of particle density showed an increasing tendency for MMP9 and a decreasing tendency for TIMP1 from the proximal to the distal small intestine under control conditions. In the diabetic ileum, the number of MMP9-indicating gold particles decreased in myenteric ganglia, endothelial cells of capillaries and intestinal smooth muscle cells, however, it remained unchanged in all duodenal compartments. The MMP9/TIMP1 ratio was also decreased in ileal ganglia only. However, a marked segment-specific induction was revealed in MMP9 and TIMP1 at the mRNA levels.

CONCLUSION

These findings support that the regional decrease in MMP9 expression in myenteric ganglia and their microenvironment may contribute to extracellular matrix accumulation, resulting in a region-specific thickening of ganglionic BM.

Development of the Autonomic Nervous System: Clinical Implications

Investigations of the cellular and molecular mechanisms that mediate the development of the autonomic nervous system have identified critical genes and signaling pathways that, when disrupted, cause disorders of the autonomic nervous system. This review summarizes our current understanding of how the autonomic nervous system emerges from the organized spatial and temporal patterning of precursor cell migration, proliferation, communication, and differentiation, and discusses potential clinical implications for developmental disorders of the autonomic nervous system, including familial dysautonomia, Hirschsprung disease, Rett syndrome, and congenital central hypoventilation syndrome.

Submucosal Supernumerary Smooth Muscle Coat: A Common Histologic Finding in Mowat-Wilson Syndrome With or Without Hirschsprung Disease

BACKGROUND

Mowat-Wilson syndrome (MWS) is a multiorgan system disorder caused by ZEB2 (zinc finger E-box-binding homeobox 2) mutations or deletions. One common manifestation is constipation, and approximately half of the patients have Hirschsprung disease (HSCR). In addition to classic histologic features of HSCR, an unusual supernumerary intestinal muscle coat was recently reported in a patient of MWS with HSCR. A similar smooth muscle alteration, segmental additional circular muscle coat, had been described in the specimens from patients with intestinal pseudo-obstruction without MWS or HSCR.

METHOD

Rectal biopsies and rectosigmoidectomy specimens from MWS patients were identified by retrospective reviews of surgical pathology records. Routinely prepared glass slides were examined to determine whether any smooth muscle structural alteration was present. Clinical information was obtained by chart review.

RESULTS

Six MWS patients were identified. A supernumerary smooth muscle coat in the submucosa was present in 3 of them, including 2 of the 4 patients with HSCR.

CONCLUSION

The structural anomaly, termed submucosal supernumerary smooth muscle coat, is not a syndrome-specific pathological feature. However, it appears to be more common than expected in MWS and is consistent with contemporary models for the roles of ZEB2 and related cell signaling pathways in the patterning of intestinal musculature during embryonic development.

Large intestine embryogenesis: Molecular pathways and related disorders (Review)

The large intestine, part of the gastrointestinal tract (GI), is composed of all three germ layers, namely the endoderm, the mesoderm and the ectoderm, forming the epithelium, the smooth muscle layers and the enteric nervous system, respectively. Since gastrulation, these layers develop simultaneously during embryogenesis, signaling to each other continuously until adult age. Two invaginations, the anterior intestinal portal (AIP) and the caudal/posterior intestinal portal (CIP), elongate and fuse, creating the primitive gut tube, which is then patterned along the antero‑posterior (AP) axis and the radial (RAD) axis in the context of left‑right (LR) asymmetry. These events lead to the formation of three distinct regions, the foregut, midgut and hindgut. All the above‑mentioned phenomena are under strict control from various molecular pathways, which are critical for the normal intestinal development and function. Specifically, the intestinal epithelium constitutes a constantly developing tissue, deriving from the progenitor stem cells at the bottom of the intestinal crypt. Epithelial differentiation strongly depends on the crosstalk with the adjacent mesoderm. Major molecular pathways that are implicated in the embryogenesis of the large intestine include the canonical and non‑canonical wingless‑related integration site (Wnt), bone morphogenetic protein (BMP), Notch and hedgehog systems. The aberrant regulation of these pathways inevitably leads to several intestinal malformation syndromes, such as atresia, stenosis, or agangliosis. Novel theories, involving the regulation and homeostasis of intestinal stem cells, suggest an embryological basis for the pathogenesis of colorectal cancer (CRC). Thus, the present review article summarizes the diverse roles of these molecular factors in intestinal embryogenesis and related disorders.

Decreased expression of β1 integrin in enteric neural crest cells of the endothelin receptor B null mouse model

BACKGROUND

Interactions between enteric neural crest-derived cells (ENCC) and the surrounding intestinal microenvironment, such as the extracellular matrix (ECM), are critical for regulating enteric nervous system (ENS) development. Integrins are the major receptors for ECM molecules, such as laminin, which have been reported to be involved in the pathogenesis of Hirschsprung's disease. In this study, we examined the expression of β1 integrin in the endothelin receptor B (Ednrb) knock out (KO) mouse gut, which presents with an aganglionic colon.

METHODS

A Sox10-Venus-positive Ednrb KO mouse, where ENCC is labeled with fluorescent protein, 'Venus', was created. Sox10-Venus-positive Ednrb wild type (WT) were used as controls. Small intestine, proximal colon and distal colon were dissected on E13.5 and E15.5 and β1 integrin expression of the gut tissue was examined by immunohistochemistry and real time RT-PCR. The cells of the gut dissected on E11.5 were isolated and cultured for 2 days. Venus-positive ENCC were immunostained with β1 integrin and Tuj-1, which is a marker for neurons.

RESULTS

The expression of β1 integrin was not significantly different between KO and WT in all parts of the gut examined. However, the β1 integrin expression in the isolated ENCC was significantly decreased in KO compared to WT. The average threshold area was 42.98 ± 17.47% in KO and 73.53 ± 13.77 in WT (p < 0.001).

CONCLUSIONS

We demonstrated that β1 integrin expression was specifically decreased in ENCC in Ednrb KO mice. Our results suggest that impaired interaction between integrin and its ligands may disturb normal ENS development, resulting in an aganglionic colon.

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

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

Collagen 18 and agrin are secreted by neural crest cells to remodel their microenvironment and regulate their migration during enteric nervous system development

The enteric nervous system (ENS) arises from neural crest cells that migrate, proliferate, and differentiate into enteric neurons and glia within the intestinal wall. Many extracellular matrix (ECM) components are present in the embryonic gut, but their role in regulating ENS development is largely unknown. Here, we identify heparan sulfate proteoglycan proteins, including collagen XVIII (Col18) and agrin, as important regulators of enteric neural crest-derived cell (ENCDC) development. In developing avian hindgut, Col18 is expressed at the ENCDC wavefront, while agrin expression occurs later. Both proteins are normally present around enteric ganglia, but are absent in aganglionic gut. Using chick-mouse intestinal chimeras and enteric neurospheres, we show that vagal- and sacral-derived ENCDCs from both species secrete Col18 and agrin. Whereas glia express Col18 and agrin, enteric neurons only express the latter. Functional studies demonstrate that Col18 is permissive whereas agrin is strongly inhibitory to ENCDC migration, consistent with the timing of their expression during ENS development. We conclude that ENCDCs govern their own migration by actively remodeling their microenvironment through secretion of ECM proteins.

Altered expression of laminin alpha1 in aganglionic colon of endothelin receptor-B null mouse model of Hirschsprung's disease

PURPOSE

Laminin, an extracellular matrix molecule, is essential for normal development of the nervous system. The alpha1 subunit of laminin-1 (LAMA1) has been reported to promote neurites and outgrowth and is expressed only during embryogenesis. Previously, we developed a Sox10 transgenic version of the Endothelin receptor-B (Ednrb) mouse to visualize Enteric neural crest-derived cell (ENCC)s with a green fluorescent protein, Venus. We designed this study to investigate the expression of LAMA1 using Sox10-VENUS mice gut.

METHODS

We harvested the gut on days 13.5 (E13.5) and 15.5 (E15.5) of gestation. Sox10-VENUS⁺/Ednrb ^-/- mice (n = 8) were compared with Sox10-VENUS⁺/Ednrb ^+/+ mice (n = 8) as controls. Gene expression of LAMA1 was analysed by real-time RT-PCR. Fluorescent immunohistochemistry was performed to assess protein distribution.

RESULTS

The relative mRNA expression levels of LAMA1 were significantly increased in HD in the proximal and distal colon on E15.5 compared to controls (p < 0.05), whereas there were no significant differences on E13.5. LAMA1 was expressed in the serosa, submucosa and basal lamina in the gut, and was markedly increased in the proximal and distal colon of HD on E15.5.

CONCLUSIONS

Altered LAMA1 expression in the aganglionic region may contribute to impaired ENCC migration, resulting in HD. These data could help in understanding the pathophysiologic interactions between LAMA1 and ENCC migration.

The effect of laminin-1 on enteric neural crest-derived cell migration in the Hirschsprung's disease mouse model

BACKGROUND/AIM

Laminin-1 regulates neurite outgrowth in various neuronal cells. We have previously demonstrated that laminin-1 promotes enteric neural crest-derived cell (ENCC) migration by using Sox10-VENUS transgenic mice, in which ENCCs are labeled with a green fluorescent protein, Venus. Mice lacking the endothelin-B receptor gene, Ednrb ^-/- mice, are widely used as a model for Hirschsprung's disease (HD). The aim of this study was to investigate the effects of laminin-1on ENCC migration in Sox10-VENUS⁺/Ednrb ^-/- mice, a newly created HD mice model.

METHODS

Fetal guts were dissected on embryonic day 12.5 (E12.5). Specimens were incubated either with, or without laminin-1 for 24 h and images were taken under a stereoscopic microscope. The length from the stomach to the wavefront of ENCC migration (L-E) and the total length of the gut (L-G) were measured. Changes in the ratio of L-E to L-G (L-E/L-G) after 24 h were calculated.

RESULTS

On E12.5, the wavefront of ENCC migration in the HD gut samples was located in the midgut, whereas the wavefront of ENCC in Sox10-VENUS⁺/Ednrb ^+/+ (WT) samples had reached the hindgut. After 24 h, L-E/L-G had increased by 1.49%, from 34.97 to 36.46%, in HD gut and had increased by 1.07%, from 48.08 to 49.15%, in HD with laminin-1, suggesting there was no positive effect of laminin-1 administration on ENCC migration in HD.

CONCLUSIONS

Our results suggest that laminin-1 does not have a positive effect on ENCC migration in HD mice on E12.5, in contrast to the phenomenon seen in normal mice gut specimens, where laminin-1 promotes ENCC migration during the same period. This suggests that there is an impairment in the interaction between ENCC and extracellular environmental factors, which are required for normal development of the enteric nervous system, resulting in an aganglionic colon in HD.

Enteric nervous system development: A crest cell's journey from neural tube to colon

The enteric nervous system (ENS) is comprised of a network of neurons and glial cells that are responsible for coordinating many aspects of gastrointestinal (GI) function. These cells arise from the neural crest, migrate to the gut, and then continue their journey to colonize the entire length of the GI tract. Our understanding of the molecular and cellular events that regulate these processes has advanced significantly over the past several decades, in large part facilitated by the use of rodents, avians, and zebrafish as model systems to dissect the signals and pathways involved. These studies have highlighted the highly dynamic nature of ENS development and the importance of carefully balancing migration, proliferation, and differentiation of enteric neural crest-derived cells (ENCCs). Proliferation, in particular, is critically important as it drives cell density and speed of migration, both of which are important for ensuring complete colonization of the gut. However, proliferation must be tempered by differentiation among cells that have reached their final destination and are ready to send axonal extensions, connect to effector cells, and begin to produce neurotransmitters or other signals. Abnormalities in the normal processes guiding ENCC development can lead to failure of ENS formation, as occurs in Hirschsprung disease, in which the distal intestine remains aganglionic. This review summarizes our current understanding of the factors involved in early development of the ENS and discusses areas in need of further investigation.

Endothelin-3 stimulates cell adhesion and cooperates with β1-integrins during enteric nervous system ontogenesis

Endothelin-3 (EDN3) and β1-integrins are required for the colonization of the embryonic gut by enteric neural crest cells (ENCCs) to form the enteric nervous system (ENS). β1-integrin-null ENCCs exhibit migratory defects in a region of the gut enriched in EDN3 and in specific extracellular matrix (ECM) proteins. We investigated the putative role of EDN3 on ENCC adhesion properties and its functional interaction with β1-integrins during ENS development. We show that EDN3 stimulates ENCC adhesion to various ECM components in vitro. It induces rapid changes in ENCC shape and protrusion dynamics favouring sustained growth and stabilization of lamellipodia, a process coincident with the increase in the number of focal adhesions and activated β1-integrins. In vivo studies and ex-vivo live imaging revealed that double mutants for Itgb1 and Edn3 displayed a more severe enteric phenotype than either of the single mutants demonstrated by alteration of the ENS network due to severe migratory defects of mutant ENCCs taking place early during the ENS development. Altogether, our results highlight the interplay between the EDN3 and β1-integrin signalling pathways during ENS ontogenesis and the role of EDN3 in ENCC adhesion.

How Tissue Mechanical Properties Affect Enteric Neural Crest Cell Migration

Neural crest cells (NCCs) are a population of multipotent cells that migrate extensively during vertebrate development. Alterations to neural crest ontogenesis cause several diseases, including cancers and congenital defects, such as Hirschprung disease, which results from incomplete colonization of the colon by enteric NCCs (ENCCs). We investigated the influence of the stiffness and structure of the environment on ENCC migration in vitro and during colonization of the gastrointestinal tract in chicken and mouse embryos. We showed using tensile stretching and atomic force microscopy (AFM) that the mesenchyme of the gut was initially soft but gradually stiffened during the period of ENCC colonization. Second-harmonic generation (SHG) microscopy revealed that this stiffening was associated with a gradual organization and enrichment of collagen fibers in the developing gut. Ex-vivo 2D cell migration assays showed that ENCCs migrated on substrates with very low levels of stiffness. In 3D collagen gels, the speed of the ENCC migratory front decreased with increasing gel stiffness, whereas no correlation was found between porosity and ENCC migration behavior. Metalloprotease inhibition experiments showed that ENCCs actively degraded collagen in order to progress. These results shed light on the role of the mechanical properties of tissues in ENCC migration during development.

Sonic hedgehog controls enteric nervous system development by patterning the extracellular matrix

The enteric nervous system (ENS) develops from neural crest cells that migrate along the intestine, differentiate into neurons and glia, and pattern into two plexuses within the gut wall. Inductive interactions between epithelium and mesenchyme regulate gut development, but the influence of these interactions on ENS development is unknown. Epithelial-mesenchymal recombinations were constructed using avian hindgut mesenchyme and non-intestinal epithelium from the bursa of Fabricius. These recombinations led to abnormally large and ectopically positioned ganglia. We hypothesized that sonic hedgehog (Shh), a secreted intestinal epithelial protein not expressed in the bursa, mediates this effect. Inhibition of Shh signaling, by addition of cyclopamine or a function-blocking antibody, resulted in large, ectopic ganglia adjacent to the epithelium. Shh overexpression, achieved in ovo using Shh-encoding retrovirus and in organ culture using recombinant protein, led to intestinal aganglionosis. Shh strongly induced the expression of versican and collagen type IX, whereas cyclopamine reduced expression of these chondroitin sulfate proteoglycans that are known to be inhibitory to neural crest cell migration. Shh also inhibited enteric neural crest-derived cell (ENCC) proliferation, promoted neuronal differentiation, and reduced expression of Gdnf, a key regulator of ENS formation. Ptc1 and Ptc2 were not expressed by ENCCs, and migration of isolated ENCCs was not inhibited by Shh protein. These results suggest that epithelial-derived Shh acts indirectly on the developing ENS by regulating the composition of the intestinal microenvironment.

Laminin-1 promotes enteric nervous system development in mouse embryo

BACKGROUND/AIM

Neuronal development is regulated by extracellular environmental factors including nerve growth factor (NGF) and laminin. We have previously demonstrated that laminin-1 promotes neurite outgrowth of dorsal root ganglion cells by modulating NGF and integrin signaling. However, information about their effects on the enteric nervous system (ENS) is limited. Recently, we succeeded in visualizing enteric neural crest-derived cell (ENCC) migration using SOX10-Venus transgenic mice, in which ENCC are labeled with a green fluorescent protein, Venus. In this study, we examine the effects of NGF and laminin-1 in ENCC migration using SOX10-Venus mice gut.

METHODS

Pregnant SOX10-Venus mice were killed on day 12.5 of gestation. The colorectum was dissected from embryos (n = 10) and placed in culture medium including NGF with or without laminin-1 for 12 h. Extension rates of ENCC migration, colorectum and ENCC migration per colorectum were calculated.

RESULTS

Venus positive-ENCC extension rate was significantly higher in the laminin group (n = 5) compared to control (n = 5), 22.84 and 13.96 %, respectively (p < 0.05). The extension rate of the colorectum was not significantly different between the two groups.

CONCLUSIONS

Our results suggest that laminin promotes ENCC migration in mice. This technique allowed us to visualize the effects of extracellular molecules on ENCC migration and it potentially provides us with an insight into the pathophysiology of developmental disorders of the ENS, such as Hirschsprung's disease.

Enteric neural crest-derived cells promote their migration by modifying their microenvironment through tenascin-C production

The enteric nervous system (ENS) is derived from vagal and sacral neural crest cells that migrate, proliferate, and differentiate into enteric neurons and glia within the gut wall. The mechanisms regulating enteric neural crest-derived cell (ENCC) migration are poorly characterized despite the importance of this process in gut formation and function. Characterization of genes involved in ENCC migration is essential to understand ENS development and could provide targets for treatment of human ENS disorders. We identified the extracellular matrix glycoprotein tenascin-C (TNC) as an important regulator of ENCC development. We find TNC dynamically expressed during avian gut development. It is absent from the cecal region just prior to ENCC arrival, but becomes strongly expressed around ENCCs as they enter the ceca and hindgut. In aganglionic hindguts, TNC expression is strong throughout the outer mesenchyme, but is absent from the submucosal region, supporting the presence of both ENCC-dependent and independent expression within the gut wall. Using rat-chick coelomic grafts, neural tube cultures, and gut explants, we show that ENCCs produce TNC and that this ECM protein promotes their migration. Interestingly, only vagal neural crest-derived ENCCs express TNC, whereas sacral neural crest-derived cells do not. These results demonstrate that vagal crest-derived ENCCs actively modify their microenvironment through TNC expression and thereby help to regulate their own migration.

Altered neuronal density and neurotransmitter expression in the ganglionated region of Ednrb null mice: implications for Hirschsprung's disease

BACKGROUND

Hirschsprung's disease (HSCR) is a congenital condition in which enteric ganglia, formed from neural crest cells (NCC), are absent from the terminal bowel. Dysmotility and constipation are common features of HSCR that persist following surgical intervention. This persistence suggests that the portion of the colon that remains postoperatively is not able to support normal bowel function. To elucidate the defects that underlie this condition, we utilized a murine model of HSCR.

METHODS

Mice with NCC-specific deletion of Ednrb were used to measure the neuronal density and neurotransmitter expression in ganglia.

KEY RESULTS

At the site located proximal to the aganglionic region of P21 Ednrb null mice, the neuronal density is significantly decreased and the expression of neurotransmitters is altered compared with het animals. The ganglia in this colonic region are smaller and more isolated while the size of neuronal cell bodies is increased. The percentage of neurons expressing neuronal nNOS and VIP is significantly increased in Ednrb nulls. Conversely, the percentage of choline acetyltransferase (ChAT) expressing neurons is decreased, while Substance P is unchanged between the two genotypes. These changes are limited to the colon and are not detected in the ileum.

CONCLUSIONS & INFERENCES

We demonstrate changes in neuronal density and alterations in the balance of expression of neurotransmitters in the colon proximal to the aganglionic region in Ednrb null mice. The reduced neuronal density and complementary changes in nNOS and ChAT expression may account for the dysmotility seen in HSCR.

Enteric neurons synthesize netrins and are essential for the development of the vagal sensory innervation of the fetal gut

During fetal life, vagal sensory fibers establish a reproducible distribution in the gut that includes an association with myenteric ganglia. Previous work has shown that netrin is expressed in the bowel wall and, by acting on its receptor, deleted in colorectal cancer (DCC), mediates the guidance of vagal sensory axons to the developing gut. Because the highest concentration of netrins in fetal bowel is in the endoderm, we tested the hypothesis that the ingrowth of vagal afferents to the gut would be independent of the presence of enteric neurons, although enteric neurons might influence the internal distribution of these fibers. Surprisingly, experiments indicated that the vagal sensory innervation is intrinsic neuron-dependent. To examine the vagal innervation in the absence of enteric ganglia, fetal Ret -/- mice were labeled by applying DiI bilaterally to nodose ganglia. In Ret -/- mice, DiI-labeled vagal sensory axons descended in paraesophageal trunks as far as the proximal stomach, which contains neurons, but did not enter the aganglionic bowel. To determine whether neurons produce netrins, enteric neural-crest-derived cells (ENCDCs) were immunoselected from E15 rat gut. Transcripts encoding netrin-1 and -3 were not detected in the ENCDCs, but appeared after they had given rise to neurons. When these neurons were cocultured with cells expressing c-Myc-tagged netrin-1, the neurons displayed netrin-1, but not c-Myc, immunoreactivity. Enteric neurons thus synthesize netrins. The extent to which neuronal netrin accounts for the dependence of the vagal sensory innervation on intrinsic neurons, remains to be determined.

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.

The relationship between expressions of the laminin gene and RET gene in Hirschsprung's disease

BACKGROUND

The cause of Hirschsprung's disease (HD) remains unclear, but currently there are two theories: the mutation of the RET gene and the change of enteric microenvironment. This study was undertaken to elucidate the cause of HD by assessing the expression of laminin (LN), laminin gene, and the RET gene in the aganglionic segment, transitional zone and normal segment of the colon in patients with HD.

METHODS

Specimens of the aganglionic segment, transitional zone, and normal segment of the colon from 27 cases of HD were stained immunohistologically by a PV 9000 polymer detection system. Photos were taken by the RS image system, and the staining area of each image was calculated by a JD 801 image analysis system. The qualitative expressions of the laminin gene and RET gene of these three segments in the 27 cases were detected by reverse transcription-polymerase chain reaction (RT-PCR), and the difference of the expressions was shown by the alpha 9900 image analysis system. The quantitative expressions of the laminin gene and RET gene in the three segments were detected by real-time quantitative PCR, and the difference of the expression was shown by SDS software.

RESULTS

The laminin and laminin gene were expressed in all the three segments. The expression was higher in the aganglionic segment than in the dilated segment, and the expression decreased stepwisely from the aganglionic segment to the normal segment, while the expression of the RET gene was opposite, showing an increased segmenting from the aganglionic segment to the normal segment. The correlation between the expressions of the two genes was negatively correlated.

CONCLUSIONS

The highly increased expression of LN in the aganglionic segment may cause early differentiation, early maturation and premature ecesis of enteric nervous cells. The change of the microenvironment of colon wall may be the cause of HD. The negative correlation between the expression of the two genes may be closely related to the occurrence of HD.

Platelet-derived growth factor signals play critical roles in differentiation of longitudinal smooth muscle cells in mouse embryonic gut

In the development of mouse gut, longitudinal smooth muscle cells (LMC) and interstitial cells of Cajal (ICC) originate from common precursor cells expressing c-Kit. Recently, some gastrointestinal stromal tumours, which develop from smooth muscle layers of the gut and have gain-of-function mutations of c-kit, have been reported to have gain-of-function mutations of platelet-derived growth factor (PDGF) receptor alpha gene. These data raise the possibility that PDGF signalling might be involved in the development of LMC. Therefore, we examined the expression pattern of the PDGF signal family of embryonic gut by immunohistochemistry and in situ hybridization, and investigated the role of PDGF signals in the development of smooth muscle layers in mouse gut using a new organ culture system. During embryonic development, the circular muscle layer expressed PDGF-A, enteric neurons expressed PDGF-B and common precursor cells of LMC and ICC expressed both PDGF receptor alpha and beta. The selective PDGF receptor inhibitor AG1295 suppressed the differentiation of LMC in gut explants. We conclude that PDGF signals play critical roles in the differentiation of LMC in mouse embryonic gut.

Hyaluronan content of Wharton's jelly in healthy and Down syndrome fetuses

The mechanisms by which the excess genetic material of chromosome 21 results in the dysmorphologic features of Down syndrome (DS) are largely unknown. It has been found that the extracellular matrix of nuchal skin of DS fetuses exhibits an higher content of hyaluronan (HA) compared to that of euploid fetuses. Since HA plays a central role in many morphogenetic processes during embryogenesis, an alteration in its metabolism could be involved in the pathogenesis of several structural defects of DS. The extracellular matrix of umbilical cord (UC) is the mammalian tissue with one of the highest content of HA. Therefore we sought to explore the quantitative HA modifications during gestation, tissue distribution and HA metabolism in euploid and DS UCs. Euploid UCs (n=28) and UCs from DS fetuses (n=13) were obtained after termination of pregnancy, spontaneous abortion, or at delivery. Quantitative and molecular size analysis were performed using HPLC and FPLC. Tissue distribution was visualized by immunohistochemistry. Gene expression for HA synthases (HAS) and hyaluronidases (HYAL) were quantified by real-time PCR techniques and HYAL activity was detected by zymography. In euploid UC only HA of a molecular weight of 1700 kDA was present while in DS UC an additional lower weight HA molecule of 1100 kDA was found. Immunohistochemistry showed a larger amount of Wharton's jelly HA in DS UCs than in euploid UC. Real-time PCR analysis showed that HAS 2 and HYAL 2 were expressed at significant levels in all specimens. A higher expression of HAS 2 and a lower expression of HYAL 2 was found in the Wharton's jelly of DS fetuses compared to that of euploid fetuses at 14 weeks of gestation. On the contrary, at term HYAL 2 expression was higher in DS specimens than in those from euploid fetuses. Zymographic studies showed a similar behavior with a lower HYAL activity at early gestation and a higher HYAL activity at term gestation in DS UCs compared to euploid specimens. Therefore we can conclude that HA is more represented in DS UCs than in euploid UCs. A complex alteration of the HA metabolism characterized by an increased synthesis of lower weight HA molecules is a peculiarity of DS UCs.

Guidance cues involved in the development of the peripheral autonomic nervous system

All peripheral autonomic neurons arise from neural crest cells that migrate away from the neural tube and navigate to the location where ganglia will form. After differentiating into neurons, their axons then navigate to a variety of targets. During the development of the enteric nervous system, GDNF appears to play a role in inducing vagal neural crest cells to enter the gut, in retaining neural crest cells within the gut and in promoting the migration of neural crest cells along the gut. Sema3A regulates the entry of extrinsic axons into the distal hindgut, netrin-DCC signaling is responsible for the centripetal migration of cells to form the submucosal ganglia within the gut, Slit-Robo signaling prevents trunk level neural crest cells from entering the gut, and neurturin plays a role in the innervation of the circular muscle layer. During the development of the sympathetic nervous system, the migration of trunk neural crest cells through the somites is influenced by ephrin-Bs, Sema3A and F-spondin. The migration of neural crest cells ventrally beyond the somites requires neuregulin signaling and the clumping of cells into columns adjacent to the dorsal aorta is regulated by Sema3A. The rostral migration of cells to form the superior cervical ganglion (SCG) and the extension of axons along blood vessels involves artemin signaling through Ret and GFRalpha3, and the entry of sympathetic axons into target tissues involves neurotrophins and GDNF. Relatively little is known about the development of parasympathetic ganglia, but GDNF appears to play a role in the migration of some cranial ganglion precursors to their correct location, and both GDNF and neurturin are involved in the growth of parasympathetic axons into particular targets.

Proteoglycans in the developing brain: new conceptual insights for old proteins

Proteoglycans are a heterogeneous class of proteins bearing sulfated glycosaminoglycans. Some of the proteoglycans have distinct core protein structures, and others display similarities and thus may be grouped into families such as the syndecans, the glypicans, or the hyalectans (or lecticans). Proteoglycans can be found in almost all tissues being present in the extracellular matrix, on cellular surfaces, or in intracellular granules. In recent years, brain proteoglycans have attracted growing interest due to their highly regulated spatiotemporal expression during nervous system development and maturation. There is increasing evidence that different proteoglycans act as regulators of cell migration, axonal pathfinding, synaptogenesis, and structural plasticity. This review summarizes the most recent data on structures and functions of brain proteoglycans and focuses on new physiological concepts for their potential roles in the developing central nervous system.

Endothelin and the development of the enteric nervous system

1. The enteric nervous system (ENS) is derived from cells that migrate to the bowel from the neural crest. These émigrés must find the gut, reach their correct locations within its wall and finally differentiate as neurons or glia. 2. Because the crest-derived precursor population is multipotent when it colonizes the bowel, the enteric micro-environment plays a prominent role in ENS development. 3. A number of molecules of the enteric micro-environment have been found to promote the development of neurons. 4. However, endothelin (ET)-3 appears to be different from any of these in that its role appears to be to prevent premature neuronal differentiation. 5. By activating ETB receptors, ET-3 inhibits the differentiation of crest-derived cells into neurons and promotes the development of smooth muscle. 6. The effect of ET-3 on smooth muscle down-regulates the secretion of laminin-1, which is a promoter of the formation of neurons. 7. In the absence of ET-3/ETB, crest-derived cells develop as neurons and, thus, cease migrating before they complete the colonization of the bowel. This premature development leaves the terminal colon aganglionic.

Lessons from genetically engineered animal models. II. Disorders of enteric neuronal development: insights from transgenic mice

Understanding the development of congenital defects of the enteric nervous system, such as Hirschsprung's disease, was, until recently, an intractable problem. The analysis of transgenic mice, however, has now led to the discovery of a number of genetic abnormalities that give rise to aganglionic congenital megacolon or neuronal intestinal dysplasia. The identification of the responsible genes has enabled the developmental actions of their protein products to be investigated, which, in turn, has made it possible to determine the causes of aganglionoses. Two models of pathogenesis have emerged. One, associated with mutations in genes encoding endothelin-3 or its receptor, endothelin B, posits the premature differentiation of migrating neural crest-derived progenitors, causing the precursor pool to become depleted before the bowel has been fully colonized. The second, associated with mutations in genes encoding glial cell line-derived neurotrophic factor (GDNF), its preferred receptor GFRalpha1, or their signaling component, Ret, appears to deprive a GDNF-dependent common progenitor of adequate support and/or mitogenic drive. In both cases, the terminal bowel becomes aganglionic when the number of colonizing neuronal precursors is inadequate.

Inhibition of in vitro enteric neuronal development by endothelin-3: mediation by endothelin B receptors

The terminal colon is aganglionic in mice lacking endothelin-3 or its receptor, endothelin B. To analyze the effects of endothelin-3/endothelin B on the differentiation of enteric neurons, E11-13 mouse gut was dissociated, and positive and negative immunoselection with antibodies to p75(NTR)were used to isolate neural crest- and non-crest-derived cells. mRNA encoding endothelin B was present in both the crest-and non-crest-derived cells, but that encoding preproendothelin-3 was detected only in the non-crest-derived population. The crest- and non-crest-derived cells were exposed in vitro to endothelin-3, IRL 1620 (an endothelin B agonist), and/or BQ 788 (an endothelin B antagonist). Neurons and glia developed only in cultures of crest-derived cells, and did so even when endothelin-3 was absent and BQ 788 was present. Endothelin-3 inhibited neuronal development, an effect that was mimicked by IRL 1620 and blocked by BQ 788. Endothelin-3 failed to stimulate the incorporation of [3H]thymidine or bromodeoxyuridine. Smooth muscle development in non-crest-derived cell cultures was promoted by endothelin-3 and inhibited by BQ 788. In contrast, transcription of laminin alpha1, a smooth muscle-derived promoter of neuronal development, was inhibited by endothelin-3, but promoted by BQ 788. Neurons did not develop in explants of the terminal bowel of E12 ls/ls (endothelin-3-deficient) mice, but could be induced to do so by endothelin-3 if a source of neural precursors was present. We suggest that endothelin-3/endothelin B normally prevents the premature differentiation of crest-derived precursors migrating to and within the fetal bowel, enabling the precursor population to persist long enough to finish colonizing the bowel.

Development of the human gastrointestinal tract: twenty years of progress

A combination of approaches has begun to elucidate the mechanisms of gastrointestinal development. This review describes progress over the last 20 years in understanding human gastrointestinal development, including data from both human and experimental animal studies that address molecular mechanisms. Rapid progress is being made in the identification of genes regulating gastrointestinal development. Genes directing initial formation of the endoderm as well as organ-specific patterning are beginning to be identified. Signaling pathways regulating the overall right-left asymmetry of the gastrointestinal tract and epithelial-mesenchymal interactions are being clarified. In searching for extrinsic developmental regulators, numerous candidate trophic factors have been proposed, but compelling evidence remains elusive. A critical gene that initiates pancreas development has been identified, as well as a number of genes regulating liver, stomach, and intestinal development. Mutations in genes affecting neural crest cell migration have been shown to give rise to Hirschsprung's disease. Considerable progress has been achieved in understanding specific phenomena, such as the transcription factors regulating expression of sucrase-isomaltase and fatty acid-binding protein. The challenge for the future is to integrate these data into a more complete understanding of the physiology of gastrointestinal development.

Motility disorders in childhood

Motility disorders are very common in childhood, causing a number of gastrointestinal symptoms: recurrent vomiting, abdominal pain and distension, constipation and obstipation, and loose stools. The disorders result from disturbances of gut motor control mechanisms caused by either intrinsic disease of nerve and muscle, central nervous system dysfunction or perturbation of the humoral environment in which they operate. Intrinsic gut motor disease and central nervous system disorder are most usually congenital in origin, and alterations of the humoral environment acquired. Irritable bowel syndrome occurs in children as well as adults and is multifactorial in origin, with an interplay of psychogenic and organic disorders.

Transgenic expression of the endothelin-B receptor prevents congenital intestinal aganglionosis in a rat model of Hirschsprung disease

The spotting lethal rat, a naturally occurring rodent model of Hirschsprung disease, carries a deletion in the endothelin-B receptor (EDNRB) gene that abrogates expression of functional EDNRB receptors. Rats homozygous for this mutation (sl) exhibit coat color spotting and congenital intestinal aganglionosis. These deficits result from failure of the neural crest-derived epidermal melanoblasts and enteric nervous system (ENS) precursors to completely colonize the skin and intestine, respectively. We demonstrate that during normal rat development, the EDNRB mRNA expression pattern is consistent with expression by ENS precursors throughout gut colonization. We used the human dopamine-beta-hydroxylase (DbetaH) promoter to direct transgenic expression of EDNRB to colonizing ENS precursors in the sl/sl rat. The DbetaH-EDNRB transgene compensates for deficient endogenous EDNRB in these rats and prevents the intestinal defect. The transgene has no effect on coat color spotting, indicating the critical time for EDNRB expression in enteric nervous system development begins after separation of the melanocyte lineage from the ENS lineage and their common precursor. The transgene dosage affects both the incidence and severity of the congenital intestinal defect, suggesting dosage-dependent events downstream of EDNRB activation in ENS development.

Hirschsprung's disease: a search for etiology

In 1967, Okamoto et al suggested that the absence of ganglion cells in Hirschsprung's disease (HD) was attributable to failure of migration of neural crest cells. The earlier the arrest of migration, the longer the aganglionic segment. Since then, this hypothesis generally has been accepted. However, subsequent experiments using mouse models of intestinal aganglionosis indicate that nerve cells may reach the correct position but then fail to develop or survive. An alternative hypothesis has been proposed that the aganglionosis may be caused by failure of differentiation as a result of microenvironmental changes after the migration has occurred. Extracellular matrix proteins are recognized as important microenvironmental factors. It has been shown that enteric neurogenesis is dependent on extracellular matrices, which provide a migration pathway for neural crest-derived cells and promote the maturation of settled neural crest-derived cells. Altered distributions of extracellular matrices have been shown in human HD cases and murine HD models, suggesting the role of extracellular matrices in the pathogenesis of HD. Recent studies suggest that intestinal smooth muscle cells, target cells of enteric neurons, play an important role in guiding and influencing its own innervation. Normal maturation was inhibited in neurons cultured with smooth muscle cells of aganglionic colon in comparison to normal colon. Furthermore, it was demonstrated that levels of neurotrophic factors, crucial in the development and survival of enteric neurons, are decreased in circular muscle layers of aganglionic colon in comparison to normoganglionic colon. The smooth muscle cells of the aganglionic colon may represent an unfavorable microenvironment for neuronal development compared with the normally innervated region. Recently, markedly increased immunoreactivity of major histocompatibility complex (MHC) class II antigens and ICAM-1 was demonstrated in aganglionic bowel, suggesting the immunological mechanisms may be involved in the etiology of HD. Genetic factors have been implicated in the etiology of this condition because HD is known to occur in families and in association with some chromosomal abnormalities. Recent expansion of molecular genetics identified multiple susceptibility genes of HD, including the RET gene, the glial cell line-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Of these, inactivating mutations of the RET gene are the most frequent, occurring in 50% of familial and 15% to 20% of sporadic cases of HD. To date, despite extensive research, the exact etiology of this condition remains poorly understood. The present report describes the authors' current understanding of and recent progress in the etiology of HD.

Development of LBP110 expression by neural crest-derived enteric precursors: migration and differentiation potential in ls/ls mutant mice

Neural crest-derived cells acquire a 110-kD laminin-binding protein (LBP110) when they colonize the murine bowel. Laminin stimulates LBP110-expressing cells to develop as neurons. We have followed the development of LBP110 by neural crest-derived cells as they enter the gut of control and ls/ls mutant mice. The expression of neurofilament and choline acetyltransferase was used as markers of a neuronal phenotype. Tyrosine hydroxylase was used as a marker for the mash-1-dependent lineage of enteric precursors, while calcitonin gene-related peptide was used as a marker for the mash-1-independent lineage of crest-derived cells. A subset of cells expressing LBP110 was located along the vagi at E10 at cervical and thoracic levels. At E12, cells expressing LBP110 extended from the foregut to the midgut. The expression of neurofilament protein lagged behind that of LBP110 by about 0.5 day and then became coincident with LBP110 immunoreactivity. By E15, cells doubly labeled with antibodies to LBP110 and neurofilament protein were located along the entire extent of the bowel up to but not including the terminal colon. By E16, both the proximal and terminal colon contained cells expressing LBP110 and neurofilaments. The pattern of immunoreactivity could not be distinguished between ls/ls and control animals prior to E16. By E16, when the terminal colon of control animals contained many cells expressing LBP110 and neurofilaments, the terminal colon of ls/ls animals lacked cells expressing these proteins; nevertheless, structures outside of the terminal colon were heavily endowed with cells expressing LBP110 and neurofilaments. These ectopically located cells derived from both mash-1-dependent and -independent lineages of crest-derived precursors.

Role of the extracellular matrix in neural crest cell migration

Development of the neural crest involves a remarkable feat of coordinated cell migration in which cells detach from the neural tube, take varying routes of migration through the embryonic tissues and then differentiate at the end of their journey to participate in the formation of a number of organ systems. In general, neural crest cells appear to migrate without the guidance of long-range physical or chemical cues, but rather they respond to heterogeneity in the extracellular matrix that forms their migration substrate. Molecules such as fibronectin and laminin act as permissive substrate components, encouraging neural crest cell attachment and spreading, whereas chondroitin sulphate proteoglycans are nonpermissive for migration. A balance between permissive and nonpermissive substrate components seems to be necessary to ensure successful migration, as indicated by a number of studies in mouse mutant systems where nonpermissive molecules are over-expressed, leading to inhibition of neural crest migration. The neural crest expresses cell surface receptors that permit interaction with the extracellular matrix and may also modify the matrix by secretion of proteases. Thus the principles that govern the complex migration of neural crest cells are beginning to emerge.

The alpha1 subunit of laminin-1 promotes the development of neurons by interacting with LBP110 expressed by neural crest-derived cells immunoselected from the fetal mouse gut

A plasmalemmal protein, LBP110, which binds to the alpha1 chain of laminin-1, is acquired by the neural crest-derived precursors of enteric neurons after they colonize the gut. We tested the hypothesis that laminin-1 interacts with LBP110 to promote enteric neuronal development. The effects of laminin-1 on neuronal development were studied in cultures of cells immunoselected from fetal mouse gut (E14-15) with antibodies to LBP110 or p75NTR, a marker for enteric crest-derived cells. No matter which antibody was used, the development of cells expressing neuronal markers was increased three- to fourfold by culturing the cells on a laminin-1-containing substrate. To determine whether this effect of laminin-1 is due to the selective adherence of a neurocompetent subset of precursors, immunoselected cells were permitted to preadhere to poly-D-lysine. Addition of soluble laminin-1 24 h later promoted neuronal but not glial development. The laminin-1-induced increment in neuronal development was abolished both by a peptide containing the sequence of the LBP110-binding domain, IKVAV, and by antibodies to laminin alpha1 that recognize the IKVAV domain. Neither reagent affected the total number of cells. In contrast, the response to laminin-1 was not affected by control peptides, preimmune sera, or antibodies to laminin beta1. Laminin-1 transiently induced the expression of nuclear Fos immunoreactivity; this action was blocked specifically by the IKVAV peptide. These data are consistent with the hypothesis that LBP110 interacts with the IKVAV domain of laminin alpha1 to promote the differentiation of neurons from enteric crest-derived precursors.

Impaired expression of neural cell adhesion molecule L1 in the extrinsic nerve fibers in Hirschsprung's disease

Immunohistochemical studies on the ganglionic and aganglionic segment in Hirschsprung's disease (HD) were carried out using antibodies against three neural membrane proteins, Thy-1, integrin alpha5, and L1. Enteric neural elements were immunostained with antibodies against neurofilament, which is the neuronal cytoskeletal protein. In ganglionic segments, neurofilament-immunoreactivity was detected in neuronal cell bodies and fine nerve fibers of the myenteric and submucosal plexuses. All of these neural elements were immunopositive for Thy-1, integrin alpha5, and L1. In aganglionic segments, no intrinsic neurons were detected, and instead, hypertrophied nerve bundles were observed in intermuscular space, in submucosa, and in circular muscle layer by immunochemistry for neurofilament. These hypertrophied nerve bundles were immunopositive with anti-Thy-1 and anti-integrin alpha5 antibodies. However, they were not immunostained with anti-L1 in all five cases. These findings indicate that the expression of L1 molecule, which plays an important role in cell adhesion, neural cell migration, and neurite outgrowth, is impaired in the extrinsic nerve fibers in aganglionic colon. And this may perturb neural crest migration and adequate neurite outgrowth, with resulting aganglionic segment and abnormal nerve bundles of extrinsic fibers in HD.

Altered RET gene mRNA expression in Hirschsprung's disease

The RET proto-oncogene is a major cause of Hirschsprung's disease (HD) as demonstrated by the experimentally produced intestinal aganglionosis in mice with a null mutation of this gene and by the increased evidence of RET mutations in patients with HD. To evaluate the possible implication of the RET gene for the development of HD, we examined mRNA expression level of the RET gene in the bowel specimen of seven HD patients by using the reverse transcription-polymerase chain reaction technique. A significantly less intense signal for RET mRNA was found in the aganglionic bowel compared with the ganglionic bowel. In the hypoganglionic transitional zone, the RET mRNA level was higher than that of an aganglionic segment but lower than that observed in the ganglionic portion. In two patients where semiquantitative analysis was performed, the RET mRNA level in the aganglionic bowels was estimated to be approximately 1/500 of that in the ganglionic bowels. Because expression of RET mRNA plays an important role in establishing the enteric neuronal lineage, decreased RET mRNA expression in the aganglionic bowel may suggest maldevelopment of neural crest-derived cells in Hirschsprung's disease.

Intestinal motility during ontogeny and intestinal pseudo-obstruction in children

From the fragmentary studies performed to date of both functional obstruction and the ontogeny of intestinal motility, several conclusions can be drawn. The development of motor activity that is primarily dependent on neuronal activity, such as sucking, swallow-induced peristalsis of the esophagus, and cyclic fasting small intestinal motor activity, occurs according to a timetable that is similar in all species studies is gestationally dependent, but its timing during gestation is species specific. Postprandial events, including gastric emptying and continuous postprandial motor activity in the small intestine, in contrast seem to be dependent on the nature of the humoral response to food, provided that the musculature of the gut and enteric nerves are able to respond to it. Although these activities are primarily determined by neuronal development, there is a limited amount of information to suggest that their appearance may be pharmacologically manipulated to advance the timing and rate of development. It is commonplace now for cortisol to be used to induce the production of surfactant in mothers of babies who are at risk of hyaline membrane disease. A limited amount of information suggests that cortisol may have similar effects in inducing duodenal motor activity, and, thus, it may be possible to advance the timing and rate of development of intestinal motility in the very preterm infant by its use. There are, however, no studies to date to prove this. It is now clear that intestinal pseudo-obstruction is a heterogeneous disorder associated with various pathologies, some of which are intrinsic to the gut, whereas others are multisystem diseases affecting the intestine. In addition, although intestinal pseudo-obstruction was originally thought to involve the small intestine, it is now realized that it may not affect only one region, as in achalasia or Hirschsprung's disease, but also it may present diffusely throughout the gut. The motility changes caused by the disease processes are nonspecific, although neuropathic and myopathic changes are distinct and due to the destruction of the particular motor control system involved. The mechanisms of the ontogenic and disease changes described in this article are, however, almost totally unexplored. The recent upsurge of interest in the area with the development of advances in cellular and molecular biology, at least the early events, is now beginning to unravel. At the present time, the stage is being set for probably the most exciting phase of understanding of the nature of the ontogeny of intestinal motor activity, which the author expects will enable us to manipulate motor activity in normal preterm infants and, it is hoped, congenital dysmotile states.

Hirschprung's disease

Current evidence on the pathogenesis of Hirschprung's disease, then, favours the 'abnormal microenvironment' hypothesis wherein the developing and migrating normal neural crest cells confront a segmentally abnormal and hostile microenvironment in the colon. This hypothesis would account both for the congenital absence of ganglion cells in the wall of colon and also for the range of enteric neuronal abnormalities encountered including neuronal dysplasia, hypoganglionosis, and zonal aganglionosis. The abnormal constitution of the mesenchymal and basement membrane extracellular matrix in the affected segment of colon is presumably genetically determined and further understanding of the pathogenesis of this disorder will emerge as molecular geneticists characterise the specific genes and gene products associated with Hirschprung's disease. Advances in this field should permit gene probes to be developed to facilitate prenatal and postnatal diagnosis.

Abnormal expression and distribution of nidogen in Hirschsprung's disease

Hirschsprung's disease (congenital colonic aganglionosis) is associated with abnormalities in the distributions and amounts of basement membrane and other extracellular matrix components in the human gut. The authors have investigated the possible significance of nidogen in Hirschsprung's disease, because this glycoprotein is necessary for the formation of ternary complexes with the other basement membrane components, laminin and collagen type IV, and thus may contribute the pathology of the disease. Increased nidogen immunoreactivity in the smooth muscle basement membranes and muscularis mucosae of the distal aganglionic zone in Hirschsprung's bowel was observed, the nidogen immunoreactivity demonstrating that the thickness of the muscularis mucosae was increased in this region. However, steady-state nidogen mRNA levels were found to be significantly lower in both proximal and distal Hirschsprung's bowel (relative to controls). In contrast, no significant differences were observed in the steady-state levels of the mRNAs coding for laminin subunits. These results indicate that although abnormalities in the amount or distribution of nidogen may contribute to the abnormalities seen in the extracellular matrix in Hirschsprung's disease, the levels of expression of the genes coding for either nidogen or laminin are unlikely to be primarily responsible for the lesions.

Molecular analysis of smooth muscle development in the mouse

Little is currently known regarding the ontogeny of smooth muscle tissues during normal mammalian development. The alpha-smooth muscle and gamma-smooth muscle isoactins have been shown to be excellent molecular markers of smooth muscle cell phenotype. This study characterizes both the temporal and spatial patterns of alpha-smooth muscle and gamma-smooth muscle isoactin expression in the developing mouse. In situ analysis was performed on serial sections of whole mouse embryos on embryonic day 9, 11, 13, 15, and 17 using alpha-smooth muscle and gamma-smooth muscle isoactin-specific riboprobes. Distinct temporal and spatial patterns of alpha-smooth muscle and gamma-smooth muscle isoactin gene expression were observed in the developing gastrointestinal tract, urogenital tract, respiratory tract, and vascular system. Independent expression of the alpha-smooth muscle isoactin was observed during the early stages of skeletal, cardiac, and smooth muscle myogenesis as well as in a novel subset of distinct organs including the postnatal component of the hindgut, allantois, and primitive placenta. The results of this study indicate that distinct cellular phenotypes are involved in smooth muscle myogenesis and suggest that organ-specific mechanisms might exist for the initiation of smooth muscle development in vivo. In addition, the pattern of independent alpha-smooth muscle isoactin expression observed in this study provides novel information regarding the early stages of hindgut and placental development, and suggests that a common functional phenotype may be associated with the early stages of skeletal, cardiac, and smooth muscle myogenesis.

Neural crest development. Do developing enteric neurons need endothelins?

Recent experiments have led to the unexpected finding that endothelin-3 and the endothelin B receptor are absolutely necessary for the development of the enteric nervous system in the colon, but it is not yet clear why.

A high-resolution linkage map of the lethal spotting locus: a mouse model for Hirschsprung disease

Mice homozygous for the lethal spotting (ls) mutation exhibit aganglionic megacolon and a white spotted coat owing to a lack of neural crest-derived enteric ganglia and melanocytes. The ls mutation disrupts the migration, differentiation, or survival of these neural crest lineages during mammalian development. A human congenital disorder, Hirschsprung disease (HSCR), is also characterized by aganglionic megacolon of the distal bowel and can be accompanied by hypopigmentation of the skin. HSCR has been attributed to multiple loci acting independently or in combination. The ls mouse serves as one animal model for HSCR, and the ls gene may represent one of the loci responsible for some cases of HSCR in humans. This study uses 753 N2 progeny from a combination of three intersubspecific backcrosses to define the molecular genetic linkage map of the ls region and to provide resources necessary for positional cloning. Similar to some cases of HSCR, the ls mutation acts semidominantly, its phenotypic effects dependent upon the presence of modifier genes segregating in the crosses. We have now localized the ls mutation to a 0.8-cM region between the D2Mit113 and D2Mit73/D2Mit174 loci. Three genes, endothelin-3 (Edn3), guanine nucleotide-binding protein alpha-stimulating polypeptide 1 (Gnas), and phosphoenolpyruvate carboxykinase (Pck1) were assessed as candidates for the ls mutation. Only Edn3 and Gnas did not recombine with the ls mutation. Mutational analysis of the Edn3 and Gnas genes will determine whether either gene is responsible for the neural crest deficiencies observed in ls/ls mice.

Alterations of the fetal extracellular matrix in the nuchal oedema of Down's syndrome

Elevations in the lateral and dorsal neck region are known to be highly correlated with chromosomal aberrations in human fetuses. However, the morphology of the elevations is poorly described. Only in the case of Turner's syndrome has lymphatic vessel formation been shown to be deficient leading to swellings in the nuchal area. In Down's syndrome, non-echogenic nuchal oedemata can be visualized in ultrasound scan between the 10th and 15th week of gestation. In the present study, alterations in the extracellular matrix (ECM) of the skin in trisomy 21 fetuses were found to be the morphological basis of the nuchal oedema. The distribution of collagen type VI differs from that in normal fetuses, both in nuchal and leg skin. Collagen VI forms a denser mesh in trisomy 21 than in normal fetal skin, hyaluronan (HA) being the main glycosaminoglycan (GAG) component as judged from the appearance of the TEM precipitate after fixation in the presence of tannic acid. Nuchal oedema in Down's syndrome is therefore found to be an interstitial oedema. The interstitial fluid is bound to HA, leading to a swelling of the fetal dermis. No cysts or dilated vessels were found in the oedematous tissue. The presence of a high amount of HA during development can influence the behaviour of migrating cell populations, which might have a bearing on the pathogenesis of Down's syndrome.

The extracellular matrix components, tenascin and fibronectin, in Hirschsprung's disease: an immunohistochemical study

Previous in vitro studies have suggested that successful neural crest cell migration in the developing gut could be influenced by the composition of the extracellular matrix components, tenascin and fibronectin. The authors aimed to gain insight into the pathogenesis of Hirschsprung's disease (HD) by studying the distribution of tenascin and fibronectin in bowel specimens of patients with HD. Immunohistochemical examination was performed in specimens from 10 HD patients (8 aganglionic, 5 transitional, and 10 normoganglionic zones) and 18 age- and site-matched controls undergoing other types of gastrointestinal surgery. The distribution of tenascin was restricted to the basement membranes of the smooth muscle and vasculature, and in the basement membranes surrounding neuronal ganglia in all the controls and in 10 proximal normoganglionic HD specimens. More intense tenascin immunofluorescence was observed in the smooth muscle basement membranes of the muscularis externa of eight aganglionic and five transitional zones of HD. Wide-spread distribution of fibronectin was found in all the basement membranes as well as in the lamina propria and submucosa of all control and 10 normoganglionic HD sections. However, more intense immunofluorescence with fibronectin was observed in all the layers of eight aganglionic and five transitional zones of HD specimens. The present findings show that the mesenchymal and basement membrane extracellular matrix constitution is abnormal in the affected bowel of HD. Although a causal relationship has not been demonstrated, corroborative evidence from earlier animal experiments in other studies suggests that the extracellular matrix abnormalities may contribute to the pathogenesis of HD.