Sonic hedgehog regulates the proliferation, differentiation, and migration of enteric neural crest cells in gut

Hedgehog Signalling Pathway and Its Role in Shaping the Architecture of Intestinal Epithelium

The hedgehog (Hh) signalling pathway plays a key role in both embryonic and postnatal development of the intestine and is responsible for gut homeostasis. It regulates stem cell renewal, formation of the villous-crypt axis, differentiation of goblet and Paneth cells, the cell cycle, apoptosis, development of gut innervation, and lipid metabolism. Ligands of the Hh pathway, i.e., Indian hedgehog (Ihh) and Sonic hedgehog (Shh), are expressed by superficial enterocytes but act in the mesenchyme, where they are bound by a Patched receptor localised on myofibroblasts and smooth muscle cells. This activates a cascade leading to the transcription of target genes, including those encoding G1/S-specific cyclin-D2 and -E1, B-cell lymphoma 2, fibroblast growth factor 4, and bone morphogenetic protein 4. The Hh pathway is tightly connected to Wnt signalling. Ihh is the major ligand in the Hh pathway. Its activation inhibits proliferation, while its blocking induces hyperproliferation and triggers a wound-healing response. Thus, Ihh is a negative feedback regulator of cell proliferation. There are data indicating that diet composition may affect the expression of the Hh pathway genes and proteins, which in turn, induces changes in mucosal architecture. This was shown for fat, vitamin A, haem, berberine, and ovotransferrin. The Hh signalling is also affected by the intestinal microbiota, which affects the intestinal barrier integrity. This review highlights the critical importance of the Hh pathway in shaping the intestinal mucosa and summarises the results obtained so far in research on the effect of dietary constituents on the activity of this pathway.

The development of hair follicles and nail

The hair follicle and nail unit develop and regenerate through epithelial-mesenchymal interactions. Here, we review some of the key signals and molecular interactions that regulate mammalian hair follicle and nail formation during embryonic development and how these interactions are reutilized to promote their regeneration during adult homeostasis and in response to skin wounding. Finally, we highlight the role of some of these signals in mediating human hair follicle and nail conditions.

Enteric Nervous System Striped Patterning and Disease: Unexplored Pathophysiology

The enteric nervous system (ENS) controls gastrointestinal (GI) motility, and defects in ENS development underlie pediatric GI motility disorders. In disorders such as Hirschsprung's disease (HSCR), pediatric intestinal pseudo-obstruction (PIPO), and intestinal neuronal dysplasia type B (INDB), ENS structure is altered with noted decreased neuronal density in HSCR and reports of increased neuronal density in PIPO and INDB. The developmental origin of these structural deficits is not fully understood. Here, we review the current understanding of ENS development and pediatric GI motility disorders incorporating new data on ENS structure. In particular, emerging evidence demonstrates that enteric neurons are patterned into circumferential stripes along the longitudinal axis of the intestine during mouse and human development. This novel understanding of ENS structure proposes new questions about the pathophysiology of pediatric GI motility disorders. If the ENS is organized into stripes, could the observed changes in enteric neuron density in HSCR, PIPO, and INDB represent differences in the distribution of enteric neuronal stripes? We review mechanisms of striped patterning from other biological systems and propose how defects in striped ENS patterning could explain structural deficits observed in pediatric GI motility disorders.

Enteric neurospheres retain the capacity to assemble neural networks with motile and metamorphic gliocytes and ganglia

BACKGROUND

Neurosphere medium (NSM) and self-renewal medium (SRM) were widely used to isolate enteric neural stem cells (ENSCs) in the form of neurospheres. ENSCs or their neurosphere forms were neurogenic and gliogenic, but the compelling evidence for their capacity of assembling enteric neural networks remained lacking, raising the question of their aptitude for rebuilding the enteric nervous system (ENS) in ENSC therapeutics. It prompted us to explore an effective culture protocol or strategy for assembling ENS networks, which might also be employed as an in vitro model to simplify the biological complexity of ENS embedded in gut walls.

METHODS

NSM and SRM were examined for their capacity to generate neurospheres in mass culture of dispersed murine fetal enterocytes at serially diluted doses and assemble enteric neural networks in two- and three-dimensional cell culture systems and ex vivo on gut explants. Time-lapse microphotography was employed to capture cell activities of assembled neural networks. Neurosphere transplantation was performed via rectal submucosal injection.

RESULTS

In mass culture of dispersed enterocytes, NSM generated discrete units of neurospheres, whereas SRM promoted neural network assembly with neurospheres akin to enteric ganglia. Both were highly affected by seeding cell doses. SRM had similar ENSC mitosis-driving capacity to NSM, but was superior in driving ENSC differentiation in company with heightened ENSC apoptosis. Enteric neurospheres were motile, capable of merging together. It argued against their clonal entities. When nurtured in SRM, enteric neurospheres proved competent to assemble neural networks on two-dimensional coverslips, in three-dimensional hydrogels and on gut explants. In the course of neural network assembly from enteric neurospheres, neurite extension was preceded by migratory expansion of gliocytes. Assembled neural networks contained motile ganglia and gliocytes that constantly underwent shapeshift. Neurospheres transplanted into rectal submucosa might reconstitute myenteric plexuses of recipients' rectum.

CONCLUSION

Enteric neurospheres mass-produced in NSM might assemble neural networks in SRM-immersed two- or three-dimensional environments and on gut explants, and reconstitute myenteric plexuses of the colon after rectal submucosal transplantation. Our results also shed first light on the dynamic entity of ENS and open the experimental avenues to explore cellular activities of ENS and facilitate ENS demystification.

Harnessing the Power of Enteric Glial Cells' Plasticity and Multipotency for Advancing Regenerative Medicine

The enteric nervous system (ENS), known as the intrinsic nervous system of the gastrointestinal tract, is composed of a diverse array of neuronal and glial cell subtypes. Fascinating questions surrounding the generation of cellular diversity in the ENS have captivated ENS biologists for a considerable time, particularly with recent advancements in cell type-specific transcriptomics at both population and single-cell levels. However, the current focus of research in this field is predominantly restricted to the study of enteric neuron subtypes, while the investigation of enteric glia subtypes significantly lags behind. Despite this, enteric glial cells (EGCs) are increasingly recognized as equally important regulators of numerous bowel functions. Moreover, a subset of postnatal EGCs exhibits remarkable plasticity and multipotency, distinguishing them as critical entities in the context of advancing regenerative medicine. In this review, we aim to provide an updated overview of the current knowledge on this subject, while also identifying key questions that necessitate future exploration.

Upregulation of ENKD1 disrupts cellular homeostasis to promote lymphoma development

Diffuse large B cell lymphoma (DLBCL) is a common and aggressive form of B cell lymphoma. Approximately 40% of DLBCL patients are incurable despite modern therapeutic approaches. To explore the molecular mechanisms driving the growth and progression of DLBCL, we analyzed genes with differential expression in DLBCL using the Gene Expression Profiling Interactive Analysis database. Enkurin domain-containing protein 1 (ENKD1), a centrosomal protein-encoding gene, was found to be highly expressed in DLBCL samples compared with normal samples. The phylogenetic analysis revealed that ENKD1 is evolutionarily conserved. Depletion of ENKD1 in cultured DLBCL cells induced apoptosis, suppressed cell proliferation, and blocked cell cycle progression in the G2/M phase. Moreover, ENKD1 expression positively correlates with the expression levels of a number of cellular homeostatic regulators, including Sperm-associated antigen 5, a gene encoding an important mitotic regulator. These findings thus demonstrate a critical function for ENKD1 in regulating the cellular homeostasis and suggest a potential value of targeting ENKD1 for the treatment of DLBCL.

Embryology and anatomy of Hirschsprung disease

Bowel has its own elegant nervous system - the enteric nervous system (ENS) which is a complex network of neurons and glial clones. Derived from neural crest cells (NCCs), this little brain controls muscle contraction, motility, and bowel activities in response to stimuli. Failure of developing enteric ganglia at the distal bowel results in intestinal obstruction and Hirschsprung disease (HSCR). This Review summarises the important embryological development of the ENS including proliferation, migration, and differentiation of NCCs. We address the signalling pathways which determine NCC cell fate and discuss how they are altered in the context of HSCR. Finally, we outline the anatomical defects and the mechanisms underlying gut motility in HSCR.

Development, Diversity, and Neurogenic Capacity of Enteric Glia

Enteric glia are a fascinating population of cells. Initially identified in the gut wall as the "support" cells of the enteric nervous system, studies over the past 20 years have unveiled a vast array of functions carried out by enteric glia. They mediate enteric nervous system signalling and play a vital role in the local regulation of gut functions. Enteric glial cells interact with other gastrointestinal cell types such as those of the epithelium and immune system to preserve homeostasis, and are perceptive to luminal content. Their functional versatility and phenotypic heterogeneity are mirrored by an extensive level of plasticity, illustrated by their reactivity in conditions associated with enteric nervous system dysfunction and disease. As one of the hallmarks of their plasticity and extending their operative relationship with enteric neurons, enteric glia also display neurogenic potential. In this review, we focus on the development of enteric glial cells, and the mechanisms behind their heterogeneity in the adult gut. In addition, we discuss what is currently known about the role of enteric glia as neural precursors in the enteric nervous system.

TALPID3/KIAA0586 Regulates Multiple Aspects of Neuromuscular Patterning During Gastrointestinal Development in Animal Models and Human

TALPID3/KIAA0586 is an evolutionary conserved protein, which plays an essential role in protein trafficking. Its role during gastrointestinal (GI) and enteric nervous system (ENS) development has not been studied previously. Here, we analyzed chicken, mouse and human embryonic GI tissues with TALPID3 mutations. The GI tract of TALPID3 chicken embryos was shortened and malformed. Histologically, the gut smooth muscle was mispatterned and enteric neural crest cells were scattered throughout the gut wall. Analysis of the Hedgehog pathway and gut extracellular matrix provided causative reasons for these defects. Interestingly, chicken intra-species grafting experiments and a conditional knockout mouse model showed that ENS formation did not require TALPID3, but was dependent on correct environmental cues. Surprisingly, the lack of TALPID3 in enteric neural crest cells (ENCC) affected smooth muscle and epithelial development in a non-cell-autonomous manner. Analysis of human gut fetal tissues with a KIAA0586 mutation showed strikingly similar findings compared to the animal models demonstrating conservation of TALPID3 and its necessary role in human GI tract development and patterning.

Benzophenone-3 induced abnormal development of enteric nervous system in zebrafish through MAPK/ERK signaling pathway

Hirschsprung disease (HSCR) is a congenital disease characterized by the absence of enteric neurons, which is derived from the failure of the proliferation, differentiation or migration of the enteric neural crest cells (ENCCs). HSCR is associated with multiple risk factors, including polygenic inheritance factors and environmental factors. Genetic studies have been extensively performed, whereas studies related to environmental factors remain insufficient. Benzophenone-3 (BP-3), one important component of the ultraviolet (UV) filters, has been proved to have cytotoxicity and neurotoxicity which might be associated with HSCR. In this study, we used zebrafish as a model to investigate the relationship between BP-3 exposure and the development of the enteric nervous system (ENS) in vivo. Embryos exposed to BP-3 showed an average of 46% reduction of the number of the enteric neurons number. Besides, the ENCCs specific markers (ret and hand2) were downregulated upon BP-3 exposure. Moreover, we identified potential targets of BP-3 through Network Pharmacology Analysis and Autodock and demonstrated that the attenuation of the MAPK/ERK signaling might be the potential mechanism underlying the inhibition of the ENS development by BP-3. Importantly, MAPK/ERK signaling agonist could be used to rescue the ENS defects of zebrafish induced by BP-3. Overall, we characterized the influence of BP-3 on ENS development in vivo and explored possible molecular mechanisms.

A Rare Case of Dorsal Agenesis of Pancreas, Choledochal Cyst, and Hirschsprung Disease in a Young Patient

Dorsal pancreatic agenesis is a rare congenital pancreatic malformation. There is just 1 reported case associating it with choledochal cyst. However, no cases have reported yet with both coexisting with Hirschsprung disease. We report a case of a 23-year-old man, presenting with on and off epigastric pain, sometimes radiating to the back. His medical records showed he had Hirschsprung disease as a neonate, for which he underwent Duhamel procedure. Ultrasound imaging revealed a choledochal cyst and a nonvisualized distal portion of the pancreas. Further cross-sectional imaging confirmed the findings—a type 1 choledochal cyst and a dorsal agenesis of the pancreas in a patient with Hirschsprung disease.

Hedgehog Signaling in Intestinal Development and Homeostasis

The hedgehog (Hh) signaling pathway plays several diverse regulatory and patterning roles during organogenesis of the intestine and in the regulation of adult intestinal homeostasis. In the embryo, fetus, and adult, intestinal Hh signaling is paracrine: Hh ligands are expressed in the endodermally derived epithelium, while signal transduction is confined to the mesenchymal compartment, where at least a dozen distinct cell types are capable of responding to Hh signals. Epithelial Hh ligands not only regulate a variety of mesenchymal cell behaviors, but they also direct these mesenchymal cells to secrete additional soluble factors (e.g., Wnts, Bmps, inflammatory mediators) that feed back to regulate the epithelial cells themselves. Evolutionary conservation of the core Hh signaling pathway, as well as conservation of epithelial/mesenchymal cross talk in the intestine, has meant that work in many diverse model systems has contributed to our current understanding of the role of this pathway in intestinal organogenesis, which is reviewed here.

Gut innervation and enteric nervous system development: a spatial, temporal and molecular tour de force

During embryonic development, the gut is innervated by intrinsic (enteric) and extrinsic nerves. Focusing on mammalian ENS development, in this Review we highlight how important the different compartments of this innervation are to assure proper gut function. We specifically address the three-dimensional architecture of the innervation, paying special attention to the differences in development along the longitudinal and circumferential axes of the gut. We review recent information about the formation of both intrinsic innervation, which is fairly well-known, as well as the establishment of the extrinsic innervation, which, despite its importance in gut-brain signaling, has received much less attention. We further discuss how external microbial and nutritional cues or neuroimmune interactions may influence development of gut innervation. Finally, we provide summary tables, describing the location and function of several well-known molecules, along with some newer factors that have more recently been implicated in the development of gut innervation.

ETV2 (Ets Variant Transcription Factor 2)-Rhoj Cascade Regulates Endothelial Progenitor Cell Migration During Embryogenesis

OBJECTIVE

Endothelial progenitors migrate early during embryogenesis to form the primary vascular plexus. The regulatory mechanisms that govern their migration are not completely defined. Here, we describe a novel role for ETV2 (Ets variant transcription factor 2) in cell migration and provide evidence for an ETV2-Rhoj network as a mechanism responsible for this process. Approach and Results: Analysis of RNAseq datasets showed robust enrichment of migratory/motility pathways following overexpression of ETV2 during mesodermal differentiation. We then analyzed ETV2 chromatin immunoprecipitation-seq and assay for transposase accessible chromatin-seq datasets, which showed enrichment of chromatin immunoprecipitation-seq peaks with increased chromatin accessibility in migratory genes following overexpression of ETV2. Migratory assays showed that overexpression of ETV2 enhanced cell migration in mouse embryonic stem cells, embryoid bodies, and mouse embryonic fibroblasts. Knockout of Etv2 led to migratory defects of Etv2-EYFP⁺ angioblasts to their predefined regions of developing embryos relative to wild-type controls at embryonic day (E) 8.5, supporting its role during migration. Mechanistically, we showed that ETV2 binds the promoter region of Rhoj serving as an upstream regulator of cell migration. Single-cell RNAseq analysis of Etv2-EYFP⁺ sorted cells revealed coexpression of Etv2 and Rhoj in endothelial progenitors at E7.75 and E8.25. Overexpression of ETV2 led to a robust increase in Rhoj in both embryoid bodies and mouse embryonic fibroblasts, whereas, its expression was abolished in the Etv2 knockout embryoid bodies. Finally, shRNA-mediated knockdown of Rhoj resulted in migration defects, which were partially rescued by overexpression of ETV2.

CONCLUSIONS

These results define an ETV2-Rhoj cascade, which is important for the regulation of endothelial progenitor cell migration.

Semaphorin 3A controls enteric neuron connectivity and is inversely associated with synapsin 1 expression in Hirschsprung disease

Most of the gut functions are controlled by the enteric nervous system (ENS), a complex network of enteric neurons located throughout the wall of the gastrointestinal tract. The formation of ENS connectivity during the perinatal period critically underlies the establishment of gastrointestinal motility, but the factors involved in this maturation process remain poorly characterized. Here, we examined the role of Semaphorin 3A (Sema3A) on ENS maturation and its potential implication in Hirschsprung disease (HSCR), a developmental disorder of the ENS with impaired colonic motility. We found that Sema3A and its receptor Neuropilin 1 (NRP1) are expressed in the rat gut during the early postnatal period. At the cellular level, NRP1 is expressed by enteric neurons, where it is particularly enriched at growth areas of developing axons. Treatment of primary ENS cultures and gut explants with Sema3A restricts axon elongation and synapse formation. Comparison of the ganglionic colon of HSCR patients to the colon of patients with anorectal malformation shows reduced expression of the synaptic molecule synapsin 1 in HSCR, which is inversely correlated with Sema3A expression. Our study identifies Sema3A as a critical regulator of ENS connectivity and provides a link between altered ENS connectivity and HSCR.

Selective Induction of Human Autonomic Neurons Enables Precise Control of Cardiomyocyte Beating

The autonomic nervous system (ANS) regulates tissue homeostasis and remodelling through antagonistic effects of noradrenergic sympathetic and cholinergic parasympathetic signalling. Despite numerous reports on the induction of sympathetic neurons from human pluripotent stem cells (hPSCs), no induction methods have effectively derived cholinergic parasympathetic neurons from hPSCs. Considering the antagonistic effects of noradrenergic and cholinergic inputs on target organs, both sympathetic and parasympathetic neurons are expected to be induced. This study aimed to develop a stepwise chemical induction method to induce sympathetic-like and parasympathetic-like ANS neurons. Autonomic specification was achieved through restricting signals inducing sensory or enteric neurogenesis and activating bone morphogenetic protein (BMP) signals. Global mRNA expression analyses after stepwise induction, including single-cell RNA-seq analysis of induced neurons and functional assays revealed that each induced sympathetic-like or parasympathetic-like neuron acquired pharmacological and electrophysiological functional properties with distinct marker expression. Further, we identified selective induction methods using appropriate seeding cell densities and neurotrophic factor concentrations. Neurons were individually induced, facilitating the regulation of the beating rates of hiPSC-derived cardiomyocytes in an antagonistic manner. The induction methods yield specific neuron types, and their influence on various tissues can be studied by co-cultured assays.

Bi-allelic Variations of SMO in Humans Cause a Broad Spectrum of Developmental Anomalies Due to Abnormal Hedgehog Signaling

The evolutionarily conserved hedgehog (Hh) pathway is essential for organogenesis and plays critical roles in postnatal tissue maintenance and renewal. A unique feature of the vertebrate Hh pathway is that signal transduction requires the primary cilium (PC) where major pathway components are dynamically enriched. These factors include smoothened (SMO) and patched, which constitute the core reception system for sonic hedgehog (SHH) as well as GLI transcription factors, the key mediators of the pathway. Here, we report bi-allelic loss-of-function variations in SMO in seven individuals from five independent families; these variations cause a wide phenotypic spectrum of developmental anomalies affecting the brain (hypothalamic hamartoma and microcephaly), heart (atrioventricular septal defect), skeleton (postaxial polydactyly, narrow chest, and shortening of long bones), and enteric nervous system (aganglionosis). Cells derived from affected individuals showed normal ciliogenesis but severely altered Hh-signal transduction as a result of either altered PC trafficking or abnormal activation of the pathway downstream of SMO. In addition, Hh-independent GLI2 accumulation at the PC tip in cells from the affected individuals suggests a potential function of SMO in regulating basal ciliary trafficking of GLI2 when the pathway is off. Thus, loss of SMO function results in abnormal PC dynamics of key components of the Hh signaling pathway and leads to a large continuum of malformations in humans.

Epigenetic factors Dnmt1 and Uhrf1 coordinate intestinal development

Intestinal tract development is a coordinated process involving signaling among the progenitors and developing cells from all three germ layers. Development of endoderm-derived intestinal epithelium has been shown to depend on epigenetic modifications, but whether that is also the case for intestinal tract cell types from other germ layers remains unclear. We found that functional loss of a DNA methylation machinery component, ubiquitin-like protein containing PHD and RING finger domains 1 (uhrf1), leads to reduced numbers of ectoderm-derived enteric neurons and severe disruption of mesoderm-derived intestinal smooth muscle. Genetic chimeras revealed that Uhrf1 functions both cell-autonomously in enteric neuron precursors and cell-non-autonomously in surrounding intestinal cells, consistent with what is known about signaling interactions between these cell types that promote one another's development. Uhrf1 recruits the DNA methyltransferase Dnmt1 to unmethylated DNA during replication. Dnmt1 is also expressed in enteric neurons and smooth muscle progenitors. dnmt1 mutants have fewer enteric neurons and disrupted intestinal smooth muscle compared to wildtypes. Because dnmt1;uhrf1 double mutants have a similar phenotype to dnmt1 and uhrf1 single mutants, Dnmt1 and Uhrf1 must function together during enteric neuron and intestinal muscle development. This work shows that genes controlling epigenetic modifications are important to coordinate intestinal tract development, provides the first demonstration that these genes influence development of the ENS, and advances uhrf1 and dnmt1 as potential new Hirschsprung disease candidates.

Sonic hedgehog signalling regulates the self-renewal and proliferation of skin-derived precursor cells in mice

OBJECTIVES

The sonic hedgehog (Shh) signalling pathway has an important role in the maintenance of various stem cells and organogenesis during development. However, the effect of Shh in skin-derived precursors (SKPs), which have the capacity for multipotency and self-renewal, is not yet clear. The present study investigated the effects of the Shh signalling pathway on the proliferation and self-renewal of murine SKPs (mSKPs).

METHODS

The Shh signalling pathway was activated by treatment with purmorphamine (Shh agonist) or recombinant Shh in mSKPs. Cyclopamine (Shh antagonist) or GANT-61 (Gli inhibitor) was used to inhibit the pathway. Western blot, qPCR, and immunofluorescence were used to analyse the expression of genes related to self-renewal, stemness, epithelial-mesenchymal transition (EMT) and the Shh signalling pathway. In addition, cell proliferation and apoptosis were examined.

RESULTS

Inhibiting the Shh signalling pathway reduced mSKP proliferation and sphere formation, but increased apoptosis. Activating this signalling pathway produced opposite results. The Shh signalling pathway also controlled the EMT phenotype in mSKPs. Moreover, purmorphamine recovered the self-renewal and proliferation of aged mSKPs.

CONCLUSION

Our results suggest that the Shh signalling pathway has an important role in the proliferation, self-renewal and apoptosis of mSKPs. These findings also provide a better understanding of the cellular mechanisms underlying SKP self-renewal and apoptosis that allow more efficient expansion of SKPs.

FGF8 and Shh promote the survival and maintenance of multipotent neural crest progenitors

The developmental mechanisms that control the building of the complex head of vertebrates and particularly, facial skeletogenesis, remain poorly known. Progenitor cells derived from the embryonic neural crest (NC) are the major constituents and players of facial tissue development. Deciphering the cellular and molecular machinery that controls NC cell (NCC) differentiation into bone, cartilage, fat and other mesenchymal tissues, is thus a main issue for understanding vertebrate facial variations. In this work, we investigated the effects of fibroblast growth factor 8 (FGF8) and Sonic Hedgehog (Shh), two signaling molecules essential for craniofacial development, on the in vitro differentiation and multipotentiality of mesencephalic NCCs (MNCCs) isolated from the quail embryo. Comparison of distinct temporal treatments with FGF8 and/or Shh showed that both promoted chondrogenesis of MNCCs by increasing the amount and size of cartilage nodules. Higher rates of chondrogenesis were observed when MNCCs were treated with FGF8 during the migration phase, thus mimicking the in vivo exposure of migrating NCCs to FGF8 secreted by the isthmic brain signaling center. An in vitro cell cloning assay revealed that, after concomitant treatment with FGF8 and Shh, about 80% of NC progenitors displayed chondrogenic potential, while in untreated cultures, only 18% exhibited this potential. In addition, colony analysis showed for the first time the existence of a highly multipotent progenitor able to clonally give rise to adipocytes in addition to other cephalic NC phenotypes (i.e. glial cells, neurons, melanocytes, smooth muscle cells and chondrocytes) (GNMFCA progenitor). This progenitor was observed only when clonal cultures were treated with both FGF8 and Shh. Several other types of multipotent cells, which generated four, five or six distinct phenotypes, accounted for 55% of the progenitors in FGF8 and Shh treated cultures, versus 13,5% in the untreated ones. Together, these data reveal an essential role for both FGF8 and Shh together in maintenance of MNCC multipotentiality by favoring the development of NC progenitors endowed with a broad array of mesectodermal potentials.

Expression of Numb and Gli1 in malignant pleural mesothelioma and their clinical significance

AIM OF STUDY

Malignant pleural mesothelioma (MPM) is a highly lethal and refractory to multimodal treatment tumor. Numb is considered as a tumor suppressor playing critical roles in determining cell fate and has been shown to target the oncogenic transcription factor Gli1 for Itch-dependent ubiquitination, resulting in suppression of the oncogenic sonic hedgehog signaling in medulloblastoma. This study was designed to analysis the role of Numb and Gli1 in MPM.

MATERIALS AND METHODS

Tissues of 61 MPM patients and 22 normal pleura as control were investigated. Numb and Gli1 expression were evaluated by immunohistochemistry. The associations with clinical and pathological parameters of the two markers were statistically analyzed, and the correlation between them was also demonstrated.

RESULTS

The expression levels of Numb with nuclear Gli1 exhibited a significant inverse correlation (r = -0.361 P < 0.05). In addition, Numb has an inverse correlation with ki-67 labeling index (P < 0.05), and nuclear Gli1 was found in associated with the tumor International Mesothelioma Interest Group-stage (P < 0.05). The overall survival was influenced by the expression of Numb (P < 0.05) and histological subtype (P < 0.05), further regression analysis showed that only histological subtype has a prognostic influence on survival (P < 0.05).

CONCLUSION

The results provide new evidence of Numb and Gli1 on the clinical characteristics of MPM, which may be helpful in clinical diagnosis and targeted therapy. Further research with larger sample size is needed.

Developing neurites from mouse basal forebrain gonadotropin-releasing hormone neurons use Sonic hedgehog to modulate their growth

Hypothalamic gonadotropin-releasing hormone (GnRH) neurons are required for fertility in all mammalian species studied to date. GnRH neuron cell bodies reside in the basal forebrain, and most extend long neurites in the caudal direction to terminate at the median eminence (ME), the site of hormone secretion. Using in vitro neurite growth assays, histological methods, and genetic deletion strategies in mice we have analysed the role of the morphogen and neurite growth and guidance molecule, Sonic hedgehog (Shh), in the growth of GnRH neurites to their target. Immunohistochemistry revealed that Shh was present in the basal forebrain, the preoptic area (POA) and mediobasal hypothalamus (MBH) at gestational day 14.5 (GD 14.5), a time when GnRH neurites grow towards the ME. Furthermore, in situ hybridization revealed that mRNA encoding the Shh receptor, Smoothened (Smo), was present in GnRH neurons from GD 15.5, when the first GnRH neurites are extending towards the MBH. In vitro neurite growth assays using hypothalamic explants from GD 15.5 fetuses in 3-D collagen gels showed that Shh was able to significantly stimulate GnRH neurite outgrowth. Finally, genetic deletion of Smo specifically from GnRH neurons in vivo, using Cre-loxP technology, resulted in a significant decrease in GnRH neurites innervating the ME. These experiments demonstrate that GnRH neurites use Shh for their neurite development, provide further understanding of the mechanisms by which GnRH nerve terminals arrive at their site of hormone secretion, and identify an additional hypothalamic neuronal population for which Shh/Smo signaling is developmentally important.

Intracellular Calcium Mobilization Is Required for Sonic Hedgehog Signaling

Graded Shh signaling across fields of precursor cells coordinates patterns of gene expression, differentiation, and morphogenetic behavior as precursors form complex structures, such as the nervous system, the limbs, and craniofacial skeleton. Here we discover that intracellular calcium mobilization, a process tightly controlled and readily modulated, regulates the level of Shh-dependent gene expression in responding cells and affects the development of all Shh-dependent cell types in the zebrafish embryo. Reduced expression or modified activity of ryanodine receptor (RyR) intracellular calcium release channels shifted the allocation of Shh-dependent cell fates in the somitic muscle and neural tube. Mosaic analysis revealed that RyR-mediated calcium mobilization is required specifically in Shh ligand-receiving cells. This work reveals that RyR channels participate in intercellular signal transduction events. As modulation of RyR activity modifies tissue patterning, we hypothesize that alterations in intracellular calcium mobilization contribute to both birth defects and evolutionary modifications of morphology.

Targeting GLI Transcription Factors in Cancer

Aberrant activation of hedgehog (Hh) signaling has been observed in a wide variety of tumors and accounts for more than 25% of human cancer deaths. Inhibitors targeting the Hh signal transducer Smoothened (SMO) are widely used and display a good initial efficacy in patients suffering from basal cell carcinoma (BCC); however, a large number of patients relapse. Though SMO mutations may explain acquired therapy resistance, a growing body of evidence suggests that the non-canonical, SMO-independent activation of the Hh pathway in BCC patients can also account for this adverse effect. In this review, we highlight the importance of glioma-associated oncogene (GLI) transcription factors (the main downstream effectors of the canonical and the non-canonical Hh cascade) and their putative role in the regulation of multiple oncogenic signaling pathways. Moreover, we discuss the contribution of the Hh signaling to malignant transformation and propose GLIs as central hubs in tumor signaling networks and thus attractive molecular targets in anti-cancer therapies.

Bisphenol A stimulates adrenal cortical cell proliferation via ERβ-mediated activation of the sonic hedgehog signalling pathway

We previously demonstrated that prenatal exposure to bisphenol A (BPA) resulted in increased adrenal gland weight independent of changes in plasma ACTH levels in adult mouse offspring. This finding suggested that BPA exposure likely had a direct effect on adrenal development. Given that (1) sonic hedgehog (Shh) signaling is essential for adrenal development; (2) deletion of the Shh gene in mice results in adrenal hypoplasia; (3) BPA is known to signal through estrogen receptor β (ERβ); and (4) ERβ is highly expressed in adrenal glands; we hypothesized that BPA stimulates adrenal cell proliferation via ERβ-mediated activation of the Shh pathway. To test this hypothesis, the human adrenal cell line, H295A cells, was used as an in vitro model system. Our main findings were: (1) BPA increased cell number and protein levels of proliferating cell nuclear antigen (PCNA; a universal marker of cell proliferation), cyclin D1 and D2 (key proliferation factors), as well as Shh and its key transcriptional regulator Gli1; (2) cyclopamine, a Shh pathway inhibitor, blocked these stimulatory effects of BPA on cell proliferation; (3) BPA increased the nuclear translocation of ERβ; and (4) the ERβ-specific agonist DPN mimicked while the ERβ-specific antagonist PHTPP abrogated the stimulatory effects of BPA on cell proliferation and Shh signaling. Taken together, these findings demonstrate that BPA stimulates adrenal cell proliferation likely through ERβ-mediated activation of the Shh signaling pathway. Thus, the present study provides novel insights into the molecular mechanisms underlying our previously reported BPA-induced aberrant adrenal phenotype.

Gli family zinc finger 1 is associated with endothelin receptor type B in Hirschsprung disease

Hirschsprung disease (HSCR) is a newborn colorectal disease characterized by an absence of ganglia in the distal gut. Hedgehog (Hh) and endothelin signaling serve important roles in gastrointestinal tract formation. Alterations in the signaling pathways disrupt the development of enteric neural crest cells (ENCCs). It is not known whether there is any coordination between these pathways in the pathogenesis of HSCR. In the present study, tissue samples from 35 patients with HSCR, including stenotic aganglionosis gut and normal ganglionic gut, were obtained. The expression of Gli family zinc finger 1 (Gli1) and endothelin receptor type B (EDNRB) was determined using reverse transcription-quantitative polymerase chain reaction, immunohistochemistry and western blotting. In addition, the SK-N-SH cell line was used to investigate the association between Hh signaling and the expression of EDNRB. The results revealed aberrant expression of Gli1 in the aganglionic segments, as well as decreased expression of Gli1 in tissues from 7 patients with HSCR exhibited, whereas tissues from 9 patients with HSCR exhibited increased Gli1 expression compared with the expression in the normal tissues. There was a negative association between EDNRB expression and Gli1 expression in the same sample. Knockdown of Gli1 by small interfering RNA and inhibition of Hh signaling by Vismodegib in SK-N-SH cells increased EDNRB expression. By contrast, upregulation of Gli1 expression by plasmids and activation of Hh signaling by Purmorphamine decreased EDNRB expression. Furthermore, premature enteric ganglia were observed in 4 patients with HSCR with decreased Gli1 expression. Thus, the results of the present study suggest that altered Gli1 expression negatively regulates EDNRB expression in patients with HSCR. The increased expression of EDNRB induced by decreased Gli1 expression may represent a novel mechanism in HSCR.

Sonic Hedgehog Regulation of the Neural Precursor Cell Fate During Chicken Optic Tectum Development

During nervous system development, neurons project axons over long distances to reach the appropriate targets for correct neural circuit formation. Sonic hedgehog (Shh) is a secreted protein and plays a key role in regulating vertebrate embryogenesis, especially in central nervous system (CNS) patterning, including neuronal migration and axonal projection in the brain and spinal cord. In the developing ventral midbrain, Shh is sufficient to specify a striped pattern of cell fates. Little is known about the molecular mechanisms underlying the Shh regulation of the neural precursor cell fate during the optic tectum development. Here, we aimed at studying how Shh might regulate chicken optic tectum patterning. In the present study, in ovo electroporation methods were employed to achieve the overexpression of Shh in the optic tectum during chicken embryo development. Besides, the study combined in ovo electroporation and neuron isolation culturing to study the function of Shh in vivo and in vitro. The fluorescent immunohistochemistry methods were used to check the related indicators. The results showed that Shh overexpression caused 87.8% of cells to be distributed to the stratum griseum central (SGC) layer, while only 39.3% of the GFP-transfected cells resided in the SGC layer in the control group. Shh overexpression also reduced the axon length in vivo and in vitro. In conclusion, we provide evidence that Shh regulates the neural precursor cell fate during chicken optic tectum development. Shh overexpression impairs neuronal migration and may affect the fate determination of transfected neurons.

Defining the transcriptomic landscape of the developing enteric nervous system and its cellular environment

BACKGROUND

Motility and the coordination of moving food through the gastrointestinal tract rely on a complex network of neurons known as the enteric nervous system (ENS). Despite its critical function, many of the molecular mechanisms that direct the development of the ENS and the elaboration of neural network connections remain unknown. The goal of this study was to transcriptionally identify molecular pathways and candidate genes that drive specification, differentiation and the neural circuitry of specific neural progenitors, the phox2b expressing ENS cell lineage, during normal enteric nervous system development. Because ENS development is tightly linked to its environment, the transcriptional landscape of the cellular environment of the intestine was also analyzed.

RESULTS

Thousands of zebrafish intestines were manually dissected from a transgenic line expressing green fluorescent protein under the phox2b regulatory elements [Tg(phox2b:EGFP) ^w37 ]. Fluorescence-activated cell sorting was used to separate GFP-positive phox2b expressing ENS progenitor and derivatives from GFP-negative intestinal cells. RNA-seq was performed to obtain accurate, reproducible transcriptional profiles and the unbiased detection of low level transcripts. Analysis revealed genes and pathways that may function in ENS cell determination, genes that may be identifiers of different ENS subtypes, and genes that define the non-neural cellular microenvironment of the ENS. Differential expression analysis between the two cell populations revealed the expected neuronal nature of the phox2b expressing lineage including the enrichment for genes required for neurogenesis and synaptogenesis, and identified many novel genes not previously associated with ENS development. Pathway analysis pointed to a high level of G-protein coupled pathway activation, and identified novel roles for candidate pathways such as the Nogo/Reticulon axon guidance pathway in ENS development.

CONCLUSION

We report the comprehensive gene expression profiles of a lineage-specific population of enteric progenitors, their derivatives, and their microenvironment during normal enteric nervous system development. Our results confirm previously implicated genes and pathways required for ENS development, and also identify scores of novel candidate genes and pathways. Thus, our dataset suggests various potential mechanisms that drive ENS development facilitating characterization and discovery of novel therapeutic strategies to improve gastrointestinal disorders.

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.

Gene-environment interactions and the enteric nervous system: Neural plasticity and Hirschsprung disease prevention

Intestinal function is primarily controlled by an intrinsic nervous system of the bowel called the enteric nervous system (ENS). The cells of the ENS are neural crest derivatives that migrate into and through the bowel during early stages of organogenesis before differentiating into a wide variety of neurons and glia. Although genetic factors critically underlie ENS development, it is now clear that many non-genetic factors may influence the number of enteric neurons, types of enteric neurons, and ratio of neurons to glia. These non-genetic influences include dietary nutrients and medicines that may impact ENS structure and function before or after birth. This review summarizes current data about gene-environment interactions that affect ENS development and suggests that these factors may contribute to human intestinal motility disorders like Hirschsprung disease or irritable bowel syndrome.

Efficient Generation of Functionally Active Spinal Cord Neurons from Spermatogonial Stem Cells

Neural stem cells (NSCs) are hitherto regarded as perspective candidates for cell transplantation in clinical therapies for multilevel spinal cord injury and function restoration. However, the extreme drawbacks of NSCs available for injury transplantation still represent a significant bottleneck in neural regeneration medicine. Therefore, it is essential to establish a suitable cell reservoir as an issue-free alternative. Here, we demonstrate that spermatogonial stem cells (SSCs) derived from rat testis robustly give rise to terminally differentiated, functionally mature spinal cord neurons by using an optimized differentiation protocol. After performing a 3-week in vitro differentiation procedure, most cells exhibited neural morphological features and were Tuj-1 positive. Of note, approximately 60 % of the obtained cells coexpressed choline acetyltransferase (CHAT), acetylcholinesterase (AchE), and calcitonin gene-related peptide (CGRP). More importantly, apart from acquisition of neural antigenic and biochemical properties, nearly all neurons efficiently exhibited in vitro functionality similar to wild-type neurons, such as synapse formation, increased neuronal calcium influx, and electrophysiology. This is the first report revealing consistent and reproducible generation of large amounts of functional neurons from SSCs. Collectively, this system is suitable for studies of SSC transdifferentiation into neuronal cells and can provide sufficient neurons for the treatment of spinal cord injury as well as for genetic and small molecule screenings.

Smoothened-independent activation of hedgehog signaling by rearranged during transfection promotes neuroblastoma cell proliferation and tumor growth

BACKGROUND

Rearranged during transfection (RET) proto-oncogene encodes a receptor tyrosine kinase for glial cell line-derived neurotrophic factor (GDNF) signaling, and high RET expression is closely related to the tumorigenesis and malignancy of neuroblastoma(NB).

METHODS

We have investigated whether RET signals through hedgehog (HH) pathway in NB cell proliferation and tumor growth by in vitro cell culture and in vivo xenograft approaches.

RESULTS

The key members of both GDNF/RET and HH/GLI pathways are expressed in NB cell lines to different extents. Knockdown of RET in NB cells significantly attenuates the activity of HH signaling, whereas overexpression of RET robustly enhances the output of transcriptional activation by HH. Likewise, activation of RET by GDNF induces HH signaling, whereas knockdown of RET attenuates both basal and GDNF-induced activities of HH signaling. Moreover, protein kinase B lies on the downstream of GDNF/RET signaling module to inhibit the GSK3β, resulting in activation of HH signaling. Furthermore, either knockdown of RET by shRNA or inhibition of HH pathway by cyclopamine attenuates not only basal but also GDNF-induced proliferation of SH-SY5Y cells, and knockdown of either RET or smoothened in SH-SY5Y cell xenografts significantly attenuated the tumor growth. Finally, inhibition of HH signaling by GLI1 and GLI2 inhibitor, Gant61, reduces not only basal but also RET-induced proliferation of SH-SY5Y cells and outgrowth of xenografts.

CONCLUSION

GDNF/RET/AKT/GSK3β signaling module activates HH pathway to stimulate NB cells proliferation and tumor outgrowth.

GENERAL SIGNIFICANCE

Targeting HH pathway is a rational approach for therapeutic intervention of NB with high RET expression.

Enteric nervous system assembly: Functional integration within the developing gut

Co-ordinated gastrointestinal function is the result of integrated communication between the enteric nervous system (ENS) and "effector" cells in the gastrointestinal tract. Unlike smooth muscle cells, interstitial cells, and the vast majority of cell types residing in the mucosa, enteric neurons and glia are not generated within the gut. Instead, they arise from neural crest cells that migrate into and colonise the developing gastrointestinal tract. Although they are "later" arrivals into the developing gut, enteric neural crest-derived cells (ENCCs) respond to many of the same secreted signalling molecules as the "resident" epithelial and mesenchymal cells, and several factors that control the development of smooth muscle cells, interstitial cells and epithelial cells also regulate ENCCs. Much progress has been made towards understanding the migration of ENCCs along the gastrointestinal tract and their differentiation into neurons and glia. However, our understanding of how enteric neurons begin to communicate with each other and extend their neurites out of the developing plexus layers to innervate the various cell types lining the concentric layers of the gastrointestinal tract is only beginning. It is critical for postpartum survival that the gastrointestinal tract and its enteric circuitry are sufficiently mature to cope with the influx of nutrients and their absorption that occurs shortly after birth. Subsequently, colonisation of the gut by immune cells and microbiota during postnatal development has an important impact that determines the ultimate outline of the intrinsic neural networks of the gut. In this review, we describe the integrated development of the ENS and its target cells.

ENS Development Research Since 1983: Great Strides but Many Remaining Challenges

The first enteric nervous system (ENS) conference, organized by Marcello Costa and John Furness, was held in Adelaide, Australia in 1983. In this article, we review what was known about the development of the ENS in 1983 and then summarize some of the major advances in the field since 1983.

Mimicking natural cell environments: design, fabrication and application of bio-chemical gradients on polymeric biomaterial substrates

Gradients of biomolecules on synthetic, solid substrates can efficiently mimic the natural, graded variation of properties of the extracellular matrix (ECM).

Hirschsprung's disease: A bridge for science and surgery

BACKGROUND/PURPOSE

Understanding the true nature of the disease provided the basis for appropriate surgery for Hirschsprung's disease some 60 years ago. Nevertheless, surgical outcome remains unsatisfactory. Advances in diagnosis and treatment will depend on the elucidation of the pathogenesis and disease heterogeneity.

METHODS

This lecture outlines the author's attempt in the past 30 years to bridge some of the gaps of knowledge in Hirschsprung's disease.

RESULTS

Studies of human fetal gut and aganglionic gut gave insight into the complexity of the human enteric nervous system, but the more fruitful studies came from genetic studies in which disease-causing genes were discovered, and the importance of noncoding mutations conferring disease susceptibility was unraveled. Animal models and pluripotent stem cell studies allowed elucidation of the interacting gene-cell-microenvironment signaling pathways for neural crest proliferation, migration, and differentiation.

CONCLUSION

Hirschsprung's disease has been a bridge for science and surgery. An integrative approach could provide breakthroughs in the diagnosis and treatment strategies of this complex condition, leading to improved outcome.

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.

Detection and preliminary screening of the human gene expression profile for Hirschsprung's disease

The present study investigated a genome microarray of colorectal lesions (spasm segments) in children with Hirschsprung's disease (HSCR), and analyzed the results. In addition, the present study screened for differentially expressed genes in children with HSCR. Microarray technology was used to examine the human gene expression profiles of the colorectal lesions (spasm segments) of six children with HSCR, and three normal colon tissue samples. The data were analyzed be determining P‑values of significance and absolute fold changes. Preliminary screening was performed to identify genes exhibiting significant differential expression in children with HSCR, and these target genes were analyzed in subsequent verification and analytical investigations. Of >20,000 detected human genes, the preliminary screenings demonstrated that 3,850 genes were differentially expressed and upregulated, with P<0.05 and >2‑fold absolute changes in expression. In addition, 645 differentially expressed genes with P<0.05 and >2‑fold absolute changes were downregulated. Of the upregulated genes, 118 were involved in classic signaling pathways, compared with 11 of the downregulated genes (P<0.001; absolute fold change >2‑fold). HSCR etiology is complex and often involves multiple gene changes. Microarray technology can produce large quantities of gene expression data simultaneously, and analyzing this data using various techniques may provide a fast and efficient method for identifying novel gene targets and for investigating the mechanisms underlying HSCR pathogenesis.

Meis3 is required for neural crest invasion of the gut during zebrafish enteric nervous system development

Loss of Meis3 leads to defects in enteric neural crest cell migration, number, and proliferation during colonization of the gut. This leads to colonic aganglionosis, in which the hindgut is devoid of neurons, identifying it as a novel candidate factor in the etiology of Hirschsprung’s disease during enteric nervous system development.

During development, vagal neural crest cells fated to contribute to the enteric nervous system migrate ventrally away from the neural tube toward and along the primitive gut. The molecular mechanisms that regulate their early migration en route to and entry into the gut remain elusive. Here we show that the transcription factor meis3 is expressed along vagal neural crest pathways. Meis3 loss of function results in a reduction in migration efficiency, cell number, and the mitotic activity of neural crest cells in the vicinity of the gut but has no effect on neural crest or gut specification. Later, during enteric nervous system differentiation, Meis3-depleted embryos exhibit colonic aganglionosis, a disorder in which the hindgut is devoid of neurons. Accordingly, the expression of Shh pathway components, previously shown to have a role in the etiology of Hirschsprung’s disease, was misregulated within the gut after loss of Meis3. Taken together, these findings support a model in which Meis3 is required for neural crest proliferation, migration into, and colonization of the gut such that its loss leads to severe defects in enteric nervous system development.

Knockout mouse models of Hirschsprung's disease

PURPOSE

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cell migration. Rodent animal models of aganglionosis have contributed greatly to our understanding of the genetic basis of HSCR. Several natural or target mutations in specific genes have been reported to produce developmental defects in neural crest migration, differentiation or survival. The aim of this study was to review the currently available knockout models of HSCR to better understand the molecular basis of HSCR.

METHODS

A review of the literature using the keywords "Hirschsprung's disease", "aganglionosis", "megacolon" and "knockout mice model" was performed. Resulting publications were reviewed for relevant mouse models of human aganglionosis. Reference lists were screened for additional relevant studies.

RESULTS

16 gene knockout mouse models were identified as relevant rodent models of human HSCR. Due to the deletion of a specific gene, the phenotypes of these knockout models are diverse and range from small bowel dilatation and muscular hypertrophy to total intestinal aganglionosis.

CONCLUSIONS

Mouse models of aganglionosis have been instrumental in the discovery of the causative genes of HSCR. Although important advances have been made in understanding the genetic basis of HSCR, animal models of aganglionosis in future should further help to identify the unknown susceptibility genes in HSCR.

Epigenetic regulation of human hedgehog interacting protein in glioma cell lines and primary tumor samples

Glioma constitutes one of the most common groups of brain tumors, and its prognosis is influenced by different genetic and epigenetic modulations. In this study, we demonstrated low or no expression of hedgehog interacting protein (HHIP) in most of the cell lines and primary glioma tumor samples. We further proceeded to promoter methylation study of this gene in the same cell lines and primary tumor samples and found 87 % (7/8) HHIP methylation in glioblastoma cell lines and 75 % (33/44) in primary tumor samples. These methylation pattern correlates with low or unexpressed HHIP in both cell lines and primary tumor samples. Our results suggest the possibility of epigenetic regulation of this gene in glioma, similarly to medulloblastoma, gastric, hepatic, and pancreatic cancers. Also, HHIP might be a diagnostic or prognostic marker in glioma and help to the detection of these tumors in early stages of disease.

The enteric glia: identity and functions

Enteric glial cells were first described at the end of the 19th century, but they attracted more interest from researchers only in the last decades of the 20th. Although, they have a different embryological origin, the enteric GLIA share many characteristics with astrocytes, the main glial cell type of the central nervous system (CNS), such as in their expression of the same markers and in their functions. Here we review the construction of the enteric nervous system (ENS), with a focus on enteric glia, and also the main studies that have revealed the action of enteric glia in different aspects of gastrointestinal tract homeostasis, such as in the intestinal barrier, in communications with neurons, and in their action as progenitor cells. We also discuss recent discoveries about the roles of enteric glia in different disorders that affect the ENS, such as degenerative pathologies including Parkinson's and prion diseases, and in cases of intestinal diseases and injury.

Enteric neural crest cells regulate vertebrate stomach patterning and differentiation

In vertebrates, the digestive tract develops from a uniform structure where reciprocal epithelial-mesenchymal interactions pattern this complex organ into regions with specific morphologies and functions. Concomitant with these early patterning events, the primitive GI tract is colonized by the vagal enteric neural crest cells (vENCCs), a population of cells that will give rise to the enteric nervous system (ENS), the intrinsic innervation of the GI tract. The influence of vENCCs on early patterning and differentiation of the GI tract has never been evaluated. In this study, we report that a crucial number of vENCCs is required for proper chick stomach development, patterning and differentiation. We show that reducing the number of vENCCs by performing vENCC ablations induces sustained activation of the BMP and Notch pathways in the stomach mesenchyme and impairs smooth muscle development. A reduction in vENCCs also leads to the transdifferentiation of the stomach into a stomach-intestinal mixed phenotype. In addition, sustained Notch signaling activity in the stomach mesenchyme phenocopies the defects observed in vENCC-ablated stomachs, indicating that inhibition of the Notch signaling pathway is essential for stomach patterning and differentiation. Finally, we report that a crucial number of vENCCs is also required for maintenance of stomach identity and differentiation through inhibition of the Notch signaling pathway. Altogether, our data reveal that, through the regulation of mesenchyme identity, vENCCs act as a new mediator in the mesenchymal-epithelial interactions that control stomach development.

Gas1 is a receptor for sonic hedgehog to repel enteric axons

The myenteric plexus of the enteric nervous system controls the movement of smooth muscles in the gastrointestinal system. They extend their axons between two peripheral smooth muscle layers to form a tubular meshwork arborizing the gut wall. How a tubular axonal meshwork becomes established without invading centrally toward the gut epithelium has not been addressed. We provide evidence here that sonic hedgehog (Shh) secreted from the gut epithelium prevents central projections of enteric axons, thereby forcing their peripheral tubular distribution. Exclusion of enteric central projections by Shh requires its binding partner growth arrest specific gene 1 (Gas1) and its signaling component smoothened (Smo) in enteric neurons. Using enteric neurons differentiated from neurospheres in vitro, we show that enteric axon growth is not inhibited by Shh. Rather, when Shh is presented as a point source, enteric axons turn away from it in a Gas1-dependent manner. Of the Gαi proteins that can couple with Smo, G protein α Z (Gnaz) is found in enteric axons. Knockdown and dominant negative inhibition of Gnaz dampen the axon-repulsive response to Shh, and Gnaz mutant intestines contain centrally projected enteric axons. Together, our data uncover a previously unsuspected mechanism underlying development of centrifugal tubular organization and identify a previously unidentified effector of Shh in axon guidance.

Mutations in SGOL1 cause a novel cohesinopathy affecting heart and gut rhythm

The pacemaking activity of specialized tissues in the heart and gut results in lifelong rhythmic contractions. Here we describe a new syndrome characterized by Chronic Atrial and Intestinal Dysrhythmia, termed CAID syndrome, in 16 French Canadians and 1 Swede. We show that a single shared homozygous founder mutation in SGOL1, a component of the cohesin complex, causes CAID syndrome. Cultured dermal fibroblasts from affected individuals showed accelerated cell cycle progression, a higher rate of senescence and enhanced activation of TGF-β signaling. Karyotypes showed the typical railroad appearance of a centromeric cohesion defect. Tissues derived from affected individuals displayed pathological changes in both the enteric nervous system and smooth muscle. Morpholino-induced knockdown of sgol1 in zebrafish recapitulated the abnormalities seen in humans with CAID syndrome. Our findings identify CAID syndrome as a novel generalized dysrhythmia, suggesting a new role for SGOL1 and the cohesin complex in mediating the integrity of human cardiac and gut rhythm.

Stimulatory role of the chemokine CCL2 in the migration and peptide expression of embryonic hypothalamic neurons

Neuroinflammation is a feedback mechanism against infection, with recent studies suggesting a neuromodulatory role. The chemokine, (C-C motif) ligand 2 (CCL2), and its receptor, (C-C motif) receptor type 2 (CCR2), affect neuromodulation and migration in response to damage. Although CCL2 co-localizes with neuropeptides in the hypothalamus that control voluntary behavior, the function of CCL2/CCR2 is unknown. This led us to consider the possibility that CCL2 acting through CCR2, under natural conditions, may affect the migration and peptide levels of hypothalamic neurons that control voluntary behavior. This study used primary embryonic hypothalamic neurons to examine the effect of CCL2 on migratory behavior and on levels of the peptides, enkephalin (ENK) and galanin. Treatment with CCL2 led to a significant, dose-dependent increase in the number of migrated neurons and an increase in the velocity and distance traveled. CCL2 also significantly increased the number of ENK-expressing and CCR2/ENK co-expressing neurons and the percentage of neurons that contain higher levels of ENK. Lastly, CCL2 produced a dose-dependent increase in expression of ENK and galanin. These results provide evidence for a stimulatory effect of CCL2 on embryonic hypothalamic neurons involving changes in migratory behavior, expression, and synthesis of neuropeptides that function in controlling behavior. Our results demonstrate that the chemokine, CCL2, functions through its receptor, CCR2, to stimulate the migration and expression of the orexigenic peptides, enkephalin (ENK) and galanin (GAL), in developing embryonic hypothalamic neurons that are important for controlling ingestive behavior. This evidence reveals broad effects of CCL2 in the developing hypothalamus, showing this chemokine system to be tightly linked to the hypothalamic peptide neurons.