Analysis of the effects of endothelin-3 on the development of neural crest cells in the embryonic mouse gut

Avian ceca are indispensable for hindgut enteric nervous system development

The enteric nervous system (ENS), which is derived from enteric neural crest cells (ENCCs), represents the neuronal innervation of the intestine. Compromised ENCC migration can lead to Hirschsprung disease, which is characterized by an aganglionic distal bowel. During the craniocaudal migration of ENCCs along the gut, we find that their proliferation is greatest as the ENCC wavefront passes through the ceca, a pair of pouches at the midgut-hindgut junction in avian intestine. Removal of the ceca leads to hindgut aganglionosis, suggesting that they are required for ENS development. Comparative transcriptome profiling of the cecal buds compared with the interceca region shows that the non-canonical Wnt signaling pathway is preferentially expressed within the ceca. Specifically, WNT11 is highly expressed, as confirmed by RNA in situ hybridization, leading us to hypothesize that cecal expression of WNT11 is important for ENCC colonization of the hindgut. Organ cultures using embryonic day 6 avian intestine show that WNT11 inhibits enteric neuronal differentiation. These results reveal an essential role for the ceca during hindgut ENS formation and highlight an important function for non-canonical Wnt signaling in regulating ENCC differentiation.

EDNRB isoform 3 confers Temozolomide resistance in A375 melanoma cells by modulating membrane potential, reactive oxygen species and mitochondrial Ca2

Background

The role of endothelin receptor type B (EDNRB) isoform 3 involved in Temozolomide (TMZ)-induced melanoma cell death has not yet been elucidated.

Methods

The subcellular localization of EDNRB isoform 3 was determined by confocal and immunoblotting assays. Silencing EDNRB isoform 3 was performed by CRISPR/Cas9. Apoptosis was assessed by annexin V/propium iodide staining and caspases 3/7/9 activity. Mitochondrial membrane potential, reactive oxygen species and mitochondrial Ca²⁺ were measured by flow cytometry. Apoptosis protein array was applied.

Results

Confocal and immunoblot analyses indicate mitochondrial localization of EDNRB isoform 3 and the first N-terminal (1–22) amino acids are sufficient for its mitochondrial targeting. EDNRB isoform 3 depleted A375 cells significantly confers chemoresistance with mitochondrial depolarization, reduced reactive oxygen species, enhanced mitochondrial Ca²⁺ uptake and decreased caspase 9 activation. Additionally, apoptosis array shows that lack of EDNRB isoform 3 has relatively lower expression of phosphorylation of p53 at S392 and a slightly higher expression of Paraoxonase 2.

Conclusion

Our findings raise the possibility of targeting EDNRB isoform 3 as a new therapeutic strategy in combination with TMZ for melanoma treatment.

Downregulation of microRNA-431-5p promotes enteric neural crest cell proliferation via targeting LRSAM1 in Hirschsprung's disease

BACKGROUND

Hirschsprung's disease (HSCR) is characterized by missing of enteric neurons in the terminal areas of the whole gut, which is causally related to poor proliferation of enteric neural crest cells (ENCCs). Our aim is to explore how miR-431-5p interacts with its target gene in regulation of proliferation of ENCCs in HSCR.

METHODS

Mouse model of HSCR was established by Benzalkonium chloride (BAC) treatment. Quantitative Real-time PCR and western blotting were performed to determine the miR-431-5p and the LRSAM1 expression in colon tissues of the HSCR group (n = 8) and the control group (n = 8) and in ENCCs isolated from colon tissues. CCK-8 assay was performed to detect the proliferation of ENCCs of HSCR. ENCCs after transfection with miR-431-5p mimics or miR-431-5p inhibitor. Luciferase reporter assay was conducted to clarify the connections between miR-431-5p and LRSAM1.

RESULTS

Upregulation of miR-431-5p and downregulation of LRSAM1 were found in ENCCs of HSCR. Downregulation of miR-431-5p could promote cell proliferation of ENCCs. LRSAM1 was proved to be the target gene of miR-431-5p by luciferase reporter assay. Moreover, proliferation of ENCCs was increased in the miR-431-5p inhibitor group and was suppressed after knocking down LRSAM1.

CONCLUSION

Downregulation of miR-431-5p promoted proliferation of ENCCs via targeting LRSAM1, which provides an innovative and candidate target for treatment of HSCR.

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.

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.

Development and developmental disorders of the enteric nervous system

The enteric nervous system (ENS) arises from neural crest-derived cells that migrate into and along the gut, leading to the formation of a complex network of neurons and glial cells that regulates motility, secretion and blood flow. This Review summarizes the progress made in the past 5 years in our understanding of ENS development, including the migratory pathways of neural crest-derived cells as they colonize the gut. The importance of interactions between neural crest-derived cells, between signalling pathways and between developmental processes (such as proliferation and migration) in ensuring the correct development of the ENS is also presented. The signalling pathways involved in ENS development that were determined using animal models are also described, as is the evidence for the involvement of the genes encoding these molecules in Hirschsprung disease-the best characterized paediatric enteric neuropathy. Finally, the aetiology and treatment of Hirschsprung disease in the clinic and the potential involvement of defects in ENS development in other paediatric motility disorders are outlined.

Future therapies for Hirschsprung's disease

The current management of Hirschsprung's disease (HSCR) is still associated with significant long-term morbidities despite on-going refinements in surgical care. Over the course of the past 20 years, significant inroads have been made in our understanding of the development of the enteric nervous system and what factors are responsible for the development of HSCR. This has prompted increased interest in the possibility of using this knowledge to develop new alternative and adjunctive therapies for HSCR. The aim of this review is to provide an overview of the current progress being made toward the development of future therapies to improve the outcome for children with HSCR.

Genetic background impacts developmental potential of enteric neural crest-derived progenitors in the Sox10Dom model of Hirschsprung disease

Abnormalities in the development of enteric neural crest-derived progenitors (ENPs) that generate the enteric nervous system (ENS) can lead to aganglionosis in a variable portion of the distal gastrointestinal tract. Cumulative evidence suggests that variation of aganglionosis is due to gene interactions that modulate the ability of ENPs to populate the intestine; however, the developmental processes underlying this effect are unknown. We hypothesized that differences in enteric ganglion deficits could be attributable to the effects of genetic background on early developmental processes, including migration, proliferation, or lineage divergence. Developmental processes were investigated in congenic Sox10(Dom) mice, an established Hirschsprung disease (HSCR) model, on distinct inbred backgrounds, C57BL/6J (B6) and C3HeB/FeJ (C3Fe). Immuno-staining on whole-mount fetal gut tissue and dissociated cell suspensions was used to assess migration and proliferation. Flow cytometry utilizing the cell surface markers p75 and HNK-1 was used to isolate live ENPs for analysis of developmental potential. Frequency of ENPs was reduced in Sox10(Dom) embryos relative to wild-type embryos, but was unaffected by genetic background. Both migration and developmental potential of ENPs in Sox10(Dom) embryos were altered by inbred strain background with the most highly significant differences seen for developmental potential between strains and genotypes. In vivo imaging of fetal ENPs and postnatal ganglia demonstrates that altered lineage divergence impacts ganglia in the proximal intestine. Our analysis demonstrates that genetic background alters early ENS development and suggests that abnormalities in lineage diversification can shift the proportions of ENP populations and thus may contribute to ENS deficiencies in vivo.

The role of neural activity in the migration and differentiation of enteric neuron precursors

BACKGROUND

As they migrate through the developing gut, a sub-population of enteric neural crest-derived cells (ENCCs) begins to differentiate into neurons. The early appearance of neurons raises the possibility that electrical activity and neurotransmitter release could influence the migration or differentiation of ENNCs.

METHODS

The appearance of neuronal sub-types in the gut of embryonic mice was examined using immunohistochemistry. The effects of blocking various forms of neural activity on ENCC migration and neuronal differentiation were examined using explants of cultured embryonic gut.

KEY RESULTS

Nerve fibers were present in close apposition to many ENCCs. Commencing at E11.5, neuronal nitric oxide synthase (nNOS), calbindin and IK(Ca) channel immunoreactivities were shown by sub-populations of enteric neurons. In cultured explants of embryonic gut, tetrodotoxin (TTX, an inhibitor of action potential generation), nitro-L-arginine (NOLA, an inhibitor of nitric oxide synthesis) and clotrimazole (an IK(Ca) channel blocker) did not affect the rate of ENCC migration, but tetanus toxin (an inhibitor of SNARE-mediated vesicle fusion) significantly impaired ENCC migration as previously reported. In explants of E11.5 and E12.5 hindgut grown in the presence of TTX or tetanus toxin there was a decrease in the number nNOS+ neurons close to the migratory wavefront, but no significant difference in the proportion of all ENCC that expressed the pan-neuronal marker, Hu.

CONCLUSIONS & INFERENCES

(i) Some enteric neuron sub-types are present very early during the development of the enteric nervous system. (ii) The rate of differentiation of some sub-types of enteric neurons appears to be influenced by TTX- and tetanus toxin-sensitive mechanisms.

Effects of tissue age, presence of neurones and endothelin-3 on the ability of enteric neurone precursors to colonize recipient gut: implications for cell-based therapies

BACKGROUND Most enteric neurones arise from neural crest cells that originate in the post-otic hindbrain, and migrate into and along the developing gastrointestinal tract. There is currently great interest in the possibility of cell therapy to replace diseased or absent enteric neurones in patients with enteric neuropathies, such as Hirschsprung's disease. However, it is unclear whether neural crest stem/progenitor cells will be able to colonize colon (i) in which the mesenchyme has differentiated into distinct layers, (ii) that already contains enteric neurones or (iii) that lacks a gene expressed by the gut mesenchyme, such as endothelin-3 (Et-3). METHODS Co-cultures were used to examine the ability of enteric neural crest-derived cells (ENCCs) from E11.5 mouse gut to colonize a variety of recipient hindguts. KEY RESULTS Enteric neural crest-derived cells migrated and gave rise to neurones in E14.5 and E16.5 aneural colon in which the external muscle layers had differentiated, but they did not migrate as far as in younger colon. There was no evidence of altered ENCC proliferation, cell death or neuronal differentiation in older recipient explants. Enteric neural crest-derived cells failed to enter most recipient E14.5 and E16.5 colon explants already containing enteric neurones, and the few that did showed very limited migration. Finally, ENCCs migrated a shorter distance and a higher proportion expressed the pan-neuronal marker, Hu, in recipient E11.5 Et-3(-/-) colon compared to wild-type recipient colon. CONCLUSIONS & INFERENCES Age and an absence of Et-3 from the recipient gut both significantly reduced but did not prevent ENCC migration, but the presence of neurones almost totally prevented ENCC migration.

Development of enteric neuron diversity

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

Critical numbers of neural crest cells are required in the pathways from the neural tube to the foregut to ensure complete enteric nervous system formation

The enteric nervous system (ENS) is mainly derived from vagal neural crest cells (NCC) that arise at the level of somites 1-7. To understand how the size and composition of the NCC progenitor pool affects ENS development, we reduced the number of NCC by ablating the neural tube adjacent to somites 3-6 to produce aganglionic gut. We then back-transplanted various somite lengths of quail neural tube into the ablated region to determine the `tipping point',whereby sufficient progenitors were available for complete ENS formation. The addition of one somite length of either vagal, sacral or trunk neural tube into embryos that had the neural tube ablated adjacent to somites 3-6,resulted in ENS formation along the entire gut. Although these additional cells contributed to the progenitor pool, the quail NCC from different axial levels retained their intrinsic identities with respect to their ability to form the ENS; vagal NCC formed most of the ENS, sacral NCC contributed a limited number of ENS cells, and trunk NCC did not contribute to the ENS. As one somite length of vagal NCC was found to comprise almost the entire ENS, we ablated all of the vagal neural crest and back-transplanted one somite length of vagal neural tube from the level of somite 1 or somite 3 into the vagal region at the position of somite 3. NCC from somite 3 formed the ENS along the entire gut, whereas NCC from somite 1 did not. Intrinsic differences, such as an increased capacity for proliferation, as demonstrated in vitro and in vivo,appear to underlie the ability of somite 3 NCC to form the entire ENS.

Neural crest and the development of the enteric nervous system

The formation of the enteric nervous system (ENS) is a particularly interesting example of the migratory ability of the neural crest and of the complexity of structures to which neural crest cells contribute. The distance that neural crest cells migrate to colonize the entire length of the gastrointestinal tract exceeds that of any other neural crest cell population. Furthermore, this migration takes a long time--over 25% of the gestation period for mice and around 3 weeks in humans. After colonizing the gut, neural crest-derived cells within the gut wall then differentiate into glial cells plus many different types of neurons, and generate the most complex part of the peripheral nervous system.

Advances in ontogeny of the enteric nervous system

The neurons and glia that comprise the enteric nervous system (ENS), the intrinsic innervation of the gastrointestinal tract, are derived from vagal and sacral regions of the neural crest. In order to form the ENS, neural crest-derived precursors undergo a number of processes including survival, migration and proliferation, prior to differentiation into neuronal subtypes, some of which form functional connections with the gut smooth muscle. Investigation of the developmental processes that underlie ENS formation has progressed dramatically in recent years, in no small part due to the attention of scientists from a range of disciplines on the genesis of Hirschsprung's disease (aganglionic megacolon), the major congenital abnormality of the ENS. This review summarizes recent advances in the field of early ENS ontogeny and focuses on: (i) the spatiotemporal migratory pathways followed by vagal and sacral neural crest-derived ENS precursors, including recent in vivo imaging of migrating crest cells within the gut, (ii) the roles of the RET and EDNRB signalling pathways and how these pathways interact to control ENS development, and (iii) how perpendicular migrations of neural crest cells within the gut lead to the formation of the myenteric and submucosal plexi located between the smooth muscle layers of the gut wall.

Interactions between Sox10, Edn3 and Ednrb during enteric nervous system and melanocyte development

The requirement for SOX10 and endothelin-3/EDNRB signalling pathway during enteric nervous system (ENS) and melanocyte development, as well as their alterations in Waardenburg-Hirschsprung disease (hypopigmentation, deafness and absence of enteric ganglia) are well established. Here, we analysed the genetic interactions between these genes during ENS and melanocyte development. Through phenotype analysis of Sox10;Ednrb and Sox10;Edn3 double mutants, we show that a coordinate and balanced interaction between these molecules is required for normal ENS and melanocyte development. Indeed, double mutants present with a severe increase in white spotting, absence of melanocytes within the inner ear, and in the stria vascularis in particular, and more severe ENS defects. Moreover, we show that partial loss of Ednrb in Sox10 heterozygous mice impairs colonisation of the gut by enteric crest cells at all stages observed. However, compared to single mutants, we detected no apoptosis, cell proliferation or overall neuronal or glial differentiation defects in neural crest cells within the stomach of double mutants, but apoptosis was increased in vagal neural crest cells outside of the gut. These data will contribute to the understanding of the molecular basis of ENS, pigmentation and hearing defects observed in mouse mutants and patients carrying SOX10, EDN3 and EDNRB mutations.

Endothelin-3 regulates neural crest cell proliferation and differentiation in the hindgut enteric nervous system

Neural crest cells (NCC) migrate, proliferate, and differentiate within the wall of the gastrointestinal tract to give rise to the neurons and glial cells of the enteric nervous system (ENS). The intestinal microenvironment is critical in this process and endothelin-3 (ET3) is known to have an essential role. Mutations of this gene cause distal intestinal aganglionosis in rodents, but its mechanism of action is poorly understood. We find that inhibition of ET3 signaling in cultured avian intestine also leads to hindgut aganglionosis. The aim of this study was to determine the role of ET3 during formation of the avian hindgut ENS. To answer this question, we created chick-quail intestinal chimeras by transplanting preganglionic quail hindguts into the coelomic cavity of chick embryos. The quail grafts develop two ganglionated plexuses of differentiated neurons and glial cells originating entirely from the host neural crest. The presence of excess ET3 in the grafts results in a significant increase in ganglion cell number, while inhibition of endothelin receptor-B (EDNRB) leads to severe hypoganglionosis. The ET3-induced hyperganglionosis is associated with an increase in enteric crest cell proliferation. Using hindgut explants cultured in collagen gel, we find that ET3 also inhibits neuronal differentiation in the ENS. Finally, ET3, which is strongly expressed in the ceca, inhibits the chemoattraction of NCC to glial-derived neurotrophic factor (GDNF). Our results demonstrate multiple roles for ET3 signaling during ENS development in the avian hindgut, where it influences NCC proliferation, differentiation, and migration.

Dynamic changes in the proximal gut neural crest stem cell population are associated with successful development of the distal enteric nervous system in rats

Loss of signaling through the endothelin-B receptor (ET(B)) leads to failure of vagal neural crest (NC) cell colonization of the developing gut and causes congenital distal intestinal aganglionosis [Hirschsprung disease (HSCR)] in humans and other mammals. Several studies suggest that cell-cell interactions and the number of NC cells behind the wavefront may play an important role in successful gut colonization. We compared the number and progression of enteric nervous system stem cells in the wild-type (WT) and HSCR rat gut using whole-mount immunohistochemistry for p75, culture and isolation of NC stem cells (NCSCs) by flow cytometry. Isolation and culture demonstrates that NCSCs enter the WT cecum between embryonic day (E) 13.5 and E14.5, and the number of NCSC in the colon significantly increases after E15.5. These findings are consistent with the caudal progression of the NC-cell wavefront by whole-mount staining. During the period of WT colonic colonization of the proximal colon, we found significant differences in the small bowel NCSC pool between WT and HSCR rats. Whereas the proximal gut NCSC pool in WT rats is increasing behind the colonization wavefront, no such change occurs in the proximal NCSC pool in HSCR rats. Dynamic changes in the NCSC pool occur behind the NC colonization wavefront in the gut of WT rats. The absence of these changes in the HSCR rat may contribute to distal aganglionosis.

A targeting mutation of tyrosine 1062 in Ret causes a marked decrease of enteric neurons and renal hypoplasia

The Ret receptor tyrosine kinase plays a crucial role in the development of the enteric nervous system and the kidney. Tyrosine 1062 in Ret represents a binding site for the phosphotyrosine-binding domains of several adaptor and effector proteins that are important for the activation of intracellular signaling pathways, such as the RAS/ERK, phosphatidylinositol 3-kinase/AKT, and Jun-associated N-terminal kinase pathways. To investigate the importance of tyrosine 1062 for organogenesis in vivo, knock-in mice in which tyrosine 1062 in Ret was replaced with phenylalanine were generated. Although homozygous knock-in mice were born normally, they died by day 27 after birth and showed growth retardation. The development of the enteric nervous system was severely impaired in homozygous mutant mice, about 40% of which lacked enteric neurons in the whole intestinal tract, as observed in Ret-deficient mice. The rest of the mutant mice developed enteric neurons in the intestine to various extents, although the size and number of ganglion cells were significantly reduced. Unlike Ret-deficient mice, a small kidney developed in all knock-in mice, accompanying a slight histological change. The reduction of kidney size was due to a decrease of ureteric bud branching during embryogenesis. Thus, these findings demonstrated that the signal via tyrosine 1062 plays an important role in histogenesis of the enteric nervous system and nephrogenesis.

Temporally distinct requirements for endothelin receptor B in the generation and migration of gut neural crest stem cells

Loss of Endothelin-3/Endothelin receptor B (EDNRB) signaling leads to aganglionosis of the distal gut (Hirschsprung's disease), but it is unclear whether it is required primarily for neural crest progenitor maintenance or migration. Ednrb-deficient gut neural crest stem cells (NCSCs) were reduced to 40% of wild-type levels by embryonic day 12.5 (E12.5), but no further depletion of NCSCs was subsequently observed. Undifferentiated NCSCs persisted in the proximal guts of Ednrb-deficient rats throughout fetal and postnatal development but exhibited migration defects after E12.5 that prevented distal gut colonization. EDNRB signaling may be required to modulate the response of neural crest progenitors to migratory cues, such as glial cell line-derived neurotrophic factor (GDNF). This migratory defect could be bypassed by transplanting wild-type NCSCs directly into the aganglionic region of the Ednrb(sl/sl) gut, where they engrafted and formed neurons as efficiently as in the wild-type gut.

The neural crest: Basic biology and clinical relationships in the craniofacial and enteric nervous systems

The highly migratory, mesenchymal neural crest cell population was discovered over 100 years ago. Proposals of these cells' origin within the neuroepithelium, and of the tissues they gave rise to, initiated decades-long heated debates, since these proposals challenged the powerful germ-layer theory. Having survived this storm, the neural crest is now regarded as a pluripotent stem cell population that makes vital contributions to an astounding array of both neural and non-neural organ systems. The earliest model systems for studying the neural crest were amphibian, and these pioneering contributions have been ably refined and extended by studies in the chick, mouse, and more recently the fish to provide detailed understanding of the cellular and molecular mechanisms regulating and regulated by the neural crest. The key questions regarding control of craniofacial morphogenesis and innervation of the gut illustrate the wide range of developmental contexts in which the neural crest plays an important role. These questions also focus attention on common issues such as the role of growth factor signaling in neural crest cell development and highlight the central role of the neural crest in human congenital disease.