Evaluation of the HOX11L1 gene as a candidate for congenital disorders of intestinal innervation

Evaluating the molecular and genetic mechanisms underlying gut motility disorders

INTRODUCTION

Gastrointestinal (GI) motility disorders comprise a wide range of different diseases affecting the structural or functional integrity of the GI neuromusculature. Their clinical presentation and burden of disease depends on the predominant location and extent of gut involvement as well as the component of the gut neuromusculature affected.

AREAS COVERED

A comprehensive literature review was conducted using the PubMed and Medline databases to identify articles related to GI motility and functional disorders, published between 2016 and 2023. In this article, we highlight the current knowledge of molecular and genetic mechanisms underlying GI dysmotility, including disorders of gut-brain interaction, which involve both GI motor and sensory disturbance.

EXPERT OPINION

Although the pathophysiology and molecular mechanisms underlying many such disorders remain unclear, recent advances in the assessment of intestinal tissue samples, genetic testing with the application of 'omics' technologies and the use of animal models will provide better insights into disease pathogenesis as well as opportunities to improve therapy.

A novel mouse model of intestinal neuronal dysplasia: visualization of the enteric nervous system

PURPOSE

Intestinal neuronal dysplasia (IND) is a congenital anomaly affecting gastrointestinal neural innervation, but the pathogenesis remains unclear. The homozygous Ncx/Hox11L.1 knockout (Ncx-/-) mice exhibit megacolon and enteric ganglia anomalies, resembling IND phenotypes. Sox10-Venus transgenic mouse were used to visualize enteric neural crest cells in real time. This study aims to establish a novel mouse model of Sox10-Venus+/Ncx-/- mouse to study the pathogenesis of IND.

METHODS

Sox10-Venus+/Ncx-/- (Ncx-/-) (n = 8) mice and Sox10-Venus+/Ncx+/+ controls (control) (n = 8) were euthanized at 4-5 weeks old, and excised intestines were examined with fluorescence microscopy. Immunohistochemistry was performed on tissue sections with neural marker Tuj1.

RESULTS

Ncx-/- mice exhibited dilated cecum and small intestine. Body weight of Ncx-/- mice was lower with higher ratio of small intestine length relative to body weight. The neural network (Sox10-Venus) was observed along the intestine wall in Ncx-/- and control mice without staining. Ectopic and increased expression of Tuj1 was observed in both small intestine and proximal colon of Ncx-/- mice.

CONCLUSION

This study has established a reliable animal model that exhibits characteristics similar to patients with IND. This novel mouse model can allow the easy visualization of ENS in a time- and cost-effective way to study the pathogenesis of IND.

Challenges in the diagnosis of intestinal neuronal dysplasia type B: A look beyond the number of ganglion cells

Intestinal neuronal dysplasia type B (IND-B) is a controversial condition among gastrointestinal neuromuscular disorders. Constipation is its most common clinical manifestation in patients. Despite intense scientific research, there are still knowledge gaps regarding the diagnostic criteria for IND-B in the histopathological analysis of rectal biopsies. The guidelines published in the past three decades have directed diagnostic criteria for quantifying the number of ganglion cells in the nervous plexus of the enteric nervous system. However, it is very complex to distinguish numerically what is pathological from what is normal, mainly because of the difficulty in determining a reliable control group composed of healthy children without intestinal symptoms. Thus, a series of immunohistochemical markers have been proposed to assist in the histopathological analysis of the enteric nervous system. Several of these markers facilitate the identification of other structures of the enteric nervous system, in addition to ganglion cells. These structures may be related to the etiopathogenesis of IND-B and represent new possibilities for the histopathological diagnosis of this disease, providing a view beyond the number of ganglion cells. This review critically discusses the aspects related to the disease definitions and diagnostic criteria of this organic cause of constipation.

Genetic background-dependent abnormalities of the enteric nervous system and intestinal function in Kif26a-deficient mice

The Kif26a protein-coding gene has been identified as a negative regulator of the GDNF-Ret signaling pathway in enteric neurons. The aim of this study was to investigate the influence of genetic background on the phenotype of Kif26a-deficient (KO, -/-) mice. KO mice with both C57BL/6 and BALB/c genetic backgrounds were established. Survival rates and megacolon development were compared between these two strains of KO mice. Functional bowel assessments and enteric neuron histopathology were performed in the deficient mice. KO mice with the BALB/c genetic background survived more than 400 days without evidence of megacolon, while all C57BL/6 KO mice developed megacolon and died within 30 days. Local enteric neuron hyperplasia in the colon and functional bowel abnormalities were observed in BALB/c KO mice. These results indicated that megacolon and enteric neuron hyperplasia in KO mice are influenced by the genetic background. BALB/c KO mice may represent a viable model for functional gastrointestinal diseases such as chronic constipation, facilitating studies on the underlying mechanisms and providing a foundation for the development of treatments.

Effect of Neuroligin1 and Neurexin1 on the Colonic Motility in a Mouse Model of Neuronal Intestinal Dysplasia

Aim

To investigate the expressions of neuroligin1 (NL1) and neurexin1 (NX1) in a mouse model of neuronal intestinal dysplasia (Tlx2^−/− mice) and to explore their effects on colonic motility.

Methods

Immunohistochemistry staining was employed to explore the histological appearances of NL1, NX1, the presynaptic marker of glutamatergic synapses VGLUT1, and the subunit of NMDA receptors of NR1 in the colon of mice with or without Tlx2 mutation. Western blotting and qRT-PCR were performed to detect their relative expressions in the colon. Colonic motility was measured by a glass bead technique. Then, the Tlx2^−/− mice were intervened by Huperzine A. Variations on expressions of NL1, NX1, VGLUT1, and NR1 and variations on colonic motility were measured. Additionally, serum concentrations of Glu were measured by ELISA.

Results

Immunohistochemistry staining reveals that NL1, NX1, VGLUT1, and NR1 were mainly concentrated in the myenteric plexus of ENS. Compared to those in WT and Tlx2^+/- mice, expressions of NL1 and NX1 in colon of Tlx2^−/− mice were upregulated with increased VGLUT1 and NR1 abundances and impaired colonic motility (P < 0.05). After intervention, the upregulated expressions of NL1 and NX1 were decreased with a correlated reduce of VGLUT1 and NR1 and a recovery of the impaired colonic motility (P < 0.05). After intervention, the upregulated expressions of NL1 and NX1 were decreased with a correlated reduce of VGLUT1 and NR1 and a recovery of the impaired colonic motility (P < 0.05). After intervention, the upregulated expressions of NL1 and NX1 were decreased with a correlated reduce of VGLUT1 and NR1 and a recovery of the impaired colonic motility (

Conclusion

NL1 and NX1 are closely related to the colonic motility through their effects of targeting the formation of glutamatergic synapses and may be involved in the pathogenesis of NID. The variations of serum Glu seem to be a potential and less painful auxiliary measure for colonic motility and NID.

Intestinal Neuronal Dysplasia Type B: An Updated Review of a Problematic Diagnosis

Context.—

Intestinal neuronal dysplasia type B (IND B) is a controversial histopathologic phenotype that has been associated with intestinal dysmotility, either as an isolated condition or in conjunction with established pathologic disorders (eg, Hirschsprung disease). Many factors contribute to the debate over the existence and/or clinical significance of IND B, including a large body of published data based on inconsistent diagnostic criteria and methods, which have fostered many unwarranted conclusions that lack sufficient scientific basis.

Objective.—

To critically analyze existing published data regarding IND B to provide supporting evidence-based diagnostic practice and to stimulate necessary and scientifically sound research.

Data Sources.—

This update focuses on published literature related to the pathology of IND B because without a reliable pathologic diagnosis, studies of epidemiology, pathogenesis, natural history, management, and outcome are all suspect. Problems with existing data are identified explicitly with suggestions as to how future investigations should be designed and evaluated to better understand this entity.

Conclusions.—

Inconsistencies in diagnostic criteria and methods used to define IND B justifiably encumber the universal acceptance of IND B as a neuropathologic etiology for intestinal dysmotility. IND B will remain a controversial diagnosis until rigorous, well-controlled scientific studies are conducted to establish reproducible and reliable diagnostic criteria that reliably translate from one laboratory to another.

A critical appraisal of the morphological criteria for diagnosing intestinal neuronal dysplasia type B

Intestinal neuronal dysplasia type B is a controversial entity expressed by complex changes in the enteric nervous system. Diagnosis depends on rectal biopsy histopathology and diagnostic criteria, both qualitative and quantitative, have changed over time, hindering the diagnostic practice. We analyzed the morphological criteria for the histological diagnosis of intestinal neuronal dysplasia type B in a series of patients with intestinal neuronal dysplasia type B according to the 1990 Frankfurt Consensus criteria and verified the applicability of the numerical criteria proposed by Meier-Ruge et al in 2004 and 2006. Qualitative criteria adopted for the histological diagnosis of intestinal neuronal dysplasia type B included hyperplasia of the submucous plexus with hyperganglionosis and hypertrophy of the nerve trunks. Quantitative criteria considered more than 20% giant ganglia in the submucosa, with more than eight neurons each on 25 ganglia, and children aged over 1 year. Distal colon surgical specimens from 29 patients, aged 0-16 years, diagnosed with intestinal neuronal dysplasia type B were retrospectively analyzed using sections processed for conventional histology (H&E) and calretinin immunohistochemistry. Hyperplasia of the submucosal nerve plexi with hyperganglionosis and hypertrophy of the nerve trunks was observed in all cases. Ganglia with small, immature neurons were detected in the majority of cases. Quantitative analysis confirmed hyperganglionosis (mean number=10.7 neurons per ganglion) and hypertrophy of the nerve trunks (median=44.6 μm thickness). Neurons showed immunostaining for calretinin, but neuron counts in calretinin-stained sections were lower compared with H&E (P<0.01). No significant differences were verified between children aged under and over 1 year regarding hyperganglionosis (P=0.79), neuron counts (P=0.36), and immature ganglia (P=0.66). Only one patient met the numerical criteria proposed by Meier-Ruge et al in 2004 and 2006. In conclusion, the numerical criteria showed limited applicability when transposed to conventional histopathology. Children aged over 1 year presented very similar histological features of neuronal immaturity to younger children, questioning the need for an age criterion when diagnosing intestinal neuronal dysplasia type B.

Advances in understanding functional variations in the Hirschsprung disease spectrum (variant Hirschsprung disease)

Hirschsprung disease (HSCR) is a fairly well understood congenital, genetically based functional obstruction due to the congenital absence of ganglion cells in the distal bowel. However, although over 90% of Hirschsprung cases conform to the normally accepted histological diagnostic criteria, it has become increasingly clear that in addition to HSCR, there is a group of functional disturbances relating to a number of other congenital neurodysplastic conditions causing some degree of gastrointestinal tract malfunction. Although these represent a variety of possibly separate conditions of the enteric nervous system, this spectrum it would appear to be also influenced by similar developmental processes. The term "variant Hirschsprung" is commonly used to describe these conditions, but ganglion cells are mostly present if abnormal in number and distribution. These conditions are a problem group being amongst the most difficult to diagnose and treat with possible practical and legal consequences. The problem appears to be possibly one of definition which has proven difficult in the relative paucity of normal values, especially when correlated to age and gestation. It is the purpose of this paper to review the current position on these conditions and to explore possible shared common pathogenetic and genetic mechanisms. This article explores those conditions where a similar pathogenetic mechanisms to HSCR can be demonstrated (e.g. hypoganglionosis) as well as other neural features, which appear to represent separate conditions possibly linked to certain syndromes.

Intestinal neuronal dysplasia type B: A still little known diagnosis for organic causes of intestinal chronic constipation

Intestinal neuronal dysplasia type B (IND-B) is a controversial entity among the gastrointestinal neuromuscular disorders. It may occur alone or associated with other neuropathies, such as Hirschsprung's disease (HD). Chronic constipation is the most common clinical manifestation of patients. IND-B primarily affects young children and mimics HD, but has its own histopathologic features characterized mainly by hyperplasia of the submucosal nerve plexus. Thus, IND-B should be included in the differential diagnoses of organic causes of constipation. In recent years, an increasing number of cases of IND-B in adults have also been described, some presenting severe constipation since childhood and others with the onset of symptoms at adulthood. Despite the intense scientific research in the last decades, there are still knowledge gaps regarding definition, pathogenesis, diagnostic criteria and therapeutic possibilities for IND-B. However, in medical practice, we continue to encounter patients with severe constipation or intestinal obstruction who undergo to diagnostic investigation for HD and their rectal biopsies present hyperganglionosis in the submucosal nerve plexus and other features, consistent with the diagnosis of IND-B. This review critically discusses aspects related to the disease definitions, pathophysiology and genetics, epidemiology distribution, clinical presentation, diagnostic criteria and therapeutic possibilities of this still little-known organic cause of intestinal chronic constipation.

Variants of the ACTG2 gene correlate with degree of severity and presence of megacystis in chronic intestinal pseudo-obstruction

Chronic intestinal pseudo-obstruction (CIPO) syndromes are heterogeneous gastrointestinal disorders, caused by either neuropathy or myopathy, resulting in compromised peristalsis and intestinal obstruction. CIPO can have a profound impact on quality of life, leading the most severely affected individuals to life-long parenteral nutrition and urinary catheterization. To search for disease causing gene(s), we performed the whole exome sequencing (WES) in both eight sporadic and two familial cases, followed by targeted sequencing in additional CIPO patients. After identifying a heterozygous missense variant in the ACTG2 gene in one of 10 patients undergone WES, targeted Sanger sequencing of this gene allowed to detect heterozygous missense variants in 9 of 23 further patients with either megacystis-microcolon-intestinal hypoperistalsis syndrome or intestinal pseudo-obstruction. Variants thus identified, one of which still unreported, affect highly conserved regions of the ACTG2 gene that encodes a protein crucial for correct enteric muscle contraction. These findings provided evidence for a correlation between the clinical phenotype and genotype at the ACTG2 locus, a first step to improve the diagnosis and prognosis of these severe conditions.

Classification and diagnostic criteria of variants of Hirschsprung's disease

"Variants of Hirschsprung's disease" are conditions that clinically resemble Hirschsprung's disease (HD), despite the presence of ganglion cells in rectal suction biopsies. The diagnosis and management of these patients can be challenging. Specific histological, immunohistochemical and electron microscopic investigations are required to characterize this heterogeneous group of functional bowel disorders. Variants of HD include intestinal neuronal dysplasia, intestinal ganglioneuromatosis, isolated hypoganglionosis, immature ganglia, absence of the argyrophil plexus, internal anal sphincter achalasia and congenital smooth muscle cell disorders such as megacystis microcolon intestinal hypoperistalsis syndrome. This review article systematically classifies variants of HD based on current diagnostic criteria with an additional focus on pathogenesis, epidemiology, clinical presentation, management and outcome.

Variants of Hirschsprung disease

Variants of Hirschsprung disease are conditions that clinically resemble Hirschsprung disease, despite the presence of ganglion cells in rectal suction biopsies. The characterization and differentiation of various entities are mainly based on histologic, immunohistochemical, and electron microscopy findings of biopsies from patients with functional intestinal obstruction. Intestinal neuronal dysplasia is histologically characterized by hyperganglionosis, giant ganglia, and ectopic ganglion cells. In most intestinal neuronal dysplasia cases, conservative treatments such as laxatives and enema are sufficient. Some patients may require internal sphincter myectomy. Patients with the diagnosis of isolated hypoganglionosis show decreased numbers of nerve cells, decreased plexus area, as well as increased distance between ganglia in rectal biopsies, and resection of the affected segment has been the treatment of choice. The diagnosis of internal anal sphincter achalasia is based on abnormal rectal manometry findings, whereas rectal suction biopsies display presence of ganglion cells as well as normal acetylcholinesterase activity. Internal anal sphincter achalasia is either treated by internal sphincter myectomy or botulinum toxin injection. Megacystis microcolon intestinal hypoperistalsis is a rare condition, and the most severe form of functional intestinal obstruction in the newborn. Megacystis microcolon intestinal hypoperistalsis is characterized by massive abdominal distension caused by a largely dilated nonobstructed bladder, microcolon, and decreased or absent intestinal peristalsis. Although the outcome has improved in recent years, survivors have to be either maintained by total parenteral nutrition or have undergone multivisceral transplant. This review article summarizes the current knowledge of the aforementioned entities of variant HD.

A new experimental approach is required in the molecular analysis of intestinal neuronal dysplasia type B patients

Intestinal neuronal dysplasia type B (INDB) is characterized by the malformation of the parasympathetic submucous plexus of the gut. It is generally accepted that INDB has a genetic basis, and several genes produce an INDB-like phenotype in mice when disrupted, such as EDNRB. However, no mutations associated with this disease have been identified in several series analysed. In the present studu, we sought to determine whether the EDNRB/EDN3 signalling pathway plays a role in the pathogenesis of INDB in humans. Denaturing high performance liquid chromatography (dHPLC) techniques were employed to screen the EDNRB and EDN3 coding regions in 23 INDB patients. In addition, association studies were performed on these genes with single nucleotide polymorphisms strategically selected and genotyped by TaqMan technology. Although several novel variants were detected in both genes, none of these variants appeared to play a functional role in protein function or expression. Our results indicate that additional screening of other candidate genes in larger patient series is required to elucidate the molecular basis of INDB. Additionally, the systematic lack of positive results in the screening of candidate genes for INDB reported in the literature, together with our results, leads us to propose that INDB may alternatively arise as a consequence of gain of function mutations in genes related to enteric nervous system development. Therefore, the use of different molecular approaches, such as screening for genetic duplication or enhancer mutations, is recommended for future studies on the genetic basis of INDB.

[Intestinal neuronal dysplasia type B: how do we understand it today?]

Intestinal neuronal dysplasia type B (IND B) is currently considered to be a subtle malformation of the submucosal plexus, leading to an increased proportion of over-sized ganglia and potentially accompanied by a mild, chronic gastrointestinal motility disturbance. The diagnosis of IND B is morphologically based and involves the demonstration of an increased proportion of giant ganglia in the submucous plexus related to the patient's age. Giant ganglia are physiologically frequent in the neonatal period. Therefore, IND B should not be diagnosed prior to 1 year of age. Morphological features of IND B may occur as an isolated finding or may be observed proximal to an aganglionic segment. IND B and constipation may resolve spontaneously up to the age of 4 years. Treatment of IND B is usually conservative, surgical resection is currently deemed necessary only in a minority of patients. The pathogenesis of IND B is still incompletely understood and the etiology unknown. Future research on the basis of standardized diagnostic conditions is expected to result in a better understanding of this disease, and to reveal the cause of aberrant ganglion development.

[Intestinal neuronal dysplasia type B: how do we understand it today?]

Intestinal neuronal dysplasia type B (IND B) is currently considered to be a subtle malformation of the submucosal plexus, leading to an increased proportion of over-sized ganglia and potentially accompanied by a mild, chronic gastrointestinal motility disturbance. The diagnosis of IND B is morphologically based and involves the demonstration of an increased proportion of giant ganglia in the submucous plexus related to the patient's age. Giant ganglia are physiologically frequent in the neonatal period. Therefore, IND B should not be diagnosed prior to 1 year of age. Morphological features of IND B may occur as an isolated finding or may be observed proximal to an aganglionic segment. IND B and constipation may resolve spontaneously up to the age of 4 years. Treatment of IND B is usually conservative, surgical resection is currently deemed necessary only in a minority of patients. The pathogenesis of IND B is still incompletely understood and the etiology unknown. Future research on the basis of standardized diagnostic conditions is expected to result in a better understanding of this disease, and to reveal the cause of aberrant ganglion development.

Transcriptional regulation of TLX2 and impaired intestinal innervation: possible role of the PHOX2A and PHOX2B genes

TLX2 (also known as HOX11L1, Ncx and Enx) is a transcription factor playing a crucial role in the development of the enteric nervous system, as confirmed by mice models exhibiting intestinal hyperganglionosis and pseudo-obstruction. However, congenital defects of TLX2 have been excluded as a major cause of intestinal motility disorders in patients affected with intestinal neuronal dysplasia (IND) or pseudo-obstruction. After demonstrating the direct regulation of TLX2 expression by the homeoprotein PHOX2B, in the present work, we have focused on its paralogue PHOX2A. By co-transfections, electrophoretic mobility shift assays and chromatin immunoprecipitation, we have demonstrated that PHOX2A, like PHOX2B, is involved in the cascade leading to TLX2 transactivation and presumably in the intestinal neuronal differentiation. Based on the hypothesis that missed activation of the TLX2 gene induces the development of enteric nervous system defects, PHOX2A and PHOX2B have been regarded as novel candidate genes involved in IND and pseudo-obstruction and consequently analyzed for mutations in a specific set of 26 patients. We have identified one still unreported PHOX2A variant; however, absence of any functional effect on TLX2 transactivation suggests that regulators or effectors other than the PHOX2 genes must act in the same pathway, likely playing a non redundant and direct role in the pathogenesis of such enteric disorders.

Enteric nervous system and developmental abnormalities in childhood

ENS consists of a complex network of neurons, organised in several plexuses, which interact by means of numerous neurotransmitters. It is capable of modulating the intestinal motility, exocrine and endocrine secretions, microcirculation and immune and inflammatory responses within the gastrointestinal tract, independent of the central nervous system. Though the embryological development of various plexuses are completed by mid-way of gestation, the maturation of neurons and nerve plexuses appear to continue well after birth. Therefore, any histological or functional abnormalities related to the gastrointestinal function must be investigated with the ongoing maturational processes in mind.

The TLX2 homeobox gene is a transcriptional target of PHOX2B in neural-crest-derived cells

The TLX2 (HOX11L1, Ncx, Enx) and PHOX2B genes encode transcription factors crucial in the development of neural-crest-derived cells, leading to ANS (autonomic nervous system) specific neuronal lineages. Moreover, they share a similar expression pattern and are both involved in downstream steps of BMP (bone morphogenetic protein) signalling. In an attempt to reconstruct the gene network sustaining the correct development of the ANS, we have undertaken an in vitro experimental strategy to identify direct upstream regulators of the TLX2 gene. After characterizing a sequence displaying enhancer property in its 5' flanking region, we confirmed the functional link between the human PHOX2B and TLX2 genes. Transient transfections and electrophoretic-mobility-shift assays suggested that PHOX2B is able to bind the cell-specific element in the 5' regulatory region of the TLX2 gene, determining its transactivation in neuroblastoma cells. Such interaction was also confirmed in vivo by means of chromatin immunoprecipitation assay and, in addition, up-regulation of endogenous TLX2 mRNA level was demonstrated following PHOX2B over-expression, by quantitative real-time PCR. Finally, PHOX2B proteins carrying mutations responsible for CCHS (congenital central hypoventilation syndrome) development showed a severe impairment in activating TLX2 expression, both in vitro and in vivo. Taken together, these results support the PHOX2B-TLX2 promoter interaction, suggesting a physiological role in the transcription-factor cascade underlying the differentiation of neuronal lineages of the ANS during human embryogenesis.

Evaluation of Hox11L1 in the fmc/fmc rat model of chronic intestinal pseudo-obstruction

BACKGROUND/PURPOSE

The spontaneous rat mutation, familial megacecum and colon (fmc), is responsible for an autosomal recessive phenotype similar to intestinal pseudo-obstruction observed in Hox11L1-/- mice. We hypothesized that fmc is a mutant allele of the rat Hox11L1 gene and tested this hypothesis by direct sequencing.

METHODS

DNA was extracted from fmc/fmc rats and wild-type littermates. All exons, introns, and DNA 5' to the transcriptional start site of rat Hox11L1 were directly sequenced, and data from the mutant and wild-type animals were compared with each other and corresponding genomic data from humans and mice.

RESULTS

Alignment of sequences obtained from rat, human, and mouse indicates that putative regulatory elements of the Hox11L1 gene are conserved in rat, mice, and humans. No mutations were identified in the Hox11L1 allele of fmc/fmc rats.

CONCLUSIONS

Despite the phenotypic similarities between fmc/fmc rats and Hox11L1-/- mice, fmc does not appear to be a mutant allele of the Hox11L1 gene.

Variant Hirschsprung's disease

Conditions that clinically resemble HD despite the presence of ganglion cells on suction rectal biopsy results, can be diagnosed by providing an adequate biopsy and employing a variety of histological techniques. Intestinal neuronal dysplasia is a distinct clinical entity that can be clearly proven histologically. Patients with IND not only have abnormalities of submucosal and myenteric plexuses but also defective innervation of the muscle. Internal sphincter achalasia, which is histologically characterized by nitrergic nerve depletion, can be diagnosed on anorectal manometry and successfully treated by internal sphincter myectomy. The outcome of smooth muscle disorders is generally fatal. The need for surgical intervention should be weighed carefully and individualized because most explorations have not been helpful and are probably not necessary.

Pathogenesis of Hirschsprung's disease and its variants: recent progress

The enteric nervous system (ENS) is a complex network of interconnected neurons within the wall of the intestine that controls intestinal motility, regulates mucosal secretion and blood flow, and also modulates sensation from the gut. The cells that form the ENS in mammals are derived primarily from vagal neural crest cells. During the past decade there has been an explosion of information about genes that control the development of neural crest. Molecular-genetic analysis has identified several genes that have a role in the development of Hirschsprung's disease. The major susceptibility gene is RET, which is also involved in multiple endocrine neoplasia type 2. Recently, genetic studies have provided strong evidence in animal models that intestinal neuronal dysplasia (IND) is a real entity. HOX11L1 knockout mice and endothelin B receptor-deficient rats demonstrated abnormalities of the ENS resembling IND type B in humans. These findings support the concept that IND may be linked to a genetic defect.

Genetic background modifies intestinal pseudo-obstruction and the expression of a reporter gene in Hox11L1-/- mice

BACKGROUND & AIMS

The transcription factor Hox11L1 is expressed by enteric neurons. Two groups mutated murine Hox11L1, and reported lethal intestinal pseudo-obstruction and colonic hyperganglionosis in many, but not all, homozygous null mutants. We investigated the regulation of Hox11L1 and factors that influence the penetrance of pseudo-obstruction in Hox11L1-null mice.

METHODS

Expression of beta-galactosidase (lacZ), under control of putative Hox11L1 regulatory sequences, was assessed in transgenic mice wild-type, heterozygous, and null for native Hox11L1. Transgene expression and signs of pseudo-obstruction were compared in null mice with different genetic backgrounds.

RESULTS

In enteric neurons and other parts of the nervous system, the transgene was expressed in a pattern consistent with native Hox11L1. Enteric beta-galactosidase activity initiated in the proximal small intestine and spread cranially and caudally in a subset of postmitotic enteric neurons. Hox11L1-lacZ transgene expression persisted in Hox11L1-null animals, suggesting that Hox11L1 is not required cell autonomously for neuronal survival. Genetic background dramatically affected the phenotypes of Hox11L1-null animals, with complete penetrance of severe proximal colonic distention on a predominantly C57BL/6J (B6) background and very low penetrance of dysmotility on a 129SvJ (129) background. Coincidently, Hox11L1-lacZ expression by most enteric neurons, but not CNS neurons, was lost on a 129 background.

CONCLUSIONS

Cis-acting, 5' regulatory elements are sufficient to regulate site-specific expression of Hox11L1 in vivo. Expression of the transgene by enteric neurons and penetrance of pseudo-obstruction in Hox11L1-null animals are influenced by one or more modifier genes, counterparts of which may play a similar role in human disease.

Intestinal neuronal dysplasia

Intestinal neuronal dysplasia (IND) is a clinical condition that resembles Hirschsprung's disease. In the past many years investigators have raised doubts about the existence of IND as a distinct histopathologic entity. One strong piece of evidence that IND is a real entity stems from animal models. Recently, two different HOX11L1 knockout mouse models and a heterozygous endothelin B receptor-deficient rat demonstrated abnormalities of the submucous plexus similar to that observed in human IND. This review describes in detail the diagnostic criteria of IND, staining techniques, correlation between histological findings and clinical symptoms, and management of IND.

Abnormal vasculature in intestinal neuronal dysplasia

Intestinal neuronal dysplasia (IND) is an intestinal motility disorder, which clinically resembles Hirschsprung's disease (HD). Adventitial fibromuscular dysplasia (AFMD) consists of proliferation of smooth muscle cells and collagen fibers in the adventitia of blood vessels. The purpose of this study was to investigate vascular abnormalities in large bowel biopsies from patients with isolated HD, IND associated with HD and isolated IND. Large bowel biopsies from patients presenting with isolated HD ( n=23), IND associated with HD ( n=11), isolated IND ( n=16) and normal bowel as controls ( n=6) were investigated using acetylcholinesterase (AChE) histochemistry, van Gieson staining and alpha-smooth muscle actin (alpha-SMA) immunohistochemistry. Increased AChE activity around submucosal vessels was found in 9/16 (56%) cases with isolated IND, 3/11 (27%) cases of IND associated with HD, 5/23 (21%) isolated HD cases and 0/6 controls. AFMD was found in 10/16 (62%) of the isolated IND cases, 4/11 (362) of the cases with IND associated with HD and 4/23 (17%) cases of HD without IND using van Gieson staining. None of the control specimens revealed AFMD. Increased alpha-SMA immunoreactivity filaments were demonstrated in the submucosal vessel wall in 9/16 (56%) of isolated IND and 2/11(18%) of IND associated with HD cases. Normal alpha-SMA immunoreactivity around submucosal vessels was seen in isolated HD and controls. Abnormal submucosal vasculature is a common histological finding in isolated IND and IND associated with HD and may be a useful additional diagnostic feature in these patients.

Enteric nervous system: development and developmental disturbances--part 1

This review, which is presented in two parts, summarizes and synthesizes current views on the genetic, molecular, and cell biological underpinnings of the early embryonic phases of enteric nervous system (ENS) formation and its defects. In the first part, we describe the critical features of two principal abnormalities of ENS development: Hirschsprung's disease (HSCR) and intestinal neuronal dysplasia type B (INDB) in humans, and the similar abnormalities in animals. These represent the extremes of the diagnostic spectrum: HSCR has agreed and unequivocal diagnostic criteria, whereas the diagnosis and even existence of INDB as a clinical entity is highly controversial. The difficulties in diagnosis and treatment of both these conditions are discussed. We then review the genes now known which, when mutated or deleted, may cause defects of ENS development. Many of these genetic abnormalities in animal models give a phenotype similar or identical to HSCR, and were discovered by studies of humans and of mouse mutants with similar defects. The most important of these genes are those coding for molecules in the GDNF intercellular signaling system, and those coding for molecules in the ET-3 signaling system. However, a range of other genes for different signaling systems and for transcription factors also disturb ENS formation when they are deleted or mutated. In addition, a large proportion of HSCR cases have not been ascribed to the currently known genes, suggesting that additional genes for ENS development await discovery.