Coordinated expression of 3' hox genes during murine embryonal gut development: an enteric Hox code

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.

Intestinal expression patterns of transcription factors and markers for interstitial cells in the larval zebrafish

For the digestion of food, it is important for the gut to be differentiated regionally and to have proper motor control. However, the number of transcription factors that regulate its development is still limited. Meanwhile, the interstitial cells of the gastrointestinal (GI) tract are necessary for intestinal motility in addition to the enteric nervous system. There are anoctamine1 (Ano1)-positive and platelet-derived growth factor receptor α (Pdgfra)-positive interstitial cells in mammal, but Pdgfra-positive cells have not been reported in the zebrafish. To identify new transcription factors involved in GI tract development, we used RNA sequencing comparing between larval and adult gut. We isolated 40 transcription factors that were more highly expressed in the larval gut. We demonstrated expression patterns of the 13 genes, 7 of which were newly found to be expressed in the zebrafish larval gut. Six of the 13 genes encode nuclear receptors. The osr2 is expressed in the anterior part, while foxP4 in its distal part. Also, we reported the expression pattern of pdgfra for the first time in the larval zebrafish gut. Our data provide fundamental knowledge for studying vertebrate gut regionalization and motility by live imaging using zebrafish.

Whole genome bisulfite sequencing of sperm reveals differentially methylated regions in male partners of idiopathic recurrent pregnancy loss cases

OBJECTIVE

To study the genome wide alterations in sperm DNA methylation in male partners of idiopathic recurrent pregnancy loss (iRPL) cases and note regions as potential diagnostic markers.

DESIGN

Case-control study and methylome analysis of human sperm.

SETTING

Obstetrics and Gynaecology clinics.

PATIENT(S)

Control group consists of apparently healthy fertile men having fathered a child within the last 2 years (n = 39); and case group consists of male partners of iRPL cases having ≥2 consecutive 1st trimester pregnancy losses (n = 47).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Sperm DNA samples of controls and cases were selected for whole genome bisulfite sequencing analysis based on the previously set thresholds of global methylation levels and methylation levels of imprinted genes (KvDMR and ZAC). Whole genome bisulfite sequencing of selected sperm genomic DNA was performed to identify differentially methylated CpG sites of iRPL cases compared with fertile controls. Pathway analysis of all the differentially methylated genes was done by Database for Annotation, Visualization, and Integrated Discovery annotation tool and Kyoto Encyclopedia of Genes and Genomes tool. Differentially methylated CpGs within genes relevant to embryo and placenta development were selected to further validate their methylation levels in study population by pyrosequencing.

RESULT(S)

A total of 9497 differentially methylated CpGs with highest enrichment in intronic regions were obtained. In addition, 5352 differentially methylated regions and 2087 differentially methylated genes were noted. Signaling pathways involved in development were enriched on pathway analysis. Select CpGs within genes PPARG, KCNQ1, SETD2, and MAP3K4 showed distinct hypomethylated subpopulations within iRPL study population.

CONCLUSION(S)

Our study highlights the altered methylation landscape of iRPL sperm, and their possible implications in pathways of embryo and placental development. The CpG sites that are hypomethylated specifically in sperm of iRPL subpopulation can be further assessed as predictive biomarkers.

Shaping axial identity during human pluripotent stem cell differentiation to neural crest cells

The neural crest (NC) is a multipotent cell population which can give rise to a vast array of derivatives including neurons and glia of the peripheral nervous system, cartilage, cardiac smooth muscle, melanocytes and sympathoadrenal cells. An attractive strategy to model human NC development and associated birth defects as well as produce clinically relevant cell populations for regenerative medicine applications involves the in vitro generation of NC from human pluripotent stem cells (hPSCs). However, in vivo, the potential of NC cells to generate distinct cell types is determined by their position along the anteroposterior (A–P) axis and, therefore the axial identity of hPSC-derived NC cells is an important aspect to consider. Recent advances in understanding the developmental origins of NC and the signalling pathways involved in its specification have aided the in vitro generation of human NC cells which are representative of various A–P positions. Here, we explore recent advances in methodologies of in vitro NC specification and axis patterning using hPSCs.

The vascular nature of lung-resident mesenchymal stem cells

Human lungs bear their own reservoir of endogenous mesenchymal stem cells (MSCs). Although described as located perivascular, the cellular identity of primary lung MSCs remains elusive. Here we investigated the vascular nature of lung‐resident MSCs (LR‐MSCs) using healthy human lung tissue. LR‐MSCs predominately reside within the vascular stem cell niche, the so‐called vasculogenic zone of adult lung arteries. Primary LR‐MSCs isolated from normal human lung tissue showed typical MSC characteristics in vitro and were phenotypically and functionally indistinguishable from MSCs derived from the vascular wall of adult human blood vessels (VW‐MSCs). Moreover, LR‐MSCs expressed the VW‐MSC‐specific HOX code a characteristic to discriminate VW‐MSCs from phenotypical similar cells. Thus, LR‐MSC should be considered as VW‐MSCs. Immunofluorescent analyses of non‐small lung cancer (NSCLC) specimen further confirmed the vascular adventitia as stem cell niche for LR‐MSCs, and revealed their mobilization and activation in NSCLC progression. These findings have implications for understanding the role of MSC in normal lung physiology and pulmonary diseases, as well as for the rational design of additional therapeutic approaches.

Colonic organoids derived from human induced pluripotent stem cells for modeling colorectal cancer and drug testing

With the goal of modeling human disease of the large intestine, we sought to develop an effective protocol for deriving colonic organoids (COs) from differentiated human embryonic stem cells (hESCs) or induced pluripotent stem cells (iPSCs). Extensive gene and immunohistochemical profiling confirmed that the derived COs represent colon rather than small intestine, containing stem cells, transit-amplifying cells, and the expected spectrum of differentiated cells, including goblet and endocrine cells. We applied this strategy to iPSCs derived from patients with familial adenomatous polyposis (FAP-iPSCs) harboring germline mutations in the WNT-signaling-pathway-regulator gene encoding APC, and we generated COs that exhibit enhanced WNT activity and increased epithelial cell proliferation, which we used as a platform for drug testing. Two potential compounds, XAV939 and rapamycin, decreased proliferation in FAP-COs, but also affected cell proliferation in wild-type COs, which thus limits their therapeutic application. By contrast, we found that geneticin, a ribosome-binding antibiotic with translational 'read-through' activity, efficiently targeted abnormal WNT activity and restored normal proliferation specifically in APC-mutant FAP-COs. These studies provide an efficient strategy for deriving human COs, which can be used in disease modeling and drug discovery for colorectal disease.

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.

LncRNA HOTAIR: A master regulator of chromatin dynamics and cancer

Non-coding RNAs (ncRNAs) are emerging classes of regulatory RNA that play key roles in various cellular and physiological processes such as in gene regulation, chromatin dynamics, cell differentiation, and development. NcRNAs are dysregulated in a variety of human disorders including cancers, neurological disorders, and immunological disorders. The mechanisms through which ncRNAs regulate various biological processes and human diseases still remain elusive. HOX antisense intergenic RNA (HOTAIR) is a recently discovered long non-coding RNA (lncRNA) that plays critical role in gene regulation and chromatin dynamics, appears to be misregulated in a variety of cancers. HOTAIR interacts with key epigenetic regulators such as histone methyltransferase PRC2 and histone demethylase LSD1 and regulates gene silencing. Here, we have reviewed recent advancements in understanding the functions and regulation of HOTAIR and its association with cancer and other diseases.

Identification of a developmental gene expression signature, including HOX genes, for the normal human colonic crypt stem cell niche: overexpression of the signature parallels stem cell overpopulation during colon tumorigenesis

Our goal was to identify a unique gene expression signature for human colonic stem cells (SCs). Accordingly, we determined the gene expression pattern for a known SC-enriched region--the crypt bottom. Colonic crypts and isolated crypt subsections (top, middle, and bottom) were purified from fresh, normal, human, surgical specimens. We then used an innovative strategy that used two-color microarrays (∼18,500 genes) to compare gene expression in the crypt bottom with expression in the other crypt subsections (middle or top). Array results were validated by PCR and immunostaining. About 25% of genes analyzed were expressed in crypts: 88 preferentially in the bottom, 68 in the middle, and 131 in the top. Among genes upregulated in the bottom, ∼30% were classified as growth and/or developmental genes including several in the PI3 kinase pathway, a six-transmembrane protein STAMP1, and two homeobox (HOXA4, HOXD10) genes. qPCR and immunostaining validated that HOXA4 and HOXD10 are selectively expressed in the normal crypt bottom and are overexpressed in colon carcinomas (CRCs). Immunostaining showed that HOXA4 and HOXD10 are co-expressed with the SC markers CD166 and ALDH1 in cells at the normal crypt bottom, and the number of these co-expressing cells is increased in CRCs. Thus, our findings show that these two HOX genes are selectively expressed in colonic SCs and that HOX overexpression in CRCs parallels the SC overpopulation that occurs during CRC development. Our study suggests that developmental genes play key roles in the maintenance of normal SCs and crypt renewal, and contribute to the SC overpopulation that drives colon tumorigenesis.

Perturbation of Hoxb5 signaling in vagal and trunk neural crest cells causes apoptosis and neurocristopathies in mice

Neural crest cells (NCCs) migrate from different regions along the anterior-posterior axis of the neural tube (NT) to form different structures. Defective NCC development causes congenital neurocristopathies affecting multiple NCC-derived tissues in human. Perturbed Hoxb5 signaling in vagal NCC causes enteric nervous system (ENS) defects. This study aims to further investigate if perturbed Hoxb5 signaling in trunk NCC contributes to defects of other NCC-derived tissues besides the ENS. We perturbed Hoxb5 signaling in NCC from the entire NT, and investigated its impact in the development of tissues derived from these cells in mice. Perturbation of Hoxb5 signaling in these NCC resulted in Sox9 downregulation, NCC apoptosis, hypoplastic sympathetic and dorsal root ganglia, hypopigmentation and ENS defects. Mutant mice with NCC-specific Sox9 deletion also displayed some of these phenotypes. In vitro and in vivo assays indicated that the Sox9 promoter was bound and trans-activated by Hoxb5. In ovo studies further revealed that Sox9 alleviated apoptosis induced by perturbed Hoxb5 signaling, and Hoxb5 induced ectopic Sox9 expression in chick NT. This study demonstrates that Hoxb5 regulates Sox9 expression in NCC and disruption of this signaling causes Sox9 downregulation, NCC apoptosis and multiple NCC-developmental defects. Phenotypes such as ENS deficiency, hypopigmentation and some of the neurological defects are reported in patients with Hirschsprung disease (HSCR). Whether dysregulation of Hoxb5 signaling and early depletion of NCC contribute to ENS defect and other neurocristopathies in HSCR patients deserves further investigation.

Adriamycin-Induced Models of VACTERL Association

Animal models are of great importance for medical research. They have enabled analysis of the aetiology and pathogenesis of complex congenital malformations and have also led to major advances in the surgical and therapeutic management of these conditions. Animal models allow us to comprehend the morphological and molecular basis of disease and consequently to discover novel approaches for both surgical and medical therapy. The anthracycline antibiotic adriamycin was incidentally found to have teratogenic effects on rats, producing a range of defects remarkably similar to the VACTERL association of congenital anomalies in humans, providing a reproducible animal model of this condition. VACTERL association is a spectrum of birth defects which includes vertebral, anal, cardiovascular, tracheo-oesophageal, renal and limb anomalies. In recent years, adriamycin rodent models of VACTERL have provided valuable insights into the pathogenesis of this complex association, particularly in relation to tracheo-oesophageal malformations. The adriamycin rat model and adriamycin mouse model are now well established in the investigation of the morphology of faulty organogenesis and the regulation of gene expression in tracheo-oesophageal anomalies.

Transcriptional networks in liver and intestinal development

The development of the gastrointestinal tract is a complex process that integrates signaling processes with downstream transcriptional responses. Here, we discuss the regionalization of the primitive gut and formation of the intestine and liver. Anterior-posterior position in the primitive gut is important for establishing regions that will become functional organs. Coordination of signaling between the epithelium and mesenchyme and downstream transcriptional responses is required for intestinal development and homeostasis. Liver development uses a complex transcriptional network that controls the establishment of organ domains, cell differentiation, and adult function. Discussion of these transcriptional mechanisms gives us insight into how the primitive gut, composed of simple endodermal cells, develops into multiple diverse cell types that are organized into complex mature organs.

Morphogenetic fields in embryogenesis, regeneration, and cancer: non-local control of complex patterning

Establishment of shape during embryonic development, and the maintenance of shape against injury or tumorigenesis, requires constant coordination of cell behaviors toward the patterning needs of the host organism. Molecular cell biology and genetics have made great strides in understanding the mechanisms that regulate cell function. However, generalized rational control of shape is still largely beyond our current capabilities. Significant instructive signals function at long range to provide positional information and other cues to regulate organism-wide systems properties like anatomical polarity and size control. Is complex morphogenesis best understood as the emergent property of local cell interactions, or as the outcome of a computational process that is guided by a physically encoded map or template of the final goal state? Here I review recent data and molecular mechanisms relevant to morphogenetic fields: large-scale systems of physical properties that have been proposed to store patterning information during embryogenesis, regenerative repair, and cancer suppression that ultimately controls anatomy. Placing special emphasis on the role of endogenous bioelectric signals as an important component of the morphogenetic field, I speculate on novel approaches for the computational modeling and control of these fields with applications to synthetic biology, regenerative medicine, and evolutionary developmental biology.

Generating intestinal tissue from stem cells: potential for research and therapy

Intestinal resection and malformations in adult and pediatric patients result in devastating consequences. Unfortunately, allogeneic transplantation of intestinal tissue into patients has not been met with the same measure of success as the transplantation of other organs. Attempts to engineer intestinal tissue in vitro include disaggregation of adult rat intestine into subunits called organoids, harvesting native adult stem cells from mouse intestine and spontaneous generation of intestinal tissue from embryoid bodies. Recently, by utilizing principles gained from the study of developmental biology, human pluripotent stem cells have been demonstrated to be capable of directed differentiation into intestinal tissue in vitro. Pluripotent stem cells offer a unique and promising means to generate intestinal tissue for the purposes of modeling intestinal disease, understanding embryonic development and providing a source of material for therapeutic transplantation.

The spatio-temporal patterning of Hoxa9 and Hoxa13 in the developing zebrafish enteric nervous system

BACKGROUND

Hirschsprung's disease is characterised by the absence of ganglion cells in the distal bowel, a process which is controlled by complex genetic pathways. Homeobox genes have a major role in gut development and this is depicted by the enteric Hox code which describes the different spatial and temporal expression of Hox genes. Hoxa9 and Hoxa13 mutations have been discovered in patients with Hirschsprung's disease (HD). The aim of this study was to determine the spatio-temporal pattern of Hoxa9 and Hoxa13 in enteric nervous system (ENS) development using the zebrafish model.

METHODS

Purified plasmids that contained the gene of interest were obtained and inoculated into culture medium to exponentially increase the number of bacteria containing the plasmid. Cells were then harvested by centrifugation and plasmid DNA was extracted, which was then linearised and precipitated. RNA digoxigenin-labelled probes were made by in vitro transcription reaction. In situ hybridisation was carried out using these probes on zebrafish embryos which were collected from 24 to 120 h post fertilisation (hpf), by which time the zebrafish intestine is fully developed. Embryos were then mounted in glycerol and imaged using an Olympus B40 microscope and images were taken using an Olympus Super F1.8 digital camera.

RESULTS

At 24 hpf, Hoxa9 expression is seen in the forebrain and hindbrain and also in the very distal myotome whereas Hoxa13 expression, however, is seen only at the forebrain and hindbrain. At 48 hpf, Hoxa9- and Hoxa13-labelled cells are seen migrating distally from the forebrain into the notochord and spinal cord. At 72 hpf, Hoxa9-labelled cells can be seen throughout the spinal cord whereas Hoxa13 positive cells are seen migrating down from the spinal cord and in the proximal gut. By 96 hpf, Hoxa9- and Hoxa13-labelled cells have migrated down the full length of the spinal cord and along the proximal and mid intestine. By 120 hpf, Hoxa9 and Hoxa13 positive cells can be seen along the entire length of the zebrafish intestine.

CONCLUSIONS

These results show further evidence that Hoxa9 and Hoxa13 are involved in the early and organised patterning of ENS development in the zebrafish model.

The relationship among PDX1, CDX2, and mucin profiles in gastric carcinomas; correlations with clinicopathologic parameters

PURPOSE

Several studies performed on pancreatic-duodenal homeobox 1 (PDX1) have demonstrated a loss of expression and negative tumor modulator effect in gastric carcinoma. Relations between PDX1 and gastric metaplasia, differentiated type of gastric carcinoma, and the early stage of the disease have been exhibited in previous reports. The aim of this study was to examine expressions of PDX1, caudal type homeobox 2 (CDX2) and mucin (MUC) profiles to address the role of PDX1 in gastric carcinogenesis and its relationship with CDX2.

METHODS

Seventy gastrectomy specimens were analyzed immunohistochemically for PDX1, CDX2, MUC2, MUC5AC, and MUC6 expressions. The sum of cytoplasmic and nuclear PDX1 immunostaining and PDX1 positivity were assessed. All of the antibodies were examined for a correlation with tumor type, clinicopathologic parameters, and metaplasias. The relation of Ki-67 proliferation index with the expression profiles was also investigated.

RESULTS

Neither PDX1 (66/70) nor CDX2 (37/70) and the mucin profiles (MUC2:11/70, MUC5AC:48/70, MUC6:41/70) showed a significant difference between differentiated and undifferentiated types of gastric carcinoma and clinicopathologic parameters. The PDX1 expression frequency was 94.3%, with an average PDX1 score of 8.8 ± 4.2. PDX1 and CDX2 expression showed a significant difference (P = 0.026 and P = 0.002, respectively) among the phenotypic classification of gastric carcinomas. All of the gastric and intestinal mixed-phenotype gastric carcinomas (GI-type) showed both PDX1 and CDX2 immunopositivity. Except for the relation of PDX1 score with MUC6 expression, no significant difference was detected between PDX1 and CDX2, MUC2, and MUC5AC expressions. A relationship between CDX2 and MUC2 and also between MUC5AC and MUC6 was found statistically. The Ki-67 proliferation index revealed a significant positive correlation with PDX1, CDX2, and MUC2 positivity.

CONCLUSIONS

PDX1 expression revealed a higher positivity in gastric carcinomas than the previous studies and showed no relation with tumor type, clinicopathologic parameters, CDX2 expression, or mucin profiles. However, a significant relation of PDX1 and CDX2 expressions among phenotypic classification of gastric carcinomas reveals an idea about similar functions for PDX1 and CDX2 in the evolution of gastric carcinoma.

Boundaries, junctions and transitions in the gastrointestinal tract

Contiguous regions along the mammalian gastrointestinal tract, from the esophagus to the rectum, serve distinct digestive functions. Some organs, such as the esophagus and glandular stomach or the small bowel and colon, are separated by sharp boundaries. The duodenal, jejunal and ileal segments of the small intestine, by contrast, have imprecise borders. Because human esophageal and gastric cancers frequently arise in a background of tissue metaplasia and some intestinal disorders are confined to discrete regions, it is useful to appreciate the molecular and cellular basis of boundary formation and preservation. Here we review the anatomy and determinants of boundaries and transitions in the alimentary canal with respect to tissue morphology, gene expression, and, especially, transcriptional control of epithelial identity. We discuss the evidence for established and candidate molecular mechanisms of boundary formation, including the solitary and combinatorial actions of tissue-restricted transcription factors. Although the understanding remains sparse, genetic studies in mice do provide insights into dominant mechanisms and point the way for future investigation.

HOXB5 cooperates with NKX2-1 in the transcription of human RET

The enteric nervous system (ENS) regulates peristaltic movement of the gut, and abnormal ENS causes Hirschsprung's disease (HSCR) in newborns. HSCR is a congenital complex genetic disorder characterised by a lack of enteric ganglia along a variable length of the intestine. The receptor tyrosine kinase gene (RET) is the major HSCR gene and its expression is crucial for ENS development. We have previously reported that (i) HOXB5 transcription factor mediates RET expression, and (ii) mouse with defective HOXB5 activity develop HSCR phenotype. In this study, we (i) elucidate the underlying mechanisms that HOXB5 mediate RET expression, and (ii) examine the interactions between HOXB5 and other transcription factors implicated in RET expression. We show that human HOXB5 binds to the promoter region 5′ upstream of the binding site of NKX2-1 and regulates RET expression. HOXB5 and NKX2-1 form a protein complex and mediate RET expression in a synergistic manner. HSCR associated SNPs at the NKX2-1 binding site (-5G>A rs10900296; -1A>C rs10900297), which reduce NKX2-1 binding, abolish the synergistic trans-activation of RET by HOXB5 and NKX2-1. In contrast to the synergistic activation of RET with NKX2-1, HOXB5 cooperates in an additive manner with SOX10, PAX3 and PHOX2B in trans-activation of RET promoter. Taken together, our data suggests that HOXB5 in coordination with other transcription factors mediates RET expression. Therefore, defects in cis- or trans-regulation of RET by HOXB5 could lead to reduction of RET expression and contribute to the manifestation of the HSCR phenotype.

Smooth-muscle-specific expression of neurotrophin-3 in mouse embryonic and neonatal gastrointestinal tract

Vagal gastrointestinal (GI) afferents are essential for the regulation of eating, body weight, and digestion. However, their functional organization and the way that this develops are poorly understood. Neurotrophin-3 (NT-3) is crucial for the survival of vagal sensory neurons and is expressed in the developing GI tract, possibly contributing to their survival and to other aspects of vagal afferent development. The identification of the functions of this peripheral NT-3 thus requires a detailed understanding of the localization and timing of its expression in the developing GI tract. We have studied embryos and neonates expressing the lacZ reporter gene from the NT-3 locus and found that NT-3 is expressed predominantly in the smooth muscle of the outer GI wall of the stomach, intestines, and associated blood vessels and in the stomach lamina propria and esophageal epithelium. NT-3 expression has been detected in the mesenchyme of the GI wall by embryonic day 12.5 (E12.5) and becomes restricted to smooth muscle and lamina propria by E15.5, whereas its expression in blood vessels and esophageal epithelium is first observed at E15.5. Expression in most tissues is maintained at least until postnatal day 4. The lack of colocalization of beta-galactosidase and markers for myenteric ganglion cell types suggests that NT-3 is not expressed in these ganglia. Therefore, NT-3 expression in the GI tract is largely restricted to smooth muscle at ages when vagal axons grow into the GI tract, and when vagal mechanoreceptors form in smooth muscle, consistent with its role in these processes and in vagal sensory neuron survival.

Development of the autonomic nervous system: a comparative view

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

Dividing the tubular gut: generation of organ boundaries at the pylorus

The discrete organs that comprise the gastrointestinal tract (esophagus, stomach, small intestine, and large intestine) arise embryonically by regional differentiation of a single tube that is initially morphologically similar along its length. Regional organ differentiation programs, for example, for stomach or intestine, involve signaling cross-talk between epithelium and mesenchyme and result in the formation of precise boundaries between organs, across which dramatic differences in both morphology and gene expression are seen. The pylorus is a unique area of the gut tube because it not only marks an important organ boundary in the tubular gut (the stomach/intestinal boundary) but is also the hub for the development of multiple accessory organs (liver, pancreas, gall bladder, and spleen). This chapter examines: (a) our current understanding of the molecular and morphogenic processes that underlie the generation of the dramatic epithelial tissue boundary that compartmentalizes stomach and intestine; (b) the tissue interactions that promote development of the accessory organs in this area; and (c) the molecular interactions that specify patterning of the pyloric sphincter. Though the focus here is primarily on the mouse as a model organism, the molecular underpinnings of organ patterning near the pylorus are shared by chick and frog. Thus, further study of these conserved developmental programs could potentially shed light on the mechanisms underlying human pyloric malformations such as infantile hypertrophic pyloric stenosis.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

Establishment of intestinal identity and epithelial-mesenchymal signaling by Cdx2

We demonstrate that conditional ablation of the homeobox transcription factor Cdx2 from early endoderm results in the replacement of the posterior intestinal epithelium with keratinocytes, a dramatic cell fate conversion caused by ectopic activation of the foregut/esophageal differentiation program. This anterior homeotic transformation of the intestine was first apparent in the early embryonic Cdx2-deficient gut by a caudal extension of the expression domains of several key foregut endoderm regulators. While the intestinal transcriptome was severely affected, Cdx2 deficiency only transiently modified selected posterior Hox genes and the primary enteric Hox code was maintained. Further, we demonstrate that Cdx2-directed intestinal cell fate adoption plays an important role in the establishment of normal epithelial-mesenchymal interactions, as multiple signaling pathways involved in this process were severely affected. We conclude that Cdx2 controls important aspects of intestinal identity and development, and that this function is largely independent of the enteric Hox code.

Role of the homeodomain transcription factor Bapx1 in mouse distal stomach development

BACKGROUND & AIMS

Expansion and patterning of the endoderm generate a highly ordered, multiorgan digestive system in vertebrate animals. Among distal foregut derivatives, the gastric corpus, antrum, pylorus, and duodenum are distinct structures with sharp boundaries. Some homeodomain transcription factors expressed in gut mesenchyme convey positional information required for anterior-posterior patterning of the digestive tract. Barx1, in particular, controls stomach differentiation and morphogenesis. The Nirenberg and Kim homeobox gene Bapx1 (Nkx3-2) has an established role in skeletal development, but its function in the mammalian gut is less clear.

METHODS

We generated a Bapx1(Cre) knock-in allele to fate map Bapx1-expressing cells and evaluate its function in gastrointestinal development.

RESULTS

Bapx1-expressing cells populate the gut mesenchyme with a rostral boundary in the hindstomach near the junction of the gastric corpus and antrum. Smooth muscle differentiation and distribution of early regional markers are ostensibly normal in Bapx1(Cre/Cre) gut, but there are distinctive morphologic abnormalities near this rostral Bapx1 domain: the antral segment of the stomach is markedly shortened, and the pyloric constriction is lost. Comparison of expression domains and examination of stomach phenotypes in single and compound Barx1 and Bapx1 mutant mice suggests a hierarchy between these 2 factors; Bapx1 expression is lost in the absence of Barx1.

CONCLUSIONS

This study reveals the nonredundant requirement for Bapx1 in distal stomach development, places it within a Barx1-dependent pathway, and illustrates the pervasive influence of gut mesenchyme homeobox genes on endoderm differentiation and digestive organogenesis.

Genetic model system studies of the development of the enteric nervous system, gut motility and Hirschsprung's disease

The enteric nervous system (ENS) is the largest and most complicated subdivision of the peripheral nervous system. Its action is necessary to regulate many of the functions of the gastrointestinal tract including its motility. Whilst the ENS has been studied extensively by developmental biologists, neuroscientists and physiologists for several decades it has only been since the early 1990s that the molecular and genetic basis of ENS development has begun to emerge. Central to this understanding has been the use of genetic model organisms. In this article, we will discuss recent advances that have been achieved using both mouse and zebrafish model genetic systems that have led to new insights into ENS development and the genetic basis of Hirschsprung's disease.

Fras1, a basement membrane-associated protein mutated in Fraser syndrome, mediates both the initiation of the mammalian kidney and the integrity of renal glomeruli

FRAS1 is mutated in some individuals with Fraser syndrome (FS) and the encoded protein is expressed in embryonic epidermal cells, localizing in their basement membrane (BM). Syndactyly and cryptophthalmos in FS are sequelae of skin fragility but the bases for associated kidney malformations are unclear. We demonstrate that Fras1 is expressed in the branching ureteric bud (UB), and that renal agenesis occurs in homozygous Fras1 null mutant blebbed (bl) mice on a C57BL6J background. In vivo, the bl/bl bud fails to invade metanephric mesenchyme which undergoes involution, events replicated in organ culture. The expression of glial cell line-derived neurotrophic factor and growth-differentiation factor 11 was defective in bl/bl renal primordia in vivo, whereas, in culture, the addition of either growth factor restored bud invasion into the mesenchyme. Mutant primordia also showed deficient expression of Hoxd11 and Six2 transcription factors, whereas the activity of bone morphogenetic protein 4, an anti-branching molecule, was upregulated. In wild types, Fras1 was also expressed by nascent nephrons. Foetal glomerular podocytes expressed Fras1 transcripts and Fras1 immunolocalized in a glomerular BM-like pattern. On a mixed background, bl mutants, and also compound mutants for bl and my, another bleb strain, sometimes survive into adulthood. These mice have two kidneys, which contain subsets of glomeruli with perturbed nephrin, podocin, integrin α3 and fibronectin expression. Thus, Fras1 protein coats branching UB epithelia and is strikingly upregulated in the nephron lineage after mesenchymal/epithelial transition. Fras1 deficiency causes defective interactions between the bud and mesenchyme, correlating with disturbed expression of key nephrogenic molecules. Furthermore, Fras1 may also be required for the formation of normal glomeruli.

Pancreatic duodenal homeobox-1 (PDX1) functions as a tumor suppressor in gastric cancer

AIM

Pancreatic duodenal homeobox-1 (PDX1) is a transcription factor of homeobox genes family important in differentiation and development of the pancreas, duodenum and antrum. This study aims to clarify the putative role of PDX1 in gastric carcinogenesis.

METHODS

PDX1 expression was detected in gastric tissues with chronic gastritis and cancer as well as gastric cancer cell lines by immunohistochemistry, western blot, reverse transcription-polymerase chain reaction (RT-PCR) or quantitative real-time RT-PCR assays. The effects of PDX1 on cell proliferation, apoptosis, clone formation and migration were evaluated using cancer cell lines after transient or stable transfection with PDX1-expressing vector. The ability of PDX1 stable transfectant in tumor formation in xenograft mice was assessed.

RESULTS

PDX1 was strongly expressed in normal gastric glands, but was absent in 29 of 39 of human gastric cancer and most gastric cancer cell lines. Negative correlation between PDX1 and Ki-67 expression was found in both gastric tissues and cell lines. Ectopic overexpression of PDX1 significantly inhibited cell proliferation and induced apoptosis, accompanied by the activation of caspases 3, 8, 9 and 10. Overexpression of PDX1 also impaired the ability of cancer cells in clonal formation and migration in vitro. Furthermore, stable transfection with PDX1 reduced the ability of cancer cells in tumor formation in nude mice.

CONCLUSIONS

PDX1 expression is lost in gastric cancers. Its effect on cell proliferation/apoptosis, migration and tumor formation in vitro and in vivo suggested that this protein functions as a putative tumor suppressor in gastric cancer.

Endoderm-derived Sonic hedgehog and mesoderm Hand2 expression are required for enteric nervous system development in zebrafish

The zebrafish enteric nervous system (ENS), like those of all other vertebrate species, is principally derived from the vagal neural crest cells (NCC). The developmental controls that govern the migration, proliferation and patterning of the ENS precursors are not well understood. We have investigated the roles of endoderm and Sonic hedgehog (SHH) in the development of the ENS. We show that endoderm is required for the migration of ENS NCC from the vagal region to the anterior end of the intestine. We show that the expression of shh and its receptor ptc-1 correlate with the development of the ENS and demonstrate that hedgehog (HH) signaling is required in two phases, a pre-enteric and an enteric phase, for normal ENS development. We show that HH signaling regulates the proliferation of vagal NCC and ENS precursors in vivo. We also show the zebrafish hand2 is required for the normal development of the intestinal smooth muscle and the ENS. Furthermore we show that endoderm and HH signaling, but not hand2, regulate gdnf expression in the intestine, highlighting a central role of endoderm and SHH in patterning the intestine and the ENS.

In vivo gene expression profiling of human intestinal epithelial cells: analysis by laser microdissection of formalin fixed tissues

Background

The small intestinal epithelium mediates vital functions of nutrient absorption and host defense. The spatial organization of the epithelial cells along the crypt-villus axis segregates them into regions of specialized function. However, the differences in transcriptional programming and the molecular machinery that governs the migration, adhesion, and differentiation of intestinal epithelial cell lineages in humans remain under-explored. To increase our understanding of these mechanisms, we have evaluated gene expression patterns of ileal epithelial cells isolated by laser capture microdissection from either the villus epithelial or crypt cell regions of healthy human small intestinal mucosa. Expression profiles in villus and crypt epithelium were determined by DNA microarray, quantitative real-time PCR, and immunohistochemistry based methods. The expression levels of selected epithelial biomarkers were also compared between gastrointestinal tissues.

Results

Previously established biomarkers as well as a novel and distinct set of genes believed to be linked to epithelial cell motility, adhesion, and differentiation were found to be enriched in each of the two corresponding cell populations (GEO accession: GSE10629). Additionally, high baseline expression levels of innate antimicrobials, alpha defensin 5 (HD5) and regenerating islet-derived 3 alpha (Reg3A), were detected exclusively within the small bowel crypt, most notably in the ileum in comparison to other sites along the gastrointestinal tract.

Conclusion

The elucidation of differential gene expression patterns between crypt and villus epithelial cell lineages in human ileal tissue provides novel insights into the molecular machinery that mediates their functions and spatial organization. Moreover, our findings establish an important framework of knowledge for future investigations of human gastrointestinal diseases.

Perturbation of hoxb5 signaling in vagal neural crests down-regulates ret leading to intestinal hypoganglionosis in mice

BACKGROUND & AIMS

The enteric nervous system (ENS) controls intestinal peristalsis, and defective development of this system results in hypo/aganglionosis, as seen in Hirschsprung's disease. In the embryo, vagal neural crest cells (NCC) migrate and colonize the intestine rostrocaudally then differentiate into the ganglia of the ENS. Vagal NCC express the homeobox gene Hoxb5, a transcriptional activator, in human and mouse, so we used transgenic mice to investigate the function of Hoxb5 and the receptor tyrosine kinase gene Ret, which is affected in many patients with Hirschsprung's disease, in ENS development.

METHODS

We perturbed the Hoxb5 pathway by expressing a chimeric protein enb5, in which the transcription activation domain of Hoxb5 was replaced with the repressor domain of the Drosophila engrailed protein (en), in vagal NCC. This enb5 transcriptional repressor competes with wild-type Hoxb5 for binding to target genes, exerting a dominant negative effect.

RESULTS

We observed that 30.6% +/- 2.3% of NCC expressed enb5 and that these enb5-expressing NCC failed to migrate to the distal intestine. A 34%-37% reduction of ganglia (hypoganglionosis) and slow peristalsis and, occasionally, absence of ganglia and intestinal obstruction were observed in enb5-expressing mice. Ret expression was markedly reduced or absent in NCC and ganglia, and enb5 blocked Hoxb5 induction of Ret in neuroblastoma cells.

CONCLUSIONS

Our data indicate that Ret is a downstream target of Hoxb5 whose perturbation causes Ret haploinsufficiency, impaired NCC migration, and hypo/aganglionosis, suggesting that Hoxb5 may contribute to the etiology of Hirschsprung's disease.

Suppressed recombination on mouse chromosome 15 defined regions of chromosomal inversions associated with koala (koa) and hairy ears (eh) mutations

Koala (Koa) and hairy ears (Eh) mutations of mice are associated with chromosomal inversions in the distal half of chromosome 15. Since these two mutant mice show some common phenotypic features including extra hair on pinna and craniofacial dysmorphogenesis and have similar inverted regions, we determined the inverted regions of these two chromosomal inversions to examine whether a common gene is responsible for the phenotypes of these two mutants. The inverted regions were identified as the recombination-suppressed regions by linkage analysis. The length of the recombination-suppressed regions of Koa and Eh were approximately 52 and 47 Mb, respectively, and these inverted regions were not the same. These results indicate that the phenotypes of Koa and Eh mutant mice are likely to be caused by different genes.

The contribution of the sonic hedgehog cascade in the development of the enteric nervous system in fetal rats with anorectal malformations

OBJECTIVE

This study was designed to determine the expression of Sonic hedgehog (Shh) and its downstream genes during development of the enteric nervous system (ENS) in ethylenethiourea (ETU)-exposed fetal rats with anorectal malformations (ARMs).

MATERIAL AND METHODS

Anorectal malformations were induced by 1% ETU (125 mg/kg) given on gestational day 10, and the litter was harvested at term. The fetal anorectum and rectosigmoid region, including any communication with the urinary tract, were collected for gene expression studies and immunofluorescence study of the ENS. Gene expression of Shh cascade was performed using reverse transcription and real-time polymerase chain reaction (PCR). The myenteric plexuses of the ENS in normal and ARM rats were visualized with fluorescent antibodies.

RESULTS

Reverse transcription-PCR confirmed expression of Shh and its target genes in all parts of the ARMs. Quantitative PCR demonstrated that levels of expression of the genes of the Shh cascade were low in the ARMs. The immunoreactivity of neuromarkers was markedly reduced in high ARMs and slightly reduced in low ARMs.

CONCLUSION

This study demonstrates reduced expression of Shh and its target genes in ARMs in ETU-exposed fetal rats. Neurons in the myenteric plexus were decreased in high and low types of ARMs. Our results support a role for the Shh cascade during development of the ENS during hindgut development.

Hox gene function in vertebrate gut morphogenesis: the case of the caecum

The digestive tract is made of different subdivisions with various functions. During embryonic development, the developing intestine expresses combinations of Hox genes along its anterior to posterior axis, suggesting a role for these genes in this regionalization process. In particular, the transition from small to large intestine is labelled by the transcription of all Hoxd genes except Hoxd12 and Hoxd13, the latter two genes being transcribed only near the anus. Here, we describe two lines of mice that express Hoxd12 ectopically within this morphological transition. As a consequence, budding of the caecum is impeded, leading to complete agenesis in homozygous individuals. This effect is concurrent with a dramatic reduction of both Fgf10 and Pitx1 expression. Furthermore, the interactions between ;anterior' Hox genes and ectopic Hoxd12 suggest a model whereby anterior and posterior Hox products compete in controlling Fgf10 signalling, which is required for the growth of this organ in mice. These results illuminate components of the genetic cascade necessary for the emergence of this gut segment, crucial for many vertebrates.

Stephen L. Gans Distinguished Overseas Lecture. The neural crest in pediatric surgery

AIM

This review highlights the relevance of the neural crest (NC) as a developmental control mechanism involved in several pediatric surgical conditions and the investigative interest of following some of its known signaling pathways.

METHODS

The participation of the NC in facial clefts, ear defects, branchial fistulae and cysts, heart outflow tract and aortic arch anomalies, pigmentary disorders, abnormal enteric innervation, neural tumors, hemangiomas, and vascular anomalies is briefly reviewed. Then, the literature on clinical and experimental esophageal atresia-tracheoesophageal fistula (EA-TEF) and congenital diaphragmatic hernia (CDH) is reviewed for the presence of associated NC defects. Finally, some of the molecular signaling pathways involved in both conditions (sonic hedgehog, Hox genes, and retinoids) are summarized.

RESULTS

The association of facial, cardiovascular, thymic, parathyroid, and C-cell defects together with anomalies of extrinsic and intrinsic esophageal innervation in babies and/or animals with both EA-TEF and CDH strongly supports the hypothesis that NC is involved in the pathogenesis of these malformative clusters. On the other hand, both EA-TEF and CDH are observed in mice mutant for genes involved in the previously mentioned signaling pathways.

CONCLUSIONS

The investigation of NC-related molecular pathogenic pathways involved in malformative associations like EA-TEF and CDH that are induced by chromosomal anomalies, chemical teratogens, and engineered mutations is a promising way of clarifying why and how some pediatric surgical conditions occur. Pediatric surgeons should be actively involved in these investigations.

Characterization of chromosomal inversion of the mouse hairy ears (Eh) mutation associated with cleft palate

The hairy ears (Eh) mutation in the mouse originated from neutron irradiation experiments and is associated with chromosomal inversion on chromosome 15. Eh/+ mice have small pinna and extra hairs on the pinna but the phenotypic features of Eh/Eh mice are unclear. In this study we found that Eh/Eh mice died shortly after birth and had a cleft palate caused by impaired growth of palate shelves. Because genes located on the breakpoints of inversion are likely to be responsible for the defects associated with chromosomal inversions, we determined the breakpoints of the Eh inversion. We used a new genetic method that uses recombinant chromosomes resulting from crossing over between two overlapping inversions to determine the breakpoints. Koa is a mouse mutation associated with inversion of chromosome 15, which partially overlaps with the Eh inversion. We made Eh +/+ Koa double heterozygotes and obtained the recombinant chromosomes possessing deletion and duplication of the regions flanked by the breakpoints of both inversions, which were generated by crossing over within the overlapped region of these inversions. By defining the deleted regions we identified the breakpoints of the Eh inversion. We then examined the expression of genes in the vicinities of the breakpoints and found ectopic expression of the Hoxc5 gene and a transcript with unknown function in the developing palate of Eh/Eh mice, which is likely to be responsible for the cleft palate.

Correlation between genetic variations in Hox clusters and Hirschsprung's disease

Interactions between migrating neural crest cells and the environment of the gut are crucial for the development of the enteric nervous system (ENS). A key signalling mediator is the RET-receptor-tyrosine-kinase which, when defective, causes Hirschprung's disease (HSCR, colon aganglionosis). RET mutations alone cannot account for the variable HSCR phenotype, invoking interactions with as yet unknown, and probably inter-related, loci involved in ENS development. Homeobox (HOX) genes have a major role in gut development as depicted by the enteric Hox code. We investigated whether DNA alterations in HOX genes, either alone or in combination with RET, are implicated in HSCR. Genotyping effort was minimized by applying the HapMap data on Han Chinese from Beijing (CHB). 194 HSCR patients and 168 controls were genotyped using Sequenom technology for 72 tag, single nucleotide polymorphisms (SNPs) distributed along the HOX clusters. The HapMap frequencies were compared to those in our population and standard statistics were used for frequency comparisons. The multifactor-dimensionality-reduction method was used for multilocus analysis, in which RET promoter SNP genotypes were included. Genetic interactions were found between two HOX loci (5'-HOXA13 and 3'UTR-HOXB7) and the RET loci tested. Minor allele frequencies (MAF) of the SNPs tested in our sample were not significantly different from those reported by HapMap when the sample sizes of the populations compared were considered. This is the first evaluation of the HOX genes in HSCR and the first application of HapMap data in a Chinese population. The interacting HOX loci may affect the penetrance of the RET risk allele. HapMap data for the CHB population correlated well with the general Chinese population.

FGF10 signaling controls stomach morphogenesis

Maintenance of progenitor cell properties in development is required for proper organogenesis of most organs, including those derived from the endoderm. FGF10 has been shown to play a role in both lung and pancreatic development. Here we find that FGF10 signaling controls stomach progenitor maintenance, morphogenesis and cellular differentiation. Through a characterization of the initiation of terminal differentiation of the three major gastric regions in the mouse, forestomach, corpus and antrum, we first describe the existence of a "secondary transition" event occurring in mouse stomach between E15.5 and E16.5. This includes the formation of terminally differentiated squamous cells, parietal, chief and gastric endocrine cells from a pre-patterned gastric progenitor epithelium. Expression analysis of both FGF and Notch signaling components suggested a role of these networks in such progenitors, which was tested through ectopically expressing FGF10 in the developing posterior stomach. These data provide evidence that gastric gland specification and progenitor cell maintenance is controlled by FGF10. The glandular proliferative niche was disrupted in pPDX-FGF10(FLAG) mice leading to aberrant gland formation, and endocrine and parietal cell differentiation was attenuated. These effects were paralleled by changes in Hes1, Shh and Wnt6 expression, suggesting that FGF10 acts in concert with multiple morphogenetic signaling systems during gastric development.

A dynamic expression survey identifies transcription factors relevant in mouse digestive tract development

Tissue-restricted transcription factors (TFs), which confer specialized cellular properties, are usually identified through sequence homology or cis-element analysis of lineage-specific genes; conventional modes of mRNA profiling often fail to report non-abundant TF transcripts. We evaluated the dynamic expression during mouse gut organogenesis of 1381 transcripts, covering nearly every known and predicted TF, and documented the expression of approximately 1000 TF genes in gastrointestinal development. Despite distinctive structures and functions, the stomach and intestine exhibit limited differences in TF genes. Among differentially expressed transcripts, a few are virtually restricted to the digestive tract, including Nr2e3, previously regarded as a photoreceptor-specific product. TFs that are enriched in digestive organs commonly serve essential tissue-specific functions, hence justifying a search for other tissue-restricted TFs. Computational data mining and experimental investigation focused interest on a novel homeobox TF, Isx, which appears selectively in gut epithelium and mirrors expression of the intestinal TF Cdx2. Isx-deficient mice carry a specific defect in intestinal gene expression: dysregulation of the high density lipoprotein (HDL) receptor and cholesterol transporter scavenger receptor class B, type I (Scarb1). Thus, integration of developmental gene expression with biological assessment, as described here for TFs, represents a powerful tool to investigate control of tissue differentiation.

Retinoic acid regulates morphogenesis and patterning of posterior foregut derivatives

Retinoic acid (RA) is an embryonic signaling molecule regulating a wide array of target genes, thereby being a master regulator of patterning and differentiation in a variety of organs. Here we show that mouse embryos deficient for the RA-synthesizing enzyme retinaldehyde dehydrogenase 2 (RALDH2), if rescued from early lethality by maternal RA supplementation between E7.5 and E8.5, lack active RA signaling in the foregut region. The resulting mutants completely fail to develop lungs. Development of more posterior foregut derivatives (stomach and duodenum), as well as liver growth, is also severely affected. A primary lung bud is specified in the RA-deficient embryos, which fails to outgrow due to defective FGF10 signaling and lack of activation of FGF-target genes, such as Pea3 and Bmp4 in the epithelium. Specific Hox and Tbx genes may mediate these RA regulatory effects. Development of foregut derivatives can be partly restored in mutants by extending the RA supplementation until at least E10.5, but lung growth and branching remain defective and a hypoplastic lung develops on the right side only. Such conditions poorly restore FGF10 signaling in the lung buds. Explant culture of RALDH2-deficient foreguts show a capacity to undergo lung budding and early branching in the presence of RA or FGF10. Our data implicate RA as a regulator of gene expression in the early embryonic lung and stomach region upstream of Hox, Tbx and FGF10 signaling.

Expression profiling the developing mammalian enteric nervous system identifies marker and candidate Hirschsprung disease genes

The enteric nervous system (ENS) is composed of neurons and glial cells, organized as interconnected ganglia within the gut wall, which controls peristalsis of the gut wall and secretions from its glands. The Ret receptor tyrosine kinase is expressed throughout enteric neurogenesis and is required for normal ENS development; humans with mutations in the RET locus have Hirschsprung disease (HSCR, an absence of ganglia in the colon), and mice lacking Ret have total intestinal aganglionosis. The Ret mutant mouse provides a tool for identifying genes implicated in development of the ENS. By using RNA from WT and Ret mutant (aganglionic) gut tissue and DNA microarrays, we have conducted a differential screen for ENS-expressed genes and have identified hundreds of candidate ENS-expressed genes. Forty-seven genes were selected for further analysis, representing diverse functional classes. We show that all of the analyzed genes are expressed in the ENS and that the screen was sensitive enough to identify genes marking only subpopulations of ENS cells. Our screen, therefore, was reliable and sensitive and has identified many previously undescribed genes for studying ENS development. Moreover, two of the genes identified in our screen Arhgef3 and Ctnnal1, have human homologues that map to previously identified HSCR susceptibility loci, thus representing excellent candidates for HSCR genes. This comprehensive profile of ENS gene expression refines our understanding of ENS development and serves as a resource for future developmental, biochemical, and human genetic studies.

lessen encodes a zebrafish trap100 required for enteric nervous system development

The zebrafish enteric nervous system (ENS), like those of all other vertebrate species, is principally derived from the vagal neural crest. The developmental controls that govern the specification and patterning of the ENS are not well understood. To identify genes required for the formation of the vertebrate ENS, we preformed a genetic screen in zebrafish. We isolated the lessen (lsn) mutation that has a significant reduction in the number of ENS neurons as well as defects in other cranial neural crest derived structures. We show that the lsn gene encodes a zebrafish orthologue of Trap100, one of the subunits of the TRAP/mediator transcriptional regulation complex. A point mutation in trap100 causes a premature stop codon that truncates the protein, causing a loss of function. Antisense-mediated knockdown of trap100 causes an identical phenotype to lsn. During development trap100 is expressed in a dynamic tissue-specific expression pattern consistent with its function in ENS and jaw cartilage development. Analysis of neural crest markers revealed that the initial specification and migration of the neural crest is unaffected in lsn mutants. Phosphohistone H3 immunocytochemistry revealed that there is a significant reduction in proliferation of ENS precursors in lsn mutants. Using cell transplantation studies, we demonstrate that lsn/trap100 acts cell autonomously in the pharyngeal mesendoderm and influences the development of neural crest derived cartilages secondarily. Furthermore, we show that endoderm is essential for ENS development. These studies demonstrate that lsn/trap100 is not required for initial steps of cranial neural crest development and migration, but is essential for later proliferation of ENS precursors in the intestine.

Reciprocal epithelial-mesenchymal FGF signaling is required for cecal development

Fibroblast growth factor (FGF) signaling mediates reciprocal mesenchymal-epithelial cell interactions in the developing mouse lung and limb. In the gastrointestinal (GI) tract, FGF10 is expressed in the cecal mesenchyme and signals to an epithelial splice form of FGF receptor (FGFR) 2 to regulate epithelial budding. Here, we identify FGF9 as a reciprocal epithelial-mesenchymal signal required for cecal morphogenesis. Fgf9 null (Fgf9(-/-)) mouse embryos have agenesis of the embryonic cecum, lacking both mesenchymal expansion and an epithelial bud. In the cecal region of Fgf9(-/-) embryos, mesenchymal expression of Fgf10 and Bmp4 is notably absent, whereas the expression of epithelial markers, such as sonic hedgehog, is not affected. Using epithelial and whole explant cultures, we show that FGF9 signals to mesenchymal FGFRs and that FGF10 signals to epithelial FGFRs. Taken together, these data show that an epithelial FGF9 signal is necessary for the expansion of cecal mesenchyme and the expression of mesenchymal genes that are required for epithelial budding. Thus, these data add to our understanding of FGF-mediated reciprocal epithelial-mesenchymal signaling.

HoxB2 binds mutant SOD1 and is altered in transgenic model of ALS

Mutations in Cu/Zn superoxide dismutase (SOD1) cause approximately 20% of familial amyotrophic lateral sclerosis by a toxic gain of function; however, the precise mechanisms remain unclear. Here, we report the identification of HoxB2, a homeodomain-containing transcription factor, as a G93A mutant SOD1 interactive protein in a yeast two-hybrid screen. We show that HoxB2 co-precipitates and co-localizes with mutant SOD1 in neuronal cell lines, as well as in brain and spinal cord of G93A mutant SOD1 transgenic mice. Mutagenesis further shows that this interaction is mediated by the central homeodomain of HoxB2. In motor neuron-like NSC-34 cells, overexpression of HoxB2 or its homeodomain decreases the insolubility of mutant SOD1 and inhibits G93A or G86R mutant SOD1-induced neuronal cell death. In human and mouse tissues, we show that expression of HoxB2 persists in adult spinal cord and is primarily localized in nuclei of motor neurons. In G93A transgenic mice, HoxB2 co-localizes with mutant SOD1 and is redistributed to perikarya and proximal neurites of motor neurons. In addition, there is progressive accumulation of HoxB2 and mutant SOD1 as punctate inclusions in the neuropil surrounding motor neurons. Taken together, our findings demonstrate that interaction of HoxB2 with mutant SOD1 occurs in motor neurons of G93A mutant SOD1 transgenic mice and suggest that this interaction may modulate the neurotoxicity of mutant SOD1.

Regulation of smooth muscle-specific gene expression by homeodomain proteins, Hoxa10 and Hoxb8

Smooth muscle cells arise from different populations of precursor cells during embryonic development. The mechanisms that specify the smooth muscle cell phenotype in each of these populations of cells are largely unknown. In many tissues and organs, homeodomain transcription factors play a key role in directing cell specification. However, little is known about how these proteins regulate smooth muscle differentiation. Using degenerate reverse transcription-PCR coupled to cDNA library screening we identified two homeodomain proteins, Hoxa10 and Hoxb8, which are expressed in adult mouse smooth muscle tissues. All three of the previously described transcripts of the Hoxa10 gene, Hoxa10-1, Hoxa10-2, and Hoxa10-3, were identified. Hoxa10-1 directly activated the smooth muscle-specific telokin promoter but did not activate the SM22alpha, smooth muscle alpha-actin, or smooth muscle myosin heavy chain promoters. Small interfering RNA-mediated knock-down of Hoxa10-1 demonstrated that Hoxa10-1 is required for high levels of telokin expression in smooth muscle cells from uterus and colon. On the other hand, Hoxb8 inhibited the activity of the telokin, SM22alpha, and smooth muscle alpha-actin promoters. Cotransfection of Hoxa10-1 together with Hoxa10-2 or Hoxb8 suggested that Hoxa10-2 and Hoxb8 act as competitive inhibitors of Hoxa10-1. Results from gel mobility shift assays demonstrated that Hoxa10-1, Hoxa10-2, and Hoxb8 bind directly to multiple sites in the telokin promoter. Mutational analysis of telokin promoter reporter genes demonstrated that the three homeodomain protein binding sites located between -80 and -75, +2 and +6, and +14 and +17 were required for maximal promoter activation by Hoxa10-1 and maximal inhibition by Hoxb8. Together these data demonstrate that the genes encoding smooth muscle-restricted proteins are direct transcriptional targets of clustered homeodomain proteins and that different homeodomain proteins have distinct effects on the promoters of these genes.

Organization of Hox genes in ascidians: Present, past, and future

Hox genes have been regarded to play a central role in anterior-posterior patterning of the animal body. Variations of Hox genes among animal species in the number, order on a chromosome, and the developmental expression pattern may reflect an evolutionary history. Therefore, it is definitely necessary to characterize Hox genes of wide variety of animal species, especially the species occupying key positions in the animal phylogeny. Ascidians, belonging to the subphylum Urochordata, are one of the sister groups of vertebrates in the phylum Chordata. Recent studies have shown that nine Hox genes of Ciona intestinalis, an ascidian species, are present on two chromosomes in the genome. In this review, we discuss the present state of Hox genes in ascidians, focusing on their novel chromosomal organization and expression pattern with unique features and how the novel organization has evolved in relation to the unique body plan of ascidians.

Hoxb3 vagal neural crest-specific enhancer element for controlling enteric nervous system development

The neural and glial cells of the intrinsic ganglia of the enteric nervous system (ENS) are derived from the hindbrain neural crest at the vagal level. The Hoxb3 gene is expressed in the vagal neural crest and in the enteric ganglia of the developing gut during embryogenesis. We have identified a cis-acting enhancer element b3IIIa in the Hoxb3 gene locus. In this study, by transgenic mice analysis, we examined the tissue specificity of the b3IIIa enhancer element using the lacZ reporter gene, with emphasis on the vagal neural crest cells and their derivatives in the developing gut. We found that the b3IIIa-lacZ transgene marks only the vagal region and not the trunk or sacral region. Using cellular markers, we showed that the b3IIIa-lacZ transgene was expressed in a subset of enteric neuroblasts during early development of the gut, and the expression was maintained in differentiated neurons of the myenteric plexus at later stages. The specificity of the b3IIIa enhancer in directing gene expression in the developing ENS was further supported by genetic analysis using the Dom mutant, a spontaneous mouse model of Hirschsprung's disease characterized by the absence of enteric ganglia in the distal gut. The colonization of lacZ-expressing cells in the large intestine was incomplete in all the Dom/b3IIIa-lacZ hybrid mutants we examined. To our knowledge, this is the only vagal neural crest-specific genetic regulatory element identified to date. This element could be used for a variety of genetic manipulations and in establishing transgenic mouse models for studying the development of the ENS.