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

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

The large intestine from fetal period to adulthood and its impact on the course of colonoscopy.

The human large intestine in the living adult has a total length of about 1300 mm, ranging from 1100 to 2108 mm. The development of the gut continues after birth, up to the age 4-5. The large intestine ascends at the beginning in the right abdominal quadrant, then it traverses the abdominal cavity, and finally it descends to the anus. The left and right colic flexures are the basic flexions between the transverse, ascending and descending colon, respectively. Additionally, there are secondary bendings between intestinal segments. The angles between the neighbouring parts can vary between examined subjects. Most of the angulations can be found in the transverse (range 2-9) and sigmoid colon (range 1-9), making them the most troublesome parts to pass with a colonoscope. Colonoscopy (usually performed in the left lateral or supine position) is one of the most important examination of the large intestine mucus membrane. During this procedure the endoscope is passed through the colon into the cecum or terminal ilium. The individual anatomical features (tortuosity, supernumerary loops and elongation) may slow down or interfere with the progress of the scope. We summarize current knowledge on the human large intestine from the fetal period to adulthood and carve out some aspects that are currently less known to colonoscopists.

Distinct human stem cell populations in small and large intestine.

The intestine is composed of an epithelial layer containing rapidly proliferating cells that mature into two regions, the small and the large intestine. Although previous studies have identified stem cells as the cell-of-origin for intestinal epithelial cells, no studies have directly compared stem cells derived from these anatomically distinct regions. Here, we examine intrinsic differences between primary epithelial cells isolated from human fetal small and large intestine, after in vitro expansion, using the Wnt agonist R-spondin 2. We utilized flow cytometry, fluorescence-activated cell sorting, gene expression analysis and a three-dimensional in vitro differentiation assay to characterize their stem cell properties. We identified stem cell markers that separate subpopulations of colony-forming cells in the small and large intestine and revealed important differences in differentiation, proliferation and disease pathways using gene expression analysis. Single cells from small and large intestine cultures formed organoids that reflect the distinct cellular hierarchy found in vivo and respond differently to identical exogenous cues. Our characterization identified numerous differences between small and large intestine epithelial stem cells suggesting possible connections to intestinal disease.

Hepatic flexure in right sub diaphragmatic space and its embryological basis and clinical importance.

The knowledge of variations in the large intestine and liver is of clinical importance from the anatomical and embryological points of view. Different positions of the hepatic flexure of large intestine, although generally asymptomatic, may have different impact on manifestations of disease. During routine cadaveric study of the abdominal region we observed a case where the hepatic flexure was interposed between the right dome of the diaphragm and the anterior surface of the liver. The liver appeared bilobulated and on the anterior surface the right and left hepatic lobes were separated by a deep furrow. The left wall of the furrow was attached to the falciform ligament. We have tried to explain such high position of hepatic flexure from an embryological point of view and to evaluate its possible clinical relevance. This abnormal site of hepatic flexure could cause chronic respiratory infections, twisting of the gut, volvulus and intestinal obstruction. Moreover it may alter the normal liver dullness on percussion. So clinicians and surgeons should be aware of this variant position of the hepatic flexure.

Distinct developmental requirements for isolated lymphoid follicle formation in the small and large intestine: RANKL is essential only in the small intestine.

Cryptopatches (CPs) and isolated lymphoid follicles (ILFs) are organized intestinal lymphoid tissues that develop postnatally in mice and include stromal cells expressing the receptor activator of nuclear factor kappa-B ligand (RANKL). We investigated how stromal RANKL influences the development and differentiation of CPs and ILFs by analyzing the development of these lymphoid structures in knockout mice lacking RANKL. We found that RANKL(-/-) mice had a fourfold reduction in the overall density of CPs in the small intestine compared to control mice, with the largest decrease in the proximal small intestine. No B cells were present in CPs from the small intestine of RANKL(-/-) mice and ILF formation was completely blocked. In sharp contrast, colonic ILFs containing B cells were present in RANKL(-/-) mice. Stromal cells within CPs in the small intestine of RANKL(-/-) mice did not express CXCL13 (originally called B lymphocyte chemoattractant) and often lacked other normally expressed stromal cell antigens, whereas colonic lymphoid aggregates in RANKL(-/-) mice retained stromal CXCL13 expression. The CXCL13-dependent maturation of precursor CPs into ILFs is differentially regulated in the small intestine and colon, with an absolute requirement for RANKL only in the small intestine.

Wnt signaling specifies and patterns intestinal endoderm.

Wnt signaling has been implicated in many developmental processes, but its role in early endoderm development is not well understood. Wnt signaling is active in posterior endoderm as early as E7.5. Genetic and chemical activation show that the Wnt pathway acts directly on endoderm to induce the intestinal master regulator Cdx2, shifting global gene away from anterior endoderm and toward a posterior, intestinal program. In a mouse embryonic stem cell differentiation platform that yields pure populations of definitive endoderm, Wnt signaling induces intestinal gene expression in all cells. We have identified a set of genes specific to the anterior small intestine, posterior small intestine, and large intestine during early development, and show that Wnt, through Cdx2, activates large intestinal gene expression at high doses and small intestinal gene expression at lower doses. These findings shed light on the mechanism of embryonic intestinal induction and provide a method to manipulate intestinal development from embryonic stem cells.

Female pelvic congenital malformations. Part I: embryology, anatomy and surgical treatment.

This review covers the most important female congenital pelvic malformations. The first part focuses on the embryological development of the urogenital and anorectal apparatus, morphological features, and the diagnostic and surgical approach to abnormalities. Comprehension of the embryological development of the urogenital and anorectal apparatus is essential to understand the morphology of congenital pelvic abnormalities and their surgical treatment. Congenital pelvic malformations are characterized by specific common features; the severity of which often subverts the pelvic morphology completely and makes it difficult to comprehend before surgery. The development of imaging, mainly magnetic resonance imaging and ultrasound, in the investigation of pelvic floor disorders has recently become a fundamental tool for surgeons to achieve better understanding of the anatomy. Forty years ago, the primary aim of clinicians was to save the lives of such patients and to achieve anatomical normality. However, nowadays, functional reconstruction and recovery are essential parts of surgical management. Introduction of minimally invasive surgery has allowed the improvement of cosmetic results that is so important in paediatric or adolescent patients after reconstructive surgery. The option of sharing the complexity of pelvic congenital diseases by entrusting specific competencies to subspecialists (paediatric urologists, urogynaecologists, neurourologists, paediatric endocrinologists and neonatologists) has improved the quality of care for patients. However, at the same time, active interaction between various specialists remains fundamental. The exchange of knowledge and expertise, not only during the diagnostic-therapeutic process but also during follow-up, is crucial to obtain the best anatomical and functional results throughout the life of the patient.

Regulation of Dab2 expression in intestinal and renal epithelia by development.

Disabled-2 (Dab2) is an intracellular adaptor protein proposed to function in endocytosis. Here, we investigate the intestinal and renal Dab2 expression versus maturation. Dab2 mRNA levels measured by RT-PCR are greater in the small than in the large intestine. Immunological studies localize Dab2 to the terminal web domain of the enterocytes and reveal the presence of a 96-kDa Dab2 isoform in the apical membrane of the jejunum, ileum, and renal cortex of the suckling and adult rat. A 69-kDa Dab2 isoform is only observed in the apical membranes of the suckling ileum. During the suckling period, the Dab2 mRNA levels measured in the enterocytes and crypts and those of the 96-kDa Dab2 isoform are greater in the ileum than in the jejunum. No segmental differences are observed in the adult intestine. In the intestine, the levels of Dab2 mRNA and those of the 96-kDa Dab2 isoform decrease to adult values at weaning, whereas in the kidney they increase with development. Weaning the pups on a commercial milk diet slows the periweaning decline in the levels of Dab2 mRNA in the crypts and of those of the 96-kDa isoform. This is the first report showing that the 96-kDa Dab2 isoform is expressed at the apical domain of rat small intestine, that ontogeny regulates Dab2 gene expression in intestine and kidney and that retarding weaning affects intestinal Dab2 gene expression.

Ontogeny regulates creatine metabolism in rat small and large intestine.

The ontogeny of intestinal CRT, AGAT and GAMT was investigated in foetuses, newborn, suckling, weaning and adult rats. In the colon, CRT mediates creatine transport because it was Na(+)- and Cl(-) dependent and inhibited by creatine and GPA. In addition, Northern assays showed two CRT transcripts (2.7-kb and 4.2-kb) and the in situ hybridisation revealed that CRT mRNA is restricted to the colon epithelial cells. The immunohistochemistry revealed that CRT protein was at the apical membrane of colon epithelia. Maturation decreased colonic CRT activity to undetectable levels and increased CRT mRNA abundance. Western assays revealed 57-, 65-, 80- and 116-kDa polypeptides at the intestinal apical membrane. The abundance of the 65-, 80- and 116-kDa polypeptides decreased with age, and that of 57-kDa was only observed in adult rats. The small and large intestine express AGAT and GAMT mRNAs. Maturation decreased AGAT mRNA abundance without affecting that of GAMT. For comparison, renal AGAT mRNA levels were measured and they were increased with age. The study reports for the first time that: i) the apical membrane of rat colon have an active CRT, ii) development down-regulates CRT activity via post-transcriptional mechanism(s), iii) the intestine might synthesize creatine and iv) intestinal and renal creatine synthesis is ontogenically regulated at the level of AGAT gene expression.

The role of the visceral mesoderm in the development of the gastrointestinal tract.

The gastrointestinal (GI) tract forms from the endoderm (which gives rise to the epithelium) and the mesoderm (which develops into the smooth muscle layer, the mesenchyme, and numerous other cell types). Much of what is known of GI development has been learned from studies of the endoderm and its derivatives, because of the importance of epithelial biology in understanding and treating human diseases. Although the necessity of epithelial-mesenchymal cross talk for GI development is uncontested, the role of the mesoderm remains comparatively less well understood. The transformation of the visceral mesoderm during development is remarkable; it differentiates from a very thin layer of cells into a complex tissue comprising smooth muscle cells, myofibroblasts, neurons, immune cells, endothelial cells, lymphatics, and extracellular matrix molecules, all contributing to the form and function of the digestive system. Understanding the molecular processes that govern the development of these cell types and elucidating their respective contribution to GI patterning could offer insight into the mechanisms that regulate cell fate decisions in the intestine, which has the unique property of rapid cell renewal for the maintenance of epithelial integrity. In reviewing evidence from both mammalian and nonmammalian models, we reveal the important role of the visceral mesoderm in the ontogeny of the GI tract.

Genetic sonography after first-trimester Down syndrome screening.

OBJECTIVE: Approximately 90% of Down syndrome cases are detected during first-trimester screening. We aimed to determine the potential effectiveness of second-trimester genetic sonography as a sequential screen for Down syndrome. METHODS: In this simulation study, published statistical parameters for first-trimester free beta-human chorionic gonadotropin, pregnancy-associated plasma protein-A and nuchal translucency thickness, and second-trimester ultrasound markers (nuchal fold, hyperechoic bowel, short humerus, short femur, echogenic intracardiac focus, pyelectasis and major abnormality) were used to model the effectiveness of second-trimester genetic sonography combined with first-trimester screening. RESULTS: First-trimester combined screening alone resulted in a detection rate of 88.5% with a 4.2% false-positive rate. A follow-up genetic ultrasound examination in which only one sonographic marker was found and previous results were not taken into account would detect an additional 8% of Down syndrome cases for an additional false-positive rate of 13.2%. Using individual marker likelihood ratios to modify the first-trimester risk for screen-negative patients, genetic sonography detected an additional 6.1% of Down syndrome cases for an additional 1.2% false-positive rate, giving a total detection rate of 94.6% and a total false-positive rate of 5.4%. In a contingent protocol, in which genetic sonography would be performed only for patients with a first-trimester risk of between 1/300 and 1/2500, the detection rate was 4.8% and the false-positive rate was 0.7%, giving a total detection rate of 93.3% and a total false-positive rate of 4.9%. CONCLUSION: Second-trimester genetic sonography, if used properly, can be an effective sequential screen following first-trimester Down syndrome screening. Further studies on the role of the genetic sonogram as a follow-up to first-trimester combined screening are warranted.

Expression pattern of Wnt signaling components in the adult intestine.

BACKGROUND & AIMS: In the intestine, the canonical Wnt signaling cascade plays a crucial role in driving the proliferation of epithelial cells. Furthermore, aberrant activation of Wnt signaling is strongly associated with the development of colorectal cancer. Despite this evidence, little is known about the precise identity and localization of Wnts and their downstream effectors in the adult intestine. To address this issue, we examined the expression pattern of all Wnts, Frizzleds (Fzs), low-density lipoprotein receptor-related proteins, Wnt antagonists, and T-cell factors in the murine small intestine and colon and adenomas. METHODS: Embryonic, postnatal, and adult intestinal samples were subjected to in situ hybridization by using specific RNA probes for the various genes tested. RESULTS: Our analysis showed high expression of several signaling components (including Wnt-3, Wnt-6, Wnt-9b, Frizzled 4, Frizzled 6, Frizzled 7, low-density lipoprotein receptor-related protein 5, and secreted Frizzled-related protein 5) in crypt epithelial cells. We also detected Wnt-2b, Wnt-4, Wnt-5a, Wnt-5b, Frizzled 4, and Frizzled 6 in differentiated epithelial and mesenchymal cells of the small intestine and colon. Finally, several factors (Frizzled 4, T-cell factor 1, lymphoid enhancer factor, Dickkopf 2, Dickkopf 3, and Wnt-interacting factor) displayed differential expression in normal vs neoplastic tissue. CONCLUSIONS: Our study predicts a much broader role for Wnt signaling in gut development and homeostasis than was previously anticipated from available genetic studies and identifies novel factors likely involved in promoting canonical and noncanonical Wnt signals in the intestine.

The development and distribution of the interstitial cells of Cajal in the intestine of the equine fetus and neonate.

This study set out to determine the pattern of development and distribution of the interstitial cells of Cajal (ICC) in the intestinal tract of the equine fetus and neonate. Intestinal tissue samples from 12 naturally aborted equine fetuses and three euthanized neonates were collected and fixed in formalin prior to applying standard immunohistochemical labelling techniques targeting the c-Kit protein of the ICC. At 6 months of gestation, a network of ICC was present in the myenteric plexus region of both the small and the large intestine. ICC were also present within the circular muscle layer. In the large intestine, a proximal to distal gradient of distribution was evident, with few ICC observed in the more distal parts of the large intestine in the younger fetuses compared with the near-term animals. A transmural gradient of distribution was also evident within the large intestine, with the most luminal part of the muscularis externa being the last area to be colonized by ICC. This region did not appear fully developed until the early neonatal period. An increased density of ICC was noted throughout the large intestine in the regions of the taenial bands in all animals. This study is the first to describe ICC development and distribution in the equine fetus and neonate.

[Histotopography and density of distribution of the endocrine cells in mucosal epithelium of the large intestine of human fetus]. / Gistotopografiia i plotnost' raspolozheniia éndokrinnykh kletok épiteliia slizistoi obolochki tolstoi kishki ploda cheloveka.

Histotopography and density of distribution (DD) of the endocrine cells in the mucosal epithelium of the large intestine of human fetus was studied using light microscopy. Endocrinocyte DD in the mucosal epithelium of the large intestine was found to increase progressively after their first appearance on the 9th week till the 12th week (average DD (164 cells per 1m m2 of mucosal section area--cells/mm2). Subsequently, in the 4th month, the tendency to a reduction of endocrinocyte DD (to 123 cells/mm2) was observed. In the 5th month, a sharp increase of this parameter was detected (reaching 205 cells/mm2), which represented the maximal value during all the periods of intrauterine development studied. In the 6th month cell DD decreased (164 cells/mm2). Dynamics of the changes of EC-cells, with the exception of those ones in the appendix and the rectum, was similar to that observed in the general population of endocrinocytes. In the rectum, EC-cell DD was stable during the 3rd, the 4th and the 5th months, while in the 6th months the tendency to its reduction was observed. In the appendix, the increase of EC-cell DD took place during all periods investigated. The maximal endocrinocyte DD in the epithelium of appendix in prenatal period of ontogenesis points to an essential role of endocrine apparatus function particularly in the intrauterine development.

Boundary formation by notch signaling in Drosophila multicellular systems: experimental observations and gene network modeling by Genomic Object Net.

The Delta-Notch signaling system plays an essential role in various morphogenetic systems of multicellular animal development. Here we analyzed the mechanism of Notch-dependent boundary formation in the Drosophila large intestine, by experimental manipulation of Delta expression and computational modeling and simulation by Genomic Object Net. Boundary formation representing the situation in normal large intestine was shown by the simulation. By manipulating Delta expression in the large intestine, a few types of disorder in boundary cell differentiation were observed, and similar abnormal patterns were generated by the simulation. Simulation results suggest that parameter values representing the strength of cell-autonomous suppression of Notch signaling by Delta are essential for generating two different modes of patterning: lateral inhibition and boundary formation, which could explain how a common gene regulatory network results in two different patterning modes in vivo. Genomic Object Net proved to be a useful and flexible biosimulation system that is suitable for analyzing complex biological phenomena such as patternings of multicellular systems as well as intracellular changes in cell states including metabolic activities, gene regulation, and enzyme reactions.

Localized JAK/STAT signaling is required for oriented cell rearrangement in a tubular epithelium.

Rearrangement of cells constrained within an epithelium is a key process that contributes to tubular morphogenesis. We show that activation in a gradient of the highly conserved JAK/STAT pathway is essential for orienting the cell rearrangement that drives elongation of a genetically tractable model. Using loss-of-function and gain-of-function experiments, we show that the components of the pathway from ligand to the activated transcriptional regulator STAT are required for cell rearrangement in the Drosophila embryonic hindgut. The difference in effect between localized expression of ligand (Unpaired) and dominant active JAK (Hopscotch) demonstrates that the ligand plays a cell non-autonomous role in hindgut cell rearrangement. Taken together with the appearance of STAT92E in a gradient in the hindgut epithelium, these results support a model in which an anteroposterior gradient of ligand results in a gradient of activated STAT. These results provide the first example in which JAK/STAT signaling plays a required role in orienting cell rearrangement that elongates an epithelium.

The histological observations on the large intestine of the goose (Anser anser) during the pre- and post-hatching periods.

The development of the cecum and colon in the goose was investigated during the period from the 15th to 28th day of the incubation and from 1 to 30 days of age after hatching by light microscopy. By day 15 of the incubation, in the cecum and colon, the lumen was surrounded by pseudostratified epithelium. The previllous ridges appeared at 15th and 17th days of the incubation in the colon and ceca, respectively. At the base of previllous ridges, the epithelium changed into a simple prismathic epithelium at 15th and 17th days of the incubation in the colon and cecum, respectively. The villi appeared at the 21st days of the incubation. The crypts and goblet cells appeared on the first day after hatching. In the pre-hatching period, the lamina muscularis mucosa was present only in the colon. The submucosa consisted of loosely aggregated connective tissue in the pre-hatching period. In the post-hatching period, it consisted of a very thin layer of connective tissue. Its presence was only obvious where the cells of the submucosal nerve plexus or occasional large blood vessels considerably increased its thickness. The nerve plexus corresponding to the Auerbach's plexus of the mammalian intestine and submucosal nerve plexus appeared by 15th days of the incubation. From the 15th to 28th day of incubation, the tunica muscularis consisted of circular smooth muscle cells in the ceca. On the 28th day of the incubation a thinner longitudinal muscle layer added to the circular muscle layer. In the colon there was an outer longitudinal and a thicker circular muscle layer.

Effects of pre- and postnatal protein deprivation and postnatal refeeding on myenteric neurons of the rat large intestine: a quantitative morphological study.

We investigated the effect of protein deprivation and refeeding on weight gain, the size of the colon, and the numbers and sizes of enteric neurons. Neurons were located by reduced nicotinamide adenine dinucleotide (NADH) diaphorase staining. Protein deprivation of the mother throughout pregnancy, and the mother and unweaned rat pups in the first 21 postnatal days, reduced the weights of pups to about 50% of control. The size of the colon was also reduced, by about 40%. Despite this, total numbers of neurons in the colon were not reduced. However, there was a small, but significant, 15% reduction in the areas of neuron profiles. After 21 days the remaining pups were removed from the mothers, and either maintained on the control diet, maintained on the protein-deprived diet, or changed from the protein-deprived diet to a normal diet (refed group). These rats were examined after a further 21 days. Refeeding restored body weight to 20% below control, restored colon size, and restored nerve cell size. After a total of 42 days of protein deprivation, nerve cell numbers were not significantly different from control. In undernourished rats at 21 and 42 days, neurons were less well stained than control for NADH diaphorase. Refeeding between 21 and 42 days restored the normal appearance of the neurons. It is concluded that enteric neurons are protected from loss even when there is a substantial reduction in body weight and organ size caused by protein deprivation. The neurons become smaller, but recover size after refeeding.

Notch signaling controls cell fate specification along the dorsoventral axis of the Drosophila gut.

BACKGROUND: Gut formation is a key event during animal development. Recent genetic analysis in chick, mice, and Drosophila has identified Hedgehog and TGFbeta signals as essential players for the development of the primitive gut tube along its anterior-posterior (AP) axis. However, the genetic programs that control gut patterning along its dorsoventral (DV) axis have remained largely elusive. RESULTS: We demonstrate that the activation of the Notch receptor occurs in a single row of boundary cells which separates dorsal from ventral cells in the Drosophila hindgut. rhomboid, which encodes a transmembrane protein, and knirps/knirps-related, which encode nuclear steroid receptors, are Notch target genes required for the expression of crumbs, which encodes a transmembrane protein involved in organizing apical-basal polarity. Notch receptor activation depends on the expression of its ligand Delta in ventral cells, and localizing the Notch receptor to the apical domain of the boundary cells may be required for proper signaling. The analysis of gene expression mediated by a Notch response element suggests that boundary cell-specific expression can be obtained by cooperation of Suppressor of Hairless and the transcription factor Grainyhead or a related factor. CONCLUSIONS: Our results demonstrate that Notch signaling plays a pivotal role in determining cell fates along the DV axis of the Drosophila hindgut. The finding that Notch signaling results in the expression of an apical polarity organizer which may be required, in turn, for apical Notch receptor localization suggests a simple mechanism by which the specification of a single cell row might be controlled.

Requirement of Math1 for secretory cell lineage commitment in the mouse intestine.

The mouse small intestinal epithelium consists of four principal cell types deriving from one multipotent stem cell: enterocytes, goblet, enteroendocrine, and Paneth cells. Previous studies showed that Math1, a basic helix-loop-helix (bHLH) transcription factor, is expressed in the gut. We find that loss of Math1 leads to depletion of goblet, enteroendocrine, and Paneth cells without affecting enterocytes. Colocalization of Math1 with Ki-67 in some proliferating cells suggests that secretory cells (goblet, enteroendocrine, and Paneth cells) arise from a common progenitor that expresses Math1, whereas absorptive cells (enterocytes) arise from a progenitor that is Math1-independent. The continuous rapid renewal of these cells makes the intestinal epithelium a model system for the study of stem cell regeneration and lineage commitment.