A scanning and transmission electron microscopical study of the morphogenesis of human colonic villi

The developmental mechanics of divergent buckling patterns in the chick gut

Tissue buckling is an increasingly appreciated mode of morphogenesis in the embryo, but it is often unclear how geometric and material parameters are molecularly determined in native developmental contexts to generate diverse functional patterns. Here, we study the link between differential mechanical properties and the morphogenesis of distinct anteroposterior compartments in the intestinal tract-the esophagus, small intestine, and large intestine. These regions originate from a simple, common tube but adopt unique forms. Using measured data from the developing chick gut coupled with a minimal theory and simulations of differential growth, we investigate divergent lumen morphologies along the entire early gut and demonstrate that spatiotemporal geometries, moduli, and growth rates control the segment-specific patterns of mucosal buckling. Primary buckling into wrinkles, folds, and creases along the gut, as well as secondary buckling phenomena, including period-doubling in the foregut and multiscale creasing-wrinkling in the hindgut, are captured and well explained by mechanical models. This study advances our existing knowledge of how identity leads to form in these regions, laying the foundation for future work uncovering the relationship between molecules and mechanics in gut morphological regionalization.

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 antero‑posterior (AP) axis and the radial (RAD) axis in the context of left‑right (LR) asymmetry. These events lead to the formation of three distinct regions, the foregut, midgut and hindgut. All the above‑mentioned 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 non‑canonical wingless‑related 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.

Chick midgut morphogenesis

The gastrointestinal tract is an essential system of organs required for nutrient absorption. As a simple tube early in development, the primitive gut is patterned along its anterior-posterior axis into discrete compartments with unique morphologies relevant to their functions in the digestive process. These morphologies are acquired gradually through development as the gut is patterned by tissue interactions, both molecular and mechanical in nature, involving all three germ layers. With a focus on midgut morphogenesis, we review work in the chick embryo demonstrating how these molecular signals and mechanical forces sculpt the developing gut tube into its mature form. In particular, we highlight two mechanisms by which the midgut increases its absorptive surface area: looping and villification. Additionally, we review the differentiation and patterning of the intestinal mesoderm into the layers of smooth muscle that mechanically drive peristalsis and the villification process itself. Where relevant, we discuss the mechanisms of chick midgut morphogenesis in the context of experimental data from other model systems.

Villification: how the gut gets its villi

The villi of the human and chick gut are formed in similar stepwise progressions, wherein the mesenchyme and attached epithelium first fold into longitudinal ridges, then a zigzag pattern, and lastly individual villi. We find that these steps of villification depend on the sequential differentiation of the distinct smooth muscle layers of the gut, which restrict the expansion of the growing endoderm and mesenchyme, generating compressive stresses that lead to their buckling and folding. A quantitative computational model, incorporating measured properties of the developing gut, recapitulates the morphological patterns seen during villification in a variety of species. These results provide a mechanistic understanding of the formation of these elaborations of the lining of the gut, essential for providing sufficient surface area for nutrient absorption.

Anisotropic growth shapes intestinal tissues during embryogenesis

Embryogenesis offers a real laboratory for pattern formation, buckling, and postbuckling induced by growth of soft tissues. Each part of our body is structured in multiple adjacent layers: the skin, the brain, and the interior of organs. Each layer has a complex biological composition presenting different elasticity. Generated during fetal life, these layers will experience growth and remodeling in the early postfertilization stages. Here, we focus on a herringbone pattern occurring in fetal intestinal tissues. Common to many mammalians, this instability is a precursor of the villi, finger-like projections into the lumen. For avians (chicks' and turkeys' embryos), it has been shown that, a few days after fertilization, the mucosal epithelium of the duodenum is smooth, and then folds emerge, which present 2 d later a pronounced zigzag instability. Many debates and biological studies are devoted to this specific morphology, which regulates the cell renewal in the intestine. After reviewing experimental results about duodenum morphogenesis, we show that a model based on simplified hypothesis for the growth of the mesenchyme can explain buckling and postbuckling instabilities. Being completely analytical, it is based on biaxial compressive stresses due to differential growth between layers and it predicts quantitatively the morphological changes. The growth anisotropy increasing with time, the competition between folds and zigzags, is proved to occur as a secondary instability. The model is compared with available experimental data on chick's duodenum and can be applied to other intestinal tissues, the zigzag being a common and spectacular microstructural pattern of intestine embryogenesis.

Vertebrate intestinal endoderm development

The endoderm gives rise to the lining of the esophagus, stomach and intestines, as well as associated organs. To generate a functional intestine, a series of highly orchestrated developmental processes must occur. In this review, we attempt to cover major events during intestinal development from gastrulation to birth, including endoderm formation, gut tube growth and patterning, intestinal morphogenesis, epithelial reorganization, villus emergence, as well as proliferation and cytodifferentiation. Our discussion includes morphological and anatomical changes during intestinal development as well as molecular mechanisms regulating these processes.

[Early fetal development of the small intestine mucosa in cattle (Bos primigenius taurus)]

The development of the bovine small intestine was examined in 24 embryos and fetuses by light microscopic, scanning and transmission electron microscopic methods. Special reference was paid to the genesis of the epithelium and particularly of the villi intestinales. The primitive intestine consists of one layer of epithelial cells surrounded by mesenchym and tunica serosa. The fetal intestine (up to the 24th week of gestation) shows all the morphologic structures of the adult. In small intestine the development of cryptae and villi intestinales starts before the 7th week of gestation and progresses with a proximo-distal gradient. Epithelial proliferation that gives rise to primary epithelial villi makes epithelium become temporarily stratified. Finger-like secondary villi develop by proliferation of the mesenchym. In addition to this process mucosal folds occur in duodenum giving rise to villi by segmentation. At the same time the differentiation of epithelium starts. The fetal small intestine, like many other fetal tissues displays masses of glycogen.

Fetal and neoplastic expression of the neurotensin gene in the human colon

OBJECTIVE

The authors identified various colon cancers that express the gene for the gut peptide neurotensin (NT/N). In addition, the authors sought to delineate the temporal pattern of NT/N gene expression in the human fetal colon.

SUMMARY BACKGROUND DATA

Expression of NT/N is localized to the mucosa of the adult small bowel but also has been identified in the fetal colon, which resembles the small bowel until the end of the second trimester. Ectopic NT/N expression has been shown in certain types of colon cancer, suggesting a reversion to a fetal phenotype.

METHODS

Sensitive ribonuclease protection assays were used to determine NT/N expression in colon cancers and adjacent normal mucosa as well as colon cancers established as tumor xenografts and fetal colon samples.

RESULTS

NT/N gene expression was shown in 4 of 12 (25%) human colon cancer xenografts and in 11 of 40 (28%) freshly resected colon adenocarcinomas; NT/N gene expression was not expressed in any of the samples of normal colonic mucosa adjacent to the tumors. The NT/N gene was expressed maximally in the fetal colon between 16 and 18 weeks' gestation; NT/N expression was decreased between 19 and 22 weeks and was not apparent in either the 24-week fetal colon or the adult samples.

CONCLUSIONS

The NT/N gene expression is expressed transiently in the fetal colon during a development stage that is characterized by morphologic similarity to the small bowel. In addition, NT/N is reexpressed in approximately one fourth of the human colon cancers, indicating that neoplastic transformation leads to reversion to a fetal phenotype in certain types of colon cancer. The NT/N gene will provide a useful model to further define the complex differentiation pathways in the normal gut as well as the process of fetal "dedifferentiation" in certain types of colon cancer.

The neurotensin gene is a downstream target for Ras activation

Ras regulates novel patterns of gene expression and the differentiation of various eukaryotic cell types. Stable transfection of Ha-ras into the human colon cancer line CaCo2 results in the morphologic differentiation to a small bowel phenotype. The purpose of our study was to determine whether the Ras regulatory pathway plays a role in the expression of the neurotensin gene (NT/N), a terminally differentiated endocrine product specifically localized in the gastrointestinal tract to the adult small bowel. We found that CaCo2-ras cells, but not parental CaCo2, express high levels of the human NT/N gene and, moreover, that this increase in gene expression is regulated at the level of transcription. Transfection experiments using NT/N-CAT mutation constructs identify the proximal 200 bp of NT/N flanking sequence as sufficient for maximal Ras-mediated NT/N reporter gene induction. Furthermore, a proximal AP-1/CRE motif is crucial for this Ras-mediated NT/N activation. Wild-type Ha-ras induces NT/N gene expression, albeit at lower levels than activated Ras; a dominant-negative Raf blocks this NT/N induction, suggesting that Raf lies down-stream of Ras in this pathway. In addition, postconfluent cultures of CaCo2 cells, which are differentiated to a small bowel phenotype, express the NT/N gene by 6 d after reaching confluency; this increase of NT/N expression is associated with concomitant increases of cellular p21ras protein. We conclude that Ras (both wild-type and activated) enhances expression of the NT/N gene in the gut-derived CaCo2 cell line, suggesting an important role for the Ras signaling pathway in NT/N gene transcription. Our results underscore the possibility that tissue-specific genes (such as NT/N) expressed in distinct subpopulations of the gut may be subject to Ras regulation. Finally, we speculate that the NT/N gene and the CaCo2 and CaCo2-ras cell systems will provide unique models to further define the cellular mechanisms leading to mammalian intestinal differentiation.

Morphological changes and cellular proliferation in mouse colon during fetal and postnatal development

To document regional structural and cellular proliferation changes in the developing mouse colon, tissues from fetal, suckling, and weanling mice were analyzed by light microscopy (LM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), [3H]-thymidine incorporation studies, and radioautography. The proximal and distal colon were studied independently at all ages. At 17-18 days of gestation, the mouse proximal colonic mucosa was projected into high and low longitudinal folds disposed in a V-shaped pattern. From birth up to 9 days, the mucosal folds observed by SEM can easily be misinterpreted as being a succession of high and low villus-like structures at LM level. TEM study confirmed the presence of highly specialized absorptive cells in the upper halves of the mucosal folds during this period. No recognizable crypts were noted at birth. Instead, LM and radioautography showed the presence of cell aggregates developing at the base of the epithelium at all levels of the mucosal folds. These cell aggregates evolved into rudimentary crypts giving fully differentiated crypts by day 16 with radiolabeled cells located in the midcrypt portion. As opposed to the proximal segment, a flat mucosa interspersed with well defined short crypts at birth was observed in the distal colon. During the following days, crypts further developed and by 16 days, the radiolabeled epithelial cells were still exclusively located at the base of the crypt. TEM observations illustrated that specialized cells as those found in the proximal segment did not differentiate in this segment.(ABSTRACT TRUNCATED AT 250 WORDS)

[Lysosomal structures in the intestinal epithelium of mammals during their pre- and postnatal development. A micromorphometric-functional synopsis]

The first lysosomes appear in the stratified embryonic intestinal epithelium during its transition into the simple columnar form. This occurs concurrently with the initial villogenesis. Lysosomes situated basally in the epithelium are presumably the precursor of the first giant lysosomes in the lower small intestine of rodents. Immediately after establishment of the simple configuration a special form of secondary lysosomes can be observed, i.e. glycogenosomes, in the ephemerally existing huge glycogen containing areas. During subsequent fetal intestinal development one observes two events in the epithelial cells, which are the same in principle but differ in one essential point, while they exhibit partially impressive structures. On the one hand there are autophagic degenerative lysosomal processes in the villous epithelium until birth, that lead to a surface without villi in the large intestine, where they occur particularly frequently. On the other hand giant lysosomes originate perinatally in the lower small intestine as well as in the caecum and colon ascendens, in which protein molecules, which were transported by a system of inframicrovillar membranes, are lysosomally degraded, which can be defined as a heterophagic event.

Brush border hydrolases in normal and neoplastic colonic epithelium

Previous studies have suggested that abnormal expression of enzymes characteristic of the intestinal brush border might accompany colonic neoplasia and possibly facilitate identification of epithelium at risk of malignancy. To test this possibility, the distribution of the brush border enzymes sucrase-isomaltase (SIM), maltase-glucoamylase (MGA), aminopeptidase-N (APN) and diamino-peptidylpeptidase-IV (DPPIV) were studied by the immunoperoxidase method in biopsies from the rectum and caecum of normal subjects, and neoplastic and non-neoplastic tissues from patients with adenoma or cancer. Brush border enzymes were detected by immunohistochemistry more frequently in the caecum than the rectum (P less than 0.05) of normal subjects. Diamino-peptidylpeptidase-IV and APN were present in highest concentration at the brush border of the most mature colonocytes on the luminal surface with less staining in the crypt, whereas SIM and MGA staining of the brush border was as prominent on crypt cells as surface cells. While all cancers expressed at least one enzyme, there was heterogeneity of staining within tumours and a tendency to lose polarity of enzyme expression in cells, sometimes with dense staining of the cytoplasm. Distally situated adenomas uncommonly expressed a brush border enzyme (25%) and the only enzyme expressed in them was SIM. These finding indicate that these brush border enzymes are not exclusively expressed in the small intestine; DPPIV and APN are markers of the normal mature colonocyte and should prove useful as markers of differentiation. However, the change associated with neoplasia would not appear to be of clinically predictive value.(ABSTRACT TRUNCATED AT 250 WORDS)

Asynchronous development of the rat colon

Mucosal ridge and fold formation, apoptosis and the occurrence of secondary lumina within the epithelium are morphological features associated with the development of the colon. These processes, however, do not occur synchronously in the various segments of the colon. In the caecum and ascending colon of the rat, fold formation, apoptosis and secondary lumina result in the development of villi by day 22 after conception, and by postnatal day 3 in the transverse colon. These villi persist in the rat colon until approximately postnatal day 10. The presence of colonic villi may be correlated with the increased food intake and fluid absorption during this early postnatal period. Villus formation does not take place in the developing descending colon.

Prenatal and postnatal development of the large intestine in the insectivore Suncus murinus, the laboratory shrew

Development of the large intestine in the insectivore Suncus murinus (the laboratory shrew) was investigated from day 21 to 30 of gestation and from birth to 20 days of age. Two days before birth, the stratified epithelium in the large intestine changed into a single layer. Although neither villi nor villus-like structures were ever present, fissures, corresponding to openings of the crypts, appeared on the mucosal surface before birth. These increased in number as well as in width and depth, connected with each other, and gave the mucosal surface a ridge-like appearance by 20 days of age. An elevation containing submucosae appeared shortly after birth and formed a large circular fold during the neonatal period. Goblet cells were the predominant epithelial cell type. Individual epithelial cells were mature-looking a few days before birth; goblet cells contained numerous mucous globules and absorptive cells possessed well-developed organelles. However, although goblet cells increased in number and exhibited active mucous-releasing forms after birth, absorptive cells never showed morphologic evidence of active endocytosis, such as apical endocytotic complexes and large supranuclear vacuoles. Each epithelial cell was similar in ultrastructure to that of the adult shortly after birth.

A morphological study of a human adenocarcinoma cell line (HT29) differentiating in culture. Similarities to intestinal embryonic development

HT29 cells, a human adenocarcinoma cell line, when grown in Dulbecco's modified Eagle's medium (DMEM), form a multilayer of morphologically undifferentiated and unpolarized cells. However, when DMEM is replaced by RPMI medium, after 1-4 passages, a large amount of intracellular (ICL) and intercellular (ITCL) or secondary lumina (SL) are observed. These are detected in the light microscope and appear in the electron microscope as spherical structures embedded inside a multilayer of cells and bordered with microvilli. After 4-15 passages in RPMI, the cells retain the same pattern of cell growth but in addition exhibit apical brush-border microvilli and reveal a well developed belt of tight junctions. After 15 passages a single layer of polarized cells is clearly observed and a large number of 'domes' appeared. These results show that each of these culture types mimics morphologically specific stages described during intestinal ontogenesis between the 9th and the 16th week in the human embryo.

Detection and characterization of sucrase-isomaltase in adult human colon and in colonic polyps

A panel of monoclonal antibodies specific for sucrase-isomaltase, but differing in their ability to stain the proliferative crypt cells in human jejunum, was used to investigate expression of this enzyme in adult human colon and colonic tumors. Immunofluorescence staining on cryostat sections demonstrated the presence of sucrase-isomaltase in the apical region of normal colonic crypt cells but not on surface epithelium. Colonic sucrase-isomaltase was purified by immunoprecipitation with selected monoclonal antibodies and identified predominantly as high-mannose and complex glycosylated single-chain precursors endowed with relatively low levels of enzyme activities. Most polyps examined (10/16) were also found to express significant amounts of sucrase-isomaltase. In contrast, only 3 of 45 adenocarcinomas were positive by immunofluorescence staining; no correlation was found between enzyme expression and tumor classification either by "Dukes" stage or degree of histological differentiation. These results demonstrate that colonic crypt cells and some benign tumor cells synthesize and express at their cell surface a form of sucrase-isomaltase immunologically distinct from that present in the brush borders of small intestinal villose cells.

Structural and enzymatic changes during colonic maturation in the fetal and suckling rat

To assess correlations between cellular differentiation and enzymatic maturation in the developing rat colon, tissue from fetal, suckling, weanling, and adult rats was analyzed by electron microscopy and assayed for lactase, alkaline phosphatase, and sodium-potassium-stimulated adenosine triphosphatase activities. The proximal and distal colon were analyzed independently at all ages. All three enzymes were detected in the fetal colon when the cells were highly undifferentiated. Postnatally, significant regional differences in cellular ultrastructure appeared, only some of which were directly paralleled by enzymatic changes. Each enzyme had a distinct region-specific developmental pattern. Lactase and sodium-potassium-stimulated adenosine triphosphatase were significantly enhanced at birth, decreasing to adult levels by 15 days postnatal. Regional differences were present, but the patterns were similar. These patterns did not parallel the increase in microvillar height and number and basolateral interdigitations of the surface columnar cells, the structural correlates of lactase, and sodium-potassium-stimulated adenosine triphosphatase, respectively. In contrast, developmental changes in alkaline phosphatase activity paralleled structural maturation, at least in part. The activity levels in the distal colon did not change significantly with age and few major structural changes were noted. In the proximal colon, activity increased markedly after birth, and after 10 days decreased rapidly to adult levels, a pattern that coincided with the transient appearance of villi and specialized cells with apical tubules and vesicles known to have alkaline phosphatase activity. The results show age- and region-related changes in cellular ultrastructure and enzymatic activities, only some of which appear to be directly correlated.

Expression of brush border calmodulin-binding proteins during human small and large bowel differentiation

The expression and immunocytochemical localization of three brush border cytoskeletal calmodulin-binding proteins, caldesmon, fodrin, and the 110 kDa subunit of the 110 kDa calmodulin complex, have been studied in human intestinal epithelial cells as a function of their ontogenic differentiation. At immature stages (fetal week 8), caldesmon and fodrin were present in undifferentiated intestinal epithelial cells. However, no 110 kDa protein was detectable except a 135 kDa immunoreactive species. The 110 kDa form appeared at week 12, when microvilli differentiate, and became prominent at week 14 simultaneously with the disappearance of the 135 kDa species. Finally at week 14, the calmodulin-binding protein pattern was identical to that found in adults. Immunocytochemical experiments revealed that at week 8, antibodies to caldesmon and fodrin gave a fluorescence lining at the periphery of the cells, whereas the 110 kDa immunoreactive species was hardly detectable. Then, as early as week 12 of gestation, with the three antisera, a bright fluorescence lined the apex of the cells, as in adults. In the colon, the events were delayed. This study demonstrates that the developmental pattern of the three calmodulin-binding proteins investigated, caldesmon, fodrin and the 110 kDa subunit, parallels the temporal differentiation of human intestinal brush borders and the proximo-distal morphological intestinal maturation.

The presence and significance of intraepithelial mesenchymal cells in human foetal colon

During an investigation of the morphogenesis of the human foetal colon, breaks in the basal lamina underlying the surface epithelium were frequently observed at 10 1/2-11 weeks. These occurred at those sites where the mesenchyme was sweeping up into the epithelium prior to the transformation of the epithelium from stratified to a single layer. At the same time numbers of mesenchymal cells appeared among the epithelial cells and some were observed actually in the process of passing through the gaps in the basal lamina. Close contact was apparent between some mesenchymal cells and basal epithelial cells through extended breaks in the basal lamina. Many of the mesenchymal cells within the epithelium contained numbers of apoptotic bodies. This suggests that one of the functions of the intra-epithelial mesenchymal cells is to remove the debris resulting from cell death which occurs in association with the re-arrangement of cells during development of the colon.

Human fetal colon in organ culture

Human fetal colon (14-16 weeks gestation) was cultured as explants for 15 days in serum-free Leibovitz L-15 medium at 37 degrees C. The overall morphology of the colonic explants was well maintained throughout the culture period and all epithelial cell types retained their ultrastructural characteristics. The incorporation of [3H]-leucine continued and even increased, reflecting sustained synthesis of proteins. Even though the incorporation of [3H]-thymidine into the total DNA decreased during culture, the synthesis of DNA continued. The sites of [3H]-thymidine incorporation into the different layers of the colonic wall were studied by radioautography. The incorporation of the radioactive precursor occurs mainly in the epithelium and to lesser degrees in the mesenchyme and the muscular layer. Labeled epithelial nuclei were located in the intervillous areas but not on the villi. The labeling index of the epithelial cells remained constant throughout the culture period indicating the preservation of the proliferative capacity of the epithelium. Brush-border hydrolytic activities, namely those of sucrase, maltase, lactase, trehalase, glucoamylase and alkaline phosphatase, were assayed in the colonic tissue. These enzymic activities generally decreased in the tissue and increased in the medium during the course of culture. These observations clearly demonstrate that fetal colon can be maintained viable for at least 15 days in a serum-free medium. Organ culture now provides the opportunity to study the normal function and metabolism of human colon during its development.

Localization of carbonic anhydrase activity in the developing rat colon

Carbonic anhydrase activity was localized histochemically by light and electron microscopy in the proximal and distal colon of developing rats. Fixed tissue was taken for normal morphology and carbonic anhydrase localization from fetal (20-22 days gestation), suckling (1-19 days postnatal), weanling (20-25 days postnatal), and adult rats. The proximal colon had distinct villi at birth which were diminished between days 5 and 11 postnatally. The distal colon lacked villi at birth but had rudimentary crypts (ridges and furrows) which were replaced during the suckling period by a flat mucosa interspersed with true crypts. Carbonic anhydrase first appeared in both proximal and distal colonic epithelial cells on the day of birth (22 days gestation). Goblet cells were nonreactive at each developmental period. In neonatal rats, epithelial cells in the upper half of the villi of the proximal colon and on the surface and upper crypts of the distal colon were positive for carbonic anhydrase throughout the cytoplasm. Cells at the villar base (proximal colon) or in the deep crypt (distal colon) had reaction product in the intercellular spaces but not the cytoplasm. By 11 days postnatal, cytoplasmic reaction product was present in proximal colonic cells in the upper three-fourths of the crypt and was concentrated in a heavy band in the apical cytoplasm. In the distal colon, cytoplasmic positive cells did not extend as deeply into the crypts and the apical banding pattern was weak. Intercellular spaces in the deeper crypt epithelium were positive in both proximal colon and distal colon, suggesting a membrane-bound carbonic anhydrase. It was concluded that carbonic anhydrase appeared suddenly at birth and was continuously present in mid- to upper-crypt (or upper villus in early neonatal proximal colon) non-goblet cells into adulthood. This suggests a functional role for carbonic anhydrase in chloride-bicarbonate exchange across the neonatal and adult colonic mucosa.

An ultrastructural study of meconium corpuscles in human foetal colon

In human foetal colon meconium corpuscles were observed in the colonic epithelium during the stage of secondary lumina development and enlargement. Transmission electron microscopy of these specimens revealed inclusion bodies in the superficial and deeper layers of the epithelium. Many of the membrane-bounded inclusion bodies contained well-preserved organelles and some inclusions contained nuclear fragments. There was evidence of nuclear fragmentation with condensed chromatin arranged in crescentic caps. The ultrastructural observations are typical of apoptosis, a mode of cell death first described in 1972 by Kerr and colleagues. Thus, meconium corpuscles are apoptotic bodies found as a result of the deletion of healthy normal cells during the reshaping and development of organs.

Immunohistological evidence, obtained with monoclonal antibodies, of small intestinal brush border hydrolases in human colon cancers and foetal colons

The expression of small intestinal hydrolases associated with the enterocyte brush border membrane was studied in human colon cancers and foetal colons, by means of monoclonal antibodies against human small intestinal sucrase-isomaltase (SI), maltase-glucoamylase (MGA), lactase (L), aminopeptidase N (APN), and dipeptidylpeptidase IV (DPP-IV). The enzymes were visualized by indirect immunofluorescence on cryostat sections of tumors developed in nude mice with 6 human colon carcinoma cell lines (HT-29, Caco-2, SW-480, HRT-18, HCT-8R, and Co-115), of 27 primary colorectal carcinomas from patients, and of human foetal (16 to 20 weeks of gestation) and normal adult small intestines and colons. All 5 monoclonals bound to the brush border of the adult small intestine, but not to that of the adult colon mucosa. Antibodies against SI, APN and DPP-IV also bound to the brush border of the foetal colons, to apical borders in HT-29 and Caco-2 tumors in nude mice, and to brush border-like structures in 7/27 tumors from patients. No binding was observed for MGA and L in either tumors or foetal colons. Binding of anti-SI antibodies to the brush border of the juxta-tumoral mucosal epithelium was observed in 9/11 samples tested. These data indicate that some colon tumors exhibit a typical pattern of enterocytic differentiation which is of foetal type and which involves at least 3 brush border membrane hydrolases. Monoclonal antibodies to small intestinal hydrolases may, therefore, be important tools for identification and characterization of some differentiated colonic tumors.

Developmental pattern of brush border enzymes in the human fetal colon. Correlation with some morphogenetic events

The present study is concerned with a multilevel approach to human colon organogenesis, involving scanning and transmission electron microscopy together with brush border enzymology. The results emphasize the particular developmental pattern of sucrase activity which appears towards 11 weeks, increases at 14 weeks, begins to decrease around 28 weeks and disappears totally at term. In contrast, other enzymes like aminopeptidase and alkaline phosphatase persist in the adult colon. The correlation, in the fetal large bowel, of enzyme activities and villus structures similar to those found in the small intestine is discussed.