Morphological study of the regeneration mechanism of acetic acid-injured colon crypts in the rat

The regeneration mechanism of injured rat colonic mucosa with 1% acetic acid was certified in this study. The injured colons were studied periodically on experimental days 1, 3, 5, 7, 15, and 20 with light and scanning electron microscopy. Specimens were examined in paraffin sections stained with hematoxylin and eosin; crypts were isolated with the HCl digestion method; and three-dimensional stromal collagen tissue was prepared with the NaOH cell maceration method. Damage to the mucosal and submucosal layers peaked between the 1st and 3rd days with edema, regeneration, necrosis, and inflammation. The edema and inflammation subsided, and mucosal atrophy and crypt reduction remained at around 1 week. At 2 weeks the mucosa became thick, and crypts showed many branches in their lower two-thirds; and by 3 weeks the mucosa had recovered to almost normal. The ratio of number of crypts at the base and surface was almost 1.5 on the 15th day and 1.0 on the 20th day, suggesting that each branch progresses upward to create an independent crypt. We believe that the fission mechanism plays an important role in crypt repair after acetic acid injury of the colonic mucosa. As the proliferative zone of the colonic crypt is localized at the crypt base, fission of the crypt starting at the base and progressing up to the surface is the most reasonable and efficient mechanism for repair by increasing the number of crypts.     

Normal colon of Sprague-Dawley rats

Summary The patterns of expression of the human-tumor-associated antigens, CO17-1A, GA73-3, BR55-2, GICA19-9, CA50 and carcino-embryonic antigen (CEA) were studied in the normal colonic mucosa (the last three also in the serum) of Sprague-Dawley rats. Four immunohistochemically different segments were identified: caecum, ascending colon, transverse colon and descending colon. The immunohistochemical reactions of the cells at the lower part of the crypt were essential for the distinction of the four segments. In the caecum, the MAbs 17-1A, 73-3 and 19-9 stained the glycocalyx of the cells of the lower part of the crypts and the Golgi apparatus of the intercalated cells (IC). MAb55-2 stained very weakly the goblet-like cells (GLC) of the lower part of the crypt of transverse colon, in addition to a nearly complete lack of reaction in the upper part of the crypts. In the ascending colon, the lower part of the crypts showed a characteristic diffuse staining of the intercalated cells with MAb55-2. The perinuclear and mucosal staining observed in the GLC of the transverse colon with MAbs 17-1A, 73-3 and 19-9 as against the supranuclear and Golgi zone staining observed in the GLC/goblet cells (GC)/columnar cells (CC) of the lower part of crypts of the descending colon with the same MAbs, distinguished the former segment from the latter. The IC demonstrated by immunohistochemistry in the lower parts of the crypts of caecum and ascending colon appear to correspond to the replicating cells of the colonic crypts.     

Morphology of isolated colonic crypts

The traditional paradigm of colonic fluid and electrolyte transport includes a spatial separation of absorptive and secretory processes to surface and crypt cells, respectively. Recent studies of isolated microperfused colonic crypts revealed constitutive Na-dependent fluid absorption while secretion is regulated by one or more neurohumoral agonists. One obvious reason for the difference found in microdissected crypts is their separation from the lamina propria milieu. While it has been shown that isolated crypts are devoid of obvious lamina propria elements, including pericryptal fibroblasts, detailed morphologic information of the content of isolated crypts has been lacking. To characterize the morphology of the isolated crypt, we performed transmission electron microscopy (TEM) and immunofluorescence on microdissected and Ca2+ chelated crypts. Crypt cell type analysis was carried out separately on intact rat colon using light microscopy. TEM revealed a complete lack of either lamina propria cells or extracellular material in crypts isolated by either technique. TEM also revealed a subtle difference between the two isolation methods, with intact basal membranes in microdissected crypts but focal disruption of basal membranes in Ca2+- chelated crypts. Immunofluorescent stains for two basement membrane components (laminin and collagen type IV) revealed the presence of adherent basement membrane only on microdissected crypts; evidence that the plane of separation differs in these two preparations. Crypt cell type analysis on intact rat colon revealed an equal proportion of goblet cells in the right and left colon (approximately 50%) when measuring the middle 70% of the crypts - the area studied during crypt microperfusion. This morphologic analysis will increase our understanding of the observed physiology of isolated colonic crypts.     

Cell replacement and changing transport function in the neonatal pig colon.

1. Measurements of intracellular methionine concentration in pig colon, following in vitro incubation in methionine containine medium, have been carried out during the first 10 days of post-natal life. 2. The new-born pig colon concentrates methionine within its mucosa. Autoradiography of 3H-labelled phenylalanine shows it to be accumulated to greatest extent in cells located in the surface epithelium. 3. The ability of the colonic mucosa to concentrate methionine disappears during the first few days of post-natal life. 4. Radioactive thymidine, injected at birth, shows cell mitosis to be confined to the lower third of each colonic crypt. Labelled cells later migrate out of the crypts on to the surface epithelium. The cell replacement time is 105 h. 5. The time course for the fall in the ability of the pig colon to actively accumulate methionine corresponds to that predicted if cells synthesized from birth were unable to transport this amino acid. 6. The ability of the new-born pig colon to transport amino acids, though transient, may be physiologically important. The nature of the signal which changes the physiological function of cells synthesized post-natally remains to be determined.     

Developmental expression of two antigens associated with mouse intestinal crypts.

Two monoclonal antibodies were prepared against the duodenal mucosa of four-day-old mice (MIM-1/39 and MIM 1/130). The expression of the antigens was associated with the crypts of the small and large intestine in the fetus and adult. MIM-1/39 was present in epithelial cells of the intervillous areas in the small intestine at 17 and 18 days of gestation; afterwards its expression was detected only in crypt cells from birth to adulthood. Transition from the mouth of the crypts to intestinal villi was abrupt. Expression of MIM-1/39 was first detected at time of birth in the colon: In the adult, only crypt cells expressed the antigen and goblet cells were negative. Antigen MIM-1/130 was detected from 16 to 18 days of gestation in the small intestine, in the mesenchymal matrix lying under the intervillous epithelium. After birth, it was present in the pericryptal mesenchymal matrix. This antigen was also expressed at birth in the colon and remained in the pericryptal matrix in the adult. In vivo, multiple injections of an organic extract of rat amniotic fluid to mothers, starting at 14 days of gestation, induced a profound modulation in the pattern of expression of both antigens at 17 days of gestation: The pattern of expression was comparable to that observed at least 5 days after birth in untreated animals. The expression of both antigens before crypt appearance may reflect some molecular differentiation in preparation for the formation of crypts, while their association with differentiated crypts may indicate that they have a role in the maintenance of crypt functional and/or morphological integrity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ets2 regulates colonic stem cells and sensitivity to tumorigenesis

Ets2 has both tumor repressive and supportive functions for different types of cancer. We have investigated the role of Ets2 within intestinal epithelial cells in postnatal mouse colon development and tumorigenesis. Conditional inactivation of Ets2 within intestinal epithelial cells results in over representation of Ets2-deficient colon crypts within young and adult animals. This preferential representation is associated with an increased number of proliferative cells within the stem cell region and an increased rate of crypt fission in young mice that result in larger patches of Ets2-deficient crypts. These effects are consistent with a selective advantage of Ets2-deficient intestinal stem cells in colonizing colonic crypts and driving crypt fission. Ets2-deficient colon crypts have an increased mucosal thickness, an increased number of goblet cells, and an increased density. Mice with Ets2-deficient intestinal cells develop more colon tumors in response to treatment with azoxymethane and dextran sulfate sodium. The selective population of colon crypts, the altered differentiation state and increased sensitivity to carcinogen-induced tumors all indicate that Ets2 deficiency alters colon stem cell number or behavior. Ets2-dependent, epithelial cell-autonomous repression of intestinal tumors may contribute to protection from colon cancer of persons with increased dosage of chromosome 21.     

The effects of the carcinogen, 1,2-dimethylhydrazine,on turnover 3H-thymidine labeled cells from mucosal glands of mouse colon

1,2-dimethylhydrazine (DMH), administered weekly to mice for 20 weeks, induces tumors in the distal segment of colon. Tumors are preceded by enlargement of the mucosal glands resulting from increases in the number of total cells and ³H-thymidine labeled cells/crypt. Cells located in the crypt base normally undergo 2–3 divisions as they migrate toward the lumen, and they become post-mitotic in the upper crypt. It is not known if cells in these eniarged crypts have rates of turnover similar to cells in normal crypts. Groups of w/s female mice were treated with DMH (20 mg/kg body wt) for 3,8, or 16 weeks; controls were given 0.001 M EDTA. After treatment, the animals were injected with ³H-thymidine and killed one hour or 1,2,4,7 or 17 days later. Autoradiographs were prepared from sections of distal colon. The total cells/crypt column in 30 crypts/animals were counted. Crypts were divided into 10 equal segments based on the crypt length and the labeled cells/segment were counted. The relative number of labeled cells and the distribution of these cells within crypts were similar in DMH-treated and control animals after one hour. However, as the cells migrated toward the lumen, the number of labeled cells doubled after 2 days and tripled after 4 days in DMH-treated animals but only doubled during the 4 days in controls. This difference was caused by retention of an increased number of dividing cells in the lower 4 segments of the crypts and suggests an increase in those cells that divide twice. In addition, increased numbers of labeled cells were retained in the upper 3 segments of DMH-treated animals after 4 days. These findings indicate that the crypt cells of DMH-treated animals are generally more immature than those of controls and this immaturity contributes to the enlargement of mucosal glands during carcinogenesis.     

Colonic mucosal changes in nude mice associated with orthotopic xenografts of human colon cancer cells

Summary We used the nude mouse tumour xenograft model to study the pathogenesis of mucosa alterations in the large bowel surrounding a carcinoma. In mouse colonic mucosa overlying HT-29 colonic carcinoma xenografts in the caecum, the crypts were elongated in comparison with those in distant mucosa and also frequently showed a shift towards sialomucin production. These features, which are comparable with socalled transitional mucosa (TM) in man, were absent in control animals inoculated with Indian Ink instead of HT-29 cells. Although the localization of the proliferative cell compartment in mouse colonic mucosa overlying HT-29 xenografts appeared to be confined to the lower half of the crypt as in normal mucosa, the relative length of the DNA synthesizing cell compartment along the crypts was slightly elongated. These data strongly suggest that TM should be regarded as a secondary phenomenon rather than a premalignant change in large intestinal epithelium and that higher proliferative activity of epithelial cells contributes little to the elongation of crypts in TM.     

The ultrastructure of transmissible murine colonic hyperplasia.

Transmissible murine colonic hyperplasia was examined ultrastructurally by sequential sampling after inoculation with the etiologic agent, Citobacter freundii. Light-microscopic changes in the descending colon of inoculated mice were correlated with scanning and transmission electron-microsopic findings. Bacteria were attached to the surface of the mucosa between 4 and 10 days after inoculation. Hyperplasia was most severe at 16 days and thereafter underwent regression. Regression was preceded by extrusion of infected cells from the surface mucosa and replacement by immature hyperplasia epithelium. Hyperplastic epithelium throughtout the crypt resembled undifferentiated crypt cells of controls. By 45 days, the mucosa had reverted to near normal structure. The results suggest that severe mucosal proliferation with minimal inflammatory change resulted from attachment of bacteria to the surface mucosal epithelium. The hyperplastic response appeared to be a defense mechanism of replacing infected cells with newly migrated, uninfected epithelium.     

Effect of added dietary calcium on colonic epithelial-cell proliferation in subjects at high risk for familial colonic cancer

We studied the frequency and distribution of proliferating epithelial cells lining colonic crypts in 10 subjects at high risk for familial colonic cancer, before and after oral supplementation of their conventional diets with 1.25 g of calcium as calcium carbonate. Patterns of cell proliferation were defined by dividing the colonic crypt into longitudinal compartments and comparing the numbers and fractions of tritiated thymidine--labeled epithelial cells in the various compartments. Before dietary supplementation with calcium, the profile of proliferating epithelial cells in the colonic crypts was comparable to that previously observed in subjects who had had familial colonic cancer. Two to three months after supplementation had been started, proliferation was significantly reduced and the profile of the colonic crypts approached that previously observed in subjects at low risk for colonic cancer. Our findings indicate that oral calcium supplementation induces a more quiescent equilibrium in epithelial-cell proliferation in the colonic mucosa of subjects at high risk of colon cancer, similar to that observed in subjects at low risk.     

Morphometrical and cell kinetic studies of normal human colorectal mucosa. Comparison between the proximal and the distal large intestine

Morphometric and cell kinetic studies were performed on normal mucosa in 30 specimens of surgically resected colorectum. The average crypt length was 372 +/- 57 microns in the proximal colon and 506 +/- 65 microns in the distal colon, and the average cell numbers per crypt column in these regions were 76.4 +/- 8.9 and 80.3 +/- 8.8, respectively. In the proximal and distal colon, goblet cells constituted 23.3 +/- 3.4% and 25.2 +/- 4.0%, respectively, of the total cells in each crypt, and in both regions entero-chromaffin cells constituted about 1%. The labeling indices of the proximal and distal colon were 9.4 +/- 3.9% and 8.2 +/- 2.2%, respectively. Combined microautoradiography and periodic acid-Schiff reaction on selected cases revealed that the labeling indices of columnar cells and goblet cells were 11.0 +/- 2.0% and 7.0 +/- 3.2%, respectively. It was suggested that the increased number of larger goblet cells in crypts of the sigmoid colon and rectum resulted in an increase of crypt length and a decrease in the labeling index. These results provide information on the morphological and cell kinetic characteristics of normal mucosa of the colon and rectum.     

Dietary calcium supplementation increases apoptosis in the distal murine colonic epithelium

BACKGROUND: Increased dietary calcium might reduce colorectal cancer risk, possibly by reduction of colonic epithelial hyperproliferation, but not all studies have demonstrated this. Little is known about the effects of calcium on colonic apoptosis. AIM: To quantify the effects of increasing calcium on apoptosis and cell proliferation in normal murine colonic crypt epithelium. METHODS: Twenty one day old male C57B1/6 mice were fed either control AIN-76 diet (0.5% calcium wt/wt; n = 10) or the same supplemented with calcium carbonate (1.0% calcium; n = 10) for 12 weeks. Apoptotic cells in proximal and distal segments were counted and expressed as an apoptotic index (AI: frequency of apoptosis/100 longitudinal crypts). The bromodeoxyuridine (BrdU) labelling index was also determined. Differences were analysed by the student's t test. RESULTS: In control animals, the AI was significantly higher in the caecum/proximal colon (mean, 28.6; SEM, 2.0) compared with the distal colon (mean, 19.9; SEM, 1.8; p = 0.004). In the calcium treated group, the AI in the caecum/proximal colon (mean, 30.6; SEM, 1.7) was similar to controls (p = 0.71) but the AI in the distal colon was significantly greater (mean, 32.6; SEM, 1.8; p = 0.001) than in control mice and was raised to values similar to those in the proximal colon. Calcium was also associated with reduced crypt cellularity and, in the proximal colon, a downward shift in the crypt position at which apoptosis occurred. There were no significant differences in the BrdU labelling index between groups or between proximal and distal colonic segments in each group. CONCLUSIONS: Increased dietary calcium is associated with the induction of apoptosis in normal mouse distal colonic epithelium without affecting cell proliferation. This might contribute to its putative chemopreventive role in colorectal carcinogenesis. Whether this effect is direct or indirect requires further study.     

Basal lamina fenestrations in the human colon: transmission and scanning electron microscope study

Basal lamina at the interface between colonic epithelial cells and the lamina propria was exposed by incubating colonic specimens in 1% boric acid solutions. Examination of this epithelial-stromal interface by scanning electron microscopy (SEM) showed a smooth, slightly undulating basal lamina covering crypts and luminal surfaces. The basal lamina on the luminal surfaces had numerous round or ovoid fenestrations, most measuring 2.5-4.0 microns. These were continuous with channels in the collagen fiber network of the lamina propria. Except very near the surface, no fenestrations were found in the basal lamina lining the crypts. Transmission electron microscopy (TEM) of serial thin sections of colonic mucosa without the epithelial cells removed showed only a few actual basal lamina fenestrations. Rarely, epithelial cell processes extended into the lamina propria through the basal lamina. Most of the fenestrations seen by SEM appeared to correspond spatially by TEM to foci of close contact between the basal lamina and underlying fibroblastic cell processes. At these sites the basal lamina and fibroblastic cell process might be removed along with the overlying epithelial cells during processing with boric acid. These data support functional differences in epithelial-stromal interaction between cell populations lining the luminal surface and those making up the crypt lining and pericryptal fibroblast sheath. The TEM findings demonstrate that the human colonic basal lamina is not absolutely continuous and that the development of basal lamina fenestrations and epithelial cell processes extending into the lamina propria is not pathognomonic of neoplastic transformation and stromal invasion.     

Morphometrical and Cell Kinetic Studies of Normal Human Colorectal Mucosa

Morphometric and cell kinetic studies were performed on normal mucosa in 30 specimens of surgically resected colorectum. The average crypt length was 372 ± 57μm in the proximal colon and 506 ± 65μm in the distal colon, and the average cell numbers per crypt column in these regions were 76.4 ± 8.9 and 80.3 ± 8.8, respectively. In the proximal and distal colon, goblet cells constituted 23.3 ± 3.4% and 25.2 ± 4.0%, respectively, of the total cells in each crypt, and in both regions entero chromaffin cells constituted about 1%. The labeling indices of the proximal and distal colon were 9.4 ± 3.9% and 8.2 ± 2.2%, respectively. Combined microautoradiography and periodic acid Schiff reaction on selected cases revealed that the labeling indices of columnar cells and goblet cells were 11.0 ± 2.0% and 7.0 ± 3.2%, respectively. It was suggested that the increased number of larger goblet cells in crypts of the sigmoid colon and rectum resulted in an increase of crypt length and a decrease in the labeling index. These results provide information on the morphological and cell kinetic characteristics of normal mucosa of the colon and rectum. Acta Pathol Jpn 39: 725 730, 1989.     

The presence of specialized epithelial cells on the bronchus-associated lymphoid tissue (BALT) in the mouse

The aggregation of lymphoid cells in the bronchial mucosa has been named the bronchus-associated lymphoid tissue (BALT) and investigated in comparison with the gut-associated lymphoid tissue (GALT). To elucidate precisely the structure and function of the BALT, the present study examined the age-related change in the mouse BALT by light microscopy. We also observed the characteristics of the overlying epithelium, especially the lectin-binding properties of the epithelial cells, by the combined use of light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By LM, lymphoid aggregates were not recognizable in the bronchial mucosa of young (8-10 week-old) mice, while they were commonly found at the second to fourth branching portions of the bronchial tree in older (32-40 week-old) mice. The epithelium overlying the lymphoid aggregates of the mature mice often contained a large number of mononuclear cells. Lectin cytochemistry revealed that UEA1 (Ulex europaeus agglutinin 1) positive cells were not only restricted to the overlying epithelium of the BALT in the older mice but also found in a cell group in the mucous epithelium at the branching portions in the young mice. Comparison between the LM and SEM images of the UEA1-stained whole mount specimens clarified the surface morphology of the lectin-stained epithelial cells, showing them to be non-ciliated cells with a large number of short microvillous projections on the apical surface. TEM studies further demonstrated that the UEA1 reaction products appeared on the plasma membrane of the non-ciliated cells which often enfolded lymphocytes in the old mice. Latex microbeads, which were administrated intratracheally, were selectively taken up by the UEA1-positive cells of the BALT. These results indicate that the mouse BALT has specialized epithelial cells similar to the UEA1 positive M cells in the GALT and probably functions as a part of the mucosal immune system. This study also showed the possibility that the UEA1 positive cells appear in the mucous epithelium before the formation of the BALT.     

Epithelial cell dynamics in rabbit cecum and proximal colon P1.

The large intestine of mammals has long been viewed as an osmoregulatory organ, and evidence suggests that fluid and solute transport mechanisms within the intestine are heterogeneous, varying depending on the particular segment involved. Variations in function are often matched by morphological correlates, but despite the widespread use of rabbit large intestine as an experimental model, there is a lack of knowledge about the cellular makeup and dynamics in the colonic mucosal epithelium. The presence of mitotic figures and immunohistochemical localization of proliferating cell nuclear antigen (PCNA) were used to identify the proliferative zone(s). Cellular migration patterns were determined through the use of the thymidine analog 5-bromo-2-deoxyuridine (BrdU) over a 24-, 48-, and 72-hr period. Apoptotic nuclei were identified utilizing terminal deoxynucleotidyl transferase d-UTP nick-end labeling (TUNEL). Both cecum and the initial portion of the proximal colon (P1) exhibited a proliferative zone at or near the crypt base, and migration proceeded upwards toward the surface epithelium lining the intestinal lumen, where apoptosis occurred Turnover time of crypt columnar cells was determined to be about 3 days; that of mucous cells was estimated to be about 5 weeks. Rabbit cecum and proximal colon P1 are similar in their cellular morphology and epithelial cell kinetics. In both, the major proliferative zone is located at or near the crypt base, from which crypt columnar cells migrate toward the lumenal surface epithelium over a period of 3 days. Goblet cell turnover rate is much slower than that of columnar cells.     

Identification and quantification of aberrant crypt foci and microadenomas in the human colon.

The objective of the present study was to determine whether aberrant crypt foci (ACF) similar to those observed in the colons of experimental animals exposed to colon carcinogens could be identified and quantified in the human colon. Twenty-seven colon resections from patients affected by familial adenomatous polyposis (FAP, five cases), colorectal cancer (CRC, 12 cases), and benign diseases of the large bowel (BD, 10 cases) were collected from a pathology repository or immediately after operation. Ten or more 1-cm2 formalin-fixed, methylene-blue--stained samples of colonic mucosa from each colon were scored under light microscopy for ACF. The number of ACF per cm2 and the number of crypts per ACF for each colon were calculated. The average number of ACF per cm2 in the FAP group (20 +/- 19, mean +/- SD) was significantly higher (P less than 0.01) than those of the CRC (0.37 +/- 0.41) and BD (0.18 +/- 0.35) groups. At least one ACF was found in every colon resection from CRC patients and in six out of 10 colon resections from the BD group. The average number of crypts per ACF ranged from five to 35 with absolute values from 1 to over 100. Fifty-five histologic specimens, 43 with ACF of various size and 12 without, were prepared by sectioning the colon parallel to the mucosal surface. There was a close correlation between the number of crypts per ACF in each specimen as scored by methylene-blue and histologic examination. Twenty-six aberrant crypt foci displayed dysplasia as evident by histologic analysis. In these instances we feel the term microadenoma is appropriate and, using this unique approach of examining the human colon, they can be easily identified and quantified. These lesions may well be precursors for adenomatous polyps and colorectal cancer.     

Colonic aberrant crypts may originate from impaired fissioning: relevance to increased risk of neoplasia

Colonic aberrant crypt foci (ACF) can be identified on the unembedded mucosal surface as clusters of abnormal crypts with enlarged, surface opening. Because dysplasia is frequent, and may be a precursor of carcinoma, epithelial changes have been well studied. However, the basis for the distinctive changes in crypt architecture remain unclear. We hypothesized that some of the architectural alterations of aberrant crypts may reflect impaired fissioning during normal crypt duplication cycles. Fissioning begins at the crypt base. Using morphometric and immunocytochemical approaches, we examined 55 human ACF, both dysplastic and nondysplastic, for their architectural features. Non-ACF mucosa was compared. Microscopically, all lesions contained crypts that were attached, paired, dilated, and angulated. In 3 dimensions, these features related to multiple, individual complexes of connected crypts, referred to as connected crypt structures (CCSs). CCSs terminated in enlarged surface openings (2 to 5 x normal) which are morphometrically equivalent to the macroscopic aberrant crypts (P > .1). These openings trap marker dye. Support for an origin of CCSs in impaired basal fissioning is 3-fold. Crypt profiles in ACF are twice as frequent in basal mucosa as superficially (P < .001); in normal mucosa, the ratio is 1. In a CCS with vertically connected, co-planar crypts, the upper parent crypt diameter was the sum of diameters of inferiorly attached daughter crypts (P > .1). Proliferating cell marker, Ki-67, is not expressed at attachment points. In non-ACF mucosa, isolated CCSs consistently occur at foci of mechanical crypt distortion such as mucosal folds. We conclude that a CCS is a fundamental component of ACF of all histotypes. Impairment of normal crypt fissioning is probably a major factor in the histogenesis of CCSs, which often occurs in settings of mechanical distortion of the mucosa. The pathological significance of this process may be in the formation of enlarged crypt openings. The latter could trap dietary carcinogens as they trap dye, and thereby predispose the CCS to dysplasia.     

Apoptosis, anoikis and their relevance to the pathobiology of colon cancer

The maintenance of a constant number of cells in an adult organism is a tightly regulated process. This is particularly important in organs where cells are in a constant rate of renewal during the entire lifespan. In these organs, cell number homeostasis is the direct consequence of a balance between cell proliferation and apoptosis. The colonic epithelium is an example of such a site and the high prevalence of colon cancer makes the understanding of cell number homeostasis more important to define. Normal colonic epithelium is organized in crypts where cell proliferation, migration, differentiation and apoptosis are topographically organized in a linear fashion along the crypt axis. Normal colonic crypts are composed of stem cells at the base, a proliferation and a differentiation zone in the lower third of the crypt, a migration zone in the upper two-thirds, and the surface epithelium where senescent cells are eliminated by apoptosis. Globally, apoptosis can be defined as a normal process of cell suicide, critical for development and tissue homeostasis. Colonic epithelial cells migrate from the base of the crypt to the surface epithelium in 6-7 days. The normal architecture of the crypt is maintained by a balance between cell proliferation at the base and apoptosis at the top of the crypt and surface epithelium.     

Ontogeny of cell proliferation and DNA synthesis in rat colon: role of glucocorticoids

This study was undertaken to determine whether the rat colon exhibits ontogenic changes in epithelial cell proliferation and DNA synthesis during growth. DNA synthesis was measured at intervals after birth in four colonic segments by the incorporation rates of [3H]thymidine. The labeled crypt cell index was determined by radioautography. New findings from our study are that 1) in each colonic segment of suckling rats, [3H]thymidine incorporation rate overshot the adult levels (49-119%) with a peak occurring at day 14 postpartum, 2) between days 14 and 20, the incorporation rates declined sharply to adult values and remained thereafter unchanged until adulthood; during the same period, the labeled and mitotic index decreased, respectively, from 52 to 19% and from 3.58 to 1.43%, 3) the decrease in DNA synthesis and in cell proliferation rates was concomitant with an upsurge in plasma total corticosterone initiated on day 14, and 4) treatment of 10-day-old sucklings with physiological doses of hydrocortisone for 4 consecutive days significantly depressed (P less than 0.01) colonic DNA content and DNA synthesis rates to levels about 45-67% of the control values. These data indicate that growth of the colon may be under the control of glucocorticoid secretion at the weaning period.