Establishment of a three-dimensional culture system of gastric stem cells supporting mucous cell differentiation using microfibrous polycaprolactone scaffolds.

OBJECTIVES: To generate various polycaprolactone (PCL) scaffolds and test their suitability for growth and differentiation of immortalized mouse gastric stem (mGS) cells. MATERIALS AND METHODS: Non-porous, microporous and three-dimensional electrospun microfibrous PCL scaffolds were prepared and characterized for culture of mGS cells. First, growth of mGS cells was compared on these different scaffolds after 3 days culture, using viability assay and microscopy. Secondly, growth pattern of the cells on microfibrous scaffolds was studied after 3, 6, 9 and 12 days culture using DNA PicoGreen assay and scanning electron microscopy. Thirdly, differentiation of the cells grown on microfibrous scaffolds for 3 and 9 days was analysed using lectin/immunohistochemistry. RESULTS: The mGS cells grew preferentially on microfibrous scaffolds. From 3 to 6 days, there was increase in cell number, followed by reduction by days 9 and 12. To test whether the reduction in cell number was associated with cell differentiation, cryosections of cell-containing scaffolds cultured for 3 and 9 days were probed with gastric epithelial cell differentiation markers. On day 3, none of the markers examined bound to the cells. However by day 9, approximately, 50% of them bound to N-acetyl-d-glucosamine-specific lectin and anti-trefoil factor 2 antibodies, indicating their differentiation into glandular mucus-secreting cells. CONCLUSIONS: Microfibrous PCL scaffolds supported growth and differentiation of mGS cells into mucus-secreting cells. These data will help lay groundwork for future experiments to explore use of gastric stem cells and PCL scaffolds in stomach tissue engineering.

Functional reentry and circus movement arrhythmias in the small intestine of normal and diabetic rats.

In a few recent studies, the presence of arrhythmias based on reentry and circus movement of the slow wave have been shown to occur in normal and diseased stomachs. To date, however, reentry has not been demonstrated before in any other part of the gastrointestinal system. No animals had to be killed for this study. Use was made of materials obtained during the course of another study in which 11 rats were treated with streptozotocin and housed with age-matched controls. After 3 and 7 mo, segments of duodenum, jejunum, and ileum were isolated and positioned in a tissue bath. Slow wave propagation was recorded with 121 extracellular electrodes. After the experiment, the propagation of the slow waves was reconstructed. In 10 of a total of 66 intestinal segments (15%), a circus movement of the slow wave was detected. These reentries were seen in control (n = 2) as well as in 3-mo (n = 2) and 7-mo (n = 6) diabetic rats. Local conduction velocities and beat-to-beat intervals during the reentries were measured (0.42 ± 0.15 and 3.03 ± 0.67 cm/s, respectively) leading to a wavelength of 1.3 ± 0.5 cm and a circuit diameter of 4.1 ± 1.5 mm. This is the first demonstration of a reentrant arrhythmia in the small intestine of control and diabetic rats. Calculations of the size of the circuits indicate that they are small enough to fit inside the intestinal wall. Extrapolation based on measured velocities and rates indicate that reentrant arrhythmias are also possible in the distal small intestine of larger animals including humans.

Slow wave propagation and plasticity of interstitial cells of Cajal in the small intestine of diabetic rats.

The number of myenteric interstitial cells of Cajal (ICC-MY), responsible for the generation and propagation of the slow wave in the small intestine, has been shown to decrease in diabetes, suggesting impairment of slow-wave (SW) propagation and related motility. To date, however, this expected decrease in SW propagation has neither been recorded nor analysed. Eleven rats were treated with streptozotocin and housed in pairs with 11 age-matched control animals. After 3 or 7 months, segments of duodenum, jejunum and ileum were isolated and divided into two parts. One part was processed for immediate freezing, cryosectioning and immunoprobing using anti-c-Kit antibody to quantify ICC-MY. The second part was superfused in a tissue bath, and SW propagation was recorded with 121 extracellular electrodes. In addition, a cellular automaton was developed to study the effects of increasing the number of inactive cells on overall propagation. The number of ICC-MY was significantly reduced after 3 months of diabetes, but rebounded to control levels after 7 months of diabetes. Slow-wave frequencies, velocities and extracellular amplitudes were unchanged at any stage of diabetes. The cellular automaton showed that SW velocity was not linearly related to the number of inactive cells. The depletion of ICC-MY is not as severe as is often assumed and in fact may rebound after some time. In addition, at least in the streptozotocin model, the initial reduction in ICC-MY is not enough to affect SW propagation. Diabetic intestinal dysfunction may therefore be more affected by impairments of other systems, such as the enteric system or the muscle cells.

Sequential alterations in gastric biopsies and tumor tissues support the multistep process of carcinogenesis.

Gastric cancer is the second leading cause of cancer related death worldwide. In the UAE, recent data show an increase in the number of patients with gastric cancer highlighting the need for greater understanding of its pathogenesis. Gastric cancer is generally believed to develop on a background of chronic atrophic gastritis which eventually leads to intestinal metaplasia, dysplasia and finally invasive carcinoma. Recently this multistep process of carcinogenesis has been challenged. Therefore, the aim of this study is to define alterations in antral mucosal biopsies and cancer tissues to investigate whether they could be used to assemble a tissue array supporting the multistep model of carcinogenesis. Gastric mucosal tissues were obtained from informed individuals undergoing endoscopy (for upper gastrointestinal symptoms) and gastrectomy (for adenocarcinoma) in Tawam Hospital. All tissues were processed for microscopic examination. Eighty nine antral biopsies were categorized as: normal (33%), mild superficial gastritis (34%) and severe atrophic gastritis (33%). About 5% of the latter exhibited evidence of intestinal metaplasia. Cancer tissues obtained from three patients were microscopically examined in three regions: safe resected margin, tumor edge and tumor center. Progressive changes in mucosal thickness, dysplasia and cellular transformation were observed, and when compared with alterations in biopsies, all appeared to represent a continuum of progression toward invasive adenocarcinoma. In conclusion, the tissue array presented in this study supports the multistep process of gastric carcinogenesis and will be helpful in examining the expression pattern of tumor markers or molecules that could help in the early detection of gastric cancer.

A third troponin T blood sample is not cost-effective in patients with suspected non-ST segment elevation acute coronary syndrome.

BACKGROUND: The diagnosis of acute myocardial infarction requires troponin assessment in at least two blood samples 6-9 hours apart, with an optional third sample 12-24 hours after admission if suspicion is high. Yet, in many institutions, this third sample is routinely drawn. This study aimed to evaluate cost-effectiveness of this third sample of troponin. METHODS: A total of 534 patients with possible Non ST-Elevation Acute Coronary Syndrome (NSTE-ACS) were included. Blood samples for cardiac TroponinT (cTnT) were obtained on arrival, after 6-9 hours, and 12-24 hours after admission. The costs of cTnT analysis, and hospital stay were calculated. RESULTS: Of the 534 patients, 124 had at least one elevated cTnT value. Among these, four patients (3.2%) had cTnT values increased only in the third sample. Based on their risk profile and/or ECG changes, these four patients were eligible for referral to coronary angiography even before the result of the third sample became available. The number of patients whose length of stay was extended solely because of the third sample was 275. Incremental cost of the third blood sample: [534 patients × Euro (EUR) 12 per cTnT analysis] + [275 patients × 0.5 day × EUR 1,550] = EUR 219,533. Approximately 1400 patients with suspected NSTE-ACS are admitted to our department each year. Thus, the total cost per year is: (1,400/534) × EUR 219,533 = EUR 575,555. CONCLUSION: A third troponin sample adds no vital information regarding patients' treatment or investigations plan. On the contrary, it may lead to an unnecessary extension of the admission period and increased costs.

Amplification and invasiveness of epithelial progenitors during gastric carcinogenesis in trefoil factor 1 knockout mice.

OBJECTIVE: It is not known whether or not epithelial progenitors of the pyloric antrum are involved in gastric carcinogenesis. Normally, these progenitors give rise to two main cell lineages: pit and gland mucous cells. This study was designed to examine the changes that occur in pyloric antral mucous cell lineages and their progenitors during development of gastric adenoma and carcinoma in trefoil factor 1 (TFF1) knockout mice. MATERIALS AND METHODS: Pyloric antral mucosal tissues of TFF1 knockout mice at ages from 3 days to 17 months were processed for histochemical analysis using Ulex europaeus and Grifforia simplifolica lectins as markers for pit and gland mucous cells, respectively. The dividing epithelial progenitors were identified by using immunohistochemical and electron microscopy techniques. RESULTS: TFF1 loss was associated with amplification of both mucus-secreting pit and gland cells. Both lectins examined bound not only to mature mucous cells, but also to most of epithelial progenitors which gradually amplified with age and frequently were seen in mitosis. Analysis of 12- to 17-month-old TFF1-deficient stomachs revealed occasional groups of poorly differentiated mucosal cells with features similar to those of epithelial progenitors (or stem cells), in the basal portion of the antral mucosa. These cells eventually invaded the muscularis mucosa while maintaining some capacity to differentiate. CONCLUSION: This study shows that the progenitors of pit and gland mucous cells contribute to gastric carcinogenesis in the pyloric antrum of TFF1 knockout mice, strongly supporting the concept of stem cell origin of cancer.

Establishment of a gastric epithelial progenitor cell line from a transgenic mouse expressing the simian virus 40 large T antigen gene in the parietal cell lineage.

OBJECTIVE: In this study the gastric mucosa of transgenic mice expressing the simian virus 40 large T antigen gene in the parietal cell lineage is used to establish and characterize a new epithelial progenitor cell line. In these mice, proliferation and amplification of preparietal cells preclude their maturation into acid-secreting parietal cells leading to achlorohydria, hyperplasia, dysplasia and eventually gastric adenocarcinoma. MATERIALS AND METHODS: Enzymatically dispersed gastric epithelial cells were cultured, cloned and screened using immunohistochemical methods, for expression of a variety of biomarkers of differentiated pit, parietal, enteroendocrine and neck/zymogenic cells. RESULTS: A biomarker-deficient cell line whose ultrastructural features resembled those of mouse gastric epithelial progenitor cells was established. Treatment with either hydrocortisone or oestrogen significantly enhanced proliferation of these cells, whereas retinoic acid inhibited their growth. No change in differentiation was detected with any of these treatments; however, when these cells were injected subcutaneously into nude mice, they proliferated to form tumours and undergo partial differentiation towards parietal cell lineage. CONCLUSION: This mouse gastric epithelial progenitor cell line could be useful as an in vitro model to study growth properties, proliferation and differentiation of a subpopulation of gastric epithelial progenitor cells and also to study gastric carcinogenesis.

Expression of TFF3 during multistep colon carcinogenesis.

The pathogenesis of colon cancer is not well understood. This common type of cancer is generally believed to occur in a multistep process which involves alterations of various tumor suppressor genes and oncogenes during the progression through benign lesions towards carcinoma. TFF3 is a product of the colonic epithelium and has been implicated in colonic mucosal protection and also in the aggressiveness of colon cancer cells. The aim of this study was to analyze the expression of TFF3 during propagation towards cancer development in the human colon. Colonic tissues representing colitis, adenomatous polyposis, tubulovillous adenoma, and mucoid/adeno-carcinomas were processed for immunohistochemistry using an antibody specific for human TFF3. The results were correlated with those of PCNA-labeling, quantified, and compared with those of control tissues obtained from the safe margin of macroscopically normal colonic mucosa of patients with colon cancer. The data showed marked down-regulation of TFF3 expression in adenomatous polyposis, then TFF3 expression returns to about control level during adenoma and remains high during mucoid- and adeno-carcinomas. Colonic tissues with highly invasive cancer cells were characterized by statistically significant down-regulation of TFF3 expression. The changes observed in expression of TFF3 showed an inverse correlation with cell proliferation and suggest that it might play a protective role against colon carcinogenesis.

Trefoil factor 1 is required for the commitment programme of mouse oxyntic epithelial progenitors.

BACKGROUND: Trefoil factor 1 (TFF1/pS2) is a major secretory product of the stomach and TFF1 knockout mice constantly develop adenomas and occasional carcinomas in the pyloric antrum. AIM: To analyse the role of TFF1 in the differentiation of gastric epithelial cell lineages using oxyntic mucosae from normal and TFF1 knockout mice. METHODS: The various cell lineages were labelled using specific markers of pit, neck, parietal, and enteroendocrine cells. Patterns of TFF1, TFF2, and TFF3 expressions were defined using western blotting, immunohistochemistry, and/or immunogold electron microscopy. RESULTS: In normal mice, starting from postnatal day 1 (P1), TFF1 and TFF2 were produced by mucus secreting cells of the developing epithelium. At P7, TFF3 expression occurred in pit and parietal cells. When oxyntic glands were compartmentalised, at P21 and in older mice, TFF1 and TFF2 were expressed in pit and neck cells, respectively, and TFF3 was no longer in parietal cells but became a feature of zymogenic cells. In TFF1 deficient mice, alteration of oxyntic epithelial differentiation became obvious at P21, showing significant amplification of pit cells at the expense of parietal cells. At the molecular level, lack of TFF1 induced dramatic inhibition of TFF2 expression and more precocious TFF3 expression. CONCLUSION: In the oxyntic mucosa, all three TFFs are produced in a lineage specific manner and TFF1 is essential in maintaining the normal commitment programme of epithelial progenitors.

Characterization of the rabbit gastric epithelial lineage progenitors in short-term culture.

Little is known about the mechanisms that establish and maintain the proliferation and differentiation programs of the gastric epithelium. This is largely due to the complexity of the gastric epithelial units and the presence of the different epithelial lineage progenitors among heterogeneous populations of various mature cell types. This study is undertaken to establish an in vitro system highly enriched for gastric epithelial lineage progenitors. By using adult male rabbits, a simple method of isolating gastric epithelial cell fractions enriched in lineage progenitors was applied. Cultured cells labeled with bromodeoxyuridine were characterized by using lectin and immunohistochemical studies at light- and electronmicroscopical levels. Analysis of primary cultures derived from the progenitor cell region of the epithelial units revealed that this system can support the proliferation and some of the differentiation programs of the progenitor cells. Cultured cells can be maintained for up to 5 days, while retaining most of the morphological features, molecular markers, and dynamic behavior of gastric epithelial progenitors. Differential cell counts at 1-day culture revealed that, while the undifferentiated progenitors formed about 30% of all attached cells, pre-pit, pit, and preparietal cells represented about 30%, 10%, and 2%, respectively. By 3 days, the increase in the percentage of pit and preparietal cells up to 25% and 9%, respectively, reflected their production in vitro. In conclusion, we have established a culture system enriched for gastric epithelial lineage progenitors that would hopefully allow the identification of factors and mechanisms involved in controlling their proliferative activity and differentiation pathways.

Blocking of histamine H2 receptors enhances parietal cell degeneration in the mouse stomach.

The effects of the histamine H2 receptor antagonist, ranitidine, on parietal cell lineage was studied in the mouse stomach by using light and electron microscopy techniques. Mice were continuously infused for 15, 30, and 42 hr with ranitidine. Semithin sections examined under the light microscope revealed spherical light areas in the cytoplasm of parietal cells which in thin sections under the electron microscope appeared to be vacuoles. Cells were categorized as normal, altered and damaged. While altered cells were characterized by dilated canaliculi and vacuoles, the damaged cells showed signs of necrosis or apoptosis. In control mice, altered and damaged parietal cells were consistently few and only found in the pit or base regions of the epithelial units. After 15-hr-treatment with ranitidine, 40% of the parietal cells were altered. After 30 hr infusion, altered parietal cells became 53% of the examined population, and after 42 hr, 72% of the parietal cells were affected (42% altered and 30%, damaged). The gradual increase in parietal cell vacuolation was associated with an increase in the census of pre-parietal cells. Some mice were allowed to recover from treatment for 4 days. The appearance of normal parietal cells and disappearance of damaged cells was observed and the gastric glands became morphologically normal. In conclusion, inhibiting acid secretion by blocking the histamine H2 receptors, enhanced not only the degenerative elimination of parietal cells but also the production of pre-parietal cells and thus, the recovery of the population was prompt.

Vitamin A deficiency in mice enhances the colonic level of purine enzyme activity.

BACKGROUND: Vitamin A is an important nutritional factor that regulates normal growth and functions of epithelial cells of the gastrointestinal tract. OBJECTIVE: The objective of this study was to examine the role of vitamin A on the histological and biochemical changes in the colon of mice. METHODS: To address this issue, vitamin A deficiency (VAD) was developed in mice by placing them on a VAD diet from weaning up to 120-170 days. Infiltration of inflammatory cells in the colon was determined histologically. Activities of adenosine deaminase, adenylate deaminase, purine nucleoside phosphorylase and myeloperoxidase were determined. RESULTS: VAD in mice induced a significant increase in the number of mast cells per 100 crypts. There was also an abundance of other connective tissue cells such as plasma cells, lymphocytes and neutrophils around the crypts in the lamina propria. The colonic activity of adenosine deaminase and adenylate deaminase was increased due to VAD, whereas purine nucleoside phosphorylase activity remained unchanged. Immunohistochemical analysis showed an increased expression of adenosine deaminase in VAD mice colon. The increase in myeloperoxidase activity was not statistically significant. CONCLUSIONS: VAD causes upregulation of purine enzyme, which together with an increased number of inflammatory cells might exacerbate colonic injuries in VAD condition.

Identification and characterization of a novel gastric peptide hormone: the motilin-related peptide.

BACKGROUND & AIMS: This study looked for new proteins with expression restricted to the gastric epithelium that may provide insight to the differentiation and function of the gastric unit. METHODS: A novel complementary DNA was isolated and sequenced, and its expression was examined in mouse tissues at both messenger RNA and protein levels. Subcellular localization was studied using immunoelectron microscopy. The posttraductional processing of the protein was analyzed in vitro by protein microsequencing and in vivo by Western blotting. RESULTS: We identified a novel protein that is mainly expressed by the secretory granules of the stomach enteroendocrine cells. This protein has sequence similarity with prepromotilin, the precursor of the motilin hormone and the motilin-associated peptide. As for the prepromotilin, a posttraductional maturation leads to a secreted peptide that is further cleaved at a dibasic site and gives rise to the motilin-related peptide (MTLRP) and MTLRP-associated peptide. CONCLUSIONS: We have identified and characterized a novel gene encoding the preproMTLRP protein. MTLRP presents similarity to motilin and is specifically expressed by enteroendocrine cells of the stomach and therefore represents a novel hormone.

Helicobacter pylori attaches to NeuAc alpha 2,3Gal beta 1,4 glycoconjugates produced in the stomach of transgenic mice lacking parietal cells.

Helicobacter pylori infection of the human stomach is associated with altered acid secretion, loss of acid-producing parietal cells, and, in some hosts, adenocarcinoma. We have used a transgenic mouse model to study the effects of parietal cell ablation on H. pylori pathogenesis. Ablation results in amplification of the presumptive gastric epithelial stem cell and its immediate committed daughters. The amplified cells produce sialylated oncofetal carbohydrate antigens that function as receptors for H. pylori adhesins. Attachment results in enhanced cellular and humoral immune responses. NeuAc alpha 2,3Gal beta 1,4 glycoconjugates may not only facilitate persistent H. pylori infection in a changing gastric ecosystem, but by promoting interactions with lineage progenitors and/or initiated cells contribute to tumorigenesis in patients with chronic atrophic gastritis.

Lineage commitment and maturation of epithelial cells in the gut.

The dynamic concepts of gut epithelial cell populations which heralded the era of modern gut cell biology have been generally substantiated by recent studies and are still being correlated with functional properties. Multipotent stem cells are anchored in specific locations along the gut epithelium where decisions concerning proliferation and differentiation/migration pathways are made. Stem cells give rise to lineage precursors which transform into transit cells and sequentially express lineage specific features during their differentiation program. Morphologically and functionally mature cells along the gut epithelium are dynamically heterogeneous. 1) The squamous lineage of the esophagus forms a stratified epithelium which has an average turnover time of about 7. 5 days. 2) In the stomach, the oxyntic pit-gland unit includes pit, zymogenic and parietal cells which respectively migrate outwards, inwards, and in both directions; their turnover times average 3, 194 and 54 days, respectively. 3) The mucous units of the pyloric antrum are populated by pit cells which migrate outwards and gland cells which migrate inwards; their turnover times are about 3 and 1-60 days, respectively. 4) In the crypt-villus units of the small intestine, while both absorptive and goblet cells migrate outwards and for each the turnover time is about 3 days, Paneth cells migrate inwards and their turnover time is about 15 days. 5) In the crypts of the descending colon, both vacuolated-columnar and goblet cells migrate outwards and for each the turnover time is about 5 days. The ascending colon has an additional cell type called deep crypt secretory cells which migrate inwards and their turnover time is about 14-21 days. Finally, while the factors maintaining the gut epithelium in a steady state remain to be elucidated, this epithelium represents a remarkable system for studying the biological features of stem cells and their hierarchies.

Cell lineage relationship in the stomach of normal and genetically manipulated mice.

The oxyntic mucosa of the mouse stomach is lined with a heterogeneous population of cells that form numerous short pits continuous with long tubular glands. Tritiated thymidine radioautography has made it possible to pinpoint the origin of all cell types and to follow the differentiation/migration of different cell lineages along the pit-gland unit. The proliferating multipotent stem cells functionally anchored in the upper glandular region, the isthmus, give rise to three main lineage precursors: 1) pre-pit cells, which migrate upward to the pit while differentiating into mucus-producing pit cells; 2) pre-neck cells, which migrate downward to the glandular neck while differentiating into mucus-producing neck cells that, by approaching the glandular base, gradually change their phenotype into pepsinogen- and intrinsic factor-producing zymogenic cells; 3) pre-parietal cells, which differentiate into acid-producing parietal cells in the isthmus and then undergo bipolar migration towards the pit and the glandular base. Thus, parietal cells are the only cells that complete their differentiation in the isthmus and then migrate to be scattered throughout the pit-gland unit. To determine whether parietal cells play a role in controlling decisions about cell fate within the pit-gland unit, the gastric epithelium has been examined in transgenic mice expressing the H,K-ATPase beta-subunit-1035 to +24/simian virus 40 large T antigen fusion gene. The blockade in parietal cell differentiation in these mice produces an amplification of lineage precursors, a marked depletion of zymogenic cells and an increase in pit cell census. Ablation of parietal cells in another transgenic mouse model expressing the H,K-ATPase beta-subunit-1035 to +24/diphtheria toxin fragment A fusion gene also produces amplification of lineage precursors, and similar effects on zymogenic and pit cell census. These findings strongly suggest that parietal cells produce regulatory signals that control the cellular differentiation program of both pit and zymogenic cell lineages, and would hopefully improve our ability to identify the cellular pathways leading to malignant transformation.

Identification of clathrin and clathrin adaptors on tubulovesicles of gastric acid secretory (oxyntic) cells.

gamma-Adaptin and clathrin heavy chain were identified on tubulovesicles of gastric oxyntic cells with the anti-gamma-adaptin monoclonal antibody (MAb) 100/3 and an anti-clathrin heavy chain MAb (MAb 23), respectively. In Western blots, crude gastric microsomes from rabbit and rat and density gradient-purified, H-K-ATPase-rich microsomes from these same species were immunoreactive for gamma-adaptin and clathrin. In immunofluorescent labeling of isolated rabbit gastric glands, anti-gamma-adaptin and anti-clathrin heavy chain immunoreactivity appeared to be concentrated in oxyntic cells. In primary cultures of rabbit oxyntic cells, the immunocytochemical distribution of gamma-adaptin immunoreactivity was similar to that of the tubulovesicular membrane marker in oxyntic cells, the H-K-ATPase. Further biochemical characterization of the tubulovesicular gamma-adaptin-containing complex suggested that it has a subunit composition that is typical of that for a clathrin adaptor: in addition to the gamma-adaptin subunit, it contains a beta-adaptin subunit and other subunits of apparent molecular masses of 50 kDa and 19 kDa. From solubilized gastric microsomes from rabbit, gamma-adaptin could be copurified with the major cargo protein of tubulovesicles, the H-K-ATPase. Thus this tubulovesicular coat may bind directly to the H-K-ATPase and may thereby mediate the regulated trafficking of the H-K-ATPase at the apical membrane of the oxyntic cell during the gastric acid secretory cycle. Given the similarities of the regulated trafficking of the H-K-ATPase with recycling of cargo through the apical recycling endosome of many epithelial cells, we propose that tubulovesicular clathrin and adaptors may regulate some part of an apical recycling pathway in other epithelial cells.

Stimulation of activin receptor II signaling pathways inhibits differentiation of multiple gastric epithelial lineages.

Activins are TGFbeta family members known to mediate a variety of developmental events. We examined the effects of activins on the self-renewing epithelial lineages present in gastric units of the adult mouse stomach. These lineages are descended from multipotent stem cells located in the midportion of each unit. The stem cell and its immediate descendants can be identified by their morphological features. Studies of knockout mice lacking activins A or B, and/or activin type II receptors (ActRII) revealed that ActRII-mediated signaling is not required for normal gastric epithelial morphogenesis or homeostasis. Mice homozygous for a null allele of the alpha-inhibin gene (inha[m1/m1]) develop gonadal sex cord stromal tumors that secrete large amounts of activins A and B. Analysis of inha(m1/m1) mice, with or without gonads, established that supraphysiological levels of activins block differentiation of preparietal to acid-producing parietal cells, differentiation of neck cells to pepsinogen-producing zymogenic cells, and terminal differentiation of mucus-producing pit cells. ActRII mRNA is normally present in pit, parietal, and zymogenic cells. inha(m1/m1)actRII(m1/m1) compound homozygotes develop activin-secreting gonadal tumors but have no abnormalities in their gastric epithelium, indicating that persistent stimulation of ActRII-dependent signaling pathways produces pleiotrophic effects on gastric epithelial differentiation. When a lineage-specific promoter is used to ablate mature parietal cells with an attenuated diphtheria toxin A fragment in transgenic mice, there is increased proliferation of the multipotent gastric stem cell and its committed daughters and subsequent development of gastric neoplasia. Parietal cell loss in inha(m1/m1) mice is not associated with this proliferative response. These different responses to parietal cell loss suggest that stimulation of ActRII-dependent signaling pathways in inha(m1/m1) animals affects the proliferative activity of the stem cell and its immediate descendents. This finding may have therapeutic significance.