The retinoblastoma protein, RB, is required for gastrointestinal endocrine cells to exit the cell cycle, but not for hormone expression

Important functions of the RB family proteins include inhibition of cell cycle progression and regulation of terminal differentiation. We have examined the role of RB and the related protein, p107, in regulating cell cycle activity and differentiation of gastrointestinal endocrine cells, a relatively quiescent cell population, by conditionally disrupting the RB gene in neurogenin3 (Ngn3)-expressing cells in both p107^+/+ and p107^−/− mice. Endocrine cells in the small intestine, colon, pancreas, and stomach were present in normal numbers in RB and RB-p107 mutants except for an increase in serotonin cells and decrease in ghrelin cells in the antral stomach. Deletion of RB resulted in a dramatic increase in proliferating serotonin cells in the antral stomach and intestine, whereas other enteroendocrine cell types exhibited much lower cell cycle activity or remained quiescent. The related p107 protein appears dispensable for enteroendocrine differentiation and does not functionally compensate for the loss of RB. Our results suggest that RB is required for enteroendocrine cells, particularly serotonin cells, to undergo cell cycle arrest as they terminally differentiate. RB has relatively subtle effects on enteroendocrine cell differentiation and is not required for the expression of the normal repertoire of hormones in the gastrointestinal tract.     

Neurogenin 3 and the enteroendocrine cell lineage in the adult mouse small intestinal epithelium

It is thought that small intestinal epithelial stem cell progeny, via Notch signaling, yield a Hes1-expressing columnar lineage progenitor and an Atoh1 (also known as Math1)-expressing common progenitor for all granulocytic lineages including enteroendocrine cells, one of the body's largest populations of endocrine cells. Because Neurogenin 3 (Neurog3) null mice lack enteroendocrine cells, Neurog3-expressing progenitors derived from the common granulocytic progenitor are thought to produce the enteroendocrine lineage, although more recent work indicates that Neurog3+ progenitors also contribute to non-enteroendocrine lineages. We aimed to test this model and better characterize the progenitors leading from the stem cells to the enteroendocrine lineage. We investigated clones derived from enteroendocrine precursors and found no evidence of a common granulocytic progenitor that routinely yields all granulocytic lineages. Rather, enteroendocrine cells are derived from a short-lived bipotential progenitor whose offspring, probably via Notch signaling, yield a Neurog3+ cell committed to the enteroendocrine lineage and a progenitor committed to the columnar lineage. The Neurog3+ cell population is heterogeneous; only about 1/3 are slowly cycling progenitors, the rest are postmitotic cells in early stages of enteroendocrine differentiation. No evidence was found that Neurog3+ cells contribute to non-enteroendocrine lineages. Revised lineage models for the small intestinal epithelium are introduced.     

Somatostatin-immunoreactive cells in the gastrointestinal tract of the frog Rana esculenta

The morphology and topographic distribution of somatostatin-immunoreactive cells in the stomach and small intestine of the frog Rana esculenta were studied at the light-microscopic level by the use of the peroxidase-antiperoxidase method. Scattered immunostained cells occurred in all regions of the gastrointestinal tract investigated. In the small intestine, the number of these cells decreased gradually in the oral to anal direction, i.e. from the pyloric (antral) stomach to the entrance into the colon. Most of the immunostained cells possessed thick, short cytoplasmic processes, which did not display a preferential spatial orientation. Other somatostatin-immunoreactive cells, which were exclusively located in the small intestine, gave rise to a single long extension oriented toward the lumen. In both stomach and small intestine, a complete penetration of the epithelial surface by these processes of somatostatin-immunoreactive cells was observed only occasionally. The morphological features of the somatostatin-immunostained cells speak in favor of endocrine, paracrine, and possibly also intraluminal secretory functions of the enteroendocrine somatostatin system in frogs.Fellow of the Alexander von Humboldt Foundation, Bonn, Germany     

Ngn3(+) endocrine progenitor cells control the fate and morphogenesis of pancreatic ductal epithelium

During pancreas development, endocrine and exocrine cells arise from a common multipotent progenitor pool. How these cell fate decisions are coordinated with tissue morphogenesis is poorly understood. Here we have examined ductal morphology, endocrine progenitor cell fate and Notch signaling in Ngn3^−/− mice, which do not produce islet cells. Ngn3 deficiency results in reduced branching and enlarged pancreatic duct-like structures, concomitant with Ngn3 promoter activation throughout the ductal epithelium and reduced Notch signaling. Conversely, forced generation of surplus endocrine progenitor cells causes reduced duct caliber and an excessive number of tip cells. Thus, endocrine progenitor cells normally provide a feedback signal to adjacent multipotent ductal progenitor cells that activates Notch signaling, inhibits further endocrine differentiation and promotes proper morphogenesis. These results uncover a novel layer of regulation coordinating pancreas morphogenesis and endocrine/exocrine differentiation, and suggest ways to enhance the yield of beta cells from stem cells.     

Distribution of peptide-containing neurons and endocrine cells in the rabbit gastrointestinal tract,with particular reference to the mucosa

Summary The distribution patterns of peptide-containing neurons and endocrine cells were mapped in sections of oesophagus, stomach, small intestine and large intestine of the rabbit, by use of standard immunohistochemical techniques. Whole mounts of separated layers of ileum were similarly examined. Antibodies raised against vasoactive intestinal peptide (VIP), substance P (SP), somatostatin (SOM), neuropeptide Y (NPY), enkephalins (ENK) and gastrin-releasing peptide (GRP) were used, and for each of these antisera distinct populations of immunoreactive (IR) nerve fibres were observed. Endocrine cells were labelled by the SP, SOM or NPY antisera in some regions.VIP-IR nerve fibres were common in each layer throughout the gastrointestinal tract. With the exception of the oesophagus, GRP-IR nerve fibres also occurred in each layer of the gastrointestinal tract; they formed a particularly rich network in the mucosa of the stomach and small intestine. Fewer nerve fibres containing NPY-IR or SOM-IR were seen in all areas. SOM-IR nerve fibres were very scarce in the circular and longitudinal muscle layers of each area and were absent from the gastric mucosa. The SP-IR innervation of the external musculature and ganglionated plexuses in most regions was rather extensive, whereas the mucosa was only very sparsely innervated. ENK-IR nerve fibres were extremely rare or absent from the mucosa of all areas, although immunoreactive nerve fibres were found in other layers.These studies illustrate the differences in distribution patterns of peptide-containing nerve fibres and endocrine cells along the gastrointestinal tract of the rabbit and also show that there are some marked differences in these patterns, in comparison with other mammalian species.     

The distribution of endocrine cells in the mucosa of the gastrointestinal tract of the house musk shrew,Suncus murinus (Insectivora)

Summary The distribution of endocrine cells in the gastrointestinal tract of the house musk shrew, Suncus murinus (Family Soricidae, Order Insectivora) was studied immunohistochemically. The hormones investigated were gastrin, cholecystokinin (CCK), somatostatin, secretin, glucagon, gastric inhibitory polypeptide (GIP), motilin and neurotensin. In the gastric mucosa, gastrin and somatostatin cells were only found in the pyloric regions, and no other hormonal cell-types were observed. In the intestinal mucosa, the largest number of endocrine cells belonged to the gastrin and glucagon/glicentin cell-types, whereas CCK-33/39 and secretin cells were the least numerous. Numbers of other cell-types were intermediate between these two groups. The gastrin and GIP cells were mostly localized in the proximal portion of the intestine, decreasing in number towards the distal portion. The motilin and CCK-33/39 cells were restricted to the proximal half. The glucagon/glicentin and neurotensin cells were most abundant in the middle portion. The somatostatin and secretin cells, although only present in small numbers, were randomly distributed throughout the intestine. This characteristic distribution of gastrointestinal endocrine cells is discussed in comparison with the distribution patterns of other mammals.Dr. Munemitsu Hoshino, who was Professor of the Department of Pathology and directed this study, passed away on May 23rd 1988     

Morphology and immunocytochemistry of two endocrine cell types in the guinea-pig esophageal epithelium

Summary Two types of endocrine cells in the basal layer of the keratinized stratified squamous epithelium in the guinea-pig esophagus were studied with immunohistochemistry by means of a streptavidin-biotin-bridge technique and by the immunofluorescence double-labelling technique. Cell-type I exhibited immunoreactivity to chromogranin A and to nucleosidetriphosphate-adenosinediphosphate(ADP)-phosphotransferase. Ultrastructurally, this cell type was characterized by small cytoplasmic dense-core vesicles in which immunoreactive product was localized. Cell-type II contained large membrane-limited granules, which were moderately electron dense. These granules displayed somatostatin immunoreactivity. Both cell types were located in close vicinity to non-myelinated nerve fibers and small blood vessels. The results provide evidence that, independent from the type of lining epithelium, the gastro-enteropancreatic system in guinea-pig extends to the lower portion of the esophagus.Supported by the German Research Foundation, grant He 919/6-2     

Notch signaling differentially regulates the cell fate of early endocrine precursor cells and their maturing descendants in the mouse pancreas and intestine

Notch signaling inhibits differentiation of endocrine cells in the pancreas and intestine. In a number of cases, the observed inhibition occurred with Notch activation in multipotential cells, prior to the initiation of endocrine differentiation. It has not been established how direct activation of Notch in endocrine precursor cells affects their subsequent cell fate. Using conditional activation of Notch in cells expressing Neurogenin3 or NeuroD1, we examined the effects of Notch in both organs, on cell fate of early endocrine precursors and maturing endocrine-restricted cells, respectively. Notch did not preclude the differentiation of a limited number of endocrine cells in either organ when activated in Ngn3⁺ precursor cells. In addition, in the pancreas most Ngn3⁺ cells adopted a duct but not acinar cell fate; whereas in intestinal Ngn3⁺ cells, Notch favored enterocyte and goblet cell fates, while selecting against endocrine and Paneth cell differentiation. A small fraction of NeuroD1⁺ cells in the pancreas retain plasticity to respond to Notch, giving rise to intraislet ductules as well as cells with no detectable pancreatic lineage markers that appear to have limited ultrastructural features of both endocrine and duct cells. These results suggest that Notch directly regulates cell fate decisions in multipotential early endocrine precursor cells. Some maturing endocrine-restricted NeuroD1⁺ cells in the pancreas switch to the duct lineage in response to Notch, indicating previously unappreciated plasticity at such a late stage of endocrine differentiation.     

The distribution and cellular origin of vasoactive intestinal polypeptide in the avian gastrointestinal tract and pancreas

Summary The distribution and origins of vasoactive intestinal peptide (VIP) in the gut and pancreas of the turkey were studied by radioimmunoassay of tissue extracts and by immunocytochemistry. Several antisera were used that vary in their specificity for different regions of porcine or chicken VIP. Radioimmunoassays using NH₂-terminal specific antisera that react almost equally with porcine and chicken VIP's revealed significant amounts of immunoreactive VIP in extracts of pancreas, brain and all regions of the gastrointestinal tract from crop to colon. Highest concentrations (300pmol/g) were found in the colon muscle, and concentrations were generally low (< 20 pmol/g) in the mucosal layers of the small intestine. After ion exchange chromatography of extracts on CM-Sephadex three immunoreactive forms of VIP were separated corresponding to the three molecular forms previously found in mammalian gut extracts. In immunocytochemical studies nerve fibres were found throughout the gut, and in the pancreas. Immunoreactive nerve cell bodies were also identified in the submucous plexus throughout the gut, but were particularly prominent in the oesophagus and pancreas. It has previously been shown that VIP is a strong stimulant of the flow of pancreatic juice in birds whereas the structurally related hormone secretin, which is known to control the flow of pancreatic juice in mammals, is a weak stimulant. It is proposed that in birds VIP might regulate the pancreas, and other aspects of gut function, as a neurotransmitter or neurohormone.     

Ontogeny of immunoreactive glicentin in the human gastrointestinal tract and endocrine pancreas

The gestational time of appearance and distribution of immunoreactive glicentin was compared to that of immunoreactive glucagon in the gastrointestinal tract and endocrine pancreas of human fetuses, aged between 5 and 24 weeks, by an indirect immunoperoxidase method. With the glicentin antiserum No. R 64, the first immunoreactive cells were detected at the 10th week of gestation in the oxyntic mucosa and proximal small intestine, at the 8th week in the ileum and at the 12th week in the colon. In the endocrine pancreas, the first immunoreactive cells were observed as early as 8 weeks within the walls of the primitive pancreatic ductules. At a more advanced stage of development (12 weeks), they were found interspersed among the islet cell clusters and still later (16 weeks) inside the recognizable islets of Langerhans. With the glucagon antiserum No. GB 5667, no immunoreactive cells were demonstrated in the gastrointestinal tract whatever the age of the fetuses. In the endocrine pancreas, the first immunoreactive cells were observed at the 8th week of gestation in the pancreatic parenchyma. The distribution of glucagon-containing cells in the pancreas was similar to that of glicentin immunoreactivity throughout ontogenesis. In the pancreatic islets of one 18-week-old human fetus, the study of consecutive semithin sections treated by both antisera showed that the same cells were labelled. The significance of these findings concerning the role of glicentin as a glucagon precursor is discussed.     

Review: The development of the gastrointestinal tract microbiota and intervention in neonatal ruminants

The complex microbiome colonizing the gastrointestinal tract (GIT) of ruminants plays an important role in the development of the immune system, nutrient absorption and metabolism. Hence, understanding GIT microbiota colonization in neonatal ruminants has positive impacts on host health and productivity. Microbes rapidly colonize the GIT after birth and gradually develop into a complex microbial community, which allows the possibility of GIT microbiome manipulation to enhance newborn health and growth and perhaps induce lasting effects in adult ruminants. This paper reviews recent advances in understanding how host-microbiome interactions affect the GIT development and health of neonatal ruminants. Following initial GIT microbiome colonization, continuous exposure to host-specific microorganisms is necessary for GIT development and immune system maturation. Furthermore, the early GIT microbial community structure is significantly affected by early life events, such as maternal microbiota exposure, dietary changes, age and the addition of prebiotics, probiotics and synbiotics, supporting the idea of microbial programming in early life. However, the time window in which interventions can optimally improve production and reduce gastrointestinal disease as well as the role of key host-specific microbiota constituents and host immune regulation requires further study.     

Substance P and substance K receptor binding sites in the human gastrointestinal tract: Localization by autoradiography

Quantitative receptor autoradiography was used to localize and quantify the distribution of binding sites for ¹²⁵I-radiolabeled substance P (SP), substance K (SK) and neuromedin K (NK) in the human GI tract using histologically normal tissue obtained from uninvolved margins of resections for carcinoma. The distribution of SP and SK binding sites is different for each gastrointestinal (GI) segment examined. Specific SP binding sites are expressed by arterioles and venules, myenteric plexus, external circular muscle, external longitudinal muscle, muscularis mucosa, epithelial cells of the mucosa, and the germinal centers of lymph nodules. SK binding sites are distributed in a pattern distinct from SP binding sites and are localized to the external circular muscle, external longitudinal muscle, and the muscularis mucosa. Binding sites for NK were not detected in any part of the human GI tract. These results demonstrate that: 1) surgical specimens from the human GI tract can be effectively processed for quantitative receptor autoradiography; 2) of the three mammalian tachykinins tested, SP and SK, but not NK binding sites are expressed in detectable levels in the human GI tract; 3) whereas SK receptor binding sites are expressed almost exclusively by smooth muscle, SP binding sites are expressed by smooth muscle cells, arterioles, venules, epithelial cells of the mucosa and cells associated with lymph nodules; and 4) both SP and SK binding sites expressed by smooth muscle are more stable than SP binding sites expressed by blood vessels, lymph nodules, and mucosal cells.     

Notch1 expression and ligand interactions in progenitor cells of the mouse olfactory epithelium

Despite the relatively simplified organization of the olfactory epithelium (OE), our understanding of the factors that regulate its cellular diversity is limited. Genetic and localization studies suggest that Notch signaling may be important in this process. We characterize here a population of Notch1 ⁺ olfactory basal cells in embryonic mice that coordinately express both the Notch effector Hes5 and the glycosyltransferase Lfng. These cells are distinct from Mash1 ⁺ neuronal precursors, but give rise to sensory neurons, suggesting that Notch1 signals may in part function to maintain a neurogenic progenitor pool. Furthermore, Lfng ⁺ cells also generate a population of cells in the migratory mass that appear to be ensheathing glial precursors, indicating potential multipotency in these progenitors. The Notch ligand Dll4 is expressed by basal OE cells that are interspersed with Notch1 ⁺ progenitors during later OE neurogenesis. In contrast, mice deficient in Dll1 exhibit a smaller OE and a loss of Hes5 expression, indicating an earlier function in olfactory progenitor cell development. Taken together, these results further support a role for Notch signaling in the regulation of olfactory neurogenesis and cell diversity.     

重口裂腹鱼消化道内分泌细胞的免疫组织化学鉴别和定位

重口裂腹鱼（Schizothorax davidi）俗称“雅鱼”,属鲤科,裂腹鱼亚科,主要分布于大渡河、青衣江水系上游,以动物性食性为主。因其生长缓慢,肉质鲜嫩,深受人们喜爱。随着捕捞强度的增大和自然生态环境的破坏,其资源量急剧下降。目前大多数学者使用哺乳动物抗血清对鱼类消化道内分泌细胞进行了鉴别和定位,在硬骨鱼和软骨鱼的胃肠胰中分别发现了17种和20种内分泌细胞。[第一段]     

Telocytes express PDGFRα in the human gastrointestinal tract

Telocytes (TC), a cell population located in the connective tissue of many organs of humans and laboratory mammals, are characterized by a small cell body and extremely long and thin processes. Different TC subpopulations share unique ultrastructural features, but express different markers. In the gastrointestinal (GI) tract, cells with features of TC were seen to be CD34‐positive/c‐kit‐negative and several roles have been proposed for them. Other interstitial cell types with regulatory roles described in the gut are the c‐kit‐positive/CD34‐negative/platelet‐derived growth factor receptor α (PDGFRα)‐negative interstitial cells of Cajal (ICC) and the PDGFRα‐positive/c‐kit‐negative fibroblast‐like cells (FLC). As TC display the same features and locations of the PDGFRα‐positive cells, we investigated whether TC and PDGFRα‐positive cells could be the same cell type. PDGFRα/CD34, PDGFRα/c‐kit and CD34/c‐kit double immunolabelling was performed in full‐thickness specimens from human oesophagus, stomach and small and large intestines. All TC in the mucosa, submucosa and muscle coat were PDGFRα/CD34‐positive. TC formed a three‐dimensional network in the submucosa and in the interstitium between muscle layers, and an almost continuous layer at the submucosal borders of muscularis mucosae and circular muscle layer. Moreover, TC encircled muscle bundles, nerve structures, blood vessels, funds of gastric glands and intestinal crypts. Some TC were located within the muscle bundles, displaying the same location of ICC and running intermingled with them. ICC were c‐kit‐positive and CD34/PDGFRα‐negative. In conclusion, in the human GI tract the TC are PDGFRα‐positive and, therefore, might correspond to the FLC. We also hypothesize that in human gut, there are different TC subpopulations probably playing region‐specific roles.     

Distribution and morphology of argyrophilic cells in the digestive tract of the African ostrich

We used light microscopy to elucidate the morphological features of argyrophilic cells in the digestive tract of the African ostrich (Struthio camelus). The results indicated that argyrophilic cells were found to be distributed among the epithelial cells of the mucosa or glands throughout the digestive tract, except for the esophagus; two types of argyrophilic cells were found; i.e., closed-type cells and cells with triangular or elongated shapes and with their apical cytoplasmic process in contact with the lumen (open-type cells); the greatest number of argyrophilic cells was found in the proventriculus, and the argyrophilic cell density gradually decreased from the proventriculus to the rectum; Furthermore, the number of argyrophilic cells in the duodenum and ileum was higher than that in the jejunum. This text still combined the characteristics that the argyrophilic cells in digestive tract of ostrich maybe related to different digestive function of different region and the basis of their morphology to carry on a discussion. It was speculated that argyrophilic cells in the digestive tract may have both endocrine and exocrine functions.     

Gadolinium-promoted cell cycle progression with enhanced S-phase entry via activation of both ERK and PI3K signaling pathways in NIH 3T3 cells

The aim of this study was to investigate whether Gd is able to exert the proliferation-promoting effect and to explore its possible underlying mechanism. We showed that Gd promoted cell cycle progression with increased S-phase entry in a concentration- and time-dependent manner in NIH 3T3 cells. The effect was further evidenced by the expressions of key proteins in driving cells through the G₁/S transition point of the cell cycle. In the presence of Gd, the protein levels of cyclins D, E, and A were dramatically increased and demonstrated a characteristically temporal pattern of sequential mitotic events. Additionally, the levels of phosphorylated retinoblastoma protein were also significantly increased at certain time periods. To further elucidate the underlying mechanism, extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling pathways were assessed. Both pathways were activated by Gd. Moreover, the levels of cyclin D and cyclin A were evaluated after the addition of the pharmacological inhibitors at early and late G₁ phases, correspondingly, to reveal the contribution of the two pathways in the Gd-promoted G₁/S transition. It showed that both pathways were needed for Gd-promoted cell cycle progression. The results presented here provide novel evidence to advance knowledge leading to further understanding of the mechanisms of both cell growth and death caused by Gd and may be helpful for more rational application of Gd-based compounds in the future.