Mutations of the genes encoding APC or beta-catenin in colon carcinoma induce the constitutive formation of nuclear beta-catenin/Tcf-4 complexes, resulting in activated transcription of Tcf target genes. To study the physiological role of Tcf-4 (which is encoded by the Tcf7/2 gene), we disrupted Tcf7/2 by homologous recombination. Tcf7/2-/- mice die shortly after birth. A single histopathological abnormality was observed. An apparently normal transition of intestinal endoderm into epithelium occurred at approximately embryonic day (E) 14.5. However, no proliferative compartments were maintained in the prospective crypt regions between the villi. As a consequence, the neonatal epithelium was composed entirely of differentiated, non-dividing villus cells. We conclude that the genetic program controlled by Tcf-4 maintains the crypt stem cells of the small intestine. The constitutive activity of Tcf-4 in APC-deficient human epithelial cells may contribute to their malignant transformation by maintaining stem-cell characteristics.

Depletion of epithelial stem-cell compartments in the small intestine of mice lacking Tcf-4.

Since the discovery that epidermal growth factor (EGF) can accelerate opening of the eyelids, the EGF receptor (EGF-R) has been extensively studied and is now considered to be a prototype tyrosine kinase receptor. Binding of EGF or of transforming growth factor-alpha (TGF-alpha) or other related factors activates the receptor and induces cell proliferation and differentiation. Although it is not found on haematopoietic cells, the EGF-R is widely expressed in mammals and has been implicated in various stages of embryonic development. Here we investigate the developmental and physiological roles of this receptor and its ligands by inactivating the gene encoding EGF-R. We find that EGF-R-/- mice survive for up to 8 days after birth and suffer from impaired epithelial development in several organs, including skin, lung and gastrointestinal tract.

Epithelial immaturity and multiorgan failure in mice lacking epidermal growth factor receptor

Studying the cross talk between nonpathogenic organisms and their mammalian hosts represents an experimental challenge because these interactions are typically subtle and the microbial societies that associate with mammalian hosts are very complex and dynamic. A large, functionally stable, climax community of microbes is maintained in the murine and human gastrointestinal tracts. This open ecosystem exhibits not only regional differences in the composition of its microbiota but also regional differences in the differentiation programs of its epithelial cells and in the spatial distribution of its component immune cells. A key experimental strategy for determining whether “nonpathogenic” microorganisms actively create their own regional habitats in this ecosystem is to define cellular function in germ-free animals and then evaluate the effects of adding single or several microbial species. This review focuses on how gnotobiotics—the study of germ-free animals—has been and needs to be used to examine how the gastrointestinal ecosystem is created and maintained. Areas discussed include the generation of simplified ecosystems by using genetically manipulatable microbes and hosts to determine whether components of the microbiota actively regulate epithelial differentiation to create niches for themselves and for other organisms; the ways in which gnotobiology can help reveal collaborative interactions among the microbiota, epithelium, and mucosal immune system; and the ways in which gnotobiology is and will be useful for identifying host and microbial factors that define the continuum between nonpathogenic and pathogenic. A series of tests of microbial contributions to several pathologic states, using germ-free and ex-germ-free mice, are proposed.

https://mmbr.asm.org/content/mmbr/62/4/1157.full.pdf

Creating and Maintaining the Gastrointestinal Ecosystem: What We Know and Need To Know from Gnotobiology

A literature review on kinin pharmacology that appeared in this journal in 1980 was based on a systematic effort to define two receptor types for bradykinin- (BK b) related peptides, and proposed a receptor nomenclature (B1, B2) ([Regoli and Barabe, 1980][1]). Since then, that historical paper has

The B1 Receptors for Kinins

I. Introduction: The Adrenal Functional Unit II. Interaction Between Adrenal Medulla and Adrenal Cortex A. Relationship between medullary and cortical cells B. Paracrine control of adrenocortical function by the adrenal medulla C. Gap junctions in the adrenal cortex D. Summary III. Innervation of the Adrenal Cortex A. Evidence for a nerve supply to the adrenal cortex B. The source of adrenocortical innervation C. Regulation of adrenocortical innervation D. Role of the splanchnic nerve in regulating adrenocortical neural function E. Influence of adrenal innervation on adrenocortical function F. Effects of neurotransmitter substances on adrenocortical function G. Summary IV. The Vascular System of the Adrenal Gland A. Regulation of blood flow B. Relationship between blood flow and steroid secretion C. Effects of vascular endothelial cell products on steroid secretion D. Summary V. The Intraadrenal CRH/ACTH System A. Extrapituitary effect of CRH B. Intraadrenal ACTH C. Intraadrenal CRH and CRH receptors D. F...

Intraadrenal Interactions in the Regulation of Adrenocortical Steroidogenesis

In recent years, fluorescence microscopy imaging has become an important tool for studying cell structure and function. This non invasive technique permits characterization, localisation and qualitative quantification of free ions, messengers, pH, voltage and a pleiad of other molecules constituting living cells. In this paper, we present results using various commercially available fluorescent probes as well as some developed in our laboratory and discuss the advantages and limitations of these probes in confocal microscopy studies of the cardiovascular system.

The use of confocal microscopy in the investigation of cell structure and function in the heart, vascular endothelium and smooth muscle cells

Using light and electron microscopy, we have observed the presence of rays containing medullary tissue extending across the cortex of rat adrenal glands. Within these rays chromaffin cells, as well as collagen and nerve fibers, were present. It is suggested that these endocrine cells may have a paracrine function within the cortex, possibly via their secretory product.

On the presence of chromaffin cells in the adrenal cortex: their possible role in adrenocortical function.

https://www.gastrojournal.org/article/0016-5085(88)90236-3/pdf

Biologic effects of epidermal growth factor in human fetal jejunum.

The migration of intestinal intervillous epithelial cells labeled in the fetus was followed in neonatal mice. At 17 days of gestation, a first group of pregnant mice received three intraperitoneal injections of 3H-thymidine (150 microCi/injection) administered at 30 min intervals. Two mothers were sacrificed 3 hours after the first injection. Mice from different litters were also sacrificed on days 0, 2, 4, 8, 12, 14, and 16 after birth. A second group of pregnant mice was injected at 18 1/2 days of gestation and offspring were sacrificed on days 6, 8, 10, 12, 14, and 16 after birth. Segments of duodenum and ileum were fixed in glutaraldehyde, postfixed in osmium tetroxide, dehydrated, and embedded in Epon. Sections were stained with aldehyde fuchsin and processed for radioautography. By following the leading front and trailing edge of labeled cells in the longest villi of the duodenum and ileum, we observed that 1) extrusion zones become active immediately after birth and 2) the longest villi do not elongate until 10 days after birth in the duodenum and 14 days in the ileum, that is, when all labeled epithelial cells originally present in the fetus have been extruded. Moreover, by measuring the distance between the internal limit of the inner circular layer of smooth muscle and the intervillous epithelium at 17 days of gestation (12.95 +/- 1.18 microns) or the bottom of the crypts at day 3 (14.81 +/- 0.91 microns), we propose that crypts do not develop as downgrowths: rather the intervillous epithelium is reshaped and the crypt-villus junction moves upward, away from the muscularis externa.(ABSTRACT TRUNCATED AT 250 WORDS)

Migration of fetal intestinal intervillous cells in neonatal mice.

Publisher Summary The chapter presents a study related to the use of confocal microscopy to investigate cell structure and function. The chapter discusses sample preparations to be used, labeling of structures and functional probes, parameter settings, and the development of specific ligand probes, as well as measurements and limitations of confocal microscopy. Confocal microscopy imaging studies in single cells and tissue sections confirm the importance of this noninvasive technique in the study of cell structure and function, as well as the modulation of working living cells by various constituents of cell membranes, organelles, and cytosol. The criteria that should be taken into account to obtain sufficient details from three-dimensional (3-D) reconstructions are presented. The reconstitution of interaction between two cell types is an excellent preparation for confocal microscopic studies. Site-selection probes such as receptor, protein, and second messenger probes, organelle probes, and nuclear stains all provide important indicators for the determination of actual structure and location of cell components and for the study of subcellular distribution and movement of various ions and molecules in working living cells.

Pierre Pothier

Papers

The use of confocal microscopy in the investigation of cell structure and function in the heart, vascular endothelium and smooth muscle cells

On the presence of chromaffin cells in the adrenal cortex: their possible role in adrenocortical function.

Biologic effects of epidermal growth factor in human fetal jejunum.

Migration of fetal intestinal intervillous cells in neonatal mice.

Use of confocal microscopy to investigate cell structure and function.