Development of the actin and the cytokeratin cytoskeletons of parietal cells during differentiation of the rat gastric mucosa

Available evidence strongly suggests that microfilaments and cytokeratin intermediate filaments (IF) play a role in the reorganization of the luminal pole required for the secretion of acid by parietal cells. To correlate the organization of both cytoskeletal systems with the differentiation of the secretory membranes of parietal cells, the distribution of F-actin and cytokeratin was studied during the ontogenic development of the rat. Primitive parietal cells were detected with parietal cells autoantibodies and ultrastructurally by transmission electron microscopy (TEM). The distribution of IF and of F-actin in differentiating parietal cells was determined using anticytokeratin antibodies and FITC-phalloidin, respectively. Development of both cytoskeletal systems was followed by TEM. Ultrastructurally, parietal cells are identified from day 19 on, by the presence of an incipient canaliculus, which later enlarges and fills with microvilli. No intracellular tubulovesicular system is observed. Using parietal cells autoantibodies these cells are detected from day 20 on. Immunocytochemistry and TEM demonstrate that parietal cells possess organized cytokeratin and actin cytoskeletons, which develop further as differentiation proceeds. At birth, parietal cells show an ultrastructure and a distribution of IF and microfilaments similar to that of differentiated cells. In newly born rats, the F-actin cytoskeleton redistributes after suckling. This reorganization results from an enlargement of the canalicular lumen, filled with microvilli rich in actin. Thus, functional maturation of parietal cells is paralleled by the development of organized IF and F-actin cytoskeletons associated to the secretory surface.

Cytoarchitecture of Caudiverbera caudiverbera stage VI oocytes: a light and electron microscope study

The general characteristics and salient features of the full-grown stage VI Caudiverbera caudiverbera oocyte at the light and electron microscopy level are described. The oocyte is a huge cell with radial symmetry and distinct polarity. A black animal hemisphere, rich in pigment granules and containing the nucleus, is clearly distinguished from the unpigmented white-yellowish vegetal hemisphere. The cell is surrounded by a highly invaginated plasma membrane, with numerous microvilli. The cortex underlying the plasma membrane contains cortical and pigment granules, mitochondria, rough endoplasmic reticulum and coated vesicles. Cytoskeletal components, such as actin filaments and microtubules, are also found in this region. The predominant structures, distributed throughout the cell, are the yolk platelets, which show a gradient in size with small platelets in the animal half and very large ones in the vegetal zone. Mitochondria are also very abundant in both hemispheres and clouds of these organelles are found in the perinuclear region, frequently associated with microtubules. Developed Golgi complexes are present in the cytoplasm and occasionally, annulate lamellae appear towards the inner zones. The nucleus is a large structure containing numerous nucleoli. The nuclear envelope is highly invaginated, especially at the side facing the vegetal pole. It is regularly perforated by large nuclear pores. Our results show that the structural organization of Caudiverbera oocytes, although similar to that of other amphibian oocytes, differs from them especially concerning the spatial distribution of several structural components.

Tissue uptake of human sex hormone-binding globulin and its influence on ligand kinetics in the adult female rat

The distribution of human sex hormone-binding globulin (hSHBG) and its influence upon the kinetics of its ligands were assessed in the adult female rat, which lacks a comparable protein in serum. Purified hSHBG was administered i.v. to adult female rats as a single bolus. The plasma disappearance rate of immunoreactive hSHBG had one component with a half-life of 15 h. The estradiol (E2) binding activity of serum attributable to hSHBG was elevated 2-fold; during a continuous infusion of E2, hSHBG increased E2 serum levels above those of control infused animals. Treatment with hSHBG did not modify the plasma clearance of endogenous E2, but accelerated the disappearance rate of 5 alpha-dihydrotestosterone (DHT). In animals injected with a tracer dose of radioactive steroids, pretreatment with hSHBG increased uterine and oviductal accumulation of E2- but not DHT-associated radioactivity. This effect was specific to some E2 target tissues since hSHBG did not alter the concentration of E2- or DHT-associated radioactivity in the hypophysis, liver, diaphragm, or brain. Treatment with anti-E2 antibodies, which elevated E2 binding activity in serum, decreased the accumulation of E2-associated radioactivity in uterus and oviduct. Immunofluorescent localization of hSHBG revealed intense labeling of the uterine and oviductal epithelium. We conclude that this foreign hormone-binding globulin introduced in serum at concentrations that have minimal circulating reservoir effect on E2 can reach intracellular domains and affect the concentration of this ligand in target tissues.

Redistribution of membranes and cytoskeletal proteins in chicken oxyntic cells during the HCl secretory cycle: ultrastructural and immunofluorescence study

Changes in ultrastructure and cytoskeletal organization by avian oxyntic cells, at the onset of HCl secretion, were analysed. Cells in resting state, induced by fasting and cimetidine, were compared with histamine stimulated secreting cells. Ultrastructural studies were done by transmission electron microscopy; the distribution of prekeratin, myosin, and filamin-like protein, by immunofluorescence; and that of F-actin using FITC-phalloidin. Resting cells show short pericellular clefts. These are increasingly deepened in secreting cells by a reorganization of the lateral cell borders involving displacement of the junctional complexes toward the cell base and incorporation of the tubular system to the luminal plasma membrane. In secreting cells, the processes of the secretory surface are concentrated in a pericellular groove. Histamine stimulation induces a drastic redistribution of cytoskeletal proteins. In chicken oxyntic cells, in addition to the F-actin cytoskeleton associated with the membranes of the secretory surface, there is a cytoskeletal ring containing F-actin, myosin, and a filamin-like protein, located at the level of the junctional complexes. In resting cells, filaments and masses of cytoskeletal matrix are associated with the zonula adherens. In secreting cells, the junctional complexes maintain their association with the filamentous ring, while the amorphous matrix is replaced by microfilaments that support the processes of the luminal surface. Intermediate filaments form a peripheral ring probably associated with the zonula adherens, and project from the ring toward the cell cytoplasm. Thus, with the onset of HCl secretion, the apical cytoskeletal ring of resting cells displaces toward the cell base. A role for this cytoskeletal ring in the changes in shape parallel to HCl secretion is discussed.

Distribution of intermediate filaments in epithelial cells of the amphibian urinary bladder: an immunofluorescence study

The distribution of intermediate filaments in toad and frog urinary bladder was studied on frozen sections by indirect immunofluorescence microscopy using specific antiprekeratin antibodies. Our results show that in both species, epithelial cells lining the urinary bladder are very rich in cytokeratin, organized as a filamentous network. In granular cells, the most abundant cells facing the urinary lumen, vasopressin promotes fusion of the membranous tubular structures located in the luminal cytoplasm with the apical cell membrane. A role for intermediate filaments in the membrane rearragements induced by vasopressin in these cells, is proposed.

Quantitative subcellular study of apical pole membranes from chicken oxyntic cells in resting and HCl secretory state

Vertebrate oxyntic cells, responsible for gastric HCl production, undergo a remarkable morphological reorganization in relation to their secretory cycle. In resting state, the luminal surface of the cells is smooth; a peculiar system of endocellular membranes, the tubular system, occupies the luminal cytoplasm. Actin filaments frame a cortical network between the tubular system and the luminal plasma membrane. With the onset of HCl secretion, the tubular system becomes incorporated into the luminal plasma membrane. Villous processes containing microfilaments fill the secretory surface. This morphological reorganization of membranes and cytoskeletal matrix could regulate HCl secretion by translocation of membranes containing the proton pump from the endocellular compartment to the secretory surface. In this paper, we describe the isolation of membranes that selectively belong to the tubular system or to the cytoplasmic processes of the secretory surface of chicken oxyntic cells. Chicken oxyntic cells are the main cellular component of the proventricular glands. A resting state was obtained after cimetidine treatment, whereas the HCl-secretory state was induced by histamine. We present a comparative analysis of resting and stimulated chicken gastric glands by quantitative subcellular fractionation. The HCl secretory state was related to specific modifications in membrane fractions derived from the secretory pole of oxyntic cells. Morphological and functional reorganization of oxyntic cells was closely correlated with changes in: the sedimentation pattern of the marker enzyme of the apical pole membrane (K-NPPase), the total activity of K-NPPase and nonmitochondrial Mg-ATPase, the valinomycin dependence of K-ATPase, and polypeptides that cosediment in purified membrane fractions. Changes in the distribution pattern of K-NPPase after fractionation of histamine-stimulated glands were consistent with the replacement of the small vesicles typical of resting glands by dense membrane profiles, analogous to the luminal processes of stimulated oxyntic cells. SDS-PAGE showed that, in purified membrane fractions of stimulated glands, the concentration of 28-, 43-, and 200-kD polypeptides increased while that of 95- and 250-kD polypeptides decreased. The present results define the tubular system of oxyntic cells as an organelle with properties different from those of endoplasmic reticulum, mitochondria, and plasma membrane. The biochemical and physico-chemical properties of this membraneous system changed when the organization of the membranes and the cytoskeletal matrix of the apical pole was modified by the onset of HCl secretion.

Filamin and myosin are present in the secretory pole of amphibian oxyntic cells. An immunofluorescence study

The presence of a filamin-like protein in oxyntic cells was established by indirect immunofluorescence microscopy. The location of this protein and myosin was studied, using specific antibodies, on frozen sections and isolated cells. Antifilamin and antimyosin reacted strongly with the luminal cytoplasm of the cells. In resting oxyntic cells, filamin appeared organized as a reticular sheet in the apical border. In stimulated cells, the apical concentration of filamin decreased, and its distribution appeared rather diffuse. This immunoreactive band seems to correspond to the cytoplasmic region where actin microfilaments have been described previously. The changes in the apical concentration of filamin, induced by the onset of HCl secretion, correlate with the ultrastructural reorganization of the actin network that occurs during the secretory cycle. The use of antimyosin antibodies showed that this protein forms an apical peripheral ring in both resting and stimulated cells. No clear changes in the distribution of myosin, in relation to secretion, could be established by immunofluorescence. These findings, taken together with published morphological and biochemical evidence, suggest that a three-dimensional network composed of actin and filamin is present in the secretory pole of resting amphibian oxyntic cells. The hypothesis that gel-sol transitions play a role in the structural reorganization of the secretory pole of these cells is supported by the present results.

Intermediate filaments of the cytoskeleton in glandular cells of the rat fundic mucosa: immunofluorescence and electron microscopy study

The organization of intermediate filaments (IF) in cells of the rat fundic mucosa was studied by electron microscopy and immunofluorescence microscopy using specific antiprekeratin antibodies on frozen sections and isolated cells. Our results suggest that mucous cells lining the gastric surface and the gastric pits, which appeared strongly decorated, are the most rich in IF. These cells displayed coarse bundles of IF oriented in all directions as well as desmosome-attached tonofibrils. Mucous neck cells contained fewer bundles of IF located preferentially toward the apical region. Zymogen cells showed a strong staining along the contour of the luminal border, together with a faint decoration of a fine meshwork extending throughout the cytoplasm. A poorly defined fibrillar cortex present underneath the secretory plasma membrane and sparse bundles of IF among the elements of the rough endoplasmic reticulum were seen in thin sections. In contrast, parietal cells appeared brightly stained and the prekeratinlike material formed a cortical polygonal meshwork especially visible in isolated cells. A developed system of IF formed by conspicuous bundles located underneath the secretory canaliculi, among the mitochondria and in the vicinity of the basal plasma membrane, was observed in the electron microscope.

Distribution of intermediate filaments in amphibian oxyntic cells. Biochemical and immunological characterization

Intermediate filaments of toad oxyntic cells were isolated and analysed by SDS-PAGE. The major proteins of the residue were identified as actin and a 51,000 dalton polypeptide. Immunological crossreactivity between toad oxyntic cell intermediate filament components and anti-prekeratin, was shown by double immunodiffusion tests and indirect immunofluorescence. The immunofluorescent decoration of oxyntic cells and the electron microscope images are coincident in locating the intermediate filaments mainly at the cortical and perinuclear basal zones. Furthermore, the cortical zone appears especially rich in prekeratin-like material at its adluminal third. This results in a cup-like structure that encloses the cell portion occupied by the tubulovesicular system, which does not contain intermediate filaments. The translocation of membranes occurring during the secretory cycle of the oxyntic cell, has been attributed to a system of contractile proteins. The disposition of the prekeratin-like material suggests a role for intermediate filaments in the generation of movement, produced by actin and myosin interaction, by providing a fixed plane for the anchoring of actin microfilaments.