Apical cytoplasm

About: Apical cytoplasm is a research topic. Over the lifetime, 1080 publications have been published within this topic receiving 36131 citations.

Ultrastructure of the nonciliated bronchiolar epithelial (Clara) cell of mammalian lung. III. A study of man with comparison of 15 mammalian species.

Abstract: Two morphologic characteristics have been used to define the nonciliated bronchiolar epithelial cell: (1) abundance of agranular endoplasmic reticulum (AER) and (2) numerous membrane-bound ovoid granules. In this study, we examined lobectomy specimens from three nonsmoking humans: one male (9.5 yr) and two females (62 and 43 yr) for comparison with lung specimens from mammalian species used as experimental models in lung research. Following fixation by airway infusion at constant pressure (20 cm), lung tissue was processed by a selective embedding technique and bronchioles of known anatomic location were studied by electron microscopy. Nonciliated bronchiolar epithelial cells of man contained numerous membrane-bound granules (averaging 6 per cell) in the apical cytoplasm and abundant granular endoplasmic reticulum (GER). AER was not observed. Granules averaged 0.3 μm in diameter and contained a fine granular matrix and parallel tubular arrays. After comparing these features in man with those of fifteen ot...

Polarity and nucleation of microtubules in polarized epithelial cells

Abstract: Microtubules oriented in the apicobasal axis of columnar epithelial cells are arranged with a uniform polarity with minus ends toward the apical surface, suggesting that these cytoskeletal filaments might serve as a substrate for polarized movement of membrane vesicles within the cell. It is not known whether hepatocytes, a cuboidal epithelium in which transcellular transport is a requisite step in normal apical membrane biogenesis, contain microtubules arranged with a similar polarity. In the present study, we explore the question of microtubule polarity and possible mechanisms for nucleation in the epithelial cell lines WIF-B (hepatocyte), Caco-2 (intestine), and Madin-Darby canine kidney (MDCK). Caco-2 microtubules in the apicobasal axis had uniform polarity with minus ends nearest the apical surface. After cold and nocodazole-induced depolymerization, microtubule regrowth initiated in the apical region in all three cell types. The apex of WIF-B and Caco-2 cells contained two pools of gamma-tubulin: one associated with centrosomes and the other delocalized under the apical membrane. Non-centrosomal gamma-tubulin was present in complexes that sedimented between 10S and 29S; both forms could bind microtubules. The presence of both centrosomal and noncentrosomal gamma-tubulin in apical cytoplasm suggest multiple mechanisms by which microtubule nucleation might occur in epithelial cells.

Habitat, succession, attachment, and morphology of segmented, filamentous microbes indigenous to the murine gastrointestinal tract.

Abstract: Some indigenous microorganisms localize on epithelial surfaces in various areas of the digestive tracts of animals. One of these, a segmented, filamentous microbe, localizes on the epithelium in the small bowels of mice and rats. These filamentous microbes colonize mice at weaning time and persist in adult animals for at least 2 months. Results of the study of light and electron micrographs suggest that the microorganisms are procaryotic, and that they interact with small bowel epithelial cells to form an attachment site. This site consists of modified epithelial cell membrane and apical cytoplasm adjacent to the attached bacterium. The microbe fills the site with part of its first segment. This segment has a nipple-like appendage on the end inserted into the epithelial cell. The other segments, which compose the rest of the filament, are usually separated by septa. Many of the individual segments contain intrasegmental bodies that appear to be procaryotic cells. Some of these intrasegmental bodies are similar in morphology to the first segment of each filament inserted into an epithelial cell. These intracellular bodies may be components in the life cycle of the microorganism. The organism has not yet been cultured in recognizable form. Therefore, such a hypothesis cannot be proved as yet, nor can the microbe be classified with certainty. Because it localizes in an epithelial habitat in the small bowel, however, it may be a particularly important microbial type in the gastrointestinal ecosystem of laboratory rodents.

An electron microscopic study of ciliogenesis in developing epidermis and trachea in the embryo of Xenopus laevis

Abstract: This paper describes the ultrastructural phenomena occurring during the differentiation of cilia in the epidermis and trachea of Xenopus laevis. The sequence of developmental events seems to begin with the de novo formation of clusters of small, dense “procentriole precursor bodies” which are apparently transformed into procentrioles under the influence of dense amorphous masses here termed “procentriole organizers.” The procentriole so formed is a cylinder 150 mm in diameter with nine single microtubules in its wall which probably give rise to the nine “triplet” microtubles in the wall of the definite centrioles (200 mm in diameter). The appearance of multiple centrioles in the apical cytoplasm is correlated with disappearance of procentriole precursor bodies and procentrioles. Smooth-surfaced vesicles seemingly produced in the well developed Golgi zones may contribute to the development of the ciliary membrane. Following their formation in the supranuclear cytoplasm, the centrioles or presumptive basal bodies align with their longitudinal axes perpendicular to the apical plasmalemma. A ciliary shaft then appears distal to each basal body and simultaneously small, dense bodies like those termed “procentriole precursor bodies” reappear. At this time we call the dense bodies, “axonemal precursor bodies,” because they probably provide material for the synthesis of new axial microtubules at the tip end of the growing cilium. Centriolar rootlets develop during centriolar alignment and ciliary shaft formation from a distinct, low electron-opaque, precursor substance.

Pinocytotic activity of the uterus of the rat

Abstract: With both scanning and transmission electron microscopy, large ectoplasmic projections are found intruding into the lumen from the epithelial cells of the rat uterus. These projections, which are abundant both prior to implantation and during delayed implantation, communicate with the underlying cytoplasm only by a small pedicel as though in the process of pinching off. However, introduction of tracer material into the uterine lumen demonstrates the pinocytotic nature of these projections. Within three minutes after introduction of tracer the projections, termed pinopods, contain numerous vacuoles filled with tracer. Within ten minutes large vacuoles containing tracer are present in the apical cytoplasm subjacent to the individual pinopods. The varied images observed in the experimental and control materials suggest that there is a continual turnover of pinopods. Initially a simple ectoplasmic projection, the pinopod apparently develops rapidly into a mass of ectoplasm 2–3 μ in diameter with multiple folds and pockets at its surface and numerous internal vacuoles. Following a period of active endocytosis of fluid, the pinopod becomes more spherical and, together with contained material, is withdrawn into the apical cytoplasm. It is suggested that pinocytosis might play a role in producing apposition of the blastocyst to the luminal epithelium, in passing information from the blastocyst to the stroma, and in diminishing the molecular contents of the uterine lumen during specific times in the reproductive process.