Apical cytoplasm

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

Three-dimensional organization of microtubules and microfilaments of the basal body apparatus of ciliated respiratory epithelium

Abstract: This is a descriptive study showing the three-dimensional interrelationship of cytoskeletal elements at the apex of ciliated cells of rat respiratory epithelium. Tissue specimens were serially thin sectioned in various planes and examined by transmission electron microscopy. Thicker sections were also cut at various angles and analyzed stereoscopically. Other specimens were cleared of soluble molecules by glycerination or Triton-X100 treatment and sectioned as described above. It was found that C microtubules from the triplets of each basal body diverge from the A and B microtubules, run a short distance, and converge at the basal foot. These microtubules or other microtubules arising anew then dispersed deeper into the cytoplasm. The C fibers also interdigitated with other microtubules running perpendicular to them and parallel to the ciliated surface. Ten-nanometer intermediate filaments were organized in parallel sheets between adjacent basal bodies. Sixnanometer actin filaments were distributed throughout the apical cytoplasm. Neighboring basal bodies were linked to one another by microtubules and microfilaments. Basal bodies from each cell appear to be structured for stability, flexibility, and arranged to operate as a single unit.

In vivo expression and distribution of dense granule protein 7 (GRA7) in the exoenteric (tachyzoite, bradyzoite) and enteric (coccidian) forms of Toxoplasma gondii.

Abstract: The in vivo expression and distribution of the dense granule protein GRA7 was examined in both the exoenteric (tachyzoite and bradyzoite) and enteric (coccidian) forms of Toxoplasma gondii by immunocytochemistry. There was strong staining of GRA7 in granules within all the infectious stages (tachyzoite, bradyzoite, merozoite and sporozoite). During tachyzoite development, GRA7 was secreted and was associated with the parasitophorous vacuole. In contrast, although there was staining of granules within the bradyzoites of more mature cysts, there appeared to be little staining of the tissue cyst wall or host cell. The apparent stage-specific variation in secretion of GRA7 between tachyzoites and bradyzoites was confirmed by double labelling using stage-specific markers (SAG1 and BAG1). In the enteric forms in the cat gut there was strong labelling of the PV containing early asexual and sexual stages and staining of a few granules in the apical cytoplasm of the merozoite. The positive enteric staining pattern differentiates GRA7 from the other GRA proteins (GRA1-6) which were absent in the merozoites and enteric stages. The staining pattern of GRA7 with strong staining during tachyzoite and enteric development and reduced staining in the tissue cysts is similar to that seen for NTPases. The function of GRA7 is unknown but it is unique among the dense granule proteins in being expressed in all the infectious forms of T. gondii which would point to a basic role in the vacuolar adaptations required for active parasite development.

The trophotaenial placenta of a viviparous goodeid fish. I. Ultrastructure of the internal ovarian epithelium, the maternal component.

Abstract: Embryos of goodeid fishes develop to term within the ovarian lumen, where they undergo considerable increase in weight due to transfer of maternal nutrients across a trophotaenial placenta. The placenta consists of an embryonic component, the trophotaeniae, and a maternal component, the ovarian lining. The latter was examined by transmission electron microscopy, scanning electron microscopy, and light microscopy in both gravid and non-gravid ovaries of the viviparous goodeid fish, Ameca splendens. The single median ovary of A. splendens is a hollow structure whose lumen is divided into lateral chambers by a highly folded longitudinal ovarian septum. Germinal tissue occurs within folds of the ovarian lining that extend into each of the two lateral chambers. Matrotrophic embryonic development takes place within ovarian chambers. During gestation, the lining of the ovarian lumen is in direct apposition to body surfaces and trophotaenial epithelia of developing embryos. The ovarian lining consists of a simple cuboidal epithelium, termed the internal ovarian epithelium (IOE), overlying a well-vascularized bed of connective tissue. Cells of the IOE are apically convex. Well-developed granular and agranular endoplasmic reticula and numerous large membrane-bound vesicles with electron-dense content occupy the apical cytoplasm of IOE cells. Two functional states of the same cell type are distinguished within the IOE. Phase I cells contain few, if any, large apically situated vesicles; Phase II cells contain many. Secretory products of the IOE are presumed to be an important source of nutrients for embryonic development. Structural and functional relationships of the IOE to the trophotaenial epithelium of developing embryos are discussed in relation to maternal-embryonic nutrient transfer processes.

Ultrastructure of the Ductuli Efferentes in Monkeys

Abstract: The epithelium of the ductuli efferentes in monkeys consists primarily of ciliated and nonciiated cells, although occasional macrophages, intraepithelial lymphocytes and basal cells are present. Beneath the epithelium is a thick basal lamina (2-8 Mm) deep to which are found dense bundles of collagen fibers. The ovoid or spherical nuclei (8 X 11 Mm) of the ciliated cells are large, contain predominantly electron lucent euchromatin and are located in the middle or apical regions of the cell. The smaller nuclei (5-8 Mm) of the nonciliated cells are situated near the basal lamina of the epithelium and are bizarre-shaped due to numerous indentations of the nuclear envelope. They also contain electron-dense heterochromatin especially adjacent to the inner nuclear envelope. The cytoplasm of both cell types extends from the basal lamina to the tubule lumen. The ciliated cells are characterized by numerous mitochondria and a lightly stained cytoplasm. A few dense bodies, presumably lysosomes, are also present in the supranuclear cytoplasm. In addition, well developed ciliary rootlets containing a regular pattern of 70-80 nm cross striations frequently extend to the perinuclear zone far beyond the apical cytoplasm. Micropinocytotic vesicles, membrane-bound dense bodies, and numerous vacuoles of different sizes filled with flocculent material are densely packed in the cytoplasm of the nonciliated cells. Some mitochondria and lysosomes are also scattered throughout the cytoplasm of these latter cells. In both cell types there is a paucity of other organelles, particularly Colgi and endoplasmic reticulum. These morphological features suggest a low capacity for protein synthesis and elaboration of secretory products. The nonciliated cells are known to absorb large quantities of fluid from the tubular lumen. The micropinocytotic vesicles and numerous vacuoles in these cells are likely involved in this process. The abundant mitochondria in the ciliated cells are no doubt necessary to provide energy for ciliary motion.

The distribution of MUC1, an apical membrane glycoprotein, in mammary epithelial cells at the resolution of the electron microscope: implications for the mechanism of milk secretion.

Abstract: The distribution of the glycoprotein, mucin 1 (MUC1), was determined in lactating guinea-pig mammary tissue at the resolution of the electron microscope. MUC1 was detected on the apical plasma membrane of secretory epithelial cells, the surface of secreted milk-fat globules, the limiting membranes of secretory vesicles containing casein micelles and in small vesicles and tubules in the apical cytoplasm. Some of the small MUC1-containing vesicles were associated with the surfaces of secretory vesicles and fat droplets in the cytoplasm. MUC1 was detected in much lower amounts on basal and lateral plasma membranes. By quantitative immunocytochemistry, the ratio of MUC1 on apical membranes and milk-fat globules to that on secretory vesicle membranes was estimated to be 9.2:1 (density of colloidal gold particles/microm membrane length). The ratio of MUC1 on apical membranes compared with basal/lateral membranes was approximately 99:1. The data are consistent with a mechanism for milk-fat secretion in which lipid globules acquire an envelope of membrane from the apical surface and possibly from small vesicles containing MUC1 in the cytoplasm. During established lactation, secretory vesicle membrane does not appear to contribute substantially to the milk-fat globule membrane, or to give rise in toto to the apical plasma membrane.