Journal of ultrastructure research最新文献

During ontogeny, the yolk sac of some viviparous sharks differentiates into a yolk sac placenta that persists to term. The placenta is non-invasive and non-deciduate. Hematrophic transport is the major route of nutrient transfer from mother to fetus. The placental unit consists of: (1) an umbilical stalk; (2) the smooth, proximal portion of the placenta; (3) the distal, rugose portion; (4) the egg envelope; and (5) the maternal uterine tissues. Exchange of metabolites is effected through the intervening egg envelope. The distal rugose portion of the placenta is the fetal attachment site. It consists of: (1) surface epithelial cells; (2) a collagenous stroma with vitelline capillaries; and (3) an innermost boundary cell layer. The columnar surface epithelial cells are closely apposed to the inner surface of the egg envelope. Wide spaces occur between the lateral margins of adjacent cells. Surface epithelial cells contain an extensive apical canalicular-tubular system and many whorl-like inclusions in their basal cytoplasm. Capillaries of the vitelline circulation are closely situated to these cells. A well-developed collagenous stroma separates the surface epithelium from an innermost boundary cell layer. In vitro exposure of full-term placentae to solutions of trypan blue and horseradish peroxidase (HRP) reveals little uptake by the smooth portion of the placenta but rapid absorption by the surface epithelial cells of the distal, rugose portion. HRP enters these cells by an extensive apical system of smooth-walled membranous anastomosing canaliculi and tubules. Prominent whorl-like inclusions that occupy the basal cytoplasm of the surface cells, adjacent to the pinocytotically active endothelium of the vitelline capillaries, are hypothesized to be yolk proteins that are transferred from the mother to embryo throughout gestation.

The effects of administration of anti-microtubular drugs—vinblastine and colchicine—on the ultrastructure of the zona fasciculata cells of young rat adrenal were studied. Young male rats were injected with vinblastine and sacrificed 2 hr later or with colchicine and sacrificed 3 hr after drug administration. Animals injected with isotonic saline in same experimental conditions served as controls. Ultrastructural alterations provoked by both drugs, vinblastine or colchicine, were identical and were most prominent in the Golgi areas. They appeared enlarged and crowded with round, or slightly elongated light vesicles, acid phosphatase, and osmium negatives. The Golgi dictyosomes, although keeping their normal morphology, were less numerous and presented cisternae which were narrower and shorter than controls. Electron-dense vesicles, round or elongated, and acid phosphatase positive—lysosomes—were observed in great number in the Golgi areas, intermingled with light vesicles. The relative volume of light vesicles and lysosomes of the treated animals was significantly increased when compared with controls, but the relative volume of dictyosomes was significantly decreased. Also the numerical density of light vesicles and lysosomes of the injected rats was significantly increased when compared with controls. These alterations are highly suggestive of the Golgi involvement in the adrenal secretory process.

Electron microscopic observations carried out onNostoc commune Vauch. in culture show that during development the extracellular investment undergoes evident modifications in size and structure. Since the investment of the motile hormogonium shows the characteristics of a “slime” and those of the nonmotile hormogonium and the biseriate stage show the characteristics of a “sheath,” the meaning of these two terms is discussed. In the slime, the existence of a reticular structure with polygonal meshes is recognized and is to be considered the structural basis of the organization of the investment. The transformation from slime to sheath takes place through a gradual diminution in the size of the meshes with a consequent increase of the fibril aggregation. The possibility is considered that slime-sheath reversibility as well as cessation of motility are related with modifications in the cellular secretion.

This work builds upon a previous paper (W. Colquhoun, 1984,J. Ultrastruct. Res.87, 97) in which a sputter shadowing device was briefly described. The device allowed TEM specimens to be shadowed in a conventional sputter coater. Images obtained by sputter shadowing with a standard Au/Pd target were of good quality but were slightly inferior to the best that could be obtained by e⁻-beam evaporation of tungsten. Here we show that construction and use of a tungsten target greatly improves the quality of the sputter shadowed deposit. Images of DNA and ribosomal subunits contrasted by sputter shadowing with tungsten are shown. The DNA images indicate that sputter shadowing with tungsten is a gentle contrasting technique. The sputter shadowed images of the 30 S ribosomal subunits show the major features of the particle revealed by evaporation shadowing using the most sophisticated of methods in that technology. Advantages of sputter shadowing are discussed and a rationale for the improved grain obtained by sputtering tungsten is suggested.

Direct immunological identification of cellular components has not been possible in tissues prepared for electron microscopy by conventional methods. This may be attributed, in part, to the relatively harsh reagents employed. Using an approach to preparation of biological specimens for transmission electron microscopy that aims for minimal perturbation of native protein conformation, we have obtained specimens that may be stained with antibodies. Recent investigations using these methods have revealed new information regarding the organization of epidermal cells.

Using filipin as a cytochemical probe to reveal the distribution of cholesterol, myelinated peripheral nerve fibers were examined in freeze-fracture replicas. Filipin-sterol complexes were most abundant in the Schwann cell and axonal plasma membranes. In the Schwann cell plasma membrane there was no heterogeneity in complex distribution in relation to the subjacent cytoplasmic network. In myelin lamellae there was a decrease in complexes from outer to inner lamellae and some aggregation of complexes in individual lamellae. The density of complexes in cytoplasmic organelles varied from absent in mitochondria to high in lysosome-like bodies. The results are interpreted in terms of the related biochemical composition and biophysical properties of cell membranes, with particular reference to the myelinated nerve fiber. The influence of diffusion barriers and gradients on the formation of complexes by filipin is considered.

Anterior and posterior centrioles ofPhysarum amoebae are indistinguishable by their size during interphase but there is a correlation between the size of the two centrioles in the same amoeba. The interphase length of centrioles in diploid amoebae possessing only one pair of centrioles was 11% longer than in the case of the haploid strain. Treatment with taxol led to a 23 and 32% increase of the mean length in interphase and blocked mitosis, respectively. Conversely, during control mitosis the parental centrioles showed a 12% decrease of their mean length while the size of the daughter centrioles increased progressively. Neither nocodazole nor cold treatment induce a decrease of centriole length. The mean length of the cartwheel structure (internal proximal part) although constant during mitosis could be increased 24% in the presence of taxol. Similarly there was a correlation between the number of anterior satellites and the centriole length.

During meiosis in the male of a cyprinodontid fish,Aphyosemion splendopleure, and during the organization of the spindle of division, the spindle is made of two types of tubules: microtubules (20–25 nm) and macrotubules (30–50 nm). The macrotubules are associated only with the polar region of the meiotic apparatus and are located outside the spindle of microtubules. At the end of meiosis, the spindle microtubules depolymerize whereas the macrotubules remain. One can find them throughout the entire process of spermiogenesis; later, they disappear only at the end of spermatid maturation. We have studied four populations from Cameroon, three of them with macrotubules.

A physical procedure for the visualization of cellular fine structures is described as an alternative to chemical preparative techniques. It consists of fixation by fast freezing followed by controlled etching in the cryostage of a million-volt transmission electron microscope. Whole mounts were thus observed under stable conditions with no use of chemical fixatives, solvents, or stains, with no exposure to the atmosphere, and with the improved penetration and resolution in thick specimens that characterize high-voltage electron microscopy. The preservation, contrast, and resolution exhibited by images of preparations obtained by this procedure are discussed.