Journal of ultrastructure research最新文献

Transmission electron microscopic investigations revealed extracellular three-lamellar and tubuli-like structures formed by the white rot fungusSporotrichum pulverulentum, which was grown with glucose on a rotary shaker. These structures, originating from the outermost fungal cell wall layer, were isolated by digesting the purified cell walls with snail enzyme. The resistant structures contained in the outer cell wall layer were harvested and chemically analyzed. They were composed of 80–90% carbohydrates, primarily glucose monomeres; 5–10% proteins, including five fractions with molecular weights between 30 000 and 200 000; and, finally, 5–10% lipids, none of which were phospholipids. Chemical analysis of the components after treatment with 2-mercaptoethanol/EDTA, followed by TEM observations, however, suggests that these structures consist of almost equal amounts of carbohydrate, protein, and lipid and that the additional carbohydrate is attached to them without any structural function. Several hypothesis concerning the biological function of the structures are made.

The hemoglobin of the lizardTarentola annularis has been studied within erythrocytes being digested in the gut of a parasitic pentastomide,Raillietiella sp. The hemoglobin is crystallized in the form of bundles comprised of numerous tubules (up to 2000). These tubules are simple or complex. Simple tubules are 50 nm in diameter; their wall is made up of two electron-opaque rings, separated by a clear ring. Complex tubules are up to 100 nm in diameter and show as many as 13 concentric walls. High magnification of transverse sections of simple tubules show 96 granules; each opaque ring is made up of 48 granules. Human hemoglobin is known to crystallize as 18-nm tubules, the wall of which is made up of six molecules; comparison of these data with our observations indicates that transverse sections of tubules of crystallized lizard hemoglobin should contain 24 molecules. Thus, each molecule of crystallized lizard hemoglobin consists of four granules; these granules may be considered as globin molecules. Erythrocytes in fresh lizard blood do not show crystallized hemoglobin; however, in blood treated with sodium bisulfite, they show tubules similar to that found in the parasite.

Unusual structures often found in the cytoplasm of tumor cells in a clear-cell sarcoma appeared as multilayered, concentric, oval, spiral, parallel arrays of cisternae in various planes of section. It was demonstrated that the cisternal membrane and cavity were continuous with plasmalemmas of tumor cells and the extracellular space, respectively, suggesting that the structures were formed by the intracytoplasmic infoldings of plasmalemmas. Another characteristic found in the structures was orderly microfilaments with an average diameter of 6.5 nm which were placed between the confronting plasmalemmas in the infoldings. The filaments which underlay the infolded plasmalemmas ran parallel to each other along the cytoplasmic surfaces of plasmalemmas approximately 15 nm apart. The regularly arranged filaments were found in the infolded plasmalemmas, but not beneath any other area of plasmalemmas. The short ends of long filaments appeared to bend toward the inner surfaces of plasmalemma and to be directly connected with the surface proper. These results show that the filaments may be closely associated with the plasmalemmal infoldings and included as the same category of plasmalemmal undercoat. Additionally, the biological significance of the structures is discussed.

During mid- and late gestation, the uterus of sandbar sharks possesses specialized sites for exchange of metabolites between the mother and fetus. Attachment sites are highly vascular, rugose elevations of the maternal uterine lining that interdigitate with the fetal placenta. The maternal epithelium remains intact and there is no erosion. The attachment site consists of a simple, low columnar juxtaluminal epithelium underlain by an extensive vascular network. Juxtaluminal epithelial cells possess branched microvilli, saccular invaginations of the apical surface, and coated pits. They contain numerous coated vesicles, lipid-like inclusions, a prominent rough endoplasmic reticulum, and many free ribosomes. Tight junctions join the luminal aspect of adjacent cells. Lateral cell boundaries are highly folded and interdigitated. Capillaries are closely apposed to the basal cell surfaces. The endothelium is pinocytotically active. Comparison with the uterine epithelium of non-placental sharks, mammalian epitheliochorial placentae, and selected transporting epithelia reveals that the structure of the maternal shark placenta is consistent with its putative multiple functions, viz.: (1) nutrient transfer; (2) transport of macromolecules, e.g., immunoglobulins; (3) respiration; and (4) osmotic and ionic regulation.

The smooth, proximal portion of the yolk sac placenta of the sandbar shark, Carcharhinus plumbeus is comprised of: (1) An outermost epithelial ectoderm; (2) an intervening collagenous stroma; and (3) an inner mesothelium. The surface epithelium may be one to three cell layers thick. The surface epithelium comprises two cell types. A cuboidal cell that has a dome-like apical surface covered with microvilli and an ovoid nucleus predominate. These cells contain lipid inclusions, many cytoplasmic filaments, and are joined by desmosomes. The second cell type has a convoluted nucleus and a flattened cell apex with microvilli, cilia, and paddle cilia. Golgi complexes and elements of the endoplasmic reticulum are relatively uncommon in the cytoplasm of both cell types. Microplicae also occur on the surfaces of some cells. The smooth, proximal portion of the placenta is sparsely vascularized. The innermost cellular elements of the surface epithelium rest on a prominent basal lamina. A collagenous zone separates the epithelial basal lamina from the basal lamina of the mesothelium. The mesothelial cells are squamous with a fusiform nucleus, many pinocytotic pits and vesicles, and a large number of cytoplasmic filaments. The endoplasmic reticulum, except for occasional patches of the rough type, and the Golgi complex are poorly developed. Ultrastructural tracer studies show that this portion of the placenta does not absorb horseradish peroxidase (HRP) and trypan blue.

Irregularly shaped masses of electron-dense material that are located in the perinuclear cytoplasm of Drosophila spermatocytes contain small granular and fibrillar subunits. These fibrogranular bodies can be observed to extend toward and into the nuclear pores where the material is also continuous with nucleolar material. These observations further substantiate a nucleolar origin for the fibrogranular bodies. As pores of annulate lamellae differentiate within the fibrogranular bodies, structural configurations resembling polyribosomes are noted. Microtubules can also be observed in the fibrogranular material and in some cases they are close to differentiated pores of annulate lamellae. These morphological observations tend to confirm and extend previous suggestions that the fibrogranular bodies may represent stored gene products, and that the differentiation of pores is associated with the dispersal, processing, and assembly of the material perhaps in the form of special functioning polyribosomes. The studies also raise the question of whether or not tubulin may be one of the proteins synthesized by these newly formed polyribosomes.

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.