Masayuki Miyoshi

Scanning electron microscopy of the renal corpuscle of the mesonephros in the lamprey, Entosphenus japonicus Martens.

SummaryThe renal corpuscle of the lamprey mesonephros was studied under the scanning electron microscope.Bowmans capsules with individual spaces are chockshaped sacs closely packed together along a medial artery. The lateral walls of the capsules are apposed to those of neighbouring capsules.Glomerular capillaries from the medial artery extend radially between the apposed walls of neighbouring Bowmans capsules. Bulgings of capillaries into the capsular space are associated with mesangial folds of the capsular epithelium.The transitional zone of the visceral layer with podocytes and the parietal layer of squamous epithelium is bounded by linearly arranged rod-shaped epithelial cells. Apertures of the urinary tubule are lined by cells equipped with a fascicle of cilia.

Microridges of oral mucosal epithelium in carp, Cyprinus carpio

SummaryThe surface of carp oral mucosa is characterized by various patterns of microridges about 0.3 μm wide, 0.1 μm high, and of various lengths. To elucidate the derivation and function of these microridges, the oral epithelium was examined by light- and electron microscopy. Microridges were present only on the surfaces of the superficial cells. Therefore, microridges on renewed superficial cells are presumed to be formed after old superficial cells have been discarded, and the various patterns of microridges found on the cell surface appear to indicate the progress of their development. In thin sections, the outer leaflet of the plasma membranes of microridges stained strongly with ruthenium red, and the underlying cytoplasm was packed with many fine filaments. The superficial cells contained many secretory vesicles that were PAS-positive but Alcian blue-negative at pH 2.5 and pH 1.0. However, after sulfation the vesicles gave a positive reaction with toluidine blue. These vesicles are secreted by exocytosis at the free surface of the cells. After release, the membranes of the vesicles are thought to be utilized for formation of microridges. On the basis of these observations, the possible function of microridges is discussed.

Tubular invaginations with caveolae and coated pits in the sinus endothelial cells of the rat spleen

Abstract The fine structure of plasmalemmal tubular invaginations with caveolae and coated pits in the sinus endothelial cells of the rat spleen has been demonstrated by scanning and transmission electron microscopy. In addition, the three-dimensional structure of the tubular invagination has been revealed by computer-aided reconstruction. The tubular invaginations of the plasma membrane plunged into the cytoplasm everywhere from the apical, lateral, and basal surfaces of the plasma membrane. The invaginations were tubular and branched away, and their plasma membranes were reinvaginated to form numerous caveolae and occasional coated pits. Numerous caveolae were found in clusters that looked similar to a bunch of grapes and the coated pits were present at the base of the clusters. The caveolae and coated pits derived from the tubular invaginations were almost ultrastructurally identical to those derived from the surface plasma membrane. From examination of the fractured surfaces of the endothelial cells treated with the aldehyde prefix osmium-dimethyl sulfoxide-osmium method and of ultrathin sections of those infiltrated by lanthanum nitrate, the tubular invaginations were found to not penetrate any endothelial cells. A computer-aided reconstruction revealed that the caveolae derived from the tubular invaginations were in close apposition to the surface-connected canaliculi. The reaction product of Concanavalin A conjugated to horseradish peroxidase was present on the outer leaflet of the membranes of the coated pits and coated vesicles and also in the contents of the endosomes, but it was absent from any caveolae. Based on our observations, the functional significance of the tubular invaginations in sinus endothelial cells is discussed.

Ultrastructural changes and glutathione depletion in the skeletal muscle induced by protein malnutrition.

Ultrastructural changes and glutathione level were investigated in the pectoralis muscle of rats fed a low-protein diet. Electron microscopy demonstrated the ultrastructural changes of occasional myofibrils affected with protein deficiency that were characterized with the streaming and/ or disruption of the Z-line and disintegration of sarcomeric striation. In the affected sarcomeres, sarcomere length was often elongated and fragmented thick filaments were present together with dense amorphous materials flowing from the damaged Z-line. Glutathione level of muscle in the low-protein diet group (5%casein) was reduced to about one-third of that in the control diet group (20% casein). The study suggests that depletion of glutathione by protein malnutrition is responsible for inducing myofibrillar damage through the excess leaking of Ca 2+ into the cytosol.

Junctions between the sinus endothelial cells of rat spleen

Abstract.Junctions between the sinus endothelial cells of rat spleen were examined by electron microscopy, using both freeze-fracture and detergent-extraction techniques. Adherens and tight junctions were observed. Adherens junctions were the predominant junctional structures between endothelial cells and were located on basolateral and lateral surfaces. At the basolateral adherens junctions, actin filaments were associated with the junctional membranes and were continuous with the actin filaments in stress fibers. Cross-bridges were present in the interspaces of the adherens junctions and spacing of the bridges was fairly regular. A form of tight junction, the macula occludens, was also observed between the endothelial cells, but it was not observed at every cellular apposition. Electron-dense material, adjoining the cytoplasmic surfaces of membranes in the tight junctions, separated the junctional membranes from masses of thin filaments. At basolateral tight junctions, the actin filaments were continuous with those in the stress fibers. Based on these observations, the two intercellular junctions were considered to play important roles in sinus functions.

Localization of caveolin-3 in the sinus endothelial cells of the rat spleen

Abstract. The localization of caveolins in the sinus endothelial cells of the rat spleen has been demonstrated by confocal laser scanning and electron microscopy. Caveolin-3, a muscle-specific caveolin, was detected by Western blot analysis and immunofluorescence microscopy of isolated sinus endothelial cells and tissue cryosections of the spleen. During the immunofluorescence microscopy of isolated endothelial cells, both caveolin-3 and caveolin-1 were found. In tissue cryosections of the spleen, caveolin-3, as well as caveolin-1 and -2, was present in the contours and cytoplasm of the cells. Immunogold electron microscopy of tissue cryosections revealed caveolin-3, -1, and -2 to be present in caveolae in the apical, lateral, and basal plasma membranes and some vesicular profiles in the cytoplasm of sinus endothelial cells. Furthermore, caveolin-3 was colocalized with caveolin-1 in the same caveolae in the apical, lateral, and basal plasma membranes. Stress fibers and tubulovesicular structures were situated in the vicinity of caveolae labeled with anti-caveolin-3, anti-caveolin-1, and anti-caveolin-2 antibodies. It is speculated that caveolae in sinus endothelial cells play an important role in the constriction of stress fibers.

Actin filaments in microridges of the oral mucosal epithelium in the carp Cyprinus carpio

SummaryActin filaments in the microridges on the surface of the fish oral mucosa taken from Cyprinus carpio were examined by electron microscopy after detergent extraction and decoration with myosin subfragment 1. After extraction with saponin, an irregular and densely packed meshwork of actin filaments was observed in the bases of the microridges, just lateral to the tight junctions with their fibrous undercoats. Actin filaments formed cores in the microridges and numerous linkages were seen between the filaments and the plasma membrane. Extraction with Triton X-100 and decoration with myosin subfragment 1 showed the ends of the actin filaments to be associated with the plasma membrane of the microridges, and in the bases of microridges the filament ends were anchored to intermediate filaments. Some actin filaments interconnected with the fibrous undercoats of the tight junctions. On the basis of these observations, the mechanism of the formation of microridges, including their pattern, is discussed.

Scanning- and transmission electron-microscopic study of lymphatic vessels in the splenic white pulp of the macaque monkey

SummaryThe fine structure of the lymphatic vessels in splenic white pulp of the macaque monkey was studied by scanning and transmission electron microscopy.Lymphatic vessels were slit-like or widened channels which extended along central arteries and their large branches. The walls of the vessels were very thin in comparison with those of nearby arteries. They were composed only of a layer of endothelium supported by underlying reticular cells. Endothelial cells were mostly ribbon-like and extended along the long axis of the vessels. Perikarya of the endothelial cells were slightly protruded into the lumen. The thin peripheral cytoplasm showed smooth surfaces, except for some tiny processes, especially at boundaries between adjacent cells. The basal surface of the endothelial cells was attached to the lattice of reticular cell processes forming the framework of the white pulp. Basal laminae in strands were intercalated between endothelial cells and reticular cells. Perforations were often seen through the endothelial cell cytoplasm. Lymphocytes or processes of macrophages seen in the perforations were considered to be in migration. Large patent openings through the endothelium were not observed. The wall structure of the lymphatic vessels in the splenic white pulp suggests that lymphocytes in the white pulp may move directly into the lymph flow, in addition to moving into the blood flow via the vascular sinuses.

Function of the cytoskeleton in cells with microridges from the oral epithelium of the carp Cyprinus carpio

Superficial cells of the oral mucosal epithelium in the carp and the cytoskeleton of the epithelial cells are examined by scanning and transmission electron microscopy. Microridges are formed on the surface of the epithelium. Epithelial cells contain two types of vesicles: mucous secretory vesicles and coated vesicles. Most of the mucous vesicles are situated in the center of the cell near the Golgi apparatus. In freeze-fracture replicas, intramembranous particles are abundant in the membranes of the secretory vesicles but rare in the apical plasma membrane. Coated vesicles are situated in the apical and subapical cytoplasm. A great number of thick filaments, considered to be keratin filaments, run randomly throughout the cell to form a meshwork. Thick filaments, which are sparse in the central cytoplasm, are connected to the membranes of the secretory vesicles and other membranous organelles. A layer of closely packed thin filaments, considered to be actin filaments, is found just beneath the apical plasma membrane. Microtubules also occur in the apical cytoplasm and run almost parallel to the cell surface. Both kinds of vesicles are connected to the thin and thick filaments. Their functional significance in the regulation of membrane at the free surface is discussed.

Cellular differentiation of absorptive cells in the neonatal rat colon: an electron microscopic study.

Cellular differentiation of the absorptive cells in the neonatal–suckling rat colon was investigated using horseradish peroxidase as a macromolecular tracer with a scanning or transmission electron microscope. Numerous villi were lined on oblique folds in an orderly fashion and smaller villi were lined between the folds in the proximal colon in 0- to 12-day-old rats. Three different types of absorptive cells were observed in the epithelium covering their villi: type I cells, type II cells, and type III cells. The type I cells were most numerous, and similar to typical absorptive cells of the adult rat large intestine. The type II cells endocytosed macromolecules into an apical endocytic membrane system without giant lysosome from the large intestinal lumen. The type III cells were characteristic of the well-developed endocytic membrane system, including a large supranuclear giant lysosome specialized for endocytosis, storage, and intracellular digestion as an ileal absorptive cell of the suckling rat. At no time was macromolecular tracer detected in the Golgi apparatus of the absorptive cells or in the intercellular space of the epithelium. These results suggest that the villial absorptive cells of the proximal colon have differentiated to three types at specific neonatal–suckling times. The type II and type III cells were not observed in the epithelium after the disappearance of the villi.