Journal of ultrastructure research最新文献

Whole mount and thin section preparations of intact and selectivity disrupted hamster spermatozoa revealed an organized array of cytoplasmic filaments associated with specific regions of the acrosome. The filaments were localized along the ventral surface of the spermatozoon and extended from its tip, distally to the anterior margin of the equatorial segment. Individual filaments were 11–13 nm in diameter and they were aligned parallel to one another to form a two-dimensional sheet oriented in the long axis of the spermatozoon. The filament complex adhered preferentially to the cytoplasmic surface of the outer acrosomal membrane rather than the plasma membrane. Examination of disrupted spermatozoa revealed that the distribution of this cytoskeletal assembly correlated with the distribution of a specific acrosomal matrix component. The possible role of this complex in the acrosome reaction or in the organization of acrosomal matrix domains is discussed.

The purpose of the present experiments was to study possible different pathways of intracellular transport of proteins after luminal and basolateral uptake in isolated rabbit proximal tubules. Tubules were exposed to cationized ferritin (CF) in the perfusion fluid and horseradish peroxidase (HRP) in the bath simultaneously or to HRP in the bath alone for 30 min. The peritubular fluid (bath) and perfusion fluid were then exchanged and the tubules either fixed immediately or allowed to function during chase-periods for 10, 20, 30, or 60 min before fixation to follow the migration of the proteins through the cells. The proteins were to a large extent found separated in different vacuoles and lysosomes at all time periods studied, indicating separate pathways after uptake via the luminal and basolateral membranes respectively. About 0.5% of the CF taken up by the cells was transported through the cells and became located in the intercellular spaces. HRP was transported from the peritubular fluid to the apical cytoplasm of the tubule indicated by a gradual accumulation of small HRP-containing vesicles, first in the basal part of the cells and then in the apical cytoplasm. In tubules perfused with both CF and HRP in the perfusate, the CF and HRP were found together in apical vacuoles and lysosomes. After perfusions with HRP alone, this tracer was found in similar large vacuoles and lysosomes in the apical cytoplasm, in contrast to the small HRP-filled vacuoles seen after uptake from the bath.

In electron micrographs of 50 S (large) subunits fromEscherichia coli ribosomes, the highly preferred crown view is inferred to represent the roughly hemispherical particle lying with its flat or concave face against the carbon film. Single particle averaging allows the reproducible details of the crown view particle to be recognized. Multivariate image analysis shows the most variable morphological features of this view to be the two side protrusions, the L7/L12 stalk and the L1 ridge, both of which show apparent positional variations. The invariance of the features of the particle body implies that the movements of the side protrusions are not merely a result of perspective changes produced by major rotations of the particle body out of its quasistable, flat-lying position. A bending point localized on the L7/L12 stalk is conjectured to represent a functional “hinge” that may be related to the secondary/tertiary structure of the L7/L12 dimeric protein.

In this study a rabbit antiserum against human aortic elastin, which showed a high degree of species specificity in ELISA tests, was used to examine elastin fiber formation in the human fetal aorta between the ages of 14 and 23 weeks. Elastin was first detected by the antibody in the matrix of the 14-week-old specimen in association with the microfibrillar component. At this stage of development, the sections did not reveal structures morphologically identifiable as elastin. By the 17th week, discrete loci of elastin deposition were observed together with well-defined elastin fibrils. Only by the 23rd week did the aorta show the characteristic layering of elastic fibrils separating the myoblasts of the tunica media. In the latter specimen, the newly synthesized uncrosslinked elastin appeared to be unevenly distributed on the surface of elastic fibrils where it formed continuous strips of variable width arranged mostly in the form of spirals. This observation is discussed with respect to the proposals that (a) the morphogenesis of elastic tissue is a dynamic process involving a close interrelationship between elastic fibrils and elastogenic cells and (b) the morphogenetic movement of elastogenic cells plays an important role not only in the growth of elastic fibrils but also in the ultrastructural organization of the tissue.

The relationship between the chloroplast ultrastructure and the thylakoid membrane composition was observed during the growth ofBrassica rapa ssp.oleifera, Helianthus annuus, Sisymbrium altissimum, andTanacetum vulgare. The ultrastructural measurements were made on sections cut perpendicular to the grana. In all the species the young leaves had a low proportion of P₇₀₀ chlorophyll a-protein complex (CPI in photosystem I), whereas the proportion of chlorophyll a-protein complex of photosystem II (CPa) was fairly high. The amount of chlorophyll a-protein complex of photosystem II (CPa) decreased with age, whereas the amount of P₇₀₀ chlorophyll a-protein (CPI) complexes increased. The proportion of the light-harvesting chlorophyll a/b-protein (LHCP) complexes first increased and the declined as the plants aged. The chloroplast area in longitudinal sections was highest when the total content of light-harvesting chlorophyll a/b-protein (LHCP) was high and the values declined in older plants. During ageing, the ultrastructure of the chloroplast showed increase in the size of the grana and distinct profiles of stroma thylakoids extending between large grana. The granal stacks were largest, when the proportion of P₇₀₀ chlorophyll a-protein (CPI) was high and the total amount of light-harvesting chlorophyll a/b-protein (LHCP) low. When light is not limiting, the stage of development of the plant seems to have a significant effect on the thylakoid components and thylakoid ultrastructure.

The acrosome ofMolgula manhattensis spermatozoa is a moderately electron-dense slightly depressed sphere, which is enclosed by a unit membrane. It is approximately 80 × 80 × 40 nm in length, width, and height, respectively. Neither a subacrosomal substance nor a perforatrium can be identified between the acrosome and the nuclear envelopes. During early spermiogenesis, at least three or four vesicles (50–60 nm in diameter) appear in a blister at the apex of the spermatids. Later, these vesicles attach to the inner surface of the plasmalemma enclosing the blister. They then come in contact with each other along the inner surface of the plasmalemma and fuse to form a horseshoe-shaped acrosomal vesicle which rounds up during further differentiation.

Distal nephron segments in the rat renal cortex contain distal convoluted tubule cells (DCT cells), connecting tubule cells (CNT cells), intercalated cells (I cells), and principal cells (P cells). The present study was carried out to expand present knowledge on the ultrastructure of these cells. The cells were sampled from superficial cortex and analyzed by electron microscopy. Several morphometric parameters were determined and statistical comparison between cell types was performed. Significant structural differences between the cell types were demonstrated. DCT cells showed the highest volume density of mitochondria whereas the amplification of basolateral membranes was higher in CNT cells than in I and P cells. The surface density of the membrane that bounds intermediate vesicles in the apical cytoplasm was twofold higher in I cells than in the other cell types. The morphological differentiation found in the present study adds to available evidence indicating a functional differentiation between the cell types and provides a reference for structure-function correlations in these cells.