The insertion of muscle fibers in the subepithelial connective tissue layer of the guinea pig tongue was studied light and electron microscopically. Fibers of the tractus verticalis approach the epithelium penetrating the lamina propria, both the reticular and papillar layer. Terminating muscle fibers split up and form branching finger-like cytoplasmic processes. The myotendinous junctions of such terminal processes fine structurally correspond to myotendinous junctions generally observed in skeletal or smooth muscles. The entire brush-like formation, however, is more far-reaching and highly differentiated. Filament bundles (spine-like profiles) originate from the plasmalemma and extend to the lamina densa of the basal lamina, especially in those regions where actin filaments are attached to the plasmalemma. Microfibrils (10 to 12 nm diameter) reach the lamina densa of the basal lamina. They form bundles which are continuous with fibrotubular strands of elaunin fibers and elastic fiber microfibrils. Furthermore, microfibrils are interwoven with collagen fibrils.
When Trichophyton mentagrophytes thalli are placed on a medium containing 300 microgram/ml of coumarin, their growth rate is drastically reduced and the newly formed mycelium consists of curled and branched hyphae showing subapical bulges and swollen tips. Under the electron microscope, the most relevant abnormalities concern the cell walls which are often thickened by aberrantly shaped zones that are usually smeared unevenly over the surface of the "primary" wall instead of being deposited in discrete ridges. An ultracytochemical analysis suggests that the irregular thickenings are formed of chitin. Arguments suitable to explain the phenomena observed are discussed.
A technique for visualizing "interphase chromosomes" was applied to nuclei of the angio-spermous plant, Ornithogalum virens (2 n = 6), and the male mammal, Muntiacus munjak (2 n = 7), in an attempt to correlate the numbers of "chromosomes" visible during interphase with the respective diploid chromosome numbers. The alterations in chromosome structure observed during G1, S, and G2 periods were comparable to those previously reported in Allium cepa and Chinese hamster (CHO line) cells [33], but for technical reasons it was only possible to make accurate counts of interphase chromosomes in the G1 nuclei of O. virens. In addition, from our observations of interphase chromosomes that were pulse-labelled with tritiated thymidine and a parallel study of premature chromosome condensation (PCC) using pulse-labelled M.muntjak cells, we conclude that, although chromatin decondensation may be required for DNA synthesis, extreme chromatin decondensation can occur in the absence of DNA synthesis. Generally a morphological description of alterations in chromatin during interphase only roughly parallels the G1, S, and G2 phases defined by autoradiography following incorporation of tritiated thymidine. We suggest that both methods are valid through different ways of describing interphase.
By freeze-fracture electron microscopy, particles have been observed on the protoplasmic leaflet (PF face) of cytoplasmic and intracytoplasmic membranes of the photosynthetic bacterium Rhodopseudomonas capsulata. The particles are present under all culture conditions of chemotrophically and phototrophically grown cells. However, the number of particles per microM2 increased significantly when the formation of the photosynthetic apparatus in the membrane is induced. Intracytoplasmic membranes, where the bulk of photosynthetic activity is localized, always have a higher density of particles than cytoplasmic membranes. Under all conditions particles with a diameter of 9.5 nm dominate. The frequency of particles with diameters greater or smaller than 9.5 nm changed with culture conditions. A comparison of biochemical and electron microscopic data have lead us to the conclusion that the particles, formed under conditions which allow the synthesis of the photosynthetic apparatus, are composed of photochemical reaction centers and antenna light-harvesting bacteriochlorophyll I (B 875)-protein complexes. The total molecular weight of these particles is calculated to be 500,000.
Intracellular contents of potassium and of sodium are determined for 3T3 and SV 40-3T3 cells in dependence of growth density. In parallel, total cell volume and volume of intracellular water is determined for these cells suspended in physiological buffer. Intracellular potassium concentration thus evaluated for suspended 3T3 cells exhibits a sharp decrease at cellular growth densities which lead to density dependent inhibition of cell proliferation. In the case of SV 40-3T3 cells, this drop of potassium concentration with increasing cellular growth density is not observed, which correlates well with the absence of cell density dependent inhibition of cell growth in the transformed cell line. These results support the notion that processes of stimulation of quiescent 3T3 cells or of cell density dependent inhibition of their proliferation are mediated by processes including changes of potassium transport characteristics leading to increase or decrease respectively of their intracellular potassium concentration. Furthermore, these and other results suggest, that a difference between normal and transformed cells most relevant to their different proliferation behaviour might reside in different transport characteristics for potassium of the plasma membranes of these cells.
Lipoprotein particles of the size range of very low density lipoproteins in smooth endoplasmic reticulum, peripheral elements of the Golgi apparatus, and secretory vesicles of the immature Golgi apparatus face are 55 to 80 nm in diameter. Particles in mature secretory vesicles are smaller (45 nm). Concomitant with the change in particle size, the lumina of mature vesicles increase in electron density. A technique to fractionate immature and mature secretory vesicles was based on precipitation of a cupric-ferrocyanide complex (Hatchett's brown) through the action of a NADH-ferricyanide oxido-reductase resistant to glutaraldehyde which is characteristic of the membranes of mature secretory vesicles and of the plasma membrane of liver. Mature secretory vesicle fractions so isolated were enriched in cholesterol and depleted in triglycerides relative to immature vesicles on a phospholipid basis. Lipase activity was present in secretory vesicle fractions of the Golgi apparatus as shown by biochemical analysis and by cytochemistry. Cytochemical studies showed lipase to be present in both mature and immature vesicles but most evident in immature vesicles. The findings suggest that some very low density lipoprotein particles are converted to particles of smaller diameter during transit through Golgi apparatus. A lipase-mediated hydrolysis of triglycerides may relate to the transformation.
Spread nucleolar material from A. exigua exhibits an unusual arrangement of rDNA cistrons. The cistrons form head-to-head "diamond-shaped" doublets with a short spacer separating the members of the doublet. Single cistrons are usually terminal and arrange tail-to-tail with the adjacent doublet, suggesting the possibility of a repeating unit with a tail-to-tail, "bow-tie" doublet configuration in which the cistrons (average length: 1.44 micron) could be explained by an extraordinary shrinking of the DNA strand during transcription. This suggestion is supported by the estimation of the molecular mass of an early, or the primary, transcription product (2.2 X 10(6)).
In this study, more details of the different parts of the "ocelloide" of Nematodinium are given. The "hyalosome" which has a radial symmetry is made of endoplasmic reticulum, except the mitochondrial layer. There is only one constrictor ring and only a beginning of the periocellar gallery. The basal sheet on which the crystalline lens lies is a local differentiation of the cortical layer which is observed on the ceiling of the ocellar camera. This camera is related to the intercingular sulcus. There is also an ocellar fiber. The "melanosome" which is made of a double membrane and of many couples of thylakoids is flattened dorso-ventrally. The structure of the retina is similar to that observed in the other Warnowiidae. The pigmented ring is rather well developed and is in continuity with the upper part of the retina. Owing to the simpler organization of its ocelloide, Nematodinium is situated before the genera Warnowia and Erythropsidinium in the evolutionary series.
Plasmodial veins of Physarum polycephalum were investigated by combining cinematographical and tensiometrical methods. Veins remaining on their original growing substrate show characteristic surface movements resulting from an intrinsic contraction automaticity. Radial and longitudinal components of surface movements were registered simultaneously. Both contraction activities show identical frequencies, in contrast to results derived from experiments with isolated veins. There is only one genuine frequency and therefore one has not necessarily to suppose the existence of a cooperation of two oscillating systems underlying the rhythmic contraction phenomena. The results are discussed in respect to the basis of the contraction phenomena: the cytoplasmic actomyosin fibrils of Physarum and their function in motive force generation for protoplasmic streaming.
Poly(A)-containing RNA isolated from liver nuclei of untreated rats and 3 h or 12 h after partial hepatectomy or sham operation was hybridized to the complementary DNAs (cDNAs). In the homologous reactions two major components could be seen. When compared to normal liver, the complexity of the least abundant class was lower in nuclei from livers 3 h after partial hepatectomy and was higher in those isolated 12 h after operation. The heterologous reactions revealed an increase of some abundant poly(A)-containing sequences and a loss or dilution of rare sequences 3 h after operation. The latter effect was not specific to the regeneration process but occurred after laparotomy as well. 12 h after partial hepatectomy, however, about 10% new poly(A)-containing sequences were detected, corresponding to about 5000 molecules of 4500 nucleotides length, which are unique to regenerating nuclei.
In the present communication a characterization of the 5 S rRNA genes and the tRNA genes of Tetrahymena pyriformis has been performed. The number of 5 S rRNA and tRNA genes in the macromolecular DNA has been established. Furthermore no sequence homology is observed for these genes. The number of both types of genes does not change significantly under starvation conditions. The genomic organization of the 5 S rRNA and tRNA genes has been investigated. From in vivo replication studies it is concluded, that replication of both 5 S rRNA and tRNA genes takes place throughout the whole S-period.
The system of the intermediate-sized filaments (IF) of rat kangaroo PtK2 cells which can be specifically demonstrated by immunofluorescence microscopy using certain rabbit autoantibodies and guinea pig antibodies against bovine hoof prekeratin has been studied by electron microscopy. The characteristic ornamental, curved arrays of this system are shown after fixation in situ in both thin sections and whole-cell-preparations to represent bundles of 6 to 11 nm thick filaments extending through the whole cytoplasm, although in some cells they appear to be enriched in the perinuclear region. While many individual IF are recognized in the cytoplasm the tendency of such filaments to aggregate laterally into bundles is one of their prominent features. Among such bundle formations one form that consists of tightly packed IF cemented together in a dense osmiophilic matrix is especially conspicious. The appearance and mode of arrangement of the IF is not significantly altered in cells treated with colcemid and/or cytochalasin B. Spatial relationships of IF with microfilament-containing cables and microtubules as well as with membranous structures are also described. IF are heterogeneous in width and reveal an unstained, apparently hollow core, indicative of a tubular organization. Many IF show small, sometimes periodically arranged lateral projections which seem to be involved in IF cross-linking. Associations with polyribosomes are common. The changes in the IF system during mitosis have also been examined. The structural details of the IF as well as their possible role as cytoskeletal elements involved in the control of cell shape and cytoplasmic architecture are discussed in relation to data on various intermediate-sized filaments from other cell types. The close similarity of the IF of PtK2 cells to aggregates of prekeratin filaments is emphasized. It is suggested that PtK2 cells represent an epithelial cell line growing in a state of balanced semi-keratinization.
In situ hybridization of cloned rRNA genes from Drosophila melanogaster to D. simulans metaphase chromosomes shows that in the tested wild type strains both sex chromosomes contain a nucleolus organizer region. Silver grain counts support the published data that the X chromosomal rRNA gene number is significantly higher than the Y chromosomal.
1. The uptake, binding and elimination of phalloidin in liver is compared in adult (180 to 240 g) and "baby" (17 to 19 days old) rats in vivo and in vitro. 2. In both groups there is no relation between the concentration of the poison in the liver and the toxicity. 3. Although baby rats show a significantly higher tolerance against phalloidin than the adult animals, the concentration of the poison in the liver of baby rats is higher, and the elimination is significantly slower than in adult rats. 4. The very tight binding and concentration of phalloidin in the liver is explained by an extremely low dissociation constant. 5. Furthermore, the morphological differences between the poisoning of the liver cells in the entire organ and of isolated liver cells are discussed.
