bluuebunny/crossref_metadata_2025 huggingface dataset:
DEVELOPMENT OF THE METANEPHRIC KIDNEY
Authors: Priestley G. C. , Malt R. A.
Published: May 2004

The metanephric kidney was studied in fetal and older mice beginning at 16 days after mating of the parents. Polyribosomes from fetal kidneys labeled in vitro with 14C-labeled amino acids had 10–20 times more acid-precipitable radioactivity associated with them than polysomes from adult kidneys similarly labeled. Between 3 and 6 days after birth the rate incorporation of labeled amino acids by polyribosomes from neonatal kidneys declined sharply to only twice the value found for adult kidneys. There was no change in the shape of the polyribosome profile with increasing age, but before birth few, if any, ribosomes were bound to membranes compared with 20% 2 days after birth and between 20 and 30% in the adult. Total protein represented less than 10% of the wet weight in the fetal kidney but increased to 17% of the wet weight in the adult kidney. There was a steady decline in the concentration of RNA and DNA with respect to dry weight throughout kidney development. DNA concentration declined more rapidly than RNA concentration, so that the milligram to milligram ratio of RNA to DNA increased. In males the RNA/DNA ratio was stable at 1.3 at 40 days after birth; but in females the decline in DNA concentration was more protracted, and at 200 days after birth the RNA/DNA ratio was only 0.99. Thus, total nucleic acids show only gradual changes in concentration throughout development of the kidney, but a sharp change in the synthetic activity of the ribosomes and in their binding to membranes occurs in kidneys soon after birth.
THE ULTRASTRUCTURAL BASIS OF ALVEOLAR-CAPILLARY MEMBRANE PERMEABILITY TO PEROXIDASE USED AS A TRACER
Authors: Schneeberger-Keeley Eveline E. , Karnovsky Morris J.
Published: May 2004

The permeability of the alveolar-capillary membrane to a small molecular weight protein, horseradish peroxidase (HRP), was investigated by means of ultrastructural cytochemistry. Mice were injected intravenously with HRP and sacrificed at varying intervals. Experiments with intranasally instilled HRP were also carried out. The tissue was fixed in formal-dehyde-glutaraldehyde fixative. Frozen sections were cut, incubated in Graham and Karnovsky's medium for demonstrating HRP activity, postfixed in OsO4, and processed for electron microscopy. 90 sec after injection, HRP had passed through endothelial junctions into underlying basement membranes, but was stopped from entering the alveolar space by zonulae occludentes between epithelial cells. HRP was demonstrated in pinocytotic vesicles of both endothelial and epithelial cells, but the role of these vesicles in net protein transport appeared to be minimal. Intranasally instilled HRP was similarly prevented from permeating the underlying basement membrane by epithelial zonulae occludentes. Pulmonary endothelial intercellular clefts stained with uranyl acetate appeared to contain maculae occludentes rather than zonulae occludentes. HRP did not alter the ultrastructure of these junctions.
THE ULTRASTRUCTURE OF THE M LINE IN SKELETAL MUSCLE
Authors: Knappeis Gustav G. , Carlsen Frits
Published: May 2004

By electron microscopy, the ultrastructure of the M line was investigated in fibers from frog nonglycerinated semitendinosus muscles at body length and at different degrees of shortening and stretch. The M line appeared as a line of high electron opacity in the middle of the A band. Its framework consists of: (i) three (four or five) arrays of transverse M bridges, 200 A apart, connecting each A filament with its six neighbors; (ii) M filaments, parallel to the A filaments, passing through the M line and linking each set of M bridges together. In the shortened fiber the M line remained distinct. At high degrees of stretch, the M line became fainter or indiscernible. This appearance reflects a misalignment of the M components caused by a staggering of the A filaments. The M line reappeared after release of fibers stretched 70–80% above equilibrium length. On the basis of the structural analysis, the possible function of the M line is compared with that of the Z line, and a model is suggested for the M line.
UNUSUAL FILAMENTOUS STRUCTURES IN THE PARAGONIA OF MALE DROSOPHILA
Authors: Tandler Bernard , Williamson David L. , Ehrman Lee
Published: May 2004

Drosophila paulistorum is a complex of five incipient species which when crossed produce sterile hybrid males and fertile females. Sterility of the male progeny can sometimes be induced by injecting females of one strain (Mesitas) with a homogenate of males of another strain (Santa Marta) or of hybrids between these strains, and then crossing the recipient females to Mesitas males. Filamentous structures have been found in cytoplasmic vacuoles in paragonial cells in males of these and other similar strains and their hybrids. These structures, which contain RNA, possess a helical substructure and resemble certain viruses. Large filamentous structures found in the lumen of the paragonia are also described.
FURTHER CHARACTERIZATION OF PARTICULATE FRACTIONS FROM LYSED CELL ENVELOPES OF HALOBACTERIUM HALOBIUM AND ISOLATION OF GAS VACUOLE MEMBRANES
Authors: Stoeckenius Walther , Kunau Wolf H.
Published: May 2004

Lysates of cell envelopes from Halobacterium halobium have been separated into four fractions. A soluble, colorless fraction (I) containing protein, hexosamines, and no lipid is apparently derived from the cell wall. A red fraction (II), containing approximately 40 per cent lipid, 60 per cent protein, and a small amount of hexosamines consists of cell membrane disaggregated into fragments of small size. A third fraction (III) of purple color consists of large membrane sheets and has a very similar composition to II, containing the same classes of lipids but no hexosamines; its buoyant density is 1.18 g/ml. The fourth fraction (IV) has a buoyant density of 1.23 g/ml and contains the "intracytoplasmic membranes." These consist mainly of protein, and no lipid can be extracted with chloroform-methanol. Fractions I and II, which result from disaggregation of cell wall and cell membrane during lysis, contain a high proportion of dicarboxyl amino acids; this is in good agreement with the assumption that disruption of the cell envelope upon removal of salt is due to the high charge density. The intracytoplasmic membranes (IV) represent the gas vacuole membranes in the collapsed state. In a number of mutants that have lost the ability to form gas vacuoles, no vacuole membranes or any structure that could be related to them has been found.
THE TURNOVER OF NUCLEAR DNA-LIKE RNA IN HELA CELLS
Authors: Soeiro R. , Vaughan M. H. , Warner J. R. , Darnell J. E.
Published: May 2004

The subcellular distribution of various types of RNA in HeLa cells is described. In addition, the relative rate of synthesis of the major classes of nuclear RNA has been determined. From these experiments it can be deduced that the heterogeneous nuclear RNA fraction is rapidly synthesized and degraded within the cell nucleus.
NUCLEOCYTOPLASMIC EXCHANGES DURING EARLY INTERPHASE
Authors: Feldherr Carl M.
Published: May 2004

Colloidal gold was injected into the cytoplasm of amebae (Amoeba proteus) approximately 5 min, 1 hr, and 2 hr after cytokinesis. Later, interphase cells were similarly treated. All of the amebae were fixed about 50 min after injection and were examined with the electron microscope in order to determine the distribution of the gold. It was found that for a period of 2 hr after division the uptake of gold by the nuclei was significantly greater than that during late interphase. Correlation of the gold distribution with the morphology of the nuclear envelope indicated that an inverse relationship exists between the rate of incorporation of colloid into the nucleoplasm and the degree of reconstitution of the fibrous lamina ("honeycomb" structure). These data support the view that the fibrous lamina functions in regulating nucleocytoplasmic exchanges.
ELECTRON MICROSCOPIC INVESTIGATIONS OF ACTOMYOSIN AS A FUNCTION OF IONIC STRENGTH
Authors: Ikemoto N. , Kitagawa S. , Nakamura A. , Gergely J.
Published: May 2004

Natural actomyosin at µ = 0.6 appears in various forms, including the regular arrowhead structures originally reported by Huxley (1), when it has been stained negatively with 1% uranyl acetate. In addition to the arrowheads, thin whiskers, 700–1200 A in length and 20 A in width, attached to the arm of the arrowheads have been demonstrated. The dimensions of the whiskers and arms of the arrowheads are practically the same as those of the light meromyosin (LMM) and the heavy meromyosin (HMM) moieties of the single myosin molecule, respectively. Changes in the electron microscopically distinguishable elements during aggregation of natural actomyosin on reduction of the ionic strength have been observed. At µ = 0.4, partial aggregation of the LMM whiskers begins to result in some parallel alignment of the arrowhead-bearing filaments (acto-HMM). In the range of µ = 0.3–0.1, the LMM whiskers merge into smooth filaments which are arranged alternatingly with arrowhead-bearing filaments. Thus, lateral aggregation of composite actomyosin filaments (acto-HMM + LMM whiskers) results with the LMM moieties as links. This view is supported by the following facts: (a) acto-HMM is devoid of whiskers and does not show lateral aggregation at µ = 0.1; (b) natural actomyosin digested with trypsin at µ = 0.6, which was followed by removal of LMM aggregates at low ionic strength, is essentially the same as acto-HMM at µ = 0.1; and (c) digestion with trypsin of natural actomyosin at µ = 0.2 for varying periods of time leads to a separation of arrowhead-bearing filaments from LMM aggregates.
THE INCORPORATION OF RADIOACTIVE PROLINE INTO CULTURED CELLS
Authors: Israel H. W. , Salpeter M. M. , Steward F. C.
Published: May 2004

Cultured carrot explants, stimulated to grow rapidly in a medium containing coconut milk, were labeled with radioactive proline. After an initial period of absorption (8 hr for proline-3H; 24 hr for proline-14C) the tissue was allowed to grow for a further period of 6 days in a similar medium free from the radioactivity. Samples were prepared for electron microscopy and radioautography at the end of the absorption period and also after the further growth. The distribution of the products from the radioactive proline in the cells is shown by high-resolution radioautography and is rendered quantitative for the different regions of the cells. The results show that the combined label, which was present in the form of proline and the hydroxyproline derived from it, was all in the protoplasm, not in the cell walls. Any combined label that appeared to be over the cell walls is shown to be due to scatter from adjacent cytoplasmic sites. Initially the radioactivity was concentrated in nuclei, even more so in nucleoli, but it subsequently appeared throughout the ground cytoplasm and was also concentrated in the plastids. The significance of these observations for the general concept of a plant cell wall protein and for the special problem of growth induction in otherwise quiescent cells is discussed.
The Fine Structure of the Parathyroid Gland
Authors: Trier Jerry Steven
Published: May 2004

The fine structure of the parathyroid of the macaque is described, and is correlated with classical parathyroid cytology as seen in the light microscope.

The two parenchymal cell types, the chief cells and the oxyphil cells, have been recognized in electron micrographs. The chief cells contain within their cytoplasm mitochondria, endoplasmic reticulum, and Golgi bodies similar to those found in other endocrine tissues as well as frequent PAS-positive granules. The juxtanuclear body of the light microscopists is identified with stacks of parallel lamellar elements of the endoplasmic reticulum of the ergastoplasmic or granular type.

Oxyphil cells are characterized by juxtanuclear bodies and by numerous mitochondria found throughout their cytoplasm. Puzzling lamellar whorls are described in the cytoplasm of some oxyphil cells.

The endothelium of parathyroid capillaries is extremely thin in some areas and contains numerous fenestrations as well as an extensive system of vesicles. The possible significance of these structures is discussed.

The connective tissue elements found in the perivascular spaces of macaque parathyroid are described.
Polarization Optical Properties of the Pancreatic Acinar Cell of the Mouse
Authors: Munger Bryce L.
Published: May 2004

The birefringence of fresh and fixed mouse pancreatic acinar tissue was studied, utilizing whole mounts of pancreas from which the mesentery had been removed. Fresh pancreas in Tyrode's solution demonstrated positive birefringence with respect to the radial axis (the axis radiating from the nucleus as spokes from a wheel). Formol fixation reversed the sign of birefringence to negative with respect to the radius. The magnitude of birefringence increased with longer fixation. Neutral formol also reversed the sign to radially negative, but the magnitude did not increase with longer fixation. Tissue fixed in 2 per cent osmium tetroxide or potassium permanganate demonstrated strongly negative birefringence with respect to the radius. The cytoplasm of tissue fixed in acetic acid, though finely granular, still possessed radially positive birefringence. Birefringent areas could be seen in tissue fixed in potassium dichromate, but the sign of birefringence could not be determined. Ethyl alcohol, chromic acid, picric acid, and mercuric chloride all produced a brilliant cytoplasm in which no birefringence could be demonstrated. Freezing markedly decreased the radially positive birefringence of fresh tissue.

Fresh tissue placed in increasing concentrations of glycerol demonstrated increasing radially positive birefringence. When formol-fixed tissue was placed in glycerol, the radially negative birefringence decreased. Osmium tetroxide-fixed tissue in 50 per cent glycerol was isotropic. The granularity of ethyl alcohol-fixed tissue disappeared in 50 per cent glycerol, and radially positive birefringence was evident. Frozen tissue showed increasing radially positive birefringence in increasing concentrations of glycerol.

The results are discussed in relation to theories of fixation.
Fine Structure of Changes Produced in Cultured Cells Sampled at Specified Intervals During a Single Growth Cycle of Polio Virus
Authors: Kallman Frances , Williams Robley C. , Dulbecco Renato , Vogt Marguerite
Published: May 2004

Primary suspended cultures of rhesus monkey kidney cells were infected with poliomyelitis virus, type 1 (Brunhilde strain). The release of virus from these cells over a one-step growth curve was correlated with their change in fine structure, as seen in the electron microscope. Most of the cells were infected nearly simultaneously, and morphological changes developed in the cells were sufficiently synchronous to be classified into three stages. The earliest change (stage I) became visible at a time when virus release into the culture fluid begins, some 3 hours after adsorption. Accentuation of the abnormal characteristics soon occurs, at 4 to 7 hours after adsorption, and results in stage II. Stage III represents the appearance of cells after their rate of virus release had passed its maximum, and probably the abnormal morphology of these cells reflects non-specific physiological damage. There seems to be consistency between the previously described cellular changes as seen under the light microscope and the finer scale changes reported here.

Cytoplasmic bodies, called U bodies, were seen in large number at the time when the virus release was the most rapid (stage II). While these bodies are not of proper size to be considered polio virus, they seem to be specifically related to the infection. No evidence was found for the presence of particles that could even be presumptively identified with those of polio virus.
Studies on Cartilage: Electron Microscope Observations on Normal Rabbit Ear Cartilage
Authors: Sheldon Huntington , Robinson Robert A.
Published: May 2004

Normal rabbit ear cartilage studied with the light and electron microscope shows chondrocytes in which large lipide spherules, and an abundance of glycogen, a few small mitochondria, and relatively few elements of the endoplasmic reticulum can be identified. The chondrocytes contain, in addition, a material which stains strongly with acid fuchsin and appears in the electron microscope as a relatively dense felt-work. In electron micrographs, the matrix of normal rabbit ear cartilage consists of two components: a uniformly distributed moderately dense substance which appears as a fine meshwork without any particular pattern extending from cartilage cell border to cartilage cell border; and a three-dimensional anastomotic network of more dense material, which is best described as "felt-like" lying between the cells. The similarity between the felt-like material of the matrix and the elastic fibers described in previous electron microscope observations is discussed.
Structural Characteristics of Developing Nitella Internodal Cell Walls
Authors: Green Paul B.
Published: May 2004

The Nilella intermodal cell is formed by a division of the segment cell, the latter being a direct derivative of the shoot apical cell. The internodal cell is remarkable in that it elongates from an initial length of about 20 microns to a mature length of about 60 millimeters. The structures of the apical and segment cells, and the internodal cells in all stages of development were examined with the techniques of interference, polarization, and electron microscopy. The apical and segment cells were found to be isotropic. The upper part of the segment cell, destined to form a node, shows a curious pitted structure that was characteristic of certain node structures. The lower part of the segment cell, destined to become an internodal cell, shows a vague transverse arrangement of fibrils at the inner wall surface. The internodal cells, from the time they are first formed, show negative birefringence and a transverse arrangement of microfibrils at the inner wall surface. The elongation of the internodal cell is characterized by a rise, dip, and rise in both the optical thickness and retardation of the cell wall. The dip in both these variables coincides with the attainment of the maximum relative elongation rate. After the cessation of elongation, wall deposition continues, but the fibrils at .the inner surface of the wall are now seen to occur in fields of nearly parallel microfibrils. These fields, with varying fibrillar directions, may partly overlap each other or may merge with one another. Unlike the growing wall, this wall which is deposited after the end of elongation is isotropic.
Some Observations on the Fine Structure of the Sinus Gland of a Land Crab, Gecarcinus lateralis
Authors: Hodge Mary H. , Chapman George B.
Published: May 2004

The dilated axon endings of the sinus glands of the brachyuran crab, Gecarcinus lateralis, are filled with homogeneously dense granules, each granule being bounded by a delicate membrane. The granules are of two orders of magnitude: 0.05 to 0.1 µ and 0.15 to 0.2 µ in diameter. Each axon ending contains granules of a nearly uniform size. Endings with granules of the larger size range predominate.

Non-nervous cells endogenous to the sinus gland are scattered among the nerve endings. The cell contours are irregular, and cytoplasmic processes ramify between endings.

The axons are unmyelinated, having only thin limiting membranes, and they possess many neurofibrils. Granules in preterminal portions of the axons tend to lie at the periphery of the fiber, and in some cases in chains at the core of the fiber.

The granules appear to be storage and release centers for neurosecretory substances or their precursors.
The Contribution of Lower Oxides of Osmium to the Density of Biological Specimens in Electron Microscopy
Authors: Merriam R. W.
Published: May 2004

Centrifugally stratified eggs of the sand-dollar, Dendraster excentricus, have cytoplasmic structures segregated into distinct layers. Fat droplets, yolk granules, and mitochondria are separated by "hyaline" layers of protoplasm. Aggregations of particles of 150 to 200 A diameter ("heavy bodies") are found near the mitochondrial layer and a concentration gradient of free 150 to 200 A particles corresponds to a similar gradient of basophilia in thick sections. Eggs fixed in buffered osmium-tetroxide at pH 7.4 and embedded in methacrylate were sectioned and floated on a "bleaching" solution of acidified hydrogen peroxide. "Bleached" sections showed a considerable loss in general density and especially a loss in the sharp images of cellular membranes. It was shown that such loss is not due to sublimation of structure in the electron beam. Assuming that the "bleach" acts principally to reoxidize lower oxides of osmium, it was concluded that reduced and bound lower oxides of osmium play a major role in creation of the electron micrograph image, especially in the delineation of phospholipide components of cellular membranes. Particles of 150 to 200 A diameter showed little or no loss in density, but rather a high intrinsic electron density. Refractometric data were presented to substantiate the tentative conclusions.
Calf Thymus Composition. A Comparison of Differential Centrifugation and Chemical Fractionation Procedures
Authors: Hess Eugene L. , Lagg Saima E.
Published: May 2004

The extraction behavior of thymus and the composition of fractions prepared from this organ has been studied. Sequential extraction methods using 0.15 M NaCl followed by water gave information with respect to the weight fraction of cytoplasmic and nuclear constituents. Lipide, nucleic acid, and electrophoretic analysis of the extracts provided additional information. A less complex electrophoretic pattern was obtained from subsequent extracts in the sequence.

Sucrose and saline dispersates obtained from tissue fragmented with either the Potter-Elvehjem homogenizer or in a Waring blendor were fractionated, using standard differential sedimentation methods. The fractions obtained by means of four different dispersion procedures were compared in terms of yield, chemical analysis, and electrophoretic composition.

The quantity of material in thymus having the sedimentation characteristics of liver mitochondrial and microsomal fractions was remarkably small. Both the suspension medium employed and the method used to bring about a disruption of the cells in the tissue affected the yield of "particulate" material. The components present in the later extracts in the sequence, E4 to E7, in the case of sequential extraction study resembled with respect to chemical composition and electrophoretic characteristics, the microsome fraction prepared by differential sedimentation methods.

About 76 per cent of the PNA in the tissue appeared to be in the cytoplasm. The remaining 24 per cent PNA was found in the nucleus and accounted for 1.7 per cent of nucleus on a dry weight basis.

From 75 to 88 per cent of cytoplasmic PNA was extracted from the tissue and 76 to 94 per cent of the PNA in the extract was found in the final supernatant solutions, depending upon the dispersion methods and suspension medium used in the extraction procedure.

The composition of the final supernatant fractions using differential sedimentation methods were comparable in terms of electrophoretic properties, protein concentration, nucleic acid content, and fractionation behavior to saline extracts E1 to E3, of thymus used in earlier studies.
Staining of Tissue Sections for Electron Microscopy with Heavy Metals
Authors: Watson Michael L.
Published: May 2004

Descriptions of three heavy metal stains and methods of application to tissue sections for electron microscopy are presented. Lead hydroxide stains rather selectively two types of particles in liver: those associated with the endoplasmic reticulum and containing ribonucleic acid and other somewhat larger particles. Barium hydroxide emphasizes certain bodies within vesicles of the Golgi region of hepatic cells. Alkalized lead acetate is useful as a general stain, as are also lead and barium hydroxides.
Submicroscopic Organization of Retinal Cones of the Rabbit
Authors: De Robertis Eduardo , Lasansky Arnaldo
Published: May 2004

The fine structure of the cone cell of the rabbit is described and compared wtih that of the rod. The cone outer segment consists of a pile of flattened sacs with two membranes 30 A thick and a regular clear space in between of about 30 A. The membrane of the rod sacs is slightly thicker (∼40 A) and the clear space is less regular and frequently absent in the deeper regions. The distance between sacs is from 85 to 95 A in the cone and from 110 to 120 A in the rod, and the total repeating period is about 190 A and 210 A, respectively. These results are discussed in relation to the concentration of solids in both photoreceptors.

A connecting cilium was observed in the cone cell and compared with that previously described in rods (4). This finding suggests that morphogenetically the cone may also result of the differentiation of a primitive cilium (5).

The inner segment of the cone shows a distal portion with large concentration of elongated mitochondria and a proximal one with a large Golgi complex in the axis surrounded by components of the endoplasmic reticulum. It is concluded that both photoreceptors have a similar general plan of submicroscopic organization, with some minor difference in fine structure probably related to their specific chemical composition and function.
The Influence of Age, Sex, Pregnancy, Starvation, and Other Factors on the Cytoplasmic Ribonucleoproteins of Rat Liver
Authors: Petermann Mary L. , Hamilton Mary G.
Published: May 2004

Rat liver was homogenized in 0.88 M sucrose. The DNA and total RNA were determined, and the homogenate was fractionated by differential centrifugation. The pellets obtained between 30 minutes at 20,000 g and 180 minutes at 105,000 g were analyzed for RNA and nitrogen. The ribonucleoproteins were determined in the analytical ultracentrifuge. The non-pellet RNA was calculated by difference. The results are reported as amounts per 6.7 x 10-9 mg. of DNA.

In young, growing male rats the amounts of microsomal protein and ribonucleoprotein B (83S) increased with age. Non-pregnant adult females showed less non-pellet RNA and much more ribonucleoprotein C (63S) than did adult males.

During pregnancy both of these cell constituents reverted to levels characteristic for male animals. Starvation for 5 days resulted in a reduction in the mass of liver tissue, the non-pellet RNA, the microsomal protein, and ribonucleoproteins B and C. During recovery from starvation the return of the liver to normal paralleled the rate at which body weight was restored. Treatment with cortisone, 25 mg. per rat per day for 5 days, caused an increase in microsomal protein and a decrease in ribonucleoprotein B. Treatment with 6-mercapto-purine, 50 mg. per kilo per day for 5 days, caused little change in liver composition in either males or females.
A Cytological Analysis of the Antimetabolite Activity of 5-Hydroxyuracil in Vicia faba Roots
Authors: Schreiber Richard W. , Duncan Robert E.
Published: May 2004

The effects of 5-hydroxyuracil (5-HU) (isobarbituric acid) upon cell elongation, mitosis, and DNA synthesis were studied in Vicia faba roots.

5-HU had no consistent effect upon root elongation. It blocked DNA synthesis (analyzed by photometric measurements of Feulgen dye in nuclei) during the first 6 hours of treatment; the block spontaneously disappeared by the 12th hour of treatment.

Uracil and thymine had no effect upon this block of synthesis. Both thymidine and uridine reversed the block in 6 and 9 hours respectively.

In all cases blockage of DNA synthesis was followed by inhibition of mitosis (determined by changes in the percentage of cells in mitosis) and resumption of DNA synthesis was followed by resumption of mitosis. Inhibition indices calculated from the mitotic data indicated a competitive relationship between 5-HU and thymidine and 5-HU and uridine.

5-HU is considered to block DNA synthesis by competing with thymidine for sites on enzymes involved in the synthesis. It is suggested that uridine reverses the block in synthesis by undergoing a conversion to thymidine.
RADIOAUTOGRAPHIC STUDIES OF CHOLINE INCORPORATION INTO PERIPHERAL NERVE MYELIN
Authors: Hendelman Walter J. , Bunge Richard P.
Published: May 2004

This radioautographic study was designed to localize the cytological sites involved in the incorporation of a lipid precursor into the myelin and the myelin-related cell of the peripheral nervous system. Both myelinating and fully myelinated cultures of rat dorsal root ganglia were exposed to a 30-min pulse of tritiated choline and either fixed immediately or allowed 6 or 48 hr of chase incubation before fixation. After Epon embedding, light and electron microscopic radioautograms were prepared with Ilford L-4 emulsion. Analysis of the pattern of choline incorporation into myelinating cultures indicated that radioactivity appeared all along the length of the internode, without there being a preferential site of initial incorporation. Light microscopic radioautograms of cultures at varying states of maturity were compared in order to determine the relative degree of myelin labeling. This analysis indicated that the myelin-Schwann cell unit in the fully myelinated cultures incorporated choline as actively as did this unit in the myelinating cultures. Because of technical difficulties, it was not possible to determine the precise localization of the incorporated radioactivity within the compact myelin. These data are related to recent biochemical studies indicating that the mature myelin of the central nervous system does incorporate a significant amount of lipid precursor under the appropriate experimental conditions. These observations support the concept that a significant amount of myelin-related metabolic activity occurs in mature tissue; this activity is considered part of an essential and continuous process of myelin maintenance and repair.
THE DIFFERENTIAL SENSITIVITY OF CULTURED CHICK MESODERMAL CELLS TO ACTINOMYCIN D
Authors: Piper J. A. , Klein N. W.
Published: May 2004

Cells were isolated from the somite mesoderm and from the unsegmented (presomite) mesoderm of early chick embryos and exposed to actinomycin D in single cell culture. Actinomycin D inhibited proliferation in cell cultures derived from the unsegmented mesoderm, although the same concentrations of this antibiotic did not inhibit cultures derived from the somite mesoderm. This differential sensitivity parallels the regionally specific necrosis and degeneration observed in the unsegmented mesoderm of intact chick embryos exposed to actinomycin D. In culture, both cell types exhibited approximately the same permeability to labeled actinomycin D and showed comparable inhibition of RNA, DNA, and protein syntheses in the presence of the antibiotic. However, freshly isolated mesodermal cells from the somite region had a higher content of RNA than did cells from the unsegmented region, and the somite cells maintained a higher rate of macromolecular synthesis in untreated cultures.
HORMONE STORAGE GRANULES IN THE BEEF ANTERIOR PITUITARY
Authors: Tesar Joseph T. , Koenig Harold , Hughes Charles
Published: May 2004

A method is described for isolation of relatively large quantities of large and small hormone storage granules from the beef adenohypophysis. The hormone storage granules are highly purified, as indicated by ultrastructural and biochemical criteria. The average size of large granules is 400 mµ and of small granules is 220 mµ. The large granules contain growth hormone and prolactin; the small granules contain high concentrations of follicle-stimulating, luteinizing, and thyroid-stimulating hormones. An alkaline protease with a pH optimum of 8.3 is associated with the small granule fraction.
THE FINE STRUCTURE OF PROLIFERATING CELLS IN PRENEOPLASTIC RAT LIVERS DURING AZO-DYE CARCINOGENESIS
Authors: Karasaki Shuichi
Published: May 2004

The continuous feeding of the carcinogenic aminoazo dye DAB to rats produces hyperbasophilic foci in the preneoplastic livers. After injections of thymidine-3H into the rats, such foci were isolated from the livers and studied by radioautography with the phase-contrast and electron microscopes. In these foci, the only cells found to be proliferating, as determined by the uptake of thymidine-3H into their nuclei, were a poorly differentiated type; well differentiated hepatocytes in the same regions were not labeled with the isotope. The labeled cells had an irregular cell outline and a high nucleocytoplasmic ratio; the cytoplasm had almost completely lost the specialized elements characteristic of hepatocytes; the irregular nuclei with prominent nucleoli, the altered mitochondria, and the increased free ribosomes noted in these cells are features which are characteristic of neoplastic cells induced by DAB. Thus, it seems likely that the hyperbasophilic foci represent the sites of extensive dedifferentiation of hepatocytes followed by rapid cellular proliferation, leading to neoplastic growth.
LECITHIN SYNTHESIS, INTRACELLULAR TRANSPORT, AND SECRETION IN RAT LIVER
Authors: Stein Olga , Stein Yechezkiel
Published: May 2004

Injection of choline-3H into choline-deficient rats resulted in an enhanced incorporation of the label into liver lecithin, as compared to the incorporation of label into liver lecithin of normal rats. The results obtained with the use of different lecithin precursors indicate that in the intact liver cell, both in vivo and in vitro, exchange of choline with phosphatidyl-choline is not significant. The synthesis and secretion of lecithins by the choline-deficient liver compare favorably with the liver of choline-supplemented rats, when both are presented with labeled choline or lysolecithin as lecithin precursors. Radioautography of the choline-deficient liver shows that 5 min after injection of choline-3H the newly synthesized lecithin is found in the endoplasmic reticulum (62%), mitochondria (13%), and at the "cell boundary" (20%). The ratio of the specific activity of microsomal and mitochondrial lecithin, labeled with choline, glycerol, or linoleate, was 1.53 at 5 min after injection, but the ratio of the specific activity of phosphatidyl ethanolamine (PE), labeled with ethanolamine, was 5.3. These results indicate that lecithin and PE are synthesized mainly in the endoplasmic reticulum, and are transferred into mitochondria at different rates. The site of a precursor pool of bile lecithin was studied in the intact rat and in the perfused liver. Following labeling with choline-3H, microsomal lecithin isolated from perfused liver had a specific activity lower than that of bile lecithin, but the specific activity of microsomal linoleyl lecithin was comparable to that of bile lecithin between 30 and 90 min of perfusion. It is proposed that the site of the bile lecithin pool is located in the endoplasmic reticulum and that the pool consists mostly of linoleyl lecithin.
MINOR COMPONENTS OF THE DNA OF PHYSARUM POLYCEPHALUM
Authors: Holt Charles E. , Gurney Elizabeth G.
Published: May 2004

DNA metabolism in the slime mold Physarum polycephalum was studied by centrifugation in CsCl of lysates of cultures labeled with radioactive thymidine at various times in the cell cycle. During the G2 (premitotic) phase of the cell cycle, two components of the DNA are labeled. One component is lighter (buoyant density 1.686 g/cc) than the mean of the principal DNA (1.700 g/cc), and one is heavier (approximately 1.706 g/cc). The labeled light DNA was identified chemically by its denaturability, its susceptibility to DNase, and the recovery of its radioactivity in thymine. Cell fractionation studies showed that the heavy and the principal DNA components are located in the nucleus and that the light DNA is in the cytoplasm. The light DNA comprises approximately 10% of the DNA. About ⅓–½ of the light DNA is synthesized during the S period, and the remainder is synthesized throughout G2 (there is no G1 in Physarum). The light DNA is metabolically stable. A low, variable level of incorporation of radioactive thymidine into the principal, nuclear DNA component was observed during G2.
THE ORGANIZATION OF THE NUCLEOLUS IN MERISTEMATIC PLANT CELLS
Authors: Lord A. , Lafontaine J.-G.
Published: May 2004

The architecture of the nucleolus in Allium porum and Triticum vulgare meristematic cells has been investigated by means of digestions with various enzymes. After staining with azure B at pH4, plant nucleoli exhibit lighter regions which, under electron microscopy, correspond to the fibrillar zones characterizing these organelles. Evidence is presented indicating that these latter zones contain coarse convoluted filaments quite similar to the loops first demonstrated by La Cour (24) and which are assumed to originate from the nucleolar-organizing chromosomes. These coarse, 0.2µ wide filaments are remarkably resistant to the action of deoxyribonuclease, ribonuclease, pepsin, trypsin, or of various combinations of these enzymes and, moreover, they show insignificant incorporation of labeled thymidine even after long exposure to this DNA precursor. The clearing action of pepsin on different regions of the nucleolus lends support to the hypothesis that an amorphous material or matrix pervades the mass of this organelle. This effect is particularly striking within the particulate nucleolar zones themselves. Both ribonuclease and trypsin disorganize the RNP (ribonucleoprotein) nucleolar particles. The effect of the latter enzyme on the RNP particles is taken to indicate that they contain proteins particularly susceptible to trypsin which are essential for maintenance of their morphological integrity. Trypsin also interferes with azure B-staining of the nucleolar mass as a whole and, according to radioautographic data, extracts RNA throughout this organelle. Accordingly, the hypothesis is considered that RNA is complexed with proteins not only within the particulate nucleolar portions, as is already well known, but also in the fibrillar zones.
EFFECTS OF DIVISION-SYNCHRONIZING HYPOXIC AND HYPERTHERMIC SHOCKS UPON TETRAHYMENA RESPIRATION AND INTRACELLULAR ATP CONCENTRATION
Authors: Rooney David W. , Eiler John J.
Published: May 2004

The division of Tetrahymena pyriformis GL cells was synchronized with either seven hypoxic or five hyperthermic (heat) shocks. Hyperthermic shocks of 34°C produced no reduction in respiration rate and only a 19% decline in intracellular ATP concentration. Hypoxic shocks of 0.15% ambient oxygen concentration depressed intracellular ATP concentration 50%. It therefore appears that hypoxic shock, but not hyperthermic shock, reverses progress of Tetrahymena toward fission by reducing ATP concentration through a reduction of the rate of oxidative phosphorylation. After the first synchronized division, whether synchronized by intermittent hypoxia or hyperthermia, total respiration rate increased exponentially at the same rate of increase as total respiration rate in an exponentially growing (log phase) Tetrahymena cell culture. Before the first synchronized division, the total respiration rate increased exponentially but more slowly than after completion of the first synchronized division. The pattern of increase of total respiration during division synchronized by either procedure was different than the pattern of increase of total respiration of synchronous cells observed by Zeuthen.
ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LANGERHANS
Authors: Howell S. L. , Young D. A. , Lacy P. E.
Published: May 2004

A partially purified secretory granule fraction, isolated from rat islets of Langerhans by differential centrifugation, was used for investigating the stability of the beta granules during incubation in various conditions. Effects of pH, temperature, and time were studied; the granules possessed optimal stability at 4° and pH 6.0, and could be solubilized at pH 4.0 or 8.5, or in the presence of sodium deoxycholate, but not by phospholipase c, ouabain, or alloxan. Incubation with glucose or some of its metabolites, or with tolbutamide, ATP, or cyclic 3',5'-AMP did not alter the stability of the beta granules Exogenous insulin-131I was not bound by the isolated granules under the conditions used; no specific insulin-degrading activity could be detected in subcellular fractions of the islets. These findings indicate that intracellular solubilization of the granules with subsequent diffusion of the insulin into the extracellular space is not a likely mode of insulin secretion in vivo, and suggest that a crystalline zinc-insulin complex may exist in the matrix of the beta granules.
MICROTUBULES IN THE FORMATION AND DEVELOPMENT OF THE PRIMARY MESENCHYME IN ARBACIA PUNCTULATA
Authors: Tilney Lewis G. , Gibbins John R.
Published: May 2004

To experimentally test the suggestion made in the preceding paper that the microtubules are involved in cell shape development during the formation and differentiation of the primary mesenchyme, we applied to the embryos two types of agents which affect cytoplasmic microtubules: (a) colchicine and hydrostatic pressure, which cause the microtubules to disassemble, and (b) D2O, which tends to stabilize them. When the first type of agent is applied to sea urchin gastrulae, the development of the primary mesenchyme ceases, the microtubules disappear, and the cells tend to spherulate. With D2O development also ceases, but the tubules appear "frozen," and the cell asymmetries persist unaltered. These agents appear to block development by primarily interfering with the sequential disassembly and/or reassembly of microtubules into new patterns. The microtubules, therefore, appear to be influential in the development of cell form. On the other hand through a careful analysis of the action of these agents and others on both intra- and extracellular factors, we concluded that the microtubules do rather little for the maintenance of cell shape in differentiated tissues.
A STUDY OF NEXUSES IN VISCERAL SMOOTH MUSCLE
Authors: Cobb J. L. S. , Bennett Terence
Published: May 2004

Nexuses are described between the smooth muscle cells of the gizzard of the chick and the pigeon, the vas deferens of the mouse and the guinea pig, and the taenia coli of the guinea pig. The nexuses in the gizzard were examined after osmium tetroxide and potassium permanganate had been used as fixatives. Although differences in the dimensions of the unit membranes and the nexuses were noted, the results with the two fixation techniques were complementary. The distribution of nexuses within the smooth muscle tissues examined was uneven. Nexuses were still present in both small and large pieces of tissue incubated in hypertonic solutions at varying temperatures. Other experiments showed that the degree of contraction at the time of fixation did not affect the presence of nexuses in the tissue. These results indicate that nexuses between smooth muscle cells are stable under a variety of conditions.
UNUSUALLY HIGH MITOCHONDRIAL ALPHA GLYCEROPHOSPHATE DEHYDROGENASE ACTIVITY IN RAT BROWN ADIPOSE TISSUE
Authors: Ohkawa Kin-Ichi , Vogt Molly T. , Farber Emmanuel
Published: May 2004

Brown adipose tissue of the rat has been found to have an unusually high activity of mitohondrial α-glycerophosphate dehydrogenase (α-GPD) when assayed both by a histochemical staining procedure and by a quantitative biochemical method with isolated mitochondria. In contrast to succinic, glutamic, and ß-hydroxybutyrate dehydrogenases, all mitochondrial enzymes, the activity of α-GPD in brown fat was 10 times that in liver, more than 20 times that in white adipose tissue, and 9 times that in kidney. The soluble NAD-linked α-GPD was also higher in brown adipose tissue than in white adipose tissue, liver, or kidney, but the differences were much less marked. The possible importance of the high activity of mitochondrial α-GPD in the regulation of synthesis of esterified lipid and in thermogenesis in brown fat is discussed.
STRUCTURAL AND FUNCTIONAL PROPERTIES OF POLYTENE NUCLEI ISOLATED FROM SALIVARY GLANDS OF DROSOPHILA HYDEI
Authors: Berendes Hans D. , Boyd James B.
Published: May 2004

Salivary gland nuclei of Drosophila hydei, isolated by a modification of the procedure described by Boyd et al. (9), retain their normal morphology during the isolation and subsequent incubation procedure. RNA synthesis was studied in isolated nuclei by biochemical and cytological techniques. In radioautographs 70% of the nuclei displayed a distribution of labeled RNA over the nuclear constituents similar to the distribution obtained after in vivo incorporation of radioactive precursor. Chromosome puffs and the nucleoli were specifically labeled. The remaining 30% of the nuclei showed a weak to very weak incorporation of radioactive precursor. In these nuclei most of the radioautographic grains were concentrated over the nucleolus, and a few grains were randomly distributed over the chromosomes. Actinomycin D and the absence of ATP, GTP, and CTP in the medium inhibited incorporation of radioactive precursor. The radioactive product was sensitive to combined pronase and RNase digestion. Addition of E. coli RNA polymerase to the incubation medium enhanced the specific labeling over the puffed regions. The sedimentation behavior of the RNA synthesized in isolated nuclei was different from that of RNA synthesized during a 20 min pulse of radioactive precursor administered to whole glands in vivo and in vitro. Neither the steroid ecdysterone nor a temperature treatment was effective in inducing new puffs in isolated nuclei.
ELECTRON MICROSCOPE RADIOAUTOGRAPHY AS A QUANTITATIVE TOOL IN ENZYME CYTOCHEMISTRY
Authors: Salpeter M. M.
Published: May 2004

The distribution of diisopropylfluorophosphate (DFP)-sensitive enzyme sites at the neuromuscular junction was determined quantitatively by electron microscope radioautography after incubation of muscle fragments in DFP-3H. Most of the sensitive sites were located in the subneural apparatus at a concentration of 90,000 sites per µ3 of cleft tissue or 12,000 sites per µ2 of postjunctional membrane surface area. A considerable concentration is also present in the teloglial cap. It has previously been demonstrated (Rogers et al., 1966) that one-third of the DFP-sensitive sites at the endplate can be reactivated by pyridine-2-aldoxime methiodide (2-PAM)—a compound which selectively reactivates phosphorylated acetylcholinesterase. In the present study, it was found that this ratio of 1:2 holds also on a fine-structural level. Muscle mast cells were found to have a heavy concentration of bound DFP.
LIPOFUSCIN (AGING) PIGMENT GRANULES OF THE NEWBORN HUMAN LIVER
Authors: Goldfischer Sidney , Bernstein Jay
Published: May 2004

We have observed pigmented cytoplasmic granules, with the characteristic staining properties of lipofuscin (ceroid, "wear-and-tear") pigment, in newborn human liver. The pigment is found at the periphery of the lobule in hepatocytes and some bile ductular cells. It is acid-fast, PAS-positive after diastase digestion, slightly argyophilic and sudanophilic, and markedly Schmorl's- and peroxidase positive in paraffin sections. Difficult to see in sections stained with hematoxylin and eosin, the pigment can be detected in unstained sections. The granules also resemble lipofuscin found in adult tissues, in their ultra-structural and enzymatic properties. They are polymorphic, contain granular material of moderate and high electron opacity, and are delimited by a single membrane. Acid phosphatase and ß-glucuronidase activities are visualized in the newborn granules, identifying them as lysosomes. The granules also contain copper and, to a much lesser extent, iron. The accumulation of lipofuscin pigment in lysosomes in many tissues correlates well with aging, and this process has been interpreted as a reflection of cellular degeneration or wear-and-tear. However, the presence of lipofuscin granules as a constant component of neonatal liver suggests that they are not a measure of cellular senescence.