bluuebunny/crossref_metadata_2025 huggingface dataset:
HETEROCHROMATIN IN HUMAN MALE LEUKOCYTES
Authors: Lima-de-Faria A. , Reitalu J.
Published: May 2004

Tritiated thymidine was added to peripheral blood cultures containing phytohemagglutinin so that DNA synthesis in interphase nuclei of white blood cells in the human male could be studied. After 57 hours in culture, a large heterochromatic body with a central position is seen in unlabeled Feulgen-stained nuclei. In labeled nuclei in which DNA synthesis was taking place in both the eu- and heterochromatin at the time the thymidine became available, the heterochromatin shows a higher number of silver grains per unit area, accompanied by a stronger Feulgen reaction, an indication of its higher DNA content. The time of DNA synthesis in the heterochromatin blocks is different from that in the surrounding euchromatin. The large heterochromatic block is composed of chromosome segments gathered together around the nucleolus but it is not part of this organelle. In preparations stained with azure A and acid fuchsin for demonstrating both the nucleolus and the chromosomes, six distinctly heteropyenotic chromosome segments can be seen associated with the nucleolus. Cells of all size categories were found to incorporate tritiated thymidine. The distinct appearance of autosomal heterochromatin in white blood cells may be the result of the new physiological conditions to which the cells are subjected in the medium containing phytohemagglutinin.
THE ORGANIZATION AND INNERVATION OF THE LUMINESCENT ORGAN IN A FIREFLY, PHOTURIS PENNSYLVANICA (COLEOPTERA)
Authors: Smith David S.
Published: May 2004

The organization of the luminescent organ of an adult firefly has been studied with the electron microscope, and particular attention has been given to the disposition of nerve terminals within the organ. The cytological structure of the cells of the tracheal system, the peripheral and terminal axons, the photocytes and the cells of the dorsal ("reflecting") layer is described. Previous observations on the peripheral course of nerve branches alongside the tracheal trunks at the level of the dorsal layer and photocyte epithelium have been confirmed, and specialised nerve endings containing axoplasmic components structurally identical with "synaptic vesicles" and "neurosecretory droplets" have been identified, not in association with the surface of the photocytes, but lying between the apposed surfaces of two components of the tracheal epithelium: the tracheal end-cell and the tracheolar cell. These cytological findings are discussed in terms of available biochemical and physiological evidence concerning the mechanism of light emission in the firefly, especially with respect to the possible role of chemical "transmitter" action in triggering a response in a luminescent effector system.
THE ULTRASTRUCTURE AND DISPOSITION OF VESICULATED NERVE PROCESSES IN SMOOTH MUSCLE
Authors: Thaemert J. C.
Published: May 2004

The walls of the gastrointestinal tract and urinary bladder of rats were fixed in osmium tetroxide, embedded in methacrylate, and sectioned for electron microscopy. The examination of sections of smooth muscle tissue with the electron microscope reveals the presence of bundles of unmyelinated nerve fibers within the intercellular spaces. In addition, vesiculated nerve processes, bounded on their outer surfaces by delicate plasma membranes and typically containing varying quantities of synaptic vesicles and mitochondria, make intimate contact with the surface of smooth muscle cells. These nerve processes are similar in structure and disposition to nerve endings previously described in skeletal muscle, in the central nervous system, in peripheral ganglia, in receptors, and in glands. It is concluded that the relationships existing between vesiculated nerve processes and the surface of smooth muscle cells constitute neuromuscular junctions. Profiles of protrusions of smooth muscle cells are often seen protruding into the intercellular spaces. Here they occur singly or in groups, originating from one or more cells. Because of the plane of section the protrusions may sometimes appear as individual entities between the muscle cells. In such cases care must be exercised in their identification because they have characteristics similar to sectioned nerve processes which also occur in the intercellular spaces.
THE USE OF FORMALIN FIXATION IN THE CYTOCHEMICAL DEMONSTRATION OF SUCCINIC AND DPN- AND TPN-DEPENDENT DEHYDROGENASES IN MITOCHONDRIA
Authors: Walker Donald G. , Seligman Arnold M.
Published: May 2004

Brief formalin fixation in the cold prior to histochemical assay of rat liver and pancreas for various dehydrogenases has been used successfully to circumvent the structural damage and enzymatic loss to which mitochondria of frozen sections would otherwise be subject. To obtain an optimal result a single set of conditions has been devised, including fixation prior to freezing of minute (finely diced) organ blocks in graded concentrations (0.7 to 2.0 per cent) of formaldehyde in chilled (1–4°C) Hanks' balanced salt solution, freezing at not higher than -70°C, and use of nitro-BT or, preferably, tetranitro-BT. The present histochemical study of hepatic and acinar cells indicates that not only are succinic and D-ß-hydroxybutyric dehydrogenases located exclusively in the mitochondria but so are lactic, malic, and the isocitric dehydrogenases.
LABELING WITH 14C AMINO ACIDS OF ALBUMIN-LIKE PROTEIN BY RAT LIVER RIBONUCLEOPROTEIN PARTICLES
Authors: von der Decken Alexandra
Published: May 2004

Ribonucleoprotein particles were prepared by treatment of rat liver microsomes with detergents and high concentrations of KCl. They were active in incorporating 14C amino acids into protein when incubated with cell sap together with ATP, GTP, and a system to regenerate the triphosphates. The albumin of the incubation mixture, soluble at 105,000 g, and that of the fraction released by ultrasonication of the particles were studied by immunoelectrophoresis in agar gel. When the ribonucleoprotein particles were incubated with cell sap the immunological precipitation lines formed with antiserum to rat serum albumin were highly radioactive as tested by autoradiography. After zone electrophoresis on cellulose acetate, two immunologically reactive albumins were obtained which differed in their electrophoretic mobility from rat serum albumin. Labeled albumin, when purified on DEAE-cellulose columns, retained its radioactivity as tested by autoradiography following immunoelectrophoresis. On cellulose acetate this purified albumin showed an electrophoretic mobility higher than that of rat serum albumin.
GENETIC CONTROL OF CYTODIFFERENTIATION
Authors: Rizki T. M.
Published: May 2004

The cells of the anterior region of the larval fatbody of Drosophila melanogaster accumulate kynurenine at the end of the third larval instar, whereas the cells of the posterior region are involved in pteridine metabolism. Through a series of transplantation experiments it has been demonstrated that the anterior fat cells synthesize kynurenine. The mutant vermilion lacks kynurenine, and the anterior fat cells of this mutant strain lack the autofluorescence characteristic of kynurenine. When the non-allelic suppressor gene is combined with vermilion, the synthesis of kynurenine is restored in the anterior fat cells, and some of the cells of the posterior region contain kynurenine as well. A similar extension in the number of cells containing kynurenine can be induced in the normal Ore-R strain by feeding the precursor tryptophan. It has been concluded that the absence of a physiological process in a differentiated cell does not necessarily represent a loss of the genetic potential for that process. The normal allele at the suppressor locus inhibits the occurrence of kynurenine in the posterior fat cells, whereas the mutant allele su2-s allows the expression of this potential. An inducer such as tryptophan can overcome this inhibition in the normal strain, and as a result the cells which are normally differentiated as "isoxanthopterin cells" may produce kynurenine as well.
INVERSE ENZYMATIC CHANGES IN NEURONS AND GLIA DURING INCREASED FUNCTION AND HYPOXIA
Authors: Hamberger Anders , Hydén Holger
Published: May 2004

Following stimulation of the vestibular nerve in the rabbit, respiratory enzyme activities increased in Deiters' nerve cells. The anaerobic glycolysis, measured as 10-4 µl CO2 per hour per cell, was found to decrease concomitantly by 25 to 40 per cent, suggesting a Pasteur effect. By contrast, in the surrounding glia the anaerobic glycolysis increased and the respiratory enzyme activity decreased, suggesting a Crabtree effect. The evidence is discussed for a regulatory metabolic mechanism operating between the neuron and its glia. Hypoxia of 8 per cent O2 caused an increase of both oxygen consumption and CO2 production in the nerve cells, but did not change the glia values.
THE SIZE OF THE CELLULOSE MICROFIBRIL
Authors: Colvin J. Ross
Published: May 2004

Recently the lateral width of the cellulose microfibril has been estimated as 30 A rather than about 150 to 200 A, by extrapolation of data from model shadowing experiments. The difference was attributed to a layer of metal deposited during shadowing. However, direct photographs of the same microfibrils parallel and perpendicular to the direction of shadowing, of unshadowed portions of microfibrils compared with shadowed portions of the same microfibrils, of silver-stained unshadowed microfibrils, and of unshadowed, unstained segments of microfibrils give no evidence of a layer of metal of this thickness in material shadowed under normal conditions. Furthermore, the evidence for microfibril strands of about 35 A in width from negative-staining experiments is subject to a bias from the form of the filaments and from variable positive adsorption of phosphotungstic acid by cellulose. Consequently, the conclusion that the true lateral width of native cellulose microfibrils is about one-fifth of the presently accepted value is not yet justified by unequivocal direct experimental evidence.
OBSERVATIONS ON CELL GROWTH, MITOSIS, AND DIVISION IN THE FUNGUS BASIDIOBOLUS RANARUM
Authors: Robinow C. F.
Published: May 2004

The paper describes the forward streaming, growth, and division of the vegetative cell of Basidiobolus ranarum. The cell is several hundred microns long and has a single large nucleus. Mitosis is invariably followed by cell division. Both processes have been studied in the living cell by ordinary and phase contrast microscopy. Mitosis is accompanied by a temporary coarsening of the organisation of the cytoplasm and a considerable slowing down of the rate of growth of the cell wall tube. Fixed and stained preparations have shown that there is a large number of small chromosomes and that the mitotic spindle is formed from the nucleolus. Basidiobolus appears suitable for observations on the cell duplication cycle and the physiology of mitosis.
ELECTRON MICROSCOPE STUDIES ON SALIVARY GLAND CELLS
Authors: Jacob J. , Sirlin J. L.
Published: May 2004

Salivary glands were fixed in cold 1 per cent osmium tetroxide in veronal-acetate buffer containing sucrose and embedded in methacrylate mixture or Araldite. The salivary gland nuclei of sciarids show a continuous production of nucleoli, which remain multiple and not consolidated into a single structure. The earliest recognizable nucleoli, which we call "elementary nucleoli," are aggregations of a few paired 40 A fibrils and a few 150 A particles, at many points within chromosome bands. Further development consists of the detachment of the elementary nucleoli from their points of origin and their subsequent mutual coalescence. As a result, dense patches of nucleolar material are formed which become large nucleoli at the surface of chromosomes, either attached to the band or free. The fully formed nucleoli have a characteristic dual structure with a narrow dense periphery and a broader less dense internum. Fibrils and particles are present in both regions, and the difference in density reflects differences in the packing of the two structural elements. The duality in structure is lost in later stages. The nucleolar fibrils appear to be similar to the chromosomal fibrils. The 150 A particles in nucleoli, chromosomes, and nuclear sap seem identical. The significance of these observations is discussed for nucleologenesis in general.
DENSITY GRADIENT ISOLATION OF RAT LIVER NUCLEI WITH HIGH DNA CONTENT
Authors: Fisher Richard F. , Holbrook David J. , Irvin J. Logan
Published: May 2004

Rat liver nuclei, after preliminary isolation in 2.2 molar sucrose solution, were separated into density classes by centrifugation at 95,000 g for 45 to 85 minutes in a sucrose density gradient (density range, 1.28 to 1.33). Nuclei from normal liver separated into three bands with average DNA phosphorus content per nucleus of 0.67, 0.84, and 0.93 picogram for top, middle, and bottom bands, respectively. Nuclei from regenerating liver (26 hours after one-third hepatectomy) yielded three bands and a pellet fraction with average DNA phosphorus content per nucleus of 0.76, 1.02, 1.38, and 1.51 picograms (top to bottom of tube). This method appears capable of yielding nuclei which have increased their DNA content prior to mitosis, and this procedure should be valuable in studies of biochemical changes which occur in nuclei preparing for mitosis.
A SURVEY OF DEHYDROGENASES IN VARIOUS EPITHELIAL CELLS IN THE RAT
Authors: Walker Donald G.
Published: May 2004

Several different epithelial elements that have intense active transport or protein secretory functions were histochemically assayed in several dehydrogenase media by a recently perfected method. The mitochondria represented the only site of activity, not only when tested in the succinate and D-ß-hydroxybutyrate media, but also when tested in the lactate, malate, and isocitrate media. The reaction for D-ß-hydroxybutyric dehydrogenase in the mouse kidney was curiously limited to the mitochondria of the distal segment of the proximal convoluted tubule, a finding that most convincingly shows that dehydrogenase activity may be differentiated in certain instances from diaphorase activity by the ditetrazole methods and that D-ß-hydroxybutyric dehydrogenase is not present in all mitochondria. Tetranitro-BT is favored over nitro-BT in studies conducted on most organs prepared without fixation and on formalin-fixed tissues that consist of lipid-containing or active transport cells.
THE RELATIVE EXTENSIBILITY OF CELL SURFACES
Authors: Rosenberg Murray D.
Published: May 2004

Observations have been made on the response, in vitro, of cultured and freshly dissociated cells to mechanical deformation. Large numbers of individual cells were studied by means of a special culture chamber bounded by two parallel glass coverslips whose spacing could be reduced from 140 to 2 microns in steps of roughly 0.5 micron. The degree of deformation required for herniation of the cell surface was measured. These measurements lead to the definition of a statistical index characteristic of the extensibility of cell surfaces. This index has been shown to be distinctive for several types of cells; to alter with certain stages of embryonic development; and to be stable with respect to the culturing of cells and certain alterations in the method of cell culture.
THE USE OF SHADOW-CASTING TECHNIQUE FOR MEASUREMENT OF THE WIDTH OF ELONGATED PARTICLES
Authors: Ohad I. , Danon D. , Hestrin S.
Published: May 2004

A method is described for the estimation of the true width of fibrillar or rod-like structures from electron micrographs of metal-shadowed preparations. The method is based on variations in the image width as a function of the angle (ß) between the long axis of the fibril and the direction of the shadow in the plane of the preparation. The image width when ß = 0° practically represents the real width of the elongated particle but is often indistinguishable from the background. The fibril image width is conveniently measured at ß values between 15° and 90°. The true width is obtained by plotting the image width versus sin ß and extrapolating to ß = 0°. Latex spheres are sprayed with the fibrils or rods to indicate the direction of shadow. Tobacco mosaic virus (TMV) was used as a model structure because of its known constant diameter of 150 A (5). The width (in the case of TMV equal to the diameter) found by the present method was 150 A ± 8 A.
JUNCTIONAL COMPLEXES IN VARIOUS EPITHELIA
Authors: Farquhar Marilyn G. , Palade George E.
Published: May 2004

The epithelia of a number of glands and cavitary organs of the rat and guinea pig have been surveyed, and in all cases investigated, a characteristic tripartite junctional complex has been found between adjacent cells. Although the complex differs in precise arrangement from one organ to another, it has been regularly encountered in the mucosal epithelia of the stomach, intestine, gall bladder, uterus, and oviduct; in the glandular epithelia of the liver, pancreas, parotid, stomach, and thyroid; in the epithelia of pancreatic, hepatic, and salivary ducts; and finally, between the epithelial cells of the nephron (proximal and distal convolution, collecting ducts). The elements of the complex, identified as zonula occludens (tight junction), zonula adhaerens (intermediary junction), and macula adhaerens (desmosome), occupy a juxtaluminal position and succeed each other in the order given in an apical-basal direction.

The zonula occludens (tight junction) is characterized by fusion of the adjacent cell membranes resulting in obliteration of the intercellular space over variable distances. Within the obliterated zone, the dense outer leaflets of the adjoining cell membranes converge to form a single intermediate line. A diffuse band of dense cytoplasmic material is often associated with this junction, but its development varies from one epithelium to another.

The zonula adhaerens (intermediate junction) is characterized by the presence of an intercellular space (∼200 A) occupied by homogeneous, apparently amorphous material of low density; by strict parallelism of the adjoining cell membranes over distances of 0.2 to 0.5 µ; and by conspicuous bands of dense material located in the subjacent cytoplasmic matrix.

The desmosome or macula adhaerens is also characterized by the presence of an intercellular space (∼240 A) which, in this case, contains a central disc of dense material; by discrete cytoplasmic plaques disposed parallel to the inner leaflet of each cell membrane; and by the presence of bundles of cytoplasmic fibrils converging on the plaques.

The zonula occludens appears to form a continuous belt-like attachment, whereas the desmosome is a discontinuous, button-like structure. The zomula adhaerens is continuous in most epithelia but discontinuous in some. Observations made during experimental hemoglobinuria in rats showed that the hemoglobin, which undergoes enough concentration in the nephron lumina to act as an electron-opaque mass tracer, does not penetrate the intercellular spaces beyond the zonula occludens. Similar observations were made in pancreatic acini and ducts where discharged zymogen served as a mass tracer. Hence the tight junction is impervious to concentrated protein solutions and appears to function as a diffusion barrier or "seal." The desmosome and probably also the zonula adhaerens may represent intercellular attachment devices.
ON THE THICKNESS OF THE UNIT MEMBRANE
Authors: Yamamoto Toshiyuki
Published: May 2004

Peak-to-peak distances between two dense lines of the unit membranes of cell organelles were measured on electron micrographs. These distances were compared with corresponding measurements on the plasma membrane and assigned a percentage value. The comparison between organelle and plasma membrane was always carried out with the same negative, in order to exclude as far as possible errors due to differences in focus or other causes. It was revealed by this study that the membranous structures of the cell can be classified into two groups, one thicker and one thinner. Unit membranes of the thicker group (synaptic vesicles, vesicles and capsules of multivesicular bodies, Golgi vesicles) were not significantly different in thickness from the plasma membrane. Unit membranes of the thinner group (mitochondria, nuclear membranes, Golgi lamellae, endoplasmic reticulum), however, were between 85 and 90 per cent of the thickness of the plasma membrane.
SOME OBSERVATIONS ON NEGATIVELY STAINED MITOCHONDRIA
Authors: Stoeckenius Walther
Published: May 2004

A particulate component of mitochondria is described which is observed in negatively stained preparations of unfixed whole mitochondria or their fragments. It consists of a roughly spherical particle, approximately 85 A in diameter, found on the surface of the cristae and probably also on the side of the mitochondrial envelope which faces the matrix. It is attached to the underlying membrane by a narrow stalk 40 to 50 A long. The particle appears to be rather labile and it is destroyed or at least rendered unrecognizable by all conventional fixatives used in electron microscopy, especially OsO4.
CYTOCHEMICAL STUDIES CONCERNING THE OCCURRENCE AND DISTRIBUTION OF RNA IN PLASTIDS OF ZEA MAYS
Authors: Jacobson Ann B. , Swift Hewson , Bogorad Lawrence
Published: May 2004

The occurrence of RNA in plastids from etiolated and green maize leaves was demonstrated cytochemically, with both the light and the electron microscope. Etiolated leaves were allowed to incorporate tritiated cytidine for several hours and were subsequently fixed in formalin. Radioautographs of leaf sections 2 µ thick showed silver grains over the regions of the cytoplasm containing plastids. Plastids in these sections appeared intensely basophilic when stained with azure B. Both the basophilia and radioactivity were removable with ribonuclease, clearly demonstrating the occurrence of RNA in these organelles. Examination under the electron microscope of similar plastids which had been fixed in formalin revealed a particulate component in the plastid measuring approximately 170 A in diameter. This particulate component was completely removable with ribonuclease. Thus,it was concluded that RNA occurs in a particulate form in plastids from etiolated leaves. Mature plastids, when stained with azure B, did not appear basophilic under the light microscope. Nevertheless, when formalin-fixed tissues were examined with the electron microscope, the mature plastids were seen to contain particles in the stroma, identical in appearance with those visible in the plastids in etiolated leaves. Osmium tetroxide-fixed tissues were also examined with the electron microscope. Particles similar to those seen in plastids fixed with formalin were observed, although the results obtained with this fixative were variable. It is concluded that plastids from etiolated and green maize leaves contain RNA in a particulate form which resembles ribosomes.
MORPHOLOGICAL AND PHARMACOLOGICAL EFFECTS OF RESERPINE, GIVEN ALONE OR AFTER IPRONIAZID, ON THE CATECHOL AMINES OF THE ADRENAL GLANDS OF THE RAT
Authors: Clementi Francesco , Zocche Gian Paolo
Published: May 2004

Adrenomedullary cells, after fixation with OsO4, are filled with well formed granules which are considered to represent their catechol amine content. The submicroscopic appearance of these cells was studied in reserpine-treated rats during the late phase of catechol amine depletion and during the period of its restoration. At 3 days after the beginning of reserpine treatment, the granules appeared to be emptied of their content and small vesicles containing scattered, dense deposits of, presumably, catechol amines began to be seen. At 9 days after the beginning of treatment, these deposits had already become granules and the cells had attained a completely normal appearance. The submicroscopic structure of the adrenomedullary cells of rats pretreated with iproniazid (before reserpine), in which a complete inhibition of monoamine oxidase activity had thus been obtained, was similar to that seen in non-treated animals. In numerous cases, however, some characteristic features were noted: the sacs which usually contained a dense granule of catechol amines appeared swollen and many fine granules could be seen around them; the latter were dispersed in a way suggesting that they may represent a partial breakdown of the large granules which, under the inhibitory action of iproniazid, do not release the catechol amines contained within them.
THE ABSORPTION OF FAT BY INTESTINE OF GOLDEN HAMSTER IN VITRO
Authors: Strauss Elliott W.
Published: May 2004

Everted sacs of intestine from golden hamsters were incubated at 37°C for at least 1 hour in vitro with emulsified lipid after removal of both pancreatic lipase and bile salts. The fine structure of intestinal epithelium is well preserved under these conditions. Absorption of fat by the intestinal mucosa in vitro closely resembles lipid absorption in vivo, as observed by both light and electron microscopy. The physiological significance of these observations is discussed. Tubular elements of the agranular endoplasmic reticulum are often strikingly abundant in the apical cytoplasm of intestinal absorptive cells. These have a role in the intracellular transport of fat since they frequently contain droplets of lipid derived from the incubation medium. The rate of fat accumulation in the epithelium appears to be proportional to the concentration in the medium.
INTERCELLULAR CONNECTIONS IN THE OUTGROWING STOLON OF CORDYLOPHORA
Authors: Overton Jane
Published: May 2004

Outgrowth of the stolon in the hydroid Cordylophora has been studied at the cellular level. Staining experiments and histological examination indicate that the generative region of the stolon is at its base where interstitial cells are prominent. Cells in the ectoderm at the stolon tip appear to be actively synthesizing new perisarc as the tip advances over the substrate, rather than involved in proliferation. The fine structure of cellular relationships in these regions has been considered and an attempt has been made to correlate the structure and distribution of intercellular attachments with these various functional zones along the outgrowing stolon. Intercellular attachments are similar to those previously described in Hydra, but favorable cases provide a more complete description. The series of intercellular septa each consist of two electron-opaque bodies lying close together midway between the two plasma membranes and separated from the membranes by a region of lesser density. The plasma membranes contain electron-opaque and transparent regions which alternate with the septa. These regions extend over about 70 A. The position of intercellular connections relative to the outer surface of the cenosarc varies in different parts of the stolon.
THE REPLICATION TIME AND PATTERN OF THE LIVER CELL IN THE GROWING RAT
Authors: Post Joseph , Huang Cheng-Ya , Hoffman Joseph
Published: May 2004

Three-week-old male rats of the Wistar strain were given tritiated thymidine, 1 µc/gm body weight, intraperitoneally and were killed at intervals from 0.25 to 72 hours later. Autoradiographs were made from 5 µ sections, stained by the Feulgen method. The replication time and its component intervals were determined from the scoring of the labeling of interphase nuclei as well as of prophase, metaphase, anaphase, and telophase nuclei. Absorption of the intraperitoneally injected label is rapid and is attended by "flash" labeling during interphase. The results show that at any one time about 4 per cent of the liver cells are synthesizing DNA preliminary to cell division. These cells alternate with waves of other cells and it is estimated that about 10 per cent of the liver cell population is engaged in cell duplication. The replication time is about 21.5 hours, and its component intervals occupy the following times: DNA synthesis, 9 hours; post-DNA synthesis gap, 0.50 hour; prophase, 1.3 hours; metaphase, 1.0 hour; anaphase, 0.4 hour; telophase, 0.3 hour; postmitosis gap, 9.0 hours. A group of liver cells has been recorded in at least 3 successive replication cycles.
THE OCCURRENCE OF INTRACELLULAR CHONDROITIN SULFATE
Authors: Thorp Frank K. , Dorfman Albert
Published: May 2004

Suspensions of chondrocytes were prepared by treatment with trypsin of the epiphyses of tibias and femurs of 13-day-old chick embryos. After washing to remove the matrix, such suspensions readily incorporate radioactive sulfate into both intracellular and extracellular chondroitin sulfate. Following disruption of the cells, the cell constituents were fractionated by centrifugation. Fractions obtained from cells incubated for 10 minutes showed a concentration of radioactivity in the material which sediments at 10,000 to 20,000 g. At this time the radioactivity of the extracellular chondroitin sulfate is low, but at 1 hour the radioactivity of the intracellular material is relatively unchanged, while that of the extracellular polysaccharide is markedly increased. Following incubation of the chondrocyte suspensions in a tissue culture medium, the intracellular chondroitin sulfate was isolated. This was compared with chondroitin sulfate isolated from the cartilage matrix. Chemical analysis and infrared spectroscopy indicated that both the intracellular and extracellular polysaccharides consist of a mixture of chondroitin sulfuric acids A and C. A portion of the chondroitin sulfate is not sulfated.
THE INDUCTION OF MELANIZATION IN GOLDFISH SCALES WITH ACTH, IN VITRO
Authors: Loud Alden V. , Mishima Yutaka
Published: May 2004

The induction of melanization in xanthic goldfish scales with ACTH in vitro has been studied by light and electron microscopy utilizing ammoniated silver nitrate staining of premelanin and melanin. The melanized cells (melanophores and melanocytes) and the yellow pigmented cells (lipophores and the newly described lipocytes) were found to possess many similarities at the levels of cellular and subcellular structure. The latter cells contain characteristic cytoplasmic bodies which react positively to the premelanin stain. Changes accompanying ACTH stimulation of goldfish scales in tissue culture suggest that these bodies in the lipocytes and lipophores can become melanized. Electron micrographs illustrate the intermediate staining of newly formed melanin granules in an induced melanocyte and the appearance of a transitional melanolipophore. It is postulated that ACTH can promote the association of the enzyme tyrosinase with the preformed structure of unmelanized granules.
THE UPTAKE AND DEVELOPMENT OF VACCINIA VIRUS IN STRAIN L CELLS FOLLOWED WITH LABELED VIRAL DEOXYRIBONUCLEIC ACID
Authors: Dales Samuel
Published: May 2004

Vaccinia virus which had its DNA labeled with thymidine-H3 was purified and used as inoculum for L cells growing in suspension. Samples taken over an 8-hour period after infection were studied by light and electron microscopic autoradiography. Within 20 minutes of its being taken up at the cell membrane in phagocytic vesicles, the outer coat of vaccinia becomes disrupted and the virus core containing the labeled DNA passes into the cytoplasmic matrix. Within 1 hour after inoculation the labeled material passes out of the cores into zones of viroplasm, where cores or remnants of cores are gathered and the label becomes more concentrated by 3 hours after inoculation. Most of the label is conserved in the viroplasm areas during the remainder of the experiment. However, 6 hours after inoculation a very small proportion of progeny virus in the cytoplasm, morphologically distinct from the cores of the inoculum, has associated with it labeled material, perhaps derived from the DNA of the inoculum.
CYTOCHEMICAL STUDIES OF ADENOSINE TRIPHOSPHATASES IN SKELETAL MUSCLE FIBERS
Authors: Padykula Helen A. , Gauthier Geraldine F.
Published: May 2004

Mitochondrial ATPase and myosin ATPase have been localized in the muscle fibers of the rat diaphragm. The principal fiber type possesses a structure favorable for making this cytochemical separation with the light microscope. This small red fiber has numerous large, nearly spherical, mitochondria (ca. 1.5 µ) which are aggregated beneath the sarcolemma. In the interior of the fiber, smaller paired filamentous mitochondria (ca. 0.2 µ diameter) are aligned with the I band. Distribution of mitochondria was determined by sudanophilia, succinic dehydrogenase activity, and by direct examination with the electron microscope. ATPase activity at pH 7.2 is located in the large peripheral mitochondria and in the smaller mitochondria associated with the I band. The alignment of the small mitochondria results in a discrete cross-striated appearance in fibers stained for this enzymic activity. This mitochondrial ATPase does not cleave adenosine diphosphate or adenosine monophosphate; it is not sulfhydryl dependent and, in fact, is enhanced by the mercurial, p-hydroxymercuribenzoate. It requires magnesium ion and is stimulated by dinitrophenol. It is inhibited after formol-calcium fixation, but the residual activity is demonstrable by lengthening the incubation time. At pH 9.4 the ATPase is myofibrillar in origin and is located in the A bands. This myosin ATPase activity is sulfhydryl-dependent. Mercurial at this high pH has an interesting dual effect: it suppresses myosin ATPase but evokes mitochondrial ATPase activity. A third type of ATPase activity can be demonstrated, especially in the large white fibers. This activity occurs at pH 7.2 in the presence of cysteine. Its position is manifested cytochemically as a fine reticular pattern which surrounds individual myofibrils. The distribution suggests that it may originate in the sarcoplasmic reticulum.
STUDIES ON ISOLATED NUCLEI
Authors: Maggio Rachele , Siekevitz Philip , Palade George E.
Published: May 2004

This paper describes the subfractionation of nuclei isolated from guinea pig liver by the procedure presented in the first article of the series (8). Centrifugation in a density gradient system of nuclear fractions disrupted by sonication permits the isolation of the following subfractions: (a) a nucleolar subfraction which consists mainly of nucleoli surrounded by a variable amount of nucleolus-associated chromatin and contaminated by chromatin blocks derived primarily from von Kupffer cell nuclei; (b) and (c), two nucleoplasmic subfractions (I and II) which consist mainly of chromatin threads in a coarser (I) or finer (II) degree of fragmentation. The protein, RNA, and DNA content of these subfractions was determined, and their RNA's characterized in terms of NaCl-solubility, nucleotide composition, and in vivo nucleotide turnover, using inorganic 32P as a marker. The results indicate that there are at least three types of RNA in the nucleus (one in the nucleolus and two in the nucleoplasm or chromatin), which differ from one another in NaCl-solubility, nucleotide composition, turnover, and possibly sequence. Possible relations among these RNA's and those of the cytoplasm are discussed.
STUDIES ON CILIA
Authors: Satir Peter
Published: May 2004

Upon excision into spring water, the lateral cilia of the gill of the freshwater mussel Elliptio complanatus (Solander) stop beating, but 0.04 M potassium ion can activate the gill so that these cilia again beat with metachronal rhythm. One per cent osmium tetroxide quickly pipetted onto a fully activated gill fixes the lateral cilia in a pattern that preserves the form and arrangement of the metachronal wave, and permits the cilia to be studied with the electron microscope in all stages of their beat cycle. Changes are seen in the fixed active preparation that are not present in the inactive control, i.e., in the packing of the cilia, the position of the axis of the ciliary cross-section, and the diameter of the ring of peripheral filaments. Analysis of these parameters may lead to new correlations between ciliary fine structure and function.
CYTOPLASMIC MICROTUBULES
Authors: Slautterback David B.
Published: May 2004

Small cytoplasmic tubules are present in the interstitial cells and cnidoblasts of hydra. They are referred to here as "microtubules." These tubular elements have an outside diameter of 180 A and an inside diameter of 80 A. By difference, the membranous wall is estimated to be 50 A thick. The maximum length of the microtubules cannot be determined from thin sections but is known to exceed 1.5 µ. In the interstitial cells the microtubules are found in the intercellular bridges, free in the cytoplasm and in association with the centrioles. In the cnidoblast they form a framework around the developing nematocyst and in late stages are related to the cnidocil forming a tight skein in the basal part of the cell. Especially in this cell, confluence of microtubules with small spherical vesicles of the Golgi complex has been observed. It is proposed that these tubules function in the transport of water, ions, or small molecules.
THE CYTOPLASMIC FINE STRUCTURE OF THE DIATOM, NITZSCHIA PALEA
Authors: Drum Ryan W.
Published: May 2004

The cytoplasmic fine structure of the motile, pennate diatom, Nitzschia palea was studied in thin sections viewed in the electron microscope. The cells were fixed in OsO4, embedded in methacrylate, and immersed in 10 per cent hydrofluoric acid (HF) for 36 to 40 hours to remove the siliceous cell wall prior to sectioning. The HF treatment did not cause any obvious cytoplasmic damage. The dictyosome complex is perinuclear, and located only in the central cytoplasm. Mitochondria are sparse in the central cytoplasm, but abundant in the peripheral cytoplasm, and fill many of the transvacuolar cytoplasmic strands. Characteristic, amorphous oil bodies fill certain cytoplasmic strands and probably are not leucosin. The pyrenoid appears to be membrane limited, and oil droplets are found adjacent to the pyrenoid. The pyrenoid of another diatom, Cymbella affinis, is also membrane-limited. The membrane limiting the pyrenoid may be a composite of the terminal portions of chloroplast discs, facilitating rapid movement of photosynthate into the pyrenoid matrix, where the characteristic oil droplets may be formed. Carinal fibrils are found singly in each carinal pore, and may be involved in the locomotion of Nitzschia palea.
AN ANALYSIS OF CELLULAR AND SUBCELLULAR SYSTEMS WHICH TRANSFORM THE SPECIES CHARACTER OF ACID PHOSPHATASE IN ACETABULARIA
Authors: Keck Konrad , Choules Elizabeth A.
Published: May 2004

Several species-specific molecular forms of acid phosphatase are known to exist in the unicellular green alga Acetabularia. In graft combinations between cells of Acetabularia mediterranea (med) and Acicularia Schenckii (acic) the expression of the med phosphatase is dominant over acic phosphatase. There is good evidence that in such grafts the preexisting acic phosphatase is converted on the molecular level via an intermediate form to the med phosphatase. This conversion can be initiated by the transplantation of a med cell nucleus to an anucleate acic cell, but will also take place in grafts between anucleate med and anucleate acic cells, indicating that the direct participation of a cell nucleus is not required. An incomplete conversion of acic phosphatase, which terminates at the intermediate stage, is induced in acic cells by injection of a concentrated homogenate of med cytoplasm. A similar partial conversion occurs in vitro in a mixture of homogenates from med and acic cells. Subcellular particles, such as chloroplasts or mitochondria, can be removed from the homogenates by centrifugation without impairing the reactions leading to the intermediate phosphatase type. Experimental evidence suggests that the transformation of phosphatase types is enzymatically catalyzed and may involve the conjugation of small molecules with the phosphatase protein. It was shown, however, that sialic acid is not involved, since the incubation of med or acic homogenates with neuraminidase did not modify the electrophoretic mobility of either enzyme type. Another type of phosphatase, which occurs in Acetabularia erenulata (cren) and can be distinguished electrophoretically from the aforementioned types, is not subject to interaction. In various mono- and multi-nucleate graft combinations between cren cells on one hand, and med or acic cells on the other hand, the cren phosphatase is synthesized independently of the enzyme of the graft partner.
SIZE AND SHAPE TRANSFORMATIONS CORRELATED WITH OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA
Authors: Packer Lester
Published: May 2004

It has been demonstrated that the nature of the physical change in mitochondrial membrane fragments associated with the action of the respiratory enzymes is likely one of shape or symmetry rather than size. The findings suggest that in the state of decreased scattering the macromolecules may be present in an extended physical state. Conditions favorable for phosphorylation may give rise to a folding or contraction of the molecular complex to a more symmetrical structure. Since earlier studies have shown that there is a compulsory relationship between the integrity of systems operative in oxidative phosphorylation and scattering changes, experiments of this type may lead to values for the minimal size of a phosphorylating unit, which at present is estimated to be 2.1 x 106 from light-scattering studies.
SOLUBLE EARTHWORM CUTICLE COLLAGEN: A POSSIBLE DIMER OF TROPOCOLLAGEN
Authors: Maser Morton D. , Rice Robert V.
Published: May 2004

When soluble earthworm cuticle collagen molecules are subjected to the shearing forces of a flow birefringence instrument, they are broken into particles approximately half the original size. The broken particles resemble vertebrate tropocollagen molecules in their hydrodynamic properties, in levorotatory powers, and in their appearance in the electron microscope. Most significantly, the broken earthworm particles form ordered aggregates similar to the segmented-long-spacing aggregations formed by vertebrate tropocollagen. These phenomena are explained by the suggestion that earthworm collagen molecules are dimers of tropocollagen-like particles. On this basis, an explanation is presented for the lack of striations in the gross collagen fibrils of earthworm cuticle.
STUDIES ON SMALL INTESTINAL CRYPT EPITHELIUM
Authors: Trier Jerry S.
Published: May 2004

Small intestinal crypt epithelium obtained from normal fasting humans by peroral biopsy of the mucosa was studied with the electron microscope. Paneth cells were identified at the base of the crypts by their elaborate highly organized endoplasmic reticulum, large secretory granules, and small lysosome-like dense bodies within the cytoplasm. Undifferentiated cells were characterized by smaller cytoplasmic membrane-bounded granules which were presumed to be secretory in nature, a less elaborate endoplasmic reticulum, many unattached ribosomes and, in some cells, the presence of glycogen. Some undifferentiated cells at the base of the crypts contained lobulated nuclei and striking paranuclear accumulations of mitochondria. Membrane-bounded cytoplasmic fragments, probably originating from undifferentiated and Paneth cells, were frequently apparent within crypt lumina. Of the goblet cells, some were seen actively secreting mucus. In these, apical mucus appeared to exude into the crypt lumen between gaps in the microvilli. The membrane formerly surrounding the apical mucus appeared to fuse with and become part of the plasma membrane of the cell, suggesting a merocrine secretory mechanism. Enterochromaffin cells were identified by their location between the basal regions of other crypt cells and by their unique intracytoplasmic granules.
ELECTRON MICROSCOPE STUDIES ON DEVELOPING CRAYFISH OOCYTES WITH SPECIAL REFERENCE TO THE ORIGIN OF YOLK
Authors: Beams H. W. , Kessel R. G.
Published: May 2004

The endoplasmic reticulum is composed, in places, of stacks of parallel cisternae which are limited by membranes having great numbers of ribosomes attached to their outer surface. These are connected with other cisternae of similar structure but with fewer ribosomes and without preferred orientation. The latter extend in all directions from the stacked cisternae, branching and anastomosing freely so that the entire system of membrane-limited cisternae appears interconnected; a morphological condition suitable to serve as the basis for an active transport system. Within the stacked cisternae appear granules about 40 to 60 mµ in diameter. These are thought to represent the precursors of proteinaceous yolk, and the hypothesis is advanced that most of the intracisternal granules are synthesized here, possibly under the influence of the ribosomes. They then "flow" into and along the unoriented cisternae to regions where they collect, expand the cisternae, and undergo transformation into finely granular, relatively large proteinaceous yolk bodies. The mitochondria are somewhat pleomorphic, often show atypical cristae, and frequently contain a few dense granules. Lipid is abundant. Other cytoplasmic components are illustrated.
OVERLAP OF THE BIREFRINGENT COMPONENT OF ADJACENT A REGIONS DURING THE INDUCED SHORTENING OF FIBRILS TEASED FROM DROSOPHILA MUSCLE
Authors: Aronson John
Published: May 2004

Fibrils from the indirect flight muscle of Drosophila melanogaster which have been teased into a solution containing 0.1 M KCl, 2 mM EDTA, 4 mM MgCl2, and 2.5 mM ATP at pH 7.0 can be made to shorten to 10 per cent of their initial length by reducing the level of ATP at a pH of about 8 or by briefly treating the fibrils with trypsin before lowering the level of ATP. Fibrils shortened in either of these ways, when dehydrated and immersed in nitrobenzene, display a strong positively birefringent band at the level of the Z band. In the trypsin-treated fibrils the width of this Z band increases as the fibril shortens. The data obtained are in agreement with the view that the positively birefringent Z band results from the interdigitation of A filaments in adjacent sarcomeres. With shortening to about 35 per cent of the initial length, the cytological pattern suggests that the A filaments of alternate as well as of adjacent A regions interdigitate.
THE STRUCTURE OF FLIGHT MUSCLE SARCOSOMES IN THE BLOWFLY CALLIPHORA ERYTHROCEPHALA (DIPTERA)
Authors: Smith David S.
Published: May 2004

The electron microscopic structure of sectioned indirect flight muscle fibers of the blowfly Calliphora is described. Particular attention is paid to the organization of the sarcosomes (mitochondria) of this tissue, and this description is accompanied by an account of the appearance of these bodies in negatively stained preparations. In sectioned material, it has been shown that these sarcosomes are similar to other mitochondria in the disposition of the outer and inner limiting membranes, but that the cristae, confluent with the latter, are unusually regular, and form parallel plates, containing circular fenestrations forming cylindrical channels within the matrix. Negatively stained preparations of disrupted sarcosomes reveal that both the outer limiting membrane and the cristae membranes bear large numbers of small particles, similar in appearance to those described by Fernández-Morgán and others in various mitochondria. In Calliphora, these particles consist of a sub-spherical "head" and a cylindrical "stalk," and appear to be arranged on the mitochondrial membranes either randomly distributed, or collected into circular or elongated groups. Recent suggestions concerning the nature of these submitochondrial particles are discussed, and an attempt is made to correlate the aspects of organization of Calliphora sarcosomes, revealed by conventional sectioning of the "intact" structures, and by negative staining of sarcosomal derivatives.