bluuebunny/crossref_metadata_2025 huggingface dataset:
PRIMARY CULTURES OF DISSOCIATED SYMPATHETIC NEURONS
Authors: Mains Richard E. , Patterson Paul H.
Published: May 2004

Initial studies are reported on the catecholamine metabolism of low-density cultures of dissociated primary sympathetic neurons. Radioactive tyrosine was used to study the synthesis and breakdown of catecholamines in the cultures. The dependence of catecholamine synthesis and accumulation on external tyrosine concentration was examined and a concentration which is near saturation, 30 µM, was chosen for further studies. The free tyrosine pool in the nerve cells equilibrated with extracellular tyrosine within 1 h; the total accumulation of tyrosine (free tyrosine plus protein, catecholamines, and metabolites) was linear for more than 24 h of incubation. Addition of biopterin, the cofactor of tyrosine hydroxylase, only slightly enhanced catecholamine biosynthesis by the cultured neurons. However, addition of reduced ascorbic acid, the cosubstrate for dopamine ß-hydroxylase, markedly stimulated the conversion of dopamine (DA) to norepinephrine (NE). Phenylalanine, like tyrosine, served as a precursor for some of the DA and NE produced by the cultures, but tyrosine always accounted for more than 90% of the catecholamines produced.

The DA pool labeled rapidly to a saturation level characteristic of the age of the culture. The NE pool filled more slowly and was much larger than the DA pool. The disappearance of radioactive NE and DA during chase experiments followed a simple exponential curve. Older cultures showed both more rapid production and more rapid turnover of the catecholamines than did younger cultures, suggesting a process of maturation.
PRIMARY CULTURES OF DISSOCIATED SYMPATHETIC NEURONS
Authors: Mains Richard E. , Patterson Paul H.
Published: May 2004

Several biochemical parameters of dissociated sympathetic neurons from superior cervical ganglia of the newborn rat were monitored as a function of age in culture. The neurons, which were grown in the virtual absence of non-neural cells, displayed a striking increase in their ability to synthesize and accumulate catecholamines. This capacity increased 50-fold during a 3-wk period in vitro, after which it appeared to reach a steady level. The major change took place during the second week. The time course of this change was not affected by plating the neurons at a higher cell density. The change in the catecholamine metabolism was far greater in magnitude and quite different in time course from the overall growth of the cells which was monitored by the incorporation of radioactive tyrosine into protein, lipid synthesis from radioactive choline, and incorporation of radioactive uridine into acid-precipitable material. Of the total tyrosine used by the cultures, the proportion devoted to catecholamine synthesis increased to 25% (a 10-fold rise) during the 3-wk period. This changing pattern of metabolism in the cultures suggested a process of maturation which may be similar to neuronal development in vivo.
THE CONTRACTILE BASIS OF AMOEBOID MOVEMENT
Authors: Taylor D. L. , Condeelis J. S. , Moore P. L. , Allen R. D.
Published: May 2004

Cytoplasm has been isolated from single amoeba (Chaos carolinensis) in physiological solutions similar to rigor, contraction, and relaxation solutions designed to control the contractile state of vertebrate striated muscle. Contractions of the isolated cytoplasm are elicited by free calcium ion concentrations above ca. 7.0 x 10-7 M. Amoeba cytoplasmic contractility has been cycled repeatedly through stabilized (rigor), contracted, and relaxed states by manipulating the exogenous free calcium and ATP concentrations. The transition from stabilized state to relaxed state was characterized by a loss of viscoelasticity which was monitored as changes in the capacity of the cytoplasm to exhibit strain birefringence when stretched. When the stabilized cytoplasm was stretched, birefringent fibrils were observed. Thin sections of those fibrils showed thick (150–250 Å) and thin (70 Å) filaments aligned parallel to the long axis of fibrils visible with the light microscope. Negatively stained cytoplasm treated with relaxation solution showed dissociated thick and thin filaments morphologically identical with myosin aggregates and purified actin, respectively, from vertebrate striated muscle. In the presence of threshold buffered free calcium, ATP, and magnesium ions, controlled localized contractions caused membrane-less pseudopodia to extend into the solution from the cytoplasmic mass. These experiments shed new light on the contractile basis of cytoplasmic streaming and pseudopod extension, the chemical control of contractility in the amoeba cytoplasm, the site of application of the motive force for amoeboid movement, and the nature of the rheological transformations associated with the circulation of cytoplasm in intact amoeba.
ANTAGONISM BY DIBUTYRYL ADENOSINE CYCLIC 3',5'-MONOPHOSPHATE AND TESTOSTERONE OF CELL ROUNDING REACTIONS
Authors: Storrie Brian
Published: May 2004

In an attempt to understand further the mechanism of the morphological and functional "reverse transformation" of CHO-K1 cells induced by dibutyryl adenosine cyclic 3',5'-monophosphate (cAMP) and testosterone, the kinetics of variation in the susceptibility of cells to rounding after the addition or deletion of dibutyryl cAMP and testosterone have been investigated. Changes in susceptibility to cell rounding upon removal of divalent cations or pulse exposure to concanavalin A were complete within 0.5–1 h after addition or deletion of drug. In comparison, the gross conversion of CHO-K1 cells from epithelial- to fibroblast-like morphology after drug treatment or the converse change after drug removal required 8 or 4 h, respectively. The effects on cell rounding are not caused by an effect of dibutyryl cAMP upon cell growth rate. Inhibitor experiments indicate that the changes investigated do not require continued RNA or protein synthesis and are not prevented by agents which depolymerize microtubules.
EFFECT OF SOLUTION COMPOSITION AND PROTEOLYSIS ON THE CONFORMATION OF AXONEMAL COMPONENTS
Authors: Zobel C. Richard
Published: May 2004

The effect of solution composition and enzymic proteolysis on axonemes prepared from the sperm of sea urchins, Tripneustes gratilla, has been investigated. Aliquots of axonemes, prepared by treatment of sperm with Triton X-100 and differential centrifugation, were transferred to solutions of different composition with and without intervening tryptic proteolysis, and the particle conformations observed by dark-field and electron microscopy. In most solutions particles in partially digested preparations underwent conformational transformations to coiled or helix-like forms. Proteolysis was accompanied by an increase in the ATPase activity of the digest: by centrifuging down the insoluble digestion products it was shown that digestion resulted in the appearance of ATPase activity in the soluble phase with a concomitant decrease in ATPase activity in the pellet fraction. Gel electrophoresis showed this corresponded to the appearance of dynein in the supernatant and a decrease in dynein associated with the insoluble fraction. Supernatant dynein had a greater specific ATPase activity than dynein extracted from axonemes. Observations on specimens prepared for electron microscopy by thin sectioning allowed a rough correlation to be made between the dark-field observations, chemical analyses, and morphological alterations attendant with the proteolysis and solution conditions. It is concluded that in the intact axoneme the doublet tubules are under considerable tension and that proteolytic destruction of physical restraining elements allows spontaneous conformational alterations of the digestion products. In addition, proteolysis increases the specific ATPase activity of dynein and removes a portion of it from the axonemal structure.
EFFECT OF METABOLIC INHIBITORS ON NUCLEAR PORE FORMATION DURING THE HELA S3 CELL CYCLE
Authors: Maul Helmut M. , Hsu Betty Yee Li , Borun Thaddeus M. , Maul Gerd G.
Published: May 2004

The effect of various antimetabolites on nuclear pore formation was studied in synchronized HeLa S3 cells. The nuclear size was determined by light microscopy and the pore number per unit area of nuclear surface by the freeze-etching technique and electron microscopy. It was found that the inhibition of DNA replication or ribosomal RNA synthesis has no effect on nuclear size increase or pore formation. However, the inhibition of ATP synthesis effectively stops nuclear pore formation. Cycloheximide blocks nuclear pore formation at the same time during G1 phase of the cell cycle when nuclear size increase is blocked by high concentrations of actinomycin D. This suggests that certain proteins or other factors leading to pore formation and nuclear size increase are transcribed and synthesized at about 3–4 h after mitosis, i.e., about 1–2 h before S phase begins.
SECRETORY PROTEIN SYNTHESIS IN THE STIMULATED RAT PAROTID GLAND
Authors: Lillie John H. , Han Seong S.
Published: May 2004

Administration of the ß-adrenergic drug, isoproterenol (IPR), affects the release of 98% of stored amylase from rat parotid gland acinar cells. A period of 6 h elapses from the onset of secretion to the maximum [14C]phenylalanine (Phe) incorporation into total protein and amylase. 10 h after IPR administration the rate of [14C]Phe incorporation into total protein was no longer elevated above that of control. Incorporation into amylase, however, remained elevated above the control by 2.3 times. This latent period may reflect: (a) reduced amounts of available ATP which occurs as a result of the process of secretion as well as (b) the time required for reorganization of cellular organelles and membranes after secretion. The latent period after IPR-induced secretion appears similar to the latent period which has recently been reported to occur after physiologic release of amylase from the parotid gland during the diurnal feeding cycle of the rat. These observations support the existence of a positive feedback system operant in the parotid acinar cell linking the release of secretory proteins with their synthesis. The period of greatest protein synthesis is, however, temporally dissociated from the secretory process.
Phagotrophy and Two New Structures in the Malaria Parasite Plasmodium berghei
Authors: Rudzinska Maria A. , Trager William
Published: May 2004

Blood collected from rats infected with Plasmodium berghei was centrifuged and the pellet was fixed for 1 hour in 1 per cent buffered OsO4 with 4.9 per cent sucrose. The material was embedded in n-butyl methacrylate and the resulting blocks sectioned for electron microscopy.

The parasites were found to contain, in almost all sections, oval bodies of the same density and structure as the host cytoplasm. Continuity between these bodies and the host cytoplasm was found in a number of electron micrographs, showing that the bodies are formed by invagination of the double plasma membrane of the parasite. In this way the host cell is incorporated by phagotrophy into food vacuoles within the parasite. Hematin, the residue of hemoglobin digestion, was never observed inside the food vacuole but in small vesicles lying around it and sometimes connected with it. The vesicles are pinched off from the food vacuole proper and are the site of hemoglobin digestion.

The active double limiting membrane is responsible not only for the formation of food vacuoles but also for the presence of two new structures. One is composed of two to six concentric double wavy membranes originating from the plasma membrane. Since no typical mitochondria were found in P. berghei, it is assumed that the concentric structure performs mitochondrial functions. The other structure appears as a sausage-shaped vacuole surrounded by two membranes of the same thickness, density, and spacing as the limiting membrane of the body. The cytoplasm of the parasite is rich in vesicles of endoplasmic reticulum and Palade's small particles. Its nucleus is of low density and encased in a double membrane.

The host cells (reticulocytes) have mitochondria with numerous cristae mitochondriales. In many infected and intact reticulocytes ferritin was found in vacuoles, mitochondria, canaliculi, or scattered in the cytoplasm.
The Isolation of Nucleoli from Ungerminated Pea Embryos
Authors: Johnston F. B. , Setterfield G. , Stern Herbert
Published: May 2004

A method is described for the isolation of nuclei and nucleoli from ungerminated pea embryos. Electron micrographs of the nucleolar preparation indicate a high degree of purity but only a partial preservation of composition, because of a loss of material from the nucleoli which occurs during the isolation procedure.
Electron Microscope Studies of the Human Epidermis
Authors: Hibbs Richard G. , Clark Wallace H.
Published: May 2004

The thin skin of the left upper quadrant of the human abdomen has been studied by electron microscopy. Tissue removed with a high speed rotary punch was fixed in osmium tetroxide or potassium permanganate. The latter fixative in our preparations is superior to osmium for the demonstration of epidermal cell membranes and certain other membranous structures of the epidermis. The cytoplasmic membranes of basal cells and cells of the stratum granulosum have been found to be relatively straight, while those of most spinous cells are sharply scalloped. The deep cells of the stratum spinosum in the rete ridge area show cell membranes and cytoplasmic structure intermediate between true basal cells and most cells of the stratum spinosum. The extracellular material of the desmosome has been found to consist of alternate dark and light laminae similar to those described by Odland (13) and Horstmann and Knoop (7).
Further Observations on the Nuclear Envelope of the Animal Cell
Authors: Watson Michael L.
Published: May 2004

The term pore complex is proposed for approximately cylindrical formations which are observed with the electron microscope to penetrate the nuclear envelope of cells. Cross-sections of the pore complex are somewhat annular in shape, but differ in appearance depending upon the level of the cross-section with respect to the nuclear surface. An explanation is offered for the apparent discrepancy between the width of pores in sections perpendicular to the nuclear envelope and the width of cross-sections of the pore complex in tangential sections. Channels associated with the pore complex extend deep into the nucleus. Although crescents and spirals of ribonucleoprotein particles were often seen in the immediate vicinity of the outer nuclear membrane, direct association with the pore complex was not observed. Many examples were found of pores that were not covered by a continuous membrane although the possibility of such a covering in some cases is not precluded.
A Light and Electron Microscope Study of the Epithelial Cells of the Gut of Fasciola hepatica L
Authors: Gresson R. A. R. , Threadgold L. T.
Published: May 2004

The structure of the epithelial cells of the alimentary tract of Fasciola hepatica was investigated by means of light and electron microscopy. Tissue prepared for electron microscopy was fixed in 1 per cent osmium tetroxide, buffered with veronal to a pH of 7.4, and embedded in butyl methacrylate with 1 per cent benzoyl peroxide as a catalyst. Polymerisation was carried out at 60°C. The majority, if not all, the epithelial cells pass through both absorptive and secretory cycles. The free ends of absorptive cells possess fine protoplasmic processes that project into the lumen of the gut. These are apparently concerned with the absorption of nutriment. In electron micrographs, the protoplasmic (absorptive) processes are frequently seen to be in the form of tubular loops both ends of which arise from the same cell. The free end of a process is often expanded into a ribbon-like structure. Each process possesses an external limiting membrane and an internal membranous ultrastructure. When a cell becomes glandular in function, the protoplasmic processes seem to become less numerous. The plasma membrane is invaginated into the basal part of an absorptive cell. In the neighbourhood of the lumen of the gut where two tall cells are in contact, bands of amorphous cytoplasmic material are in contact with each cell membrane.
Enzymatic Activity in the M Band
Authors: Barrnett Russell J. , Palade George E.
Published: May 2004

Experiments which combined histochemistry and electron microscopy were performed in studying the sites of enzymatic hydrolysis of thiolacetic acid in the presence of lead ions in diaphragmatic and cardiac muscle. It was found that in these striated muscles the electron opaque, final product of the histochemical reaction (PbS) was discretely deposited on the swelling of the thick elemental filaments that occurs at the M band. Additional sites of enzymatic activity occurred in mitrochondria and in round sarcoplasmic bodies. A reaction, probably non-enzymatic, also occurred in contraction bands in the area of the Z bands and in the sarcoplasmic reticulum. To ascertain the enzymatic nature of the reaction and to define the enzyme involved, control experiments were carried out and the effect of various esterase inhibitors was assayed.

It is suggested that the M band enzyme is a cholinesterase, but the enzymes in the mitochondria and the sarcoplasmic bodies that hydrolyze the substrate appear to be different. A possible role of the M band enzyme is discussed.
Alpharadiography: A Simple Method for Determination of Mass Concentration in Cells and Tissues
Authors: Bélanger Leonard F.
Published: May 2004

A simple apparatus for the production of contact microradiographs with the help of a polonium alpha source and nuclear emulsion plates is described.

This apparatus best adapted for soft tissue and low grade mineralization studies offers advantages as to resolution, geometry of specimen as well as ease of operation and cost.
Nuclear Synthesis of Cytoplasmic Ribonucleic Acid in Amoeba proteus
Authors: Prescott David M.
Published: May 2004

The enucleation technique has been applied to Amoeba proteus by several laboratories in attempts to determine whether the cytoplasm is capable of nucleus-independent ribonucleic acid synthesis. This cell is very convenient for micrurgy, but its use requires a thorough starvation period to eliminate the possibility of metabolic influence by food vacuoles and frequent washings and medium renewal to maintain asepsis. In the experiments described here, amoebae were starved for periods of 24 to 96 hours, cut into nucleated and enucleated halves, and exposed to either C-14 uracil, C-14 adenine, C-14 orotic acid, or a mixture of all three. When the starvation period was short (less than 72 hours), organisms (especially yeast cells) contained within amoeba food vacuoles frequently showed RNA synthesis in both nucleated and enucleated amoebae. When the preperiod of starvation was longer than 72 hours, food vacuole influence was apparently negligible, and a more meaningful comparison between enucleated and nucleated amoebae was possible. Nucleated cells incorporated all three precursors into RNA; enucleated cells were incapable of such incorporation.

The experiments indicate a complete dependence on the nucleus for RNA synthesis. The conflict with the experimental results of others on this problem could possibly stem from differences in culture conditions, starvation treatment, or experimental conditions. For an unequivocal answer in experiments of this design, ideally the cells should be capable of growth on an entirely synthetic medium under aseptic conditions. The use of a synthetic medium (experiments with A. proteus are done under starvation conditions) would permit, moreover, a more realistic comparison of metabolic capacities of nucleated and enucleated cells.
Phospholipide Turnover in Microsomal Membranes of the Pancreas during Enzyme Secretion
Authors: Redman Colvin M. , Hokin Lowell E.
Published: May 2004

After incubation of pigeon pancreas slices with P32 and isolation of various fractions by differential centrifugation the deoxycholate extract of the microsome fraction was found to account for over half of the phospholipide P and over half of the P32 incorporated into the phospholipides. The remaining phospholipide P and P32 were fairly evenly distributed in the nuclei, zymogen granules, mitochondria, microsomal ribonucleoprotein particles, and the soluble fraction.

When enzyme secretion was stimulated with acetylcholine about two-thirds of the increment in radioactivity in the total phospholipides was found in deoxycholate soluble components of the microsome fraction. The remainder of the increment was distributed in the other fractions. This indicates that the cellular component in which the increase in phospholipide turnover occurs on stimulation of secretion is a membranous structure. Evidence is presented which indicates that the increment in radioactivity in the non-microsomal fractions on stimulation of secretion is due to contamination of these fractions with fragments of the stimulated membranous structure.

The distribution of P32 radioactivity in each of the chromatographically separated phospholipides in the various fractions from unstimulated tissue paralleled the distribution of radioactivity in the total phospholipide fraction, indicating that individual phospholipides are not concentrated in different fractions but are associated together in the membranous structures of the microsome fraction. The major proportion of the stimulation of the turnover of the individual phospholipides also occurred in the microsome fraction.

The distribution of radioactivity from glycerol-1-C14 in the total phospholipides and in the individual phospholipides in the various fractions was similar to the distribution of P32. In the microsome fraction acetylcholine stimulated the incorporation of glycerol-1-C14 in each phospholipide which showed a stimulation of P32 incorporation.

The significance of the turnover of phosphatides in microsomal membranes in relation to the mechanism of secretion is discussed.
Electron Microscope Observations on the Behavior of the Bacterial Cytoplasmic Membrane During Cellular Division
Authors: Chapman George B.
Published: May 2004

Bacterial cells were fixed in OsO4, washed, dehydrated, and embedded in a methacrylate mixture. Ultrathin sections were cut on a Porter-Blum ultramicrotome and were examined in an RCA electron microscope, type EMU-2D.

The sections revealed that the cytoplasmic membrane undergoes a centripetal growth to form a membrane septum. This septum is formed as a double structure. Constriction of the daughter cells and deposition of cell wall material lead to the separation of the daughter cells.

The bacterial cytoplasm appears to consist largely of 200 A granules and occasionally reveals arrays of parallel dense lines.
The Fine Structure of the Retina Studied with the Electron Microscope
Authors: Tokuyasu Kiyoteru , Yamada Eichi
Published: May 2004

The morphogenesis of the outer segments of retinal rods was studied mainly in the kitten before the opening of the eye, and the probable sequence of the morphogenetic stages is deduced. Since the development of retinal rods is not synchronous, the deductions were based on observations of many single and serial sections.

One centriole extends ciliary tubules of about 0.5 µ long, in the growing primitive cilium. Beyond this length, each ciliary tubule becomes a row of small vesicles (called "ciliary vesicles" in this paper), which penetrate into the distal region of the cilium.

Where the ciliary vesicles establish contact with the plasma membrane of the distal region of the cilium, more or less deep infoldings of the plasma membrane are observed. In the distal region can be seen rows of tubular or vesicular structures. A few of these membranous structures are continuous with the bottoms of the infoldings.

At the following stage, the infoldings disappear and the ciliary vesicles lose contact with the distal plasma membrane. Nonetheless, the formation of the tubular structures continues in the distal region of the primitive outer segment.

The tubular structures appear to be transformed into the primitive rod sacs by sidewise enlargement. At a subsequent time, presumably, these primitive rod sacs flatten and are rearranged into a position perpendicular to the long axis of the outer segment.

The detailed structure of the basal body of the connecting cilium was also studied by means of serial sections.
Autoradiographs of Pollen Tube Nuclei with Calcium-45
Authors: Steffensen Dale , Bergeron John A.
Published: May 2004

Autoradiography with Ca45 has been used to obtain information about the relation between calcium and chromosomes. Labelled pollen from the Easter lily, Lilium longiflorum, was allowed to develop into pollen tubes between 5 and 6 cm. long in the styles of non-radioactive flowers. All of the nuclei, namely the tube nucleus and the two sperm nuclei, retain Ca45 after this period of growth and development.

Since the two sperm nuclei have formed during this interval by the mitotic division of the generative nucleus and growth of the tube has occurred under the influence of the tube nucleus, it is inferred that the calcium was bound in a stable nuclear component, the chromosomes.
A Neoplastic Connective Tissue Mast Cell Capable of Continuous Growth In Tissue Culture
Authors: Williams William J. , Larson Edna , Phillips Theodore L.
Published: May 2004

A neoplastic connective tissue mast cell from a dog mast cell sarcoma has been grown in tissue culture for 50 passages over a period of 2 years. The cells were grown as monolayer cultures in glass bottles, using Eagle's basal medium fortified with calf serum. The cultures were contaminated with an Alkaligenes sp. for 10 months but finally were sterilized bacteriologically by treatment with specific antiserum combined with antibiotics.

The cells grow in a fibroblastic pattern, and contain mitochondria, mast cell granules, and lipid granules or droplets. The mast cell granules stain basophilic with Giemsa's stain and metachromatically with azure A or toluidine blue. They also stain with Sudan black B and with periodic acid-Schiff stain. The interphase nuclei are vesicular, contain from 1 to 20 nucleoli, and frequently show bizarre outlines. Multinucleate cells are often seen, as are mitotic figures. Extracellular fibrous material occurs in all cultures and apparently originates from the cell surface. This material does not have the structure of connective tissue fibers and has not been identified.

The cells develop an increased number of metachromatic granules when grown in medium containing heparin and an increased number of sudanophilic granules when grown in medium containing stearic acid. Only small amounts of histamine were present in the tumor from which this cell line was derived and in the cells grown in tissue culture.
Effect of Thioacetamide on Rat Liver Regeneration
Authors: Kleinfeld R. G. , von Haam E.
Published: May 2004

The effect of thioacetamide on dividing cells of regenerating rat liver has been studied. Rats were given daily subcutaneous injections of thioacetamide as a 1 per cent solution at a dosage of 5 mg./100 gm. body weight for 7 to 10 days, subjected to partial hepatectomy, and sacrificed 28 to 31 hours later.

Thioacetamide treatment results in striking increases in the nuclear ribonucleoproteins of the liver cell without affecting the mitotic rate during regeneration (14). During mitosis, RNA-containing particles were seen within the spindle and coating the contracted chromosomes from prophase through metaphase or early anaphase. At telophase, prior to the reconstruction of the nuclear membrane, fine RNA-containing granules appeared within the compact chromosomal groups. These coalesced to form nucleoli corresponding in number to the number of nucleolar organizer regions. The nuclei and nucleoli showed a rapid increase in size during the reconstruction period when compared with corresponding figures of the control liver samples.

Electron micrographs of interphase nucleoli indicated a similar basic granular structure in both drug-treated and control animals.

The question is raised as to whether the increased nucleolar material merely made visible some of the nucleolar-chromosomal associations that normally occur in mitosis, or whether thioacetamide directly affects the synthetic activity of the contracted mitotic chromosomes.
Striation Patterns of Ox Muscle in Rigor Mortis
Authors: Locker Ronald H.
Published: May 2004

Ox muscle in rigor mortis offers a selection of myofibrils fixed at varying degrees of contraction from sarcomere lengths of 3.7 to 0.7 µ. A study of this material by phase contrast and electron microscopy has revealed four distinct successive patterns of contraction, including besides the familiar relaxed and contracture patterns, two intermediate types (2.4 to 1.9 µ, 1.8 to 1.5 µ) not previously well described.
Differential Uptake of Tritiated Thymidine into Hetero- and Euchromatin in Melanoplus and Secale
Authors: Lima-de-Faria A.
Published: May 2004

Grasshoppers of the species Melanoplus differentialis were injected with tritium-labelled thymidine. At intervals thereafter autoradiographic stripping film was applied over Feulgen squashes and sections. In this species during early prophase of meiosis the sex chromosome forms a heterochromatic block large enough to be resolved in tritium autoradiographs. A study of the squash preparations reveals that the sex chromosome is synthesizing DNA at a different period of time from the euchromatic autosomes. Since there is a developmental sequence of spermatocyte cysts along the testicular tubes it is possible from the sections to show that the heterochromatin synthesizes DNA later than does the euchromatin. To find out whether the results obtained in Melanoplus were characteristic of heterochromatin in general, young seedlings of rye were grown in a tritiated thymidine solution and Feulgen squashes were made as for Melanoplus. In rye leaf nuclei there is a large block of heterochromatin constituted by the proximal regions of the chromosomes and a euchromatic one formed by the median and distal regions of the same chromosomes. Here also the heterochromatin synthesizes DNA at a different period of time from the euchromatin. It is concluded that in rye the asynchrony of synthesis occurs within each chromosome. Counts of silver grains over the two types of chromatin in nuclei of Melanoplus and Secale disclosed that the number of grains per unit area was two to three times higher over the heterochromatin. To check the DNA content, Feulgen photometric measurements were made of Melanoplus nuclei at the same stage. The Feulgen and grain counts agree in showing that the heterochromatin contains two to three times more DNA per unit area than the euchromatin.
Entwicklung und Struktur der Proplastiden
Authors: Mühlethaler Kurt , Frey-Wyssling Albert
Published: May 2004

In this study the proplastid development in embryonic cells is described for the apical meristem of Elodea canadensis, embryo sacs from Lilies, and Begonia leaf buds. The formation of these cell organelles originates with submicroscopical particles which consist of a homogeneous stroma with a surrounding double membrane. When these proplastids reach an average size of 1 µ, the inner layer of the membrane begins to invaginate into the stroma. This process is comparable to tubuli formation in mitochondria.

Under growth conditions with sufficient exposure to light, the development of the grana and stroma lamellae proceeds without interruption. If the plants are kept in the dark, small vesicles are formed which accumulate in the prolamellar body of the proplastids. After illumination these elementary vesicles merge to form membranes which evolve into grana and stroma lamellae. The structural similarity of the early proplastid stages with the mitochondria seems to indicate that there exists some phylogenetic relationship between the two cell organelles.
THE STRUCTURE OF THE ZONULA OCCLUDENS
Authors: Wade James B. , Karnovsky Morris J.
Published: May 2004

Replicas of freeze-fractured toad urinary bladder and gallbladder were analysed in an attempt to determine the fracturing properties and structure of the zonula occludens (tight junction). Chalcroft and Bullivant have proposed that the junction has a double set of fibrils with one set associated with each of the adjacent cell membranes. However, the fracturing pattern that is observed might also result from only a single set of fibrils which is shared by the adjacent membranes if fracturing occurred around either side of the fibrils. These two models predict quite different structures at regions of the junction where tranl sitions are made between face A and face B. The relative heights of face A and face B and the shape of the transition from face A to face B do not agree with that expected according to the two fibril model but agree exactly with that expected if only a single set of fibrils existed. Further evidence for the single fibril model is derived from fractures of the mucosa membrane which cross the junction to the membrane of the adjacent cell without deflection. Such fractures reveal a single ridge which appears to be identical to the juxtaluminal fibril of the junction. In addition, small ridges are occasionally found in place of the grooves on face B which, although not consistent with the double fibril model, is expected if the single fibril model were correct. Although alternative explanations might account for these observations, we believe that the simplest and most consistent explanation is that the zonula occludens fractures as would be expected of a single set of fibrils shared by adjacent cells.
THE DISTRIBUTION AND ASYMMETRY OF MAMMALIAN CELL SURFACE SACCHARIDES UTILIZING FERRITIN-CONJUGATED PLANT AGGLUTININS AS SPECIFIC SACCHARIDE STAINS
Authors: Nicolson Garth L. , Singer S. J.
Published: May 2004

The preparation, properties, and some applications of ferritin conjugates of two plant agglutinins, concanavalin A and Ricinus communis agglutinin, are reported. These conjugates serve as specific electron-dense stains for cell- and membrane-bound saccharide residues of the α-D-mannopyranosyl and ß-D-galactopyranosyl configurations, respectively, and as examples of a wide range of ferritin-plant agglutinin conjugates useful as high resolution saccharide stains. By using a technique for preparing flattened membrane specimens, it was found with a variety of mammalian cell plasma membranes (lymphocyte, lymphoma, and myeloma and normal, spontaneously and virally transformed fibroblasts) that the ferritin conjugates were localized exclusively to the exterior face of the membrane, with essentially none found on the cytoplasmic face. On the exterior face the topographical distribution of ferritin conjugates appeared to be random. The asymmetrical distribution of saccharide residues to the outer membrane face can be explained by an "assembly line" process whereby new plasma membrane is made from intracellular precursor membranes. It also suggests that the saccharide-containing components of the plasma membrane do not rotate at any appreciable rate from one membrane surface to the other.
MIGRATION OF GLYCOPROTEIN FROM THE GOLGI APPARATUS TO THE SURFACE OF VARIOUS CELL TYPES AS SHOWN BY RADIOAUTOGRAPHY AFTER LABELED FUCOSE INJECTION INTO RATS
Authors: Bennett Gary , Leblond C. P. , Haddad Antonio
Published: May 2004

A single intravenous injection of L-[3H]fucose, a specific glycoprotein precursor, was given to young 35–45 g rats which were sacrificed at times varying between 2 min and 30 h later. Radioautography of over 50 cell types, including renewing and nonrenewing cells, was carried out for light and electron microscope study.

At early time intervals (2–10 min after injection), light microscope radioautography showed a reaction over nearly all cells investigated in the form of a discrete clump of silver grains over the Golgi region. This reaction varied in intensity and duration from cell type to cell type. Electron microscope radioautographs of duodenal villus columnar cells and kidney proximal and distal tubule cells at early time intervals revealed that the silver grains were restricted to Golgi saccules. These observations are interpreted to mean that glycoproteins undergoing synthesis incorporate fucose in the saccules of the Golgi apparatus. Since fucose occurs as a terminal residue in the carbohydrate side chains of glycoproteins, the Golgi saccules would be the site of completion of synthesis of these side chains.

At later time intervals, light and electron microscope radioautography demonstrated a decrease in the reaction intensity of the Golgi region, while reactions appeared over other parts of the cells: lysosomes, secretory material, and plasma membrane. The intensity of the reactions observed over the plasma membrane varied considerably in various cell types; furthermore the reactions were restricted to the apical surface in some types, but extended to the whole surface in others.

Since the plasma membrane is covered by a "cell coat" composed of the carbohydrate-rich portions of membrane glycoproteins, it is concluded that newly formed glycoproteins, after acquiring fucose in the Golgi apparatus, migrate to the cell surface to contribute to the cell coat. This contribution implies turnover of cell coat glycoproteins, at least in nonrenewing cell types, such as those of kidney tubules. In the young cells of renewing populations, e.g. those of gastro-intestinal epithelia, the new glycoproteins seem to contribute to the growth as well as the turnover of the cell coat. The differences in reactivity among different cell types and cell surfaces imply considerable differences in the turnover rates of the cell coats.
CHEMICAL CHARACTERIZATION OF THE ISOLATED CELL SURFACE OF AMOEBA
Authors: Allen Howard J. , Ault Charles , Winzler Richard J. , Danielli James F.
Published: May 2004

The cell surface has been isolated from uninucleate, freshwater, phagocytic amoebae by a new procedure. Several criteria were employed to demonstrate purity of the cell surface fraction. All morphological components of the tripartite surface were present in the isolated surface and the weight of the isolated surface was quantitatively accounted for by the components analyzed. Chemical analyses showed the presence of lipid, protein, and carbohydrate. Mannose was the predominant neutral sugar. Analyses for three different strains of Amoeba were similar. Phosphate was found to be the major anionic group in the cell surface material. Sulfate, uronic acid, sialic acid, muramic acid, and nonamidated glutamic acid and aspartic acid were absent. Evidence is presented suggesting that the phosphate is associated with an unidentified nonreducing polyol.
NUCLEOLAR AND PERICHROMOSOMAL RNA SYNTHESIS DURING MEIOTIC PROPHASE IN THE MOUSE TESTIS
Authors: Kierszenbaum A. L. , Tres Laura L.
Published: May 2004

The transcriptional activity during meiotic prophase in the mouse testis is studied with light microscopy and high-resolution autoradiographic techniques using [3H]uridine as a labeled precursor. In the present study, two types of RNA synthesis are detected during meiotic prophase: an extranucleolar RNA synthesis of perichromosomal localization and a nucleolar RNA synthetic activity. In some of the autosomes and close to the basal knobs, the activity of the nucleolar organizers is evidenced by the incorporation of [3H]uridine into nucleolar masses from zygotene on and at earlier labeling times. The evolution of nucleoli and the formation of a nucleolus attached to the sex pair are described during the different meiotic stages. Perichromosomal labeling, from leptotene on, reaches a maximum during middle pachytene and falls progressively to a low level at longer incorporation times. Sertoli's cell, the most active RNA synthetic cell in the seminiferous epithelium, rises to a maximum of labeling and drops at earlier times compared with the meiotic prophase cells. The condensed sex chromosomes show some scattered silver grains especially at middle pachytene. The axial chromosome cores and synaptonemal complexes are devoid of silver grains during the meiotic prophase. The observations suggest that a control mechanism operates during meiotic prophase to regulate transcriptional activity in the sex chromosomes and to provide differential RNA synthesis in autosomal bivalents at various stages of prophase and within certain segments of the chromosomes.
SYNTHESIS, MIGRATION, AND RELEASE OF PRECURSOR COLLAGEN BY ODONTOBLASTS AS VISUALIZED BY RADIOAUTOGRAPHY AFTER [3H]PROLINE ADMINISTRATION
Authors: Weinstock Melvyn , Leblond C. P.
Published: May 2004

The elaboration of dentin collagen precursors by the odontoblasts in the incisor teeth of 30–40-g rats was investigated by electron microscopy, histochemistry, and radioautography after intravenous injection of tritium-labeled proline.

At 2 min after injection, when the labeling of blood proline was high, radioactivity was restricted to the rough endoplasmic reticulum, indicating that it is the site of synthesis of the polypeptide precursors of collagen, the pro-alpha chains.

At 10 min, when the labeling of blood proline had already declined, radioactivity was observed in spherical portions of Golgi saccules containing entangled threads, and, at 20 min, radioactivity appeared in cylindrical portions containing aggregates of parallel threads. The parallel threads measured 280–350 nm in length and stained with the low pH-phosphotungstic acid technique for carbohydrate and with the silver methenamine technique for aldehydes (as did extracellular collagen fibrils). The passage of label from spherical to cylindrical Golgi portions is associated with the reorganization of entangled into parallel threads, which is interpreted as the packing of procollagen molecules.

Between 20 and 30 min, prosecretory and secretory granules respectively became labeled. These results indicate that the cylindrical portions of Golgi saccules transform into prosecretory and subsequently into secretory granules. Within these granules, the parallel threads, believed to be procollagen molecules, are transported to the odontoblast process.

At 90 min and 4 h after injection, label was present in predentin, indicating that the labeled content of secretory granules had been released into predentin. This occurred by exocytosis as evidenced by the presence of secretory granules in fusion with the plasmalemma of the odontoblast process.

It is proposed that pro-alpha chains give rise to procollagen molecules which assemble into parallel aggregates in the Golgi apparatus. Procollagen molecules are then transported within secretory granules to the odontoblast process and released by exocytosis. In predentin procollagen molecules would give rise to tropocollagen molecules, which would then polymerize into collagen fibrils.
REGULATION OF TYROSINE AMINOTRANSFERASE ACTIVITY IN TWO LIVER-DERIVED PERMANENT CELL LINES
Authors: Sellers Larry , Granner Daryl
Published: May 2004

The regulation of tyrosine aminotransferase (TAT) activity has been examined in two liver-derived heteroploid cell lines. One (hepatoma tissue culture cells [HTC]) was derived from a hepatoma, the other (rat liver culture cells [RLC]) was derived from normal liver. The two cell lines show the following striking similarities in the control of this specific protein: (a) The kinetics of TAT induction by dexamethasone phosphate (DxP) are similar in randomly growing cells of both lines; (b) During mitosis and early G1 phase of the cell cycle TAT activity cannot be induced by DxP in either cell line; (c) 2–3 h into G1, when both lines become sensitive to inducer, basal enzyme activity declines to a new steady-state level; (d) Preinduced cells collected in mitosis show approximately twice the level of TAT activity as fully induced, randomly growing cultures and this activity is maintained in early G1 with or without the inducer; and (e) Inhibition of RNA synthesis by 5 µg/ml of actinomycin D in preinduced, synchronized cells allows TAT activity to remain at constitutive levels throughout G1, even in the absence of inducer. These results are presented in support of a previously described model which states that glucocorticoid hormones exert posttranscriptional control of the synthesis of specific proteins in mammalian cells.
RNA SYNTHESIS IN THE MOUSE OOCYTE
Authors: Moore G. P. M. , Lintern-Moore Sue , Peters Hannah , Faber M.
Published: May 2004

RNA synthesis in the oocyte and granulosa cell nuclei of growing follicles has been studied in the mouse ovary. The RNA precursor [3H]uridine was administered intraperitoneally to adult mice and the amount of label incorporated into ovarian RNA was quantitated autoradiographically using grain-counting procedures. Uridine incorporation into the nucleus is low in oocytes of small, resting follicles but increases during follicle growth and reaches a peak prior to the beginning of antrum formation. Thereafter uptake rapidly declines and is very low in the oocytes of maturing follicles. Uridine incorporation into granulosa cell nuclei, in contrast to that found in the oocyte, increases gradually during most of the period of follicle growth.

Qualitative studies of the activity of endogenous, DNA-dependent RNA polymerases have also been made in fixed oocytes isolated from follicles at different stages of growth. Polymerase activity is demonstrable in the nucleolus and nucleoplasm of oocytes from growing follicles, but is absent from maturing oocytes of large follicles.
CELL DEATH IN THE EMBRYONIC CHICK SPINAL CORD
Authors: O'Connor Thomas M. , Wyttenbach Charles R.
Published: May 2004

The events which occur in the death of visceromotor neurons of the cervical region of the chick embryo's spinal cord have been analyzed by electron microscopy. These normal degenerative events are compared with those in the lumbosacral cord where nerve cell death was induced by removal of peripheral organs. The initial set of degenerative changes include a decrease in nuclear size, the clumping of chromatin beneath the nuclear envelope, an increase in electron opacity of the cells, the disappearance of Golgi bodies, and the disaggregation of polysomes. These events are followed by the loss of the nuclear envelope and most of the endoplasmic reticulum, the appearance of bundles of filaments, and the formation of many ribosome crystals. Ribosome crystals are seen only in the dying cells. Their abundance may indicate a drastic reduction in RNA synthesis as one of the initial events which lead to the death of these neurons. The neurons are finally subdivided and engulfed by cells of the normal glial population, and further breakdown of the cell fragments occurs in large phagocytic vesicles of the gliocytes.
EFFECTS OF SERUM ON MEMBRANE TRANSPORT
Authors: Strauss Phyllis R.
Published: May 2004

When monolayers of freshly obtained rabbit lung macrophages are exposed to the nucleoside analogue, showdomycin (sho), adenosine transport, measured over a 45 s interval, is irreversibly inhibited. Low doses of the drug or short periods of exposure, however, do not result in decreased transport, while higher concentrations or longer exposures result in exponential decline. The initial lag is not due to a long reaction time of sho with the transport carrier or to nonspecific sites absorbing the drug.

Previously it was shown that preincubation of monolayers with normal rabbit serum (NRS) results in increased adenosine transport. When monolayers are first exposed to sho so as to inhibit transport to varying degrees and then incubated with NRS, transport is increased over the inhibited level. Several experiments make it unlikely that serum removes the drug from the cell surface in a nonspecific fashion. Moreover, serum given before, during, or after sho alters the dose response curve so that no shoulder is seen. One way to explain these results makes use of target theory: the adenosine transport system could be comprised mainly of "coupled" or "clustered" sites of which only one is active at any time as well as "hidden" sites which are inactive. When a site in a group is irreversibly inactivated by sho, another in the group becomes activated. Serum might activate or uncouple all sites and also cause the appearance of hidden sites, which previously neither transported nor bound sho.