bluuebunny/crossref_metadata_2025 huggingface dataset:
RNA SYNTHESIS IN CHINESE HAMSTER CELLS
Authors: Enger M. D. , Tobey R. A.
Published: May 2004

Cultures of mitotic Chinese hamster cells, prepared by mechanical selection, were pulse-labeled with methionine-methyl-14C or with uridine-3H at different stages in the life cycle. The rate of 14C incorporation into 18S RNA was measured, as was the rate of uridine-3H incorporation into total RNA for both monolayer and suspension cultures. The rate of incorporation increased continuously throughout interphase in a fashion inconsistent with a gene-dosage effect upon RNA synthesis.
II. DIFFERENCES IN ADRENAL MEDULLA NUCLEAR DNA CONTENT AMONG RATS OF DIFFERENT STRAINS FOLLOWING INTERMITTENT EXPOSURE TO COLD
Authors: Tongiani Roberto , Viola-Magni Maria Pia
Published: May 2004

The amount of DNA per nucleus in the adrenal medulla cells of four different strains of rats (Wistar, Sprague-Dawley, Long-Evans, and Italico) is determined both under control conditions and after 300 hr of intermittent exposure to cold. The adrenal medulla nuclei of the four strains of rats contain the same amount of DNA; however, the loss of DNA observed after the same experimental treatment differs markedly in the different strains. The loss is small in Wistar and Sprague-Dawley rats (8–13%), larger in Long-Evans rats (20%) and still larger in Italico rats (45%). The DNA loss in Wistar rats increases if the animals are fed the same diet as the Italico rats, and the DNA loss in Italico rats is reduced if the animals are fed the same diet as the Wistar rats. The different behavior of the four strains is discussed in terms of turnover of DNA.
A STUDY OF NUCLEOLAR VACUOLES IN CULTURED TOBACCO CELLS USING RADIOAUTOGRAPHY, ACTINOMYCIN D, AND ELECTRON MICROSCOPY
Authors: Johnson J. Morris
Published: May 2004

Previously it has been found that in tobacco callus cells nucleolar vacuoles repeatedly form and contract. In this study, nucleolar vacuoles were investigated by using radioautography, actinomycin D, and electron microscopy. It was found, from grain counts of nucleoli labeled with uridine-3H, that nucleoli containing vacuoles had more than three times as many grains/µ2 of nucleolar substance as did nucleolei without vacuoles. Treatment of tobacco callus cells with various concentrations of actinomycin D caused the percentage of cells containing nucleolar vacuoles to decrease; with the highest concentration the percentage of these cells dropped from the normal level of about 70% to less than 10%. However, after removal of actinomycin D the cells regained nucleolar vacuoles up to the control level. When radioautography was used with actinomycin D, it was found that the actinomycin D inhibited the uptake of uridine-3H, i.e. inhibited RNA synthesis, in those nucleoli which lost their nucleolar vacuoles. In addition, after removal of the cells from actinomycin D, it was found that as the cells regained nucleolar vacuoles the nucleoli also began to incorporate uridine-3H. Electron micrographs showed the nucleoli to be composed of a compact, finely fibrous central portion surrounded by a layer of dense particles 100–150 A in diameter. Nucleolar vacuoles occurred in the fibrous central portion. Dense particles similar to those in the outer layer of the nucleoli were found scattered throughout the vacuoles and in a dense layer at their outer edge. These data suggest that in cultured tobacco callus cells the formation and contraction of nucleolar vacuoles is closely related to RNA synthesis in the nucleolus.
ENZYME LOCALIZATION DURING MELANOGENESIS
Authors: McCurdy Harriet M.
Published: May 2004

The DOPA-reaction was used to identify tyrosinase in the nucleus and cytoplasm of the neural crest melanoblast of Taricha torosa, the California newt. In this urodele there is a nuclear DOPA-positive response during the normal embryonic development from the late blastula stage to the nucleus of the early melanocyte. During the gastrula stages, all nuclei of this newt are DOPA-positive. This positive nuclear response fades away after the formation of the neural crest, save in the melanoblasts. The only cells that give a positive DOPA marking in the cytoplasm are the melanoblasts. This cytoplasmic reaction appears while the melanoblast nucleus still gives a DOPA-positive reaction. Tyrosinase activity, as marked by unlabeled DOPA, has ceased in the fully mature melanocyte. The red nuclei, seen in some of the animals in the maturing melanocyte and adjacent tissues, may be in the hallachrome stage of melanin formation. There is a diffuse distribution of DOPA reactivity in the resting nucleus, and an adherence of the DOPA-marking in the region of the dividing chromosomes in the mitosis of DOPA-positive nuclei of the melanoblast. These observations suggest that tyrosinase may be among the chromosomally bound enzymes of the chromatin space.
REPLICATION OF NUCLEOLUS-ASSOCIATED DNA DURING "G2 PHASE" IN PHYSARUM POLYCEPHALUM
Authors: Guttes Edmund , Guttes Sophie
Published: May 2004

In the myxomycete, Physarum polycephalum, the bulk of nuclear DNA replication occurs during a period of a few hours immediately following upon mitosis. During the remainder of the intermitotic period, incorporation of thymidine-3H continues at a low rate in the region of the nucleolus (radioautographs). A few nuclei incorporated thymidine-3H into the extranucleolar chromatin at a high rate at all times of the intermitotic period. These nuclei were exceptionally large and they frequently contained several small nucleoli of different sizes rather than the one, central nucleolus which is characteristic of a normal interphase nucleus.
THE FINE STRUCTURE OF VON EBNER'S GLAND OF THE RAT
Authors: Hand Arthur R.
Published: May 2004

The fine structure of von Ebner's gland was studied in untreated rats and rats stimulated to secrete by fasting-refeeding or injection of pilocarpine. Cytological features were similar to those reported for pancreas and parotid gland. Abundant granular endoplasmic reticulum filled the basal portion of the cell, a well-developed Golgi complex was located in the vicinity of the nucleus, and the apical portion of the cell was filled with dense secretory granules. Dense heterogeneous bodies resembling lysosomes were closely associated with the Golgi complex. Coated vesicles were seen in the Golgi region and also in continuity with the cell membrane. Granule discharge occurred by fusion of the granule membrane with the cell membrane at the secretory surface. Successive fusion of adjacent granules to the previously fused granule formed a connected string of granules in the apical cytoplasm. Myoepithelial cells were present within the basement membrane, and nerve processes were seen adjacent to acinar and myoepithelial cells. Duct cells resembled the intercalated duct cells of the major salivary glands.
COMPARISON OF MITOTIC PHENOMENA AND EFFECTS INDUCED BY HYPERTONIC SOLUTIONS IN HELA CELLS
Authors: Robbins Elliott , Pederson Thoru , Klein Paul
Published: May 2004

Interphase HeLa cells exposed to solutions that are 1.6 x isotonic manifest a series of morphological transformations, several of which grossly resemble those which occur when untreated cells enter prophase. These include chromosome condensation with preferential localization at the nuclear envelope and nucleolus, ruffling of the nuclear envelope, and polyribosome breakdown. The nucleolus loses its fibrous component and appears diffusely granular. At 2.8 x isotonicity the nuclear envelope is selectively dispersed although other membranes show morphological alterations also. The characteristic transitions of the lysosomes, Golgi complex, and microtubules seen in normal mitosis do not occur during hypertonic treatment. All the changes induced with hypertonic solutions are rapidly reversible, and the nucleus particularly goes through a recovery phase which bears some similarity to that of the telophase nucleus. The prophase-like condensation of the chromatin following exposure of the intact cell to hypertonic medium cannot be reproduced on an ultrastructural level in the isolated nucleus with any known variation in salt concentration, suggesting significant modifications of the nuclear contents during isolation. In addition to these morphological responses, hypertonic solutions also markedly and reversibly depress macromolecular synthesis. The polyribosome disaggregation that results from exposure to hypertonic solutions may be partially prevented by prior exposure to elevated Mg++ concentrations; this same ion is also partially effective in preventing the polyribosome breakdown which normally occurs as cells enter mitosis.
CYTOPLASMIC PARTICLES AND AMINOACYL TRANSFERASE I ACTIVITY
Authors: Shelton Emma , Kuff Edward L. , Maxwell Elizabeth S. , Harrington J. T.
Published: May 2004

It has been possible to show by electron microscopy of samples selected from sucrose gradients that particles of specific size and shape are present in supernatant fluids derived from nucleated animal and plant cells, but not in extracts from Escherichia coli. Aminoacyl transferase I activity in these same gradients sediments in two peaks representing material of approximately 5–7S and 18–20S. A rectangular particle, 100 x 145 A in size, sediments at 19S and coincides with the second peak of transferase I activity. The possibility that the rectangular particle may be a "carrier" particle associated with transferase I is discussed.
ULTRASTRUCTURAL CHANGES IN CELLS OF PEA EMBRYO RADICLES DURING GERMINATION
Authors: Yoo Bong Yul
Published: May 2004

Radicles (1 mm long) of pea embryo axes, excised from dormant seeds and from seeds soaked for 80 min, 8, 12, and 48 hr, were fixed in glutaraldehyde and postfixed in OsO4. The nucleus was only slightly changed by 48 hr soaking, but cytoplasmic organelles underwent developmental changes. There was proliferation of endoplasmic reticulum, the appearance of dictyosomes, and an inward migration of lipid bodies. Most of these changes were observed within 8 hr after soaking started. Plastids, mitochondria, protein bodies, and protein crystalline bodies were also identified and their developmental changes were followed.
LYSOSOMES IN SKELETAL MUSCLE TISSUE
Authors: Canonico Peter G. , Bird John W. C.
Published: May 2004

Postnuclear supernates from homogenates of skeletal muscle from rats subjected to starvation, injections of Triton WR-1339, dextran-500, and dextran + corticosterone were fractionated by means of rate and isopycnic zonal centrifugation in sucrose—0.02 M KCl gradients. Zonal fractions were analyzed for protein, RNA, cytochrome oxidase, and up to six acid hydrolases. The results indicate the presence of two groups of lysosome-like particles. One group contributes approximately 95% of the cathepsin D and acid phosphatase activity and 75% of the acid ribonuclease, ß-glucuronidase, and arylsulfatase activity in muscle. It is characterized by a modal equilibrium density of 1.18 that is decreased by starvation, but is not shifted by dextran-500 or Triton WR-1339. The second group has a higher proportion of acid ribonuclease, ß-glucuronidase, and arylsulftase; the equilibrium density can be shifted by dextran-500 and Triton WR-1339. It is suggested that this group of lysosomes is derived from macrophages and other connective tissue cells, whereas the former group represents lysosome-like particles from muscle cells.
ULTRASTRUCTURE OF BACTERIZED AND AXENIC TROPHOZOITES OF ENTAMOEBA HISTOLYTICA WITH PARTICULAR REFERENCE TO HELICAL BODIES
Authors: Rosenbaum Robert M. , Wittner Murray
Published: May 2004

Electron microscopy of bacterized and axenic trophozoites of Entamoeba histolytica showed only slight differences in ultrastructure between the two. As with other species of Entamoeba so far studied, this species lacks typical mitochondrial structures and formed endoplasmic reticulum. Dense clusters of glycogen particles are especially characteristic in axenic amebas. Microtubular structures 360 A in diameter appear randomly oriented in both bacterized and axenic trophozoites. Ribonucleoprotein (RNP) bodies are of two typical forms—elongate, parallel arrays of helices (the classical chromatoid bodies), and short helical fragments. Both kinds of helix show a recurring pitch angle of 68–80° and an over-all diameter of 480 A. RNP particles comprising the helices average 180 A in diameter. The longitudinal axes of adjacent helices are 440 A apart. Following RNase digestion of water-soluble methacrylate sections, helices show a core approximately 60 A in diameter. Short helices are also associated with digestive vacuoles. Free RNP particles per se are never seen within digestive vacuoles, but intact short helices are frequently detected closely associated with the external membrane of digestive vacuoles. In some cases, continuation of externally intact helical forms could be related to filamentous material within the vacuole. Acid phosphomonoesterase activity could be demonstrated within digestive vacuoles where deposition of reaction product is especially intense on the filamentous material.
FURTHER BIOCHEMICAL AND MORPHOLOGICAL STUDIES OF GRANULE FRACTIONS FROM RABBIT HETEROPHIL LEUKOCYTES
Authors: Baggiolini Marco , Hirsch James G. , de Duve Christian
Published: May 2004

Fractionation of rabbit heterophil leukocyte homogenates by isopycnic centrifugation as well as by zonal sedimentation has helped to characterize further the particulate components of these cells. Four classes have been identified: (A) Large (0.5–0.8 µm) and dense (1.26) azurophil or primary granules, containing all the myeloperoxidase, one-third of the lysozyme, and a major proportion of the lysosomal acid hydrolase activities of the cells. (B) Smaller (0.25–0.40 µm) and less dense (1.23) specific or secondary granules, containing 90% of the alkaline phosphatase and the remainder of the lysozyme activities, but very little if any acid hydrolases. (C) Particles of low density (1.20), containing the remainder of the lysosomal acid hydrolases. This fraction was heterogeneous, but showed abundant small rod- or dumbbell-shaped particles of moderate electron opacity, surrounded by a single membrane (tertiary granules?). The possible origin of these lysosomes from contaminating macrophages could not be ruled out but appeared unlikely. (D) Slowly sedimenting material of very low density (1.14), made up of large, empty vesicular membrane structures, and containing 10% of the alkaline phosphatase, and all of a thiol-dependent acid p-nitrophenyl phosphatase, an enzyme clearly different from the lysosomal acid phosphatase.
SEDIMENTATION PROPERTIES OF RAT LIVER MITOCHONDRIA
Authors: Loeb John N. , Kimberg Daniel V.
Published: May 2004

A prediction of the velocity of sedimentation of rat liver mitochondria in sucrose gradients is made on the basis of recent measurements of the size of isolated mitochondria suspended in sucrose medium and the model proposed by Bentzel and Solomon to describe the osmotic behavior of mitochondria. The experimentally observed velocity is extremely close to the predicted value and confirms by a different approach the estimate of mitochondrial volume made by Baudhuin and Berthet on the basis of electron microscopic measurements. Because cortisone treatment of rats is known to result in a marked increase in mitochondrial size as observed under the electron microscope, mitochondria were co-isolated from livers of control and cortisone-treated animals, and the sedimentation behavior of the mixtures was examined by sucrose density gradient centrifugation. Mitochondria from cortisone-treated animals were found to sediment 1.4 times as rapidly as those from control animals, indicating that their increased size cannot entirely be due to an increased imbibition of fluid from the surrounding sucrose medium, and that the change in size must at least in part be due to a change in content of nondiffusible mitochondrial components. Although the increase in sedimentation velocity of mitochondria from cortisone-treated animals is striking, it is less than that predicted solely on the basis of their size relative to that of control mitochondria. It is concluded that the increases in mitochondrial size and content of nondiffusible components produced by cortisone treatment are accompanied by alterations in mitochondrial composition as well.
MITOCHONDRIAL RNA FROM CULTURED ANIMAL CELLS
Authors: Montenecourt Bland S. , Langsam Margaret E. , Dubin Donald T.
Published: May 2004

Discrete RNA fractions sedimenting slightly slower than 18s ribosomal RNA have been found in mitochondrial preparations from both hamster (BHK-21) and mouse (L-929) cells. This RNA could be separated into two components, present in approximately equimolar amounts, by prolonged zonal centrifugation or acrylamide gel electrophoresis. The hamster components had sedimentation constants averaging 16.8 and 13.4, and molecular weights (estimated by gel electrophoresis) averaging 0.74 and 0.42 x 106 daltons. Mixed labeling experiments showed that the mouse components sedimented and electrophoresed 3–6% more slowly than the corresponding hamster components. The RNA from both cell lines resembled mitochondrial ribosomal RNA from yeast and Neurospora in being GC poor, and in addition the larger and smaller components resembled each other in base composition. These results, taken with those of other recent studies, are compatible with the idea that our high molecular weight mitochondrial RNA is ribosomal; such RNA would then constitute a uniquely small size-class of ribosomal RNA.
THE METHYLATION OF TRANSFER RIBONUCLEIC ACID DURING REGENERATION OF THE LIVER
Authors: Tidwell T.
Published: May 2004

Transfer ribonucleic acid1 is methylated after the molecule is synthesized; at least eight enzymes are involved in the transfer of methyl groups (derived from methionine). The time courses of methylation and synthesis of tRNA during rat liver regeneration have been compared in an in vivo radioisotopic study, using 6-orotic acid-14C and 3H-methyl-L-methionine as precursors in double label pulses. Liver regeneration is a synchronized system in which biochemical events of the cell cycle are separable. Transfer RNA methylation increase precedes by several hours tRNA synthesis during regeneration, although the curves overlap. A ratio of the relative rate of methylation to the relative rate of synthesis has been made; that curve positively correlates with the rise and fall of protein synthesis during regeneration. It is clear that methylation and synthesis of tRNA are only weakly coupled; changing methyl content of the tRNA "pool" resulting from differential tRNA methylase and polymerase activities may regulate the rate of protein synthesis in the cell cycle at the translational level. The "pool sizes" of uridine monophosphate (UMP) and S-adenosylmethionine (SAM) were measured indirectly; UMP and SAM were isolated from perchloric acid supernatants and their specific activities were computed. Differential changes in radioactivity available to tRNA methylases and polymerases are not a source of artifact. That is, the control of both the synthesis and methylation of tRNA is at the enzyme level in vivo, rather than at some enzymatic step prior to those enzymatic reactions.
A CYTOLOGICAL STUDY OF ARTIFICIAL PARTHENOGENESIS IN THE SEA URCHIN ARBACIA PUNCTULATA
Authors: Sachs Martin I. , Anderson Everett
Published: May 2004

Eggs of the sea urchin Arbacia punctulata were artificially activated with hypertonic seawater. The artificially activated eggs undergo the cortical reaction which is not distinguished by a wavelike progression as in the case of inseminated eggs. The cortical granules are released at random loci at the surface of the egg and result in spaces separated by large cytoplasmic projections. Unreacted cortical granules and ribosomes are found within the matrix comprising the large cytoplasmic projections. No "fertilization cone" is formed. The subsequent release of additional cortical granules results in the formation of a continuous perivitelline space, 15 min following activation. 85 min postactivation, an organization of annulate lamellae, endoplasmic reticulum of the smooth variety, and microtubules around a centriole is observed prior to nuclear division. Before the breakdown of the nuclear envelope a streak stage is formed. The streak is composed of a central core of annulate lamellae and is encompassed by endoplasmic reticulum and vesicular components. Condensation of chromatin is followed by the establishment of the mitotic apparatus. Centrioles were not found in the mature egg; however, they are present after activation prior to the first nuclear division, in the four-cell embryo, multicellular embryo, and at blastula. Artificially activated eggs have been observed to develop to the pluteus stage in more than 50% of the eggs treated.
THE FINE STRUCTURAL LOCALIZATION OF ENDOGENOUS AND EXOGENOUS PEROXIDASE ACTIVITY IN KUPFFER CELLS OF RAT LIVER
Authors: Fahimi H. Dariush
Published: May 2004

Endogenous peroxidase activity has been demonstrated in sections of rat liver fixed briefly by glutaraldehyde perfusion and incubated in Graham and Karnovsky's medium for cytochemical demonstration of peroxidase activity (29). In 25–40% of sinusoidal cells, an electron-opaque reaction product is localized in segments of the endoplasmic reticulum, including the perinuclear cisternae, a few Golgi vesicles and saccules and in some large membrane-bounded granules. This staining is abolished after prolonged fixation or boiling of tissue sections in glutaraldehyde, and in the absence of H2O2 or DAB from the incubation medium. Furthermore, the reaction is inhibited completely by sodium azide and high concentrations of H2O2, and partially by KCN and aminotriazole. Among the different cells in hepatic sinusoids, the nonphagocytic "fat-storing" cells (39) are always peroxidase negative, whereas the lining cells in process of erythrophagocytosis are consistently peroxidase positive. The possible biological significance of endogenous peroxidase in Kupffer cells is discussed. In addition, the uptake of exogenous horseradish peroxidase by Kupffer cells has been investigated. The exogenous tracer protein, which in contrast to endogenous peroxidase of Kupffer cells is not inhibited by prolonged aldehyde fixation, is taken up by micropinocytosis and remains confined to the lysosomal system of Kupffer cells. The significance of these observations in respect to some recent studies suggesting localization of exogenous peroxidases in the endoplasmic reticulum of Kupffer cells and peritoneal macrophages (22, 23) is briefly discussed.
SUBFRACTIONATION OF SMOOTH MICROSOMES FROM RAT LIVER
Authors: Glaumann Hans , Dallner Gustav
Published: May 2004

Total smooth microsomes from rat liver isolated on a Cs+-containing sucrose gradient were concentrated and subsequently fractionated by zone centrifugation on a stabilizing sucrose gradient. The prerequisite for fractionation is to prepare total smooth microsomes in a nonaggregated condition, as well as to utilize a procedure which counteracts enzyme inactivation. The median equilibrium density of the various smooth microsomal vesicles ranges from 1.10 to 1.18. The phospholipid/protein ratio is identical in all subfractions, but cholesterol, on a PLP basis, is enriched in the subfractions with the highest sedimentation velocity. The enzyme distribution pattern reveals a pronounced heterogeneity. A number of NADH- and NADPH-oxidizing enzymes are concentrated in the upper part of the gradient and exhibit a certain degree of separation from G6Pase. Mg++-ATPase and AMPase are enriched in the lower part of the gradient. No specific enrichment of newly synthesized NADPH-cytochrome c reductase activity occurs in any of the subfractions after phenobarbital treatment. These data demonstrate that smooth microsomes, by adequate fractionation procedure, can be separated into subfractious of heterogeneous composition.
THE ULTRASTRUCTURAL LOCALIZATION OF THE ISOZYMES OF ASPARTATE AMINOTRANSFERASE IN MURINE TISSUES
Authors: Papadimitriou J. M. , Van Duijn P.
Published: May 2004

Two isozymes of aspartate aminotransferase have been demonstrated biochemically. One isozyme is found in the mitochondrial fraction of the cytoplasm, the other ("soluble") in the supernatant. Both isozymes can be demonstrated by the cytochemical technique of Lee and Torack, as reported in the preceding report. Aldehyde fixation rapidly inactivates both isozymes, especially the soluble one. Inactivation can be delayed by addition of ketoglutarate to the fixative. The ketoglutarate probably competes with the fixative for the active site of the enzyme, thus protecting that region of the molecule. This enables adequate tissue preservation with enough remaining enzymatic activity to be demonstrated by the precipitation of oxaloacetate as the lead salt from a medium containing α-ketoglutaric acid aspartic acid, and lead nitrate. Electron-opaque material was found not only in mitochondria but, as the result of substrate protection, on the plasma membranes of many cells including erythrocytes and bacteria, the limiting membrane of peroxisomes, and the transverse tubular system of striated muscle. Occasional centrioles, neurotubules, tubules in the tails of spermatozoa, the A-I band junction in myofibrils of striated muscle, and the ground substance between cisternae of endoplasmic reticulum in intestinal goblet cells also showed precipitate. In all cases, replacement of L-aspartic acid by D-aspartic acid in the medium resulted in unstained sections. The sensitivity of extramitochondrial sites to fixation, the need of ketoglutarate as an agent for protecting the enzymatic activity during the fixation process, and the known presence of only soluble isozyme in erythrocytes indicate that enzymatic activity at these sites can be attributed to the soluble isozyme. Localization of the soluble isozyme on the plasma membrane may be related to possible involvement in depolarization phenomena, amino acid transport, or synthesis of plasma membrane-bound mucopolysaccharides.
MICRONUCLEAR RIBONUCLEIC ACID IN TETRAHYMENA PYRIFORMIS
Authors: Murti Kuruganti G. , Prescott David M.
Published: May 2004

The presence of RNA in the micronucleus of Tetrahymena pyriformis was detected by electron microscope radioautography after incubation with tritiated precursors. The specificity of RNA labeling was shown by ribonuclease digestion. The period of appearance of labeled RNA in the micronucleus is approximately coincident with the DNA synthesis period for the micronucleus. Pulse-chase experiments showed that the micronuclear RNA disappears during the interphase period. The experiments do not distinguish whether the micronuclear RNA is synthesized in situ or acquired by migration from the macronucleus. In either case it is notable that the appearance of labeled RNA is detected in the micronucleus only during the micronuclear S phase.
KINETOPLAST DEOXYRIBONUCLEIC ACID OF THE HEMOFLAGELLATE TRYPANOSOMA LEWISI
Authors: Renger Hartmut C. , Wolstenholme David R.
Published: May 2004

Cesium chloride centrifugation of DNA extracted from cells of blood strain Trypanosoma lewisi revealed a main band, ρ = 1.707, a light satellite, ρ = 1.699, and a heavy satellite, ρ = 1.721. Culture strain T. lewisi DNA comprised only a main band, ρ = 1.711, and a light satellite, ρ = 1.699. DNA isolated from DNase-treated kinetoplast fractions of both the blood and culture strains consisted of only the light satellite DNA. Electron microscope examination of rotary shadowed preparations of lysates revealed that DNA from kinetoplast fractions was mainly in the form of single 0.4 µ circular molecules and large masses of 0.4 µ interlocked circles with which longer, often noncircular molecules were associated. The 0.4 µ circular molecules were mainly in the covalently closed form: they showed a high degree of resistance to thermal denaturation which was lost following sonication; and they banded at a greater density than linear DNA in cesium chloride-ethidium bromide gradients. Interpretation of the large masses of DNA as comprising interlocked covalently closed 0.4 µ circles was supported by the findings that they banded with single circular molecules in cesium chloride-ethidium bromide gradients, and following breakage of some circles by mild sonication, they disappeared and were replaced by molecules made up of low numbers of apparently interlocked 0.4 µ circles. When culture strain cells were grown in the presence of either ethidium bromide or acriflavin, there was a loss of stainable kinetoplast DNA in cytological preparations. There was a parallel loss of light satellite and of circular molecules from DNA extracted from these cells.
ELECTRON MICROSCOPE OBSERVATIONS ON THE FUSION OF CHICK MYOBLASTS IN VITRO
Authors: Shimada Yutaka
Published: May 2004

The process of myoblast fusion was observed in embryonic chick skeletal muscle cells grown in monolayer cultures at the fine structural level. At the first step, the sarcolemmas of cells destined to fuse are closely applied to each other. They are linked in some places by fasciae adherentes; in other places, engulfment of small processes of one cell by another is seen. At a somewhat more advanced stage of myogenesis, vesicles and tubules are formed between the adjacent cytoplasms; presumably, the apposed membranes have opened at several points and their edges have fused to each other. Finally, remnants of cell membranes (vesicles and tubules) disappear completely, and the confluent cytoplasm is formed. The cytoplasmic contents of the multinucleated cells are often poorly admixed, giving the cytoplasm a mosaic appearance in which different zones can be designated as arising from separate cells. This observation suggests, however, that there is slow diffusion of myoblast contents (ribosomes and, possibly, other materials) into the myotube. In agreement with the previous works at the light microscopic level, the present study suggests the occurence of fusion between mononucleated cells, between mononucleated cells and multinucleated myotubes, and between nascent multinucleated myotubes.
ON THE POSSIBLE FUNCTION OF COATED VESICLES IN MELANOGENESIS OF THE REGENERATING FOWL FEATHER
Authors: Maul Gerd G. , Brumbaugh J. A.
Published: May 2004

How tyrosinase becomes associated with the premelanosomes was investigated by histochemical demonstration of tyrosinase activity by the use of dihydroxyphenylalanine (DOPA) in melanocytes of regenerating fowl feathers. The reaction product of DOPA was localized in the anastomosing membrane tubules associated with the concave side of some dictyosomes of the Golgi apparatus and in coated vesicles most of which were in connection with the dictyosomes. No reaction product was found in early premelanosomes. In premelanosomes, the reaction product of DOPA appears first in vesicles approximately 400 A in diameter which are surrounded by a matrix with a characteristic periodicity. These observations seem to allow the speculation that the coated vesicles function in the transport of tyrosinase, and that the premelanosomes are formed in a process which is not necessarily dependent on the Golgi apparatus as was assumed earlier.
THE EFFECTS OF VARYING CONCENTRATIONS OF COLCHICINE ON THE PROGRESSION OF GRASSHOPPER NEUROBLASTS INTO METAPHASE
Authors: Mueller G. A. , Gaulden Mary Esther , Drane Wanzer
Published: May 2004

The effects of four concentrations of colchicine (2.5 x 10-7, x 10-5, x 10-3, and x 10-2 M) on the cell cycle of grasshopper neuroblasts have been determined by direct observations on living cells. The lowest concentration, 2.5 x 10-7 M, does not completely disorganize the spindle but does retard its action. The three higher concentrations disorganize the spindle, so that all cells reaching metaphase are blocked in a c-mitotic condition throughout the period of observations (308 min at 38°C, the minimum duration of the cell cycle in untreated neuroblasts). Continuous treatment with all concentrations reduces the rate at which neuroblasts enter metaphase, the extent of the reduction being a function of increasing concentration and time of exposure. After a short exposure to 2.5 x 10-5 M colchicine, the neuroblasts recover from the inhibiting effects on progression through the cycle to metaphase, but they show no recovery from the inhibiting effects on spindle formation for more than 3 hr. Apparent stimulation of progression rate occurs early in exposure to all concentrations and during recovery from a short exposure to 2.5 x 10-5 M. Morphological alterations in the chromatin of telophase, interphase, and prophase cells are induced by the higher concentrations of colchicine. The data indicate that caution should be exercised in the use of colchicine for determining cell cycle duration and/or the effects of physical and chemical agents on the cycle.
THE DISTRIBUTION OF INORGANIC CATIONS IN MOUSE TESTIS
Authors: Kierszenbaum Abraham L. , Libanati Cesar M. , Tandler Carlos J.
Published: May 2004

For localization of pyroantimonate-precipitable cations, mouse testes were fixed with a saturated aqueous solution of potassium pyroantimonate (pH about 9.2, without addition of any conventional fixative), hardened with formaldehyde, and postosmicated. A good preservation of the cell membranes and over-all cell morphology is obtained as well as a consistent and reproducible localization of the insoluble antimonate salts of magnesium, calcium, and sodium. Four sites of prominent antimonate deposits are revealed, besides a more or less uniform distribution of the precipitates. These sites are: (a) In the walls of the seminiferous tubules, localized in two concentric layers corresponding to the inner and outer layers of the tubular wall; (b) Around the blood vessels and adjacent connective tissue; (c) At the area of contact between the Sertoli cell and spermatids, where a double line of precipitate surrounds the head of the mature spermatids; and (d) In the cell nuclei, disposed between regions of the condensed chromatin. The nucleus of mature spermatids did not show any sign of antimonate precipitation. The implications of this inorganic cation distribution are discussed with relation to their anionic counterparts, their localization in other animal and plant tissues, and the possibility that those sites may represent barriers to the free passage of ions.
A NEW CHONDRODYSTROPHIC MUTANT IN MICE
Authors: Seegmiller R. , Fraser F. C. , Sheldon H.
Published: May 2004

The occurrence of a new mutation affecting cartilage and bone in mice is reported. The gene is lethal, shows autosomal recessive inheritance, and has high penetrance. It is not allelic to shorthead and probably not to phocomelia or achondroplasia. It results in a foreshortened face, cleft palate, defective trachea, and shortened long bones with flared metaphyses. Chondrocytes of epiphyseal cartilage from the mutant are not aligned in columns, and there is a decrease in the usual staining of the cartilage matrix. Electron microscope observations show large, wide collagen fibrils with "native" banding in the matrix of mutant cartilage, which are not present in normal cartilage. Possible explanations for the expression of this genetic disorder of cartilage development are put forward.
PHOSPHOLIPID METABOLISM IN INTACT AND MODIFIED ERYTHROCYTE MEMBRANES
Authors: Redman Colvin M.
Published: May 2004

Erythrocyte membranes incorporated labeled phosphate from γ-adenosine triphosphate (AT32P) into phosphatidic acid and the polyphosphoinositides. Inositol-3H and palmitate-14C were also incorporated into the phospholipids but α-glycerophosphate-32P was not. The incorporation of γ-AT32P into phospholipids was increased when the erythrocyte ghosts were incubated in hypotonic media which lysed the cells. Lysis had little or no effect on the incorporation of inositol-3H and palmitate-14C into the phospholipids.

If erythrocyte membranes were prepared in 1 mM ethylenediaminetetraacetate (EDTA), instead of 1 mM MgCl2, then the tonicity of the incubating medium did not influence the incorporation of γ-AT32P into the phospholipids. Erythrocyte ghosts, prepared by lysis in water, EDTA, or 1 mM calcium, lead, mercury, zinc, or cadmium, failed to reconstitute when placed in isotonic medium, inasmuch as they did not retain potassium against a chemical gradient. Ghosts prepared by lysis in 1 mM magnesium, barium, or strontium could be reconstituted. Ghosts which failed to reconstitute incorporated more labeled phosphate from γ-AT32P into the phospholipids than did intact or reconstituted ghosts. The larger incorporation of labeled phosphate by leaky ghosts was not due to a greater entrance of γ-AT32P into those cells.

Primaquine phosphate and digitonin, at concentrations which are known to cause cells to form smaller vesicles or to lyse cells by removing cholesterol, did not increase the incorporation of labeled phosphate into the phospholipids.

It is suggested that the increased metabolism of phospholipids may be involved in a membrane repair mechanism.
ERYTHROPOIESIS DURING AMPHIBIAN METAMORPHOSIS
Authors: Maniatis George M. , Ingram Vernon M.
Published: May 2004

Rabbit antibodies were prepared against the major hemoglobin components of the larval and adult stages of R. catesbeiana. The properties of the antisera were studied by double immunodiffusion, precipitation, and complement fixation. The antisera to tadpole and frog hemoglobins did not cross-react with either hemoglobin or apohemoglobin. The anti-serum against frog hemoglobin was used for the detection of frog hemoglobin in tadpoles undergoing either natural or thyroxine-induced metamorphosis. It was shown that frog hemoglobin is detectable first in the liver, indicating that the liver is the site of erythrocyte maturation during metamorphosis.
ERYTHROPOIESIS DURING AMPHIBIAN METAMORPHOSIS
Authors: Maniatis George M. , Ingram Vernon M.
Published: May 2004

Rabbit antibodies specific for the major tadpole and frog hemoglobin components of R. catesbeiana were used for the detection of the two hemoglobins inside single cells. The antisera, after fractionation by ammonium sulfate precipitation and diethylaminoethyl (DEAE)-cellulose chromatography, were conjugated with fluorescein isothiocyanate for the antifrog hemoglobin serum and tetramethylrhodamine isothiocyanate for the antitadpole hemoglobin serum. The conjugated fractions, refractionated by stepwise elution from a DEAE-cellulose column, were used for the fluorescent staining of blood smears, liver tissue imprints, and smears of liver cell suspensions. Both simultaneous and sequential staining with the two fluorescent preparations indicated that larval and adult hemoglobins were not present within the same erythrocyte during metamorphosis. In other experiments, erythroid cells from animals in metamorphosis were spread on agar containing specific antiserum. Precipitates were formed around the cells which contain the particular hemoglobin. The percentages of cells containing either tadpole or frog hemoglobin were estimated within the experimental error of the method. The data showed that the two hemoglobins are in different cells. It is concluded that the hemoglobin change observed during the metamorphosis of R. catesbeiana is due to the appearance of a new population of erythroid cells containing exclusively frog hemoglobin.
ENZYME ACTIVITIES IN CHICK EMBRYONIC CARTILAGE
Authors: Arsenis C. , Eisenstein R. , Soble L. W. , Kuettner K. E.
Published: May 2004

Some characteristic enzymatic activities were determined in chick embryonic cartilage and compared with the analogous activities in bone and liver. Chondrocytes were isolated, broken by sonication, and subjected to subcellular fractionation to yield a nuclear pellet, the mitochondrial, lysosomal, and microsomal fractions, and the high speed supernatant solution. It was established that these fractions are characterized by enzymatic activities usually associated with similar fractions in other tissues, but with some quantitative differences. Lysozyme, a particulate-associated enzyme in other tissues, was not detected in any subcellular fraction even by the sensitive technique of microzone electrophoresis and is therefore considered to be primarily extracellular in cartilage.
Collagen Formation by Fibroblasts of the Chick Embryo Dermis
Authors: Porter Keith R. , Pappas George D.
Published: May 2004

This investigation has sought to determine the relation between collagen fiber and fibroblast during fibrogenesis. Toward this end the surfaces of chick fibroblasts grown under in vitro conditions have been examined with the electron microscope after fixation in OsO4. Supplementary information has been obtained from thin sections of fibroblasts fixed in situ during phases of fiber production.

The evidence provided by these studies and by various conditions of the experiments indicates that the unit fibrils of collagen form in close association with the cell surface. They were never observed within the cell. When these unit fibrils form in bundles it appears as though templates of some nature, possibly coinciding with stress fibers within the cell cortex, influence the polymerization of the fibrils out of material available at the cell surface. From here the fibrils and bundles of them are shed into the intercellular spaces and there grow to limited diameters by accretion of materials from the general milieu.
Heteromorphic Change of Adult Fibroblasts by Ribonucleoproteins
Authors: Benitez Helena H. , Murray Margaret R. , Chargaff Erwin
Published: May 2004

Cultures of subcutaneous areolar fibroblasts from adult rats, when confronted in vitro with microsomes from rat liver or kidney, are changed heteromorphically so as to resemble cultures of nervous tissue. Similar effects follow exposure to the deoxycholate-insoluble fraction of microsomes, and to purified RNA from rat liver or from yeast. An equivalent ribonucleoside mixture has no heteromorphic effect.

The degree of heteromorphosis can be related quantitatively to the amount of RNA administered, up to a maximum of 150 γ per slide, above which toxicity intervenes. Ribonuclease destroys in considerable degree the effectiveness of the active agents.

Heteromorphosis cannot be induced in this adult tissue by a short exposure (1 to 3 hours) followed by removal to normal medium. A 24 hour exposure to microsome suspensions, however, is followed by partial change lasting for at least several days. Results are most clear cut when cultures of the explant type are maintained continuously in contact with the RNA-containing agents; nevertheless, cell suspensions exposed for 2 to 3 days to heteromorphic agents in suitable concentration appear to be permanently changed.

Interspecies experiments between rat and mouse indicate that rat fibroblasts are more labile than mouse, and/or rat microsomes are more potent as agents of heteromorphosis. Mouse liver microsomes have no morphogenetic effect on homologous fibroblasts, but exert a slight action on rat fibroblasts. Rat microsomes have a growth-stimulating effect, but no heteromorphic action, on mouse fibroblasts.

Purified protein from snake venom, which is highly active as a growth factor for avian nervous tissue, is growth-stimulating to rat fibroblasts but has no heteromorphic action on this material.
The Absence of Histone in the Bacterium Escherichia coli
Authors: Zubay G. , Watson M. R.
Published: May 2004

The deoxyribonucleic acid (DNA) from Escherichia coli has been isolated as an extract containing about 50 per cent by weight protein. The protein component differs both in composition and chemical behaviour from histone which occurs in combination with the DNA in most cells of higher organisms. Although this result suggests the absence of histone-like protein, it is not clear whether the bacterial protein found is naturally bound to the bacterial DNA in the cell or becomes attached to the DNA during the course of isolation.
The Incorporation of Leucine-C14 into Microsomal Particles and other Subcellular Components of the Pea Epicotyl
Authors: Ts'o Paul O. P. , Sato Clifford S.
Published: May 2004

Incorporation of leucine-C14 into subcellular fractions of the apical section of pea seedlings has been studied as a function of the length of incubation. The specific activity of the microsomes was higher than that of the supernatant for short but not for long incubations, in agreement with observations on other systems. In this developing tissue the nuclei and especially the mitochondria appear to incorporate amino acid very rapidly. An insoluble fraction of the microsome pellet, which is presumably a liponucleoprotein complex, was found to possess, after 1 hour of incubation, a specific activity much greater than that of the purified microsomal particles or the supernatant fraction.

Ninety-eight per cent of the leucine-C14 in the purified microsomal particles has been shown to possess bound amino groups, presumably in peptide linkages, by the DNP-end group method. These particles liberate but little peptide or protein of very high specific activity when they are destroyed by removal of Mg or by hydrolysis of RNA.

Microsomal particles were fractionated into an RNA fraction and five protein fractions by means of density gradient centrifugation. By this method 95 per cent of the RNA can be separated from 90 per cent of the protein of the particle. Furthermore, the RNA fraction has been shown to contain very little protein of high specific activity. A particular protein fraction which contains the remaining 5 per cent of the RNA, possessed after 1 hour of incubation a specific activity 2 to 9 times higher than the protein of the other fractions.
The Accumulation of Soluble Deoxyribosidic Compounds in Relation to Nuclear Division in Anthers of Lilium longiflorum
Authors: Foster T. S. , Stern Herbert
Published: May 2004

Intervals of sporogenous DNA synthesis in lily anthers are associated with marked accumulations of methanol- and acid-soluble deoxyribosidic compounds. There are differences in solubility between compounds accumulating at meiosis and those accumulating at mitosis. The formation of these compounds appears to be related to a breakdown of somatic DNA.
Cytological Evidence that Both RNA and DNA May Form a Complex with the Same Protein
Authors: Littau Virginia C.
Published: May 2004

Deoxyribonucleic acid can be added back to protein sites from which the original nucleic acid, ribo- or deoxyribo-, is removed. If sections of frozen-substituted ovarian follicle cells of a leafhopper are first extracted by hot trichloracetic acid to remove nucleic acids and then immersed in a solution of a commerical preparation of deoxyribonucleic acid, the nucleic acid becomes attached to nuclear and cytoplasmic sites and can be rendered visible by the Feulgen reaction. The addition occurs in certain other tissues as well.

The results are discussed in relation to biochemical and other cytochemical investigations of the nucleoprotein complex.
The Fine Structure of a Multiterminal Innervation of an Insect Muscle
Authors: Edwards George A.
Published: May 2004

The detailed structure of nerve branches, neuromuscular junctions, and muscle fibers of a multiterminal innervation of cockroach abdominal muscle has been studied with the electron microscope. The muscle fiber is of the banded myofibril type; with paired mitochondria and abundant endoplasmic reticulum. The peripheral nerve branches are multiaxonal with large central axon and several small peripheral tunicated axons. Tracheoblasts closely accompany the nerve branches. The multiple neuromuscular junctions show typical axonal vesicles, muscle aposynaptic granules, and close plasma membrane apposition with no interposition of basement membrane material.