bluuebunny/crossref_metadata_2025 huggingface dataset:
MORPHOLOGICAL AND BIOCHEMICAL STUDIES OF ISOLATED MITOCHONDRIA FROM FETAL, NEONATAL, AND ADULT LIVER AND FROM NEOPLASTIC TISSUES
Authors: Mintz Helen A. , Yawn David H. , Safer Brian , Bresnick Edward , Liebelt Annabel G. , Blailock Zack R. , Rabin Erwin R. , Schwartz Arnold
Published: May 2004

A combined morphological and biochemical investigation of mitochondria from developing and rapidly growing tissues ( tumors, fetal, and very early neonatal rat liver) revealed mitochondria which were deficient in respiratory control, showed no valinomycin induced K+ accumulation or spontaneous Ca++ uptake, and were unable to undergo a swelling-contraction cycle. Electron microscopic examination of fetal and neonatal livers and a mammary tumor revealed mitochondria which differed from controls with respect to matrix density and ability to undergo reversible structural changes. The importance of isolation and assay media in interpretation of results is emphasized.
THE MECHANISM OF ACTION OF COLCHICINE
Authors: Borisy G. G. , Taylor E. W.
Published: May 2004

Colchicine forms a complex in vivo with a protein present in fertilized or unfertilized sea urchin eggs; similar binding was obtained in vitro with the soluble fraction from egg homogenates. Kinetic parameters and binding equilibrium constant were essentially the same in vivo and in vitro. The binding site protein was shown to have a sedimentation constant of 6S by zone centrifugation. The protein was present in extracts of the isolated mitotic apparatus at a concentration which was several times higher than in whole-egg homogenates. It was extracted from the mitotic apparatus at low ionic strength under conditions which lead to the disappearance of microtubules. No binding could be detected to the 27S protein, previously described by Kane, which is a major protein component of the isolated mitotic apparatus. The properties of the colchicine-bindinG protein, (binding constant, sedimentation constant, Sephadex elution volume) are similar to those obtained with the protein from mammalian cells, sea-urchin sperm tails, and brain tissue, and thus support the conclusion that the protein is a subunit of microtubules.
STUDIES ON THE HUMAN OOCYTE AND ITS FOLLICLE
Authors: Hertig Arthur T. , Adams Eleanor C.
Published: May 2004

Oocytes in primordial ("resting") follicles in adult human ovaries contain a complex paranuclear structure identified by light microscopists as Balbiani's vitelline body. By electron microscopy this structure is composed of a mass of mitochondria with associated endoplasmic reticulum, multiple compound aggregates which form a ring around the cytocentrum, and a single stack or coil of annulate lamellae either attached to the nuclear membrane or free in the cytoplasm. The compound aggregates contain vacuoles and finely divided electron-opaque material. Evidence is presented for the probable transport of this material between the oocyte and its environment. The cytocentrum contains a central aggregate of amorphous electron-opaque deposits which appear to become periodically aligned on fine fibrils to form the long coarse fibers at the periphery of the cytocentrum. The apparent prevalence of annulate lamellae attached or adjacent to the nuclear membrane of oocytes in ovaries removed during the mid-follicular (estrogenic) phase of the cycle indicates the need for further study of a possible hormonal influence on the resting oocyte. By light microscopy phosphatases were not found within the oocyte, but adenosine-monophosphatase activity is present in the cortical cells surrounding primordial follicles, and also at the periphery of each primitive follicle cell, most prominently at the oocyte side. Glucose-6-phosphate dehydrogenase activity is present within the oocyte cytoplasm.
SCHWANN CELL PROLIFERATION IN DEVELOPING MOUSE SCIATIC NERVE
Authors: Asbury A. K.
Published: May 2004

Proliferation of Schwann cells in neonatal mouse sciatic nerve was studied radioautographically in 1-µ glycol methacrylate sections. 28 mice were injected with thymidine-3H, 4 µc/g, 48 hr after birth, and were killed serially over the next 4 days. For the cell cycle following injection, the generation time was approximately 24 hr as determined by grain-count halving data; the duration of synthesis phase was 8 hr as determined from a curve constructed from the per cent of mitotic figures containing label; and the labeling index was 9% at 2 hr after injection. With these estimates, the per cent of Schwann cells proliferating was calculated to be 27%. In addition, roughly 25% of dividing cells appeared to cease division during the cell cycle under study. The relationship of these findings to other events during maturation of nerve is discussed.
TUBULAR AND FIBRILLAR COMPONENTS OF MATURE AND DIFFERENTIATING SIEVE ELEMENTS
Authors: Cronshaw James , Esau Katherine
Published: May 2004

An ontogenetic study of the sieve element protoplast of Nicotiana tabacum L. by light and electron microscopy has shown that the P-protein component (slime) arises as small groups of tubules in the cytoplasm. These subsequently enlarge to form comparatively large compact masses of 231 ± 2.5 (SE)A (n = 121) tubules, the P-protein bodies. During subsequent differentiation of the sieve element, the P-protein body disaggregates and the tubules become dispersed throughout the cell. This disaggregation occurs at about the same stage of differentiation of the sieve elements as the breakdown of the tonoplast and nucleus. Later, the tubules of P-protein are reorganized into smaller striated 149 ± 4.5 (SE)A (n = 43) fibrils which are characteristic of the mature sieve elements. The tubular P-protein component has been designated P1-protein and the striated fibrillar component P2-protein. In fixed material, the sieve-plate pores of mature sieve elements are filled with proteinaceous material which frays out into the cytoplasm as striated fibrils of P2-protein. Our observations are compatible with the view that the contents of contiguous mature sieve elements, including the P-protein, are continuous through the sieve-plate pores and that fixing solutions denature the proteins in the pores. They are converted into the electron-opaque material filling the pores.
PRESERVATION OF MYELIN LAMELLAR STRUCTURE IN THE ABSENCE OF LIPID
Authors: Napolitano Leonard , Lebaron Francis , Scaletti Joseph
Published: May 2004

The fine structure of myelin was studied in glutaraldehyde-fixed rat sciatic nerves depleted of lipid by acetone, chloroform:methanol (2:1 v/v), and chloroform:methanol:concentrated HCl (200:100:1, v/v/v). One portion of each of these nerves, plus the extracts, was saponified and analyzed by gas-liquid chromatography for fatty acids. The remainder of each nerve was stained in osmium tetroxide in CCl4 (5g/100cc) and was embedded in Epon 812. Thin sections, examined in the electron microscope, revealed the preservation of myelin lamellar structure with a 170 A periodicity in nerves depleted of 98% of their lipids. Preservation of myelin lamellar structure depended on glutaraldehyde fixation and the introduction of osmium tetroxide in a nonpolar vehicle (CCl4) after the lipids had been extracted. It is concluded that the periodic lamellar structure in electron micrographs of myelin depleted of lipid results from the complexing of osmium tetroxide, plus uranyl and lead stains, with protein.
STUDIES ON THE MAINTENANCE OF ORAL DEVELOPMENT IN TETRAHYMENA PYRIFORMIS GL-C
Authors: Frankel J.
Published: May 2004

The effects of puromycin on synchronized Tetrahymena pyriformis were investigated at two different concentrations, 43 µg per ml and 430 µg per ml. The rate of incorporation of histidine-14C into hot TCA-insoluble material was reduced by 30% at the low concentration and by 80–90% at the high concentration. The rate of oxygen uptake was lowered by only 10–20% at both concentrations. Cell division was prevented at both concentrations, if the drug was added prior to a "transition point" at about 45 min after the end of the synchronizing treatment. Development of "anarchic field" oral primordia was arrested, while primordia in early stages of membranelle differentiation were resorbed. Resorption began shortly after addition of the drug, and proceeded most rapidly at the lower concentration. If the drug was added after the "transition point," cell division and oral primordium formation were completed with only slight delay at the low concentration, and with considerable delay (in some cases complete arrest) at the high concentration. The results thus indicate that protein synthesis is involved in the later as well as the earlier stages of development; what specially characterizes the earlier stages, prior to the "transition point," is a dramatic response to partial inhibition of protein synthesis. It is suggested that this response involves the activation or release of a latent intracellular degradative system which is specific for developing structures.
ULTRASTRUCTURE AND BIREFRINGENCE OF THE ISOLATED MITOTIC APPARATUS OF MARINE EGGS
Authors: Rebhun Lionel I. , Sander Greta
Published: May 2004

Isolated mitotic apparatuses (MA) of clam and sea urchin eggs were investigated by polarizing and electron microscopy. Examination of fixed MA in oils of different refractive index revealed that at least 90% of the retardation of isolated MA is due to positive, form birefringence, the remaining retardation deriving from positive, intrinsic birefringence. Electron micrographs reveal the isolated MA to be composed of microtubules, ribosome-like particles, and a variety of vesicles. In the clam MA the number of vesicles and ribosome-like particles relative to the number of microtubules is much lower than in the sea urchin MA. In clam MA this allows form and intrinsic birefringence to be related directly to microtubules. The relation of birefringence to microtubules in isolated sea urchin MA is more complex since ribosome-like particles adhere to microtubules, are oriented by them, and are likely to contribute to the form birefringence of the isolated MA. However, comparison of values of retardation for clam and sea urchin MA, indicates that the major part of the birefringence in sea urchin MA is also due to microtubules. The interpretation of the structures giving rise to birefringence in the MA of the living cells is likely to be even more complex since masking substances, compression, or tension on the living MA may alter the magnitude or sign of the birefringence.
THE FINE STRUCTURE OF CHONDROCOCCUS COLUMNARIS
Authors: Pate Jack L. , Ordal Erling J.
Published: May 2004

Cells of Chondrococcus columnaris were sectioned and examined in the electron microscope after fixation by two different methods. After fixation with osmium tetroxide alone, the surface layers of the cells consisted of a plasma membrane, a dense layer (mucopeptide layer), and an outer unit membrane. The outer membrane appeared distorted and was widely separated from the rest of the cell. The intracytoplasmic membranes (mesosomes) appeared as convoluted tubules packaged up within the cytoplasm by a unit membrane. The unit membrane surrounding the tubules was continuous with the plasma membrane. When the cells were fixed with glutaraldehyde prior to fixation with osmium tetroxide, the outer membrane was not distorted and separated from the rest of the cell, structural elements (peripheral fibrils) were seen situated between the outer membrane and dense layer, and the mesosomes appeared as highly organized structures produced by the invagination and proliferation of the plasma membrane. The mesosomes were made up of a series of compound membranes bounded by unit membranes. The compound membranes were formed by the union of two unit membranes along their cytoplasmic surfaces.
ULTRASTRUCTURE OF THE PELLICULAR COMPLEX OF PLASMODIUM FALLAX
Authors: Aikawa Masamichi
Published: May 2004

The exoerythrocytic merozoites of Plasmodium fallax grown in a tissue-culture system have been investigated by negative staining and thin-sectioning techniques, and the respective results have been compared. Negative staining provided additional information, corroborated findings obtained with thin sectioning, and contributed particularly to the study of the pellicular complex of the merozoites which has been demonstrated as being composed of three layers: a thin outer membrane, a thick interrupted inner membrane, and a partial layer of microtubules. Observations made of negatively stained parasites revealed that the thick, interrupted inner membrane in thin sections is actually a labyrinthine structure and covers the entire surface of the merozoite, except at the regions of the conoid and the cytostome. The microtubules which radiate from the conoid to the posterior end demonstrated a transverse periodicity and filamental subunits parallel to the axis of the microtubule. The detailed structure of the conoid and the cytostome is also described.
MICROBODIES IN EXPERIMENTALLY ALTERED CELLS
Authors: Svoboda Donald , Grady Harold , Azarnoff Daniel
Published: May 2004

A rapid and sustained increase in the number of microbodies in liver and kidney cells can be induced in male rats by ethyl chlorophenoxyisobutyrate (CPIB), a hypolipidemic drug. This phenomenon permits investigation of several aspects of microbody behavior in experimental conditions. Reversal experiments demonstrate that liver cells revert to normal between 2 and 3 weeks after withdrawal of CPIB and that one of the mechanisms for removal of excess microbodies is their incorporation into structures indistinguishable from lysosomes. In a state of rapid cell division, such as that present during liver regeneration, microbody proliferation apparently occupies a high biological priority. In necrotic or degenerating cells microbody structure remains relatively normal. The increase in microbodies induced by CPIB is inhibited by chloramphenicol. No increase in microbodies occurred in female rats or in chickens, guinea pigs, or rabbits at the dosage used (0.25% in diet). No changes in microbodies were seen in monkey liver. Catalase activity was generally parallel to the numerical response in microbodies. Additional observations suggest that the microbody response to CPIB is not related to hepatomegaly induced by this agent but may be related to the hypolipidemic effect of CPIB, though hypolipidemia per se is not a specific or sufficient cause of microbody proliferation.
AN ANALYSIS OF HETEROCHROMATIN IN MAIZE ROOT TIPS
Authors: Himes Marion
Published: May 2004

The B chromosomes of maize are condensed in appearance during interphase and are relatively inert genetically; therefore they fulfill the definition of heterochromatin. This heterochromatin was studied in root meristem cells by radioautography following administration of tritiated thymidine and cytidine, and was found to behave in a characteristic way, i.e. it showed asynchronous DNA synthesis and very low, if any, RNA synthesis. A cytochemical comparison of normal maize nuclei with nuclei from isogenic maize stock containing approximately 15–20 B-chromosomes in addition to the normal complement has revealed the following: (a) the DNA and histone contents are greater in nuclei with B chromosomes; (b) the proportion of DNA to histone is identical with that of nuclei containing only normal chromosomes; (c) the amount of nonhistone protein in proportion to DNA in interphase is less in nuclei with B chromosomes than in normal nuclei. In condensed B chromosomes the ratio of nonhistone protein to DNA is similar to that in other condensed chromatin, such as metaphase chromosomes and degenerating nuclei. The B chromosomes appear to have no effect on nucleolar RNA and protein. Replication of B chromosomes is precisely controlled and is comparable to that of the ordinary chromosomes not only in synthesis for mitosis but also in formation of polyploid nuclei of root cap and protoxylem cells.
THE ULTRASTRUCTURAL BASIS OF CAPILLARY PERMEABILITY STUDIED WITH PEROXIDASE AS A TRACER
Authors: Karnovsky Morris J.
Published: May 2004

The transendothelial passage of horseradish peroxidase, injected intravenously into mice, was studied at the ultrastructural level in capillaries of cardiac and skeletal muscle. Peroxidase appeared to permeate endothelial intercellular clefts and cell junctions. Abnormal peroxidase-induced vascular leakage was excluded. Neutral lanthanum tracer gave similar results. The endothelial cell junctions were considered to be maculae occludentes, with gaps of about 40 A in width between the maculae, rather than zonulae occludentes. Some observations in favor of concurrent vesicular transport of peroxidase were also made. It is concluded that the endothelial cell junctions are most likely to be the morphological equivalent of the small pore system proposed by physiologists for the passage of small, lipid-insoluble molecules across the endothelium.
THE MECHANISM OF DENUCLEATION IN CIRCULATING ERYTHROBLASTS
Authors: Simpson Charles F. , Kling J. M.
Published: May 2004

Erythroblast denucleation in the peripheral blood was studied by electron microscopy. Blood was used from dogs anemic either by infection with Babesia canis or from injections of phenylhydrazine hydrochloride. One of the earliest stages of denucleation was the migration of nuclei to the plasmalemma. Mitochondria and coalesced vesicles, derived from the cell membrane of the erythroblast, congregated at the underside of the nuclear envelope unapposed by erythroblastic cell membrane. The coalesced vesicles apparently provided the limiting membrane which surrounded the deep circumference of the extruded nucleus and its associated hemoglobin rim, and also furnished a new plasma membrane for the cell in the area where the nucleus, in denucleation, had utilized the original erythroblastic plasmalemma.
STATIONARY PHASE OF CULTURED MAMMALIAN CELLS (L5178Y)
Authors: Watanabe I. , Okada S.
Published: May 2004

The stationary phase of the mammalian cells L5178Y in culture can be divided into two stages: (a) an early phase characterized by the decline of mitotic index, followed by a stabilization of the cell number, and (b) a late stage, occurring several hours after the flattening of the growth curve, during which dead or dying cells appear in the cultures. The estimates of rates of cell progress showed that the rates from G1 to S and from G2 to M were affected in the early stationary phase. The main cause of cessation of increase in cell number in the early stationary phase is resulted from the decline in mitotic index, which is caused by prolongation of the G2 period. The importance of the G2 stage in regulating the cell growth is discussed in relation to other known situations in the literature.
DIFFERENTIATION OF THE SARCOPLASMIC RETICULUM AND T SYSTEM IN DEVELOPING CHICK SKELETAL MUSCLE IN VITRO
Authors: Ezerman Elizabeth B. , Ishikawa Harunori
Published: May 2004

The electron microscope was used to investigate the first 10 days of differentiation of the SR and the T system in skeletal muscle cultured from the breast muscle of 11-day chick embryos. The T-system tubules could be clearly distinguished from the SR in developing muscle cells fixed with glutaraldehyde and osmium tetroxide. Ferritin diffusion confirmed this finding: the ferritin particles were found only in the tubules identified as T system. The proliferation of both membranous systems seemed to start almost simultaneously at the earliest myotube stage. Observations suggested that the new SR membranes developed from the rough-surfaced ER as tubular projections. The SR tubules connected with one another to form a network around the myofibril. The T-system tubules were formed by invagination of the sarcolemma. The early extension of the T system by branching and budding was seen only in subsarcolemmal regions. Subsequently the T-system tubules could be seen deep within the muscle cells. Immediately after invaginating, the T-system tubule formed, along its course, specialized connections with the SR or ER: triadic structures showing various degrees of differentiation. The simultaneous occurrence of myofibril formation and membrane proliferation is considered to be important in understanding the coordinated events resulting in the differentiated myotube.
SPHEROIDAL AND RING NUCLEOLI IN AMPHIBIAN OOCYTES
Authors: Lane Nancy J.
Published: May 2004

In maturing oocytes of the newt Triturus viridescens, the nucleoli undergo a series of morphological changes that are very similar to those described by Callan for the axolotl, Ambystoma mexicanum. The nucleoli first assume the form of spheroids which then become extended into ring or necklace shapes that are DNase-sensitive; in mature oocytes the nucleoli revert to a spheroidal form. Short term in vitro incorporation studies with uridine-3H on both species show that RNA synthesis occurs in a restricted, eccentric portion of the spheroidal nucleoli, thereby producing an asymmetrical pattern of labeling. In the ring forms, however, the localization of the radioactivity suggests that synthesis takes place symmetrically throughout their entire length. The changes in nucleolar morphology apparently reflect the fact that the component DNA has undergone a redistribution from a localized region in the spheroidal nucleoli to an extended circle in the rings; the patterns of uridine-3H incorporation, therefore, parallel the distribution of DNA in both the spheroidal and the ring nucleoli. Ultrastructurally, the nucleoli contain a fibrillar component that corresponds in position to that of the DNA. The typical spheroidal nucleolus consists of a fibrillar core situated eccentrically and surrounded by a hull of granular, ribonucleoprotein material. The ring nucleoli are composed of a central fibrous region that is ensheathed all around its circumference by a layer of similar granular material. This granular substance is thicker at intervals along the length of the rings, representing the "beads" of the necklaces.
BIOGENESIS OF CHLOROPLAST MEMBRANES
Authors: Ohad I. , Siekevitz P. , Palade G. E.
Published: May 2004

This paper describes the morphology and photosynthetic activity of a mutant of Chlamydomonas reinhardi (y-1) which is unable to synthesize chlorophyll in the dark. When grown heterotrophically in the light, the mutant is indistinguishable from the wild type Chlamydomonas. When grown in the dark, chlorophyll is diluted through cell division and the photosynthetic activity (oxygen evolution, Hill reaction, and photoreduction of NADP) decays at a rate equal to or faster than that of chlorophyll dilution. However, soluble enzymes associated with the photosynthetic process (alkaline FDPase, NADP-linked G-3-P dehydrogenase, RuDP carboxylase), as well as cytochrome f and ferredoxin, continue to be present in relatively high concentrations. The enzymes involved in the synthesis of the characteristic lipids of the chloroplast (including mono- and digalactoside glycerides, phosphatidyl glycerol, and sulfolipid) are still detectable in dark-grown cells. Such cells accumulate large amounts of starch granules in their plastids. On onset of illumination, dark-grown cells synthesize chlorophyll rapidly, utilizing their starch reserve in the process. At the morphological level, it was observed that during growth in the dark the chloroplast lamellar system is gradually disorganized and drastically decreased in extent, while other subchloroplast components are either unaffected (pyrenoid and its tubular system, matrix) or much less affected (eyespot, ribosomes). It is concluded that the dark-grown mutant possesses a partially differentiated plastid and the enzymic apparatus necessary for the synthesis of the chloroplast membranes (discs). The advantage provided by such a system for the study of the biogenesis of the chloroplast photosynthetic membranes is discussed.
HIGH-RESOLUTION RADIOAUTOGRAPHY OF PHLORIZIN-3H IN RINGS OF HAMSTER INTESTINE
Authors: Stirling Charles E.
Published: May 2004

Quantitative light microscope radioautographs of galactose-3H and phlorizin-3H were prepared from freeze-dried plastic-embedded hamster small intestine incubated in vitro. The usual uphill epithelial cell accumulation of galactose accompanied by a somewhat smaller lamina propria accumulation was observed in control tissue incubated 3 min in 1 mM galactose-3H. The addition of 5 x 10-4 M phlorizin to the medium blocked uphill accumulation, but did not prevent galactose equilibration with the epithelial cells. The galactose content of the lamina propria was considerably less than the galactose content of the epithelial cell. Varying the phlorizin-3H content of the medium from 0.6 to 60 µM revealed a brush border binding of phlorizin which followed a Langmuir adsorption isotherm with a half-saturation constant of 13 µM and a maximum binding of 84 µmoles of phlorizin/liter of microvilli or 2.6 x 106 sites/epithelial cell. The phlorizin content of the epithelial cell compartment, excluding microvilli, never exceeded 10% that of the medium after 20 min of incubation. These findings directly support the view that phlorizin is a nontransported inhibitor which binds glucose-galactose carriers at the surface of epithelial cell microvilli.
ANTIGEN-INDUCED CHANGES IN LYMPHOID CELL HISTONES
Authors: Black Maurice M. , Ansley Hudson R.
Published: May 2004

Previous papers in this series have reported an acute, transitory effect of antigens on lymphoid cell nuclei. In the previous reports the effect was related to a change in ammoniacal silver (A-S) stainability of smears and cryostat sections. The variable substrate was identified as histone. This paper reports the results of an extended series of studies of histone and chromatin extracts from thymus glands exposed to antigen in vivo and in vitro. The antigen effect on A-S stainability is demonstrable not only in vitro but also in chromatin fibers representing a DNA-histone complex. However, it is not demonstrable in isolated histone fractions. The inference is drawn that the antigen-induced alteration in A-S stainability is brought about not by any quantitative change in histone, but by a biologically significant shift in histone binding, perhaps to DNA. It is suggested that alteration in DNA-histone binding during gene activation may alter A-S stainability of histones.
EFFECT OF CYCLOHEXIMIDE ON THE CELL CYCLE OF THE CRYPTS OF THE SMALL INTESTINE OF THE RAT
Authors: Verbin Robert S. , Farber Emmanuel
Published: May 2004

A single injection of 1.5 mg/kg of cycloheximide induces a complete disappearance of mitotic activity in rat intestinal crypts within 1.5–2 hr. No significant necrosis of crypt cells is observed even though this phenomenon is accompanied by a marked decrease in uptake of labeled precursors into protein and DNA. Mitoses reappear 6 hr after injection and recovery then follows a cyclic pattern over a period equivalent to one cell cycle, thereby reflecting at least a partial synchronization of cell division. Concurrent use of colchicine, an agent known to induce metaphase arrest, has demonstrated that cycloheximide, while having no apparent effect on cells already in division, prevents the entrance of new cells into visible mitosis. Analysis of the cell cycle suggests that one block initiated by cycloheximide occurs in G2, presumably as the result of an interference with the formation of protein(s) required for the normal progression of cells from this phase of the cycle into mitosis.
RADIOAUTOGRAPHIC STUDY OF CELL WALL DEPOSITION IN GROWING PLANT CELLS
Authors: Ray Peter M.
Published: May 2004

Segments cut from growing oat coleoptiles and pea stems were fed glucose-3H in presence and absence of the growth hormone indoleacetic acid (IAA). By means of electron microscope radioautography it was demonstrated that new cell wall material is deposited both at the wall surface (apposition) and within the preexisting wall structure (internally). Quantitative profiles for the distribution of incorporation with position through the thickness of the wall were obtained for the thick outer wall of epidermal cells. With both oat coleoptile and pea stem epidermal outer walls, it was found that a larger proportion of the newly synthesized wall material appeared to become incorporated within the wall in the presence of IAA. Extraction experiments on coleoptile tissue showed that activity that had been incorporated into the cell wall interior represented noncellulosic constituents, mainly hemicelluloses, whereas cellulose was deposited largely or entirely by apposition. It seems possible that internal incorporation of hemicelluloses plays a role in the cell wall expansion process that is involved in cell growth.
THE ENZYMATIC PREPARATION OF ISOLATED INTACT PARENCHYMAL CELLS FROM RAT LIVER
Authors: Howard Roger B. , Christensen A. Kent , Gibbs Frederic A. , Pesch Leroy A.
Published: May 2004

Suspensions of isolated parenchymal cells were prepared from rat liver by incubation with collagenase and hyaluronidase followed by mechanical treatment. Utilization of 0.15% collagenase together with 0.15% hyaluronidase yielded adequate numbers of cells for experimental purposes. As shown by light and electron microscopy, approximately 75% of the isolated cells retain their structural integrity. The cell suspensions are capable of maintaining endogenous respiration in the presence of 1% albumin for periods of time up to 8 hr. These cell preparations consist almost entirely of parenchymal cells and offer a unique tissue preparation for the study of hepatic metabolism.
LOCALIZATION OF ACID PHOSPHATASE IN LIPOFUSCIN GRANULES AND POSSIBLE AUTOPHAGIC VACUOLES IN INTERSTITIAL CELLS OF THE GUINEA PIG TESTIS
Authors: Frank Arthur L. , Christensen A. Kent
Published: May 2004

The intracellular localization of acid phosphatase in guinea pig testicular interstitial cells was investigated by incubating nonfrozen thick sections of glutaraldehyde-perfused testis in a modified Gomori medium and preparing the tissue for electron microscopy. Lipofuscin pigment granules in these cells contain dense pigment, granular matrix, and often a lipid droplet. Reaction product is seen in the matrix of the pigment granules, and they may therefore be called residual bodies. At least some of the dense pigment appears to be derived from myelin figures and membrane whorls, since suitable intermediates can be seen. Lipid droplets found free in the cytoplasm are another possible source of pigment. In both cases the chemical mechanism is presumed to be autoxidation of unsaturated lipid. Acid phosphatase is present in the inner cisterna of Golgi elements. Enzyme activity also appears in possible autophagic vacuoles bounded by double membranes; the reaction product lies between the membranes. Consideration of the enzyme as a tracer suggests that the autophagic vacuoles are derived from the Golgi complex. Possible stages in the formation of these vacuoles by the inner Golgi cisternae are observed.
THE FINE STRUCTURE OF THE LATERAL VESTIBULAR NUCLEUS IN THE RAT
Authors: Sotelo Constantino , Palay Sanford L.
Published: May 2004

The lateral vestibular nucleus consists of multipolar isodendritic neurons of various sizes The distal segments of some dendrites display broad expansions packed with slender mitochondria and glycogen particles. These distinctive formations are interpreted as being growing tips of dendrites, and the suggestion is advanced that they are manifestations of architectonic plasticity in the mature central nervous system. Unlike large neurons elsewhere, the giant cells (Deiters) contain small Nissl bodies interconnected in a dense mesh-work. The Nissl substance is characterized by randomly arranged cisterns of the endoplasmic reticulum and by a high proportion of free ribosomes. Whether attached or free, ribosomes usually cluster in groups of four to six, and larger polysomal arrays are rare. Free ribosomal clusters also occur in the axon hillock and the initial segment. The neuronal perikarya contain distinctive inclusions consisting of a ball of neurofilaments enveloped by a complex honeycombed membrane. The failure of these fibrillary inclusions to stain with silver suggests that the putative argyrophilia of neurofilaments may reside in an inconstant matrix surrounding them. Giant cells of Deiters are in intimate contact with two kinds of cellular elements—astroglial processes and synaptic terminals. Oligodendroglial cells are only rarely satellites of giant cells; in contrast, they are frequently satellites of small and medium-sized cells.
THE PENETRATION OF REOVIRUS RNA AND INITIATION OF ITS GENETIC FUNCTION IN L-STRAIN FIBROBLASTS
Authors: Silverstein Samuel C. , Dales Samuel
Published: May 2004

Reovirus type 3 is phagocytized by L cells and rapidly sequestered inside lysosomes. Hydrolases within these organelles are capable of stripping the viral coat proteins, but they fail to degrade the double-stranded RNA genome. These observations support the view that sojourn of reovirus in lysosomes, when the lytic enzymes uncoat its genome, is an obligatory step in the sequence of infection. Although the mechanism for transferring the uncoated RNA out of lysosomes remains to be elucidated, evidence is presented suggesting that progeny genomes are bound to site(s) possessing the fine structure of viral inclusions or factories. It appears that both the synthesis of single- and double-stranded viral RNA and the morphogenesis of progeny virus particles occur in such factories.
THE EFFECT OF PUROMYCIN ON INTRANUCLEAR STEPS IN RIBOSOME BIOSYNTHESIS
Authors: Soeiro R. , Vaughan M. H. , Darnell J. E.
Published: May 2004

Inhibition of protein synthesis by puromycin (100 γ/ml) is known to inhibit the synthesis of ribosomes. However, ribosomal precursor RNA (45S) continues to be synthesized, methylated, and processed. Cell fractionation studies revealed that, although the initial processing (45S → 32S + 16S) occurs in the presence of puromycin, the 16S moiety is immediately degraded. No species of ribosomal RNA can be found to have emerged from the nucleolus. The RNA formed in the presence of puromycin is normal as judged by its ability to enter new ribosomal particles after puromycin is removed. This sequence of events is not a result of inhibition of protein synthesis, for cycloheximide, another inhibitor of protein synthesis, either alone or in combination with puromycin allows the completion of new ribosomes.
ULTRASTRUCTURAL STUDIES OF VASOPRESSIN EFFECT ON ISOLATED PERFUSED RENAL COLLECTING TUBULES OF THE RABBIT
Authors: Ganote Charles E. , Grantham Jared J. , Moses Harold L. , Burg Maurice B. , Orloff Jack
Published: May 2004

Isolated cortical collecting tubules from rabbit kidney were studied during perfusion with solutions made either isotonic or hypotonic to the external bathing medium. Examination of living tubules revealed a reversible increase in thickness of the cellular layer, prominence of lateral cell membranes, and formation of intracellular vacuoles during periods of vasopressin-induced osmotic water transport. Examination in the electron microscope revealed that vasopressin induced no changes in cell structure in collecting tubules in the absence of an osmotic difference and significant bulk water flow across the tubule wall. In contrast, tubules fixed during vasopressin-induced periods of high osmotic water transport showed prominent dilatation of lateral intercellular spaces, bulging of apical cell membranes into the tubular lumen, and formation of intracellular vacuoles. It is concluded that the ultrastructural changes are secondary to transepithelial bulk water flow and not to a direct effect of vasopressin on the cells, and that vasopressin induces osmotic flow by increasing water permeability of the luminal cell membrane. The lateral intercellular spaces may be part of the pathway for osmotically induced transepithelial bulk water flow.
A GOLGI APPARATUS ASSOCIATED WITH MATING IN TETRAHYMENA PYRIFORMIS
Authors: Elliott Alfred M. , Zieg Roger G.
Published: May 2004

The classical Golgi apparatus has not been observed in the several strains of Tetrahymena pyriformis examined in this laboratory at the ultrastructural level when the ciliates are grown vegetatively. However, sexually active strains, when starved for the purpose of inducing conjugation, contain stacked saccules in the oral region. When such opposite mating types are mixed for mating, the stacked saccules become swollen at their ends and vesicles appear to pinch off from them. These bodies possess the configuration of the classical Golgi apparatus of other eucells. Vesicles seem to be formed from the saccules just prior to, and toward the end of conjugation, suggesting a relationship with the mating process.
THE KINETICS OF CELLULAR PROLIFERATION IN REGENERATING LIVER
Authors: Fabrikant Jacob I.
Published: May 2004

The study concerns the kinetics of cellular proliferation in the different cell populations of the normal and regenerating rat liver. A detailed analysis is presented, which includes techniques of in vivo labeling of DNA with tritiated thymidine and high-resolution radioautography, of the temporal and spatial patterns of DNA synthesis and cell division in the parenchymal cells, littoral cells, bile duct epithelium, and other cellular components in the liver during the first 64 hr of regeneration after partial hepatectomy. The analysis of cell population kinetics indicates that (a) the rate of entry of parenchymal cells into synthesis, after an initial burst of proliferative activity, was an orderly progression at 3–4%/hr; (b) most cells divided once and a few twice, a large proportion of the cell deficit being replaced by 72 hr after the onset of proliferation; (c) Ts was ∼8.0 hr; Tgg2+m/2, 3.0 hr; and M, ∼1.0 hr. Littoral cell proliferation began about 24 hr after the onset of parenchymal cell proliferation; the rate of entry of littoral cells into synthesis was greater than 4%/hr. Interlobular bile duct cell proliferation lagged well behind the parenchymal and littoral cell populations both in time and extent of proliferation.
SOME MORPHOLOGICAL ASPECTS OF ACTIVE SODIUM TRANSPORT*
Authors: Voûte Cornelis L. , Ussing Hans H.
Published: May 2004

A method was experimentally tested which allows simultaneous morphological and bioelectrical studies of a tissue that performs active sodium transport, i.e., the isolated, surviving frog skin. In a four cell lucite chamber with four separate electric potential and current circuits, skin specimens for morphological observation (light and electron microscopy) were fixed in situ in well-defined functional states. The rate of active sodium transport through the epithelium of Rana temporaria skin was modified by changing the strength of the electric current passed through the specimens. A marked, reversible swelling of the outermost layer of the stratum granulosum was observed during short circuiting of the skin compared to the homogeneous appearance of the epithelium under open circuit conditions. Doubling the ingoing current led to an additional small increase of the swelling or the appearance of islets of cell necrosis in the same layer. There were signs of a slight shrinkage of the underlying cell layers. The observations are discussed in the light of previous bioelectrical and morphological observations.
LOCALIZATION OF MYOSIN FILAMENTS IN SMOOTH MUSCLE
Authors: Kelly Robert E. , Rice Robert V.
Published: May 2004

Thick myosin filaments, in addition to actin filaments, were found in sections of glycerinated chicken gizzard smooth muscle when fixed at a pH below 6.6. The thick filaments were often grouped into bundles and run in the longitudinal axis of the smooth muscle cell. Each thick filament was surrounded by a number of thin filaments, giving the filament arrangement a rosette appearance in cross-section. The exact ratio of thick filaments to thin filaments could not be determined since most arrays were not so regular as those commonly found in striated muscle. Some rosettes had seven or eight thin filaments surrounding a single thick filament. Homogenates of smooth muscle of chicken gizzard also showed both thick and thin filaments when the isolation was carried out at a pH below 6.6, but only thin filaments were found at pH 7.4. No Z or M lines were observed in chicken gizzard muscle containing both thick and thin filaments. The lack of these organizing structures may allow smooth muscle myosin to disaggregate readily at pH 7.4.
STUDIES ON BLOOD CAPILLARIES
Authors: Bruns Romaine R. , Palade George E.
Published: May 2004

The wall of the blood capillaries of skeletal muscles (diaphragm, tongue, hind legs) and myocardium of the rat, guinea pig, and hamster consists of three consecutive layers or tunics: the endothelium (inner layer), the basement membrane with its associated pericytes (middle layer), and the adventitia (outer layer). The flattened cells of the endothelium have a characteristic, large population of cytoplasmic vesicles which, within the attenuated periphery of the cells, may attain a maximum frequency of 120/µ2 of cell front and occupy ∼18% of the cytoplasmic volume; these values decrease as the cells thicken toward the perikaryon. The vesicles are 650–750 A in over-all diameter and are bounded by typical unit membranes. They occur as single units or are fused to form short chains of two to three vesicles. Each configuration may lie entirely within the cytoplasm or open onto the cell surface. In the latter case, the unit membrane of the vesicle is continuous, layer by layer, with the plasmalemma. Chains of vesicles opening simultaneously on both the blood and tissue fronts of the endothelial tunic have not been observed either in sections or in a tridimensional reconstruction of a sector of endothelial cell cytoplasm. Adjacent endothelial cells are closely apposed to one another and appear to be joined over a large part of their margins, possibly over their entire perimeter, by narrow belts of membrane fusion (zonulae occludentes). Except for tongue capillaries, patent intercellular gaps are rare or absent. The middle layer is formed by a continuous basement membrane (∼500 A thick) and by pericytes which lie in between leaflets of this membrane. The tips of the pericyte pseudopodia penetrate through the inner leaflet of the basement membrane and join the endothelium in maculae occludentes. The adventitia is a discontinuous layer comprising cellular (macrophages, fibroblasts, mast cells) and extracellular (fibrils, amorphous matrix) elements. The same general type of construction appears to be used along the entire length of the capillary.
STUDIES ON LYSOSOMES
Authors: Brittinger Günter , Hirschhorn Rochelle , Douglas Steven D. , Weissmann Gerald
Published: May 2004

Pure suspensions of human lymphocytes were separated from peripheral blood by means of nylon wool, homogenized in 0.34 M sucrose-0.01 M EDTA solution, and fractionated by differential centrifugation. The bulk of acid hydrolase activity was found to be concentrated in a 20,000 g x 20 min granular fraction, whereas nuclear, debris, and supernatant fractions contained lesser concentrations of hydrolases. Acid hydrolase activity present in the granular fraction showed appropriate "latency" as judged by its dose-dependent release into the 20,000 g x 20 min supernatant after exposure to membrane-disruptive agents such as streptolysin S, filipin, and lysolecithin. Heparin proved to be necessary in the suspending medium so that reproducible homogenization and cell fractionation could be obtained. Even excessive contamination of lymphocyte suspensions with platelets did not appreciably alter the acid hydrolase activity of lymphocyte homogenates or the distribution of enzymes in subcellular fractions. Discontinuous density-gradient centrifugation of a 500 g x 10 min supernatant, containing both acid hydrolase-rich organelles and mitochondria, resulted in partial resolution of hydrolase-rich organelles from mitochondria. Fine structural studies of the intact lymphocytes showed the presence of acid phosphatase-positive, membrane-bounded organelles. Electron microscopy of the "large granule" (20,000 g x 20 min) fraction of such lymphocytes demonstrated 80–90% mitochondria, 5–10% platelets, and 5–10% membrane-bounded acid phosphatase-positive structures. The data indicate the presence in human peripheral blood lymphocytes of acid hydrolase-rich granules which possess many of the biochemical and structural characteristics of lysosomes in other tissues.
ATTACHMENT OF INTRANUCLEAR ANNULATE LAMELLAE TO THE NUCLEAR ENVELOPE
Authors: Everingham John W.
Published: May 2004

Oocytes of four species of ascidians were examined with the electron microscope. Prior to fixation, oocytes were subjected to centrifugal forces of 10–15,000 g for 5–10 min and were compared with uncentrifuged oocytes. Intranuclear annulate lamellae (IAL) are distributed uniformly around the periphery of the nucleus of the uncentrifuged oocyte. Centrifugation produces a marked flattening of the oocyte nucleus, migration of nucleoli to the centrifugal end, and often a condensation of the nucleoplasm at the centrifugal end. In contrast, the distribution of IAL is unchanged by centrifugation. Furthermore, numerous IAL profiles appear to be touching the nuclear envelope, and, in a few of these, direct continuity of the IAL with the nuclear envelope is demonstrated.
STRUCTURAL MODULATIONS OF PLASMALEMMAL VESICLES
Authors: Palade G. E. , Bruns R. R.
Published: May 2004

Structural modulations affecting a small fraction of the population of plasmalemmal vesicles of vascular endothelia are described. They include forms which are apparently produced by the fusion of the vesicular membrane with the plasmalemma and by the successive elimination of the layers of the two fused membranes. Such modulations are assumed to represent stages in the discharge process of vesicular contents. Other forms, characterized by their flask shape and elongated neck, are assumed to represent stages in the formation and loading of membrane invaginations, followed by their being pinched off to form isolated vesicles. Stages in a membrane-fusion process leading to the formation of apertured fenestrae and channels are also described in fenestrated endothelia. The visualization of these structural details is greatly facilitated by staining tissue specimens with uranyl acetate before dehydration.
FUNCTIONAL CONSEQUENCES OF ULTRASTRUCTURAL GEOMETRY IN "BACKWARDS" FLUID-TRANSPORTING EPITHELIA
Authors: Diamond Jared M. , Bossert William H.
Published: May 2004

Many fluid-transporting epithelia possess dead-end, long, and narrow channels opening in the direction to which fluid is being transported (basal infoldings, lateral intercellular spaces, etc.). These channels have been thought to possess geometrical significance as standing-gradient flow systems, in which active solute transport into the channel makes the channel contents hypertonic and permits water-to-solute coupling. However, some secretory epithelia (choroid plexus, Malpighian tubule, rectal gland, etc.) have "backwards" channels opening in the direction from which fluid is being transported. It is shown that these backwards channels can function as standing-gradient flow systems in which solute transport out of the channel makes the channel contents hypotonic and results in coupled water flow into the channel mouth. The dependence of the transported osmolarity (isotonic or hypertonic) on channel radius, length, and other parameters is calculated for backwards channels for values of these parameters in the physiological range. In addition to backwards channels' being hypotonic rather than hypertonic, they are predicted to differ from "forwards" channels in that some restrictions are imposed by the problem of solute exhaustion, and in the presence of a sweeping-in effect on other solutes which limits the solutes that may be transported.