bluuebunny/crossref_metadata_2025 huggingface dataset:
On Flagellar Structure in Certain Flagellates
Authors: Gibbons I. R. , Grimstone A. V.
Published: May 2004

This paper describes the structure of the flagella, basal bodies, and some of the associated fibre systems in three genera of complex flagellates, Trichonympha, Pseudotrichonympha, and Holomastigotoides.

Three groups of longitudinal fibres occur in a flagellum: two central and nine outer fibres such as have been repeatedly described in other material, and an additional set of nine smaller secondary fibres not previously identified as such. Each central fibre shows a helical substructure; the pair of them are enveloped in a common sheath. Each outer fibre is a doublet with one subfibre bearing projections—called arms—that extend toward the adjacent outer fibre.

The basal body is formed by a cylinder of nine triplet outer fibres. Two subfibres of each triplet continue into the flagellum and constitute the doublets. The third subfibre terminates at the transition of basal body to flagellum, possibly giving rise to the nine radial transitional fibres that seem to attach the end of the basal body to the surface of the organism. The central and secondary flagellar fibres are not present in the lumen of the basal body, but other complex structures occur there. The form of these intraluminal structures differs from genus to genus.

The flagellar unit is highly asymmetrical. All the flagella examined have possessed the same one of the two possible enantiomorphic forms.

At least two systems of fibres are associated with the basal bodies of all three genera.
Further Electron Microscope Studies of a Mouse Leukemia Induced by Cell-Free Filtrates
Authors: de Harven Etienne , Friend Charlotte
Published: May 2004

Further electron microscope observations of tissues from Swiss and DBA/2 mice with leukemia transmissible by cell-free filtrates to the adult animals are presented. The cytological characteristics of the leukemic cells, the fine structure of the viruses, and the virus host-cell relationships have been examined. The leukemia virus has an external diameter averaging 870 A, and appears to be formed at the level of cell membranes by a budding process. The viruses are observed most frequently in intercellular spaces, but are also often found within cytoplasmic vacuoles of megakaryocytes. Lead hydroxide staining was applied to the study of the leukemic material. The viruses have been found to have a considerable affinity for this lead salt, only comparable in intensity to the affinity shown by RNP granules for the same chemical.
Regular structures in unit membranes. III. Further observations on the particulate component of the suckling rat ileum endocytic membrane complex.
Authors: Robertson J D , Knutton S , Limbrick A R , Jakoi E R , Zampighi G
Published: May 2004

Further morphological observations on the particulate components decorating the lumenal surfaces of membranes of the endocytic complex of the epithelial cells of the suckling rat ileum are presented. The particles each measure approximately 7.5 nm across and give the appearance of the capital letter H in frontal view. They consist of the enzyme n-acetyl-beta-glucosaminidase (NAG). They are arranged in rows called "decorated strips" with the symmetrical lateral bars in register and spaced approximately 14.5 nm apart. Decorated strips lie side-by-side in the external (lumenal) surface of the membrane. They are parallel and sometimes spaced approximately 14.5 nm apart making an orthogonal lattice. The lateral spacing between the decorated strips under certain conditions is reduced and sometimes there is shear between the adjacent ones. Occasionally, shear is present within the decorated strips themselves, with slight displacement of the two sides of each H-shaped particle. A purified preparation of these membranes has been studied by electron microscopy using thin sectioning, negative stain, Markham translation and optical diffraction computer image reconstruction methods. The individual particles comprising the array can be seen in the membrane surface in profile view when dried in a pool of negative stain. They appear either triangular or diamond-shaped in such views. If triangular, they appear to consist of three domains at the corners of an equilateral triangle. One side of each triangular figure is parallel to the membrane surface but separated from it by a dense band of negative stain approximately 2 nm thick that runs along the surface of the membrane. Sometimes a fourth symmetrical domain is visible within this dense band, giving a diamond-shaped figure. This fourth domain connects the particle to the membrane. Thus, each H-shaped particle is a double structure, with each half in profile view appearing as a diamond figure of four symmetrical domains. Each H-shaped particle is believed to consist of either two or four molecules of NAG.
Teleost chloride cell. II. Autoradiographic localization of gill Na,K-ATPase in killifish Fundulus heteroclitus adapted to low and high salinity environments.
Authors: Karnaky K J , Kinter L B , Kinter W B , Stirling C E
Published: May 2004

The specific binding and inhibitory action of (3H)ouabain were employed to localize transport Na,K-ATPase in the euryhaline teleost gill, a NaCl-transporting osmoregulatory tissue in which both enzyme activity and transepithelial transport vary with environmental salinity. In killifish fully adapted to 10%, 100%, or 200% seawater, the gills were internally perfused and externally irrigated in situ. After suitable internal or external exposure to (3H)ouabain, individual gill arches were excised for Na,K-ATPase assay, measurement of radiolabel binding, or quantitative high-resolution autoradiography. Internal exposure to 50 muM ouabain resulted in essentially complete enzyme inhibition, and binding paralleled the increases in enzyme activity at higher salinities; in contrast, external exposure gave minimal and erratic results consistent with leakage of external ouabain into interstitial fluid. (3H)Ouabain autoradiographs demonstrated that, irrespective of exposure or salinity, most of the gill binding was associated with chloride cell. These cells increased in size and number with salinity and, at the subcellular level, the distribution pattern for bound ouabain was always identical to that for the amplified basal-lateral (tubular system) membrane. The combined physiologicmorphologic results constitute final direct proof that chloride cells are the primary site of gill Na,K-ATPase. More important, they provide convincing evidence for unexpected increases in basal-lateral enzyme at higher salinities and thus raise a fundamental objection to the long-postulated role of the Na pump in secretory NaCl transport.
Growth control of differentiated fetal rat hepatocytes in primary monolayer culture. IX. Specific inhibition of DNA synthesis initiation by very low density lipoprotein and possible significance to the problem of liver regeneration.
Authors: Leffert H L , Weinstein D B
Published: May 2004

Rat serum very low density lipoprotein (VLDL) inhibits initiation of DNA synthesis in fetal rat hepatocyte cultures; cells engaged in synthesizing DNA resist inhibition. VLDL action is specific and apparently blocks prereplicative protein synthesis. These and other results, from studies of altered blood VLDL levels and [3H] thymidine incorporation into isolated liver nuclei in 70% hepatectomized normal and mutant hyperlipoproteinemic rats, as well as from infusion studies with a "mitogenic" hormone solution, suggest that hepatic VLDL metabolism is linked to the suppression of hepatocyte proliferation.
Direct association of messenger RNA labeled in the presence of fluoroorotate with membranes of the endoplasmic reticulum in rat liver.
Authors: Cardelli J , Long B , Pitot H C
Published: May 2004

Liver rough endoplasmic reticulum (RER) membranes were isolated from rats given [3H]orotic acid for 48 h (ribosomal RNA [rRNA] label) or for 3 h along with 5-fluoroorotate; this latter procedure permits the labeling of cytoplasmic messenger RNAs (mRNAs) in the absence of rRNA labeling. More than 50% of the labeled mRNA remained attached to membranes of the RER after complete removal of ribosomes with a buffer of high ionic strength in the presence of puromycin. Under similar conditions, membranes retained 40% of their polyadenylate as determined by a [3H]-polyuridylate hybridization assay. Treatment of mRNA-labeled endoplasmic reticulum membranes with pancreatic RNase indicates that the polyadenylate and possibly nonpolyadenylate-pyrimidine portions of the messenger are involved in the binding of mRNA to the membranes. The implication of these results in furthering our understanding of the mechanisms of the translational regulation of genetic expression is discussed.
Regular structures in unit membranes. II. Morphological and biochemical characterization of two water-soluble membrane proteins isolated from the suckling rat ileum.
Authors: Jakoi E R , Zampighi G , Robertson J D
Published: May 2004

Specialized plasma membranes from the endocytic complex of ileal epithelial cells of suckling rats were isolated by differential flotation. Thin-section and negative-stain electron microscopy showed the luminal surfaces of these membranes to be covered by an ordered array of particles 14.5-nm separations in long rows. This particulate coating was released from the membrane surfaces by 10 mM CaCl2 and recovered free of membranes after dialysis against 0.5 mM EGTA and high-speed centrifugation. Two proteins were resolved by gel filtration to be in supernate: n-acetyl-beta-glucosaminidase and a filamentous protein which attaches n-acetylglucosaminidase to the membrane surface thereby providing bidirectionality to the array of enzyme. We believe that the filamentous protein has not been previously described. Therefore we have called it ligatin from the latin ligare, which translates "to bind together". Furthermore, we suggest that the membranes of the endocytic complex contain sites for the extracellular digestion of carbohydrate moieties in the maternal milk.
Osmotic behavior and permeability of osmotically lysed mitochondria.
Authors: Bowman C L , Tedeschi H , DiDomenico B J , Tung F D
Published: May 2004

Experiments were carried out with water-treated isolated rat liver mitochondria (mitochondria ghosts) previously studied by Caplan and Greenawalt (Caplan, A.I., and J.W. Greenawalt. 1966. J. Cell Biol. 31:455-472) and Vasington and Greenawalt (Vasington, F., and J. Greenawalt. 1968. J. Cell Biol. 39:661-675). The ghosts have permeability properties and osmotic behavior comparable to those of isolated mitochondria. Although they have lost most of their internal contents, they must have resealed. Four properties were found which have not been previously described in systems derived from biological membranes: (a) an osmotic behavior in the virtual absence of internal components. (b) a self-arranging property in the formation of invaginations corresponding in morphology to the cristae. The results suggest that the assembly of the molecular components of the inner membrane is sufficient to specify the morphology. Hence the surface area to volume ratio of the vesicles may specify the presence or absence of cristae-like folds. (c) an increase in the permeability of the membranes to sucrose in the presence of iso-osmotic concentrations of sucrose. (d) an independence of the light transmitted by suspensions of the vesicles from the refractive index of the external medium. This observations run counter to the general previous experience with either mitochondria or liposomes.
The beads in the Golgi complex-endoplasmic reticulum region.
Authors: Locke M , Huie P
Published: May 2004

The region between the rough endoplasmic reticulum (ER) and the Golgi complex has been studied in a variety of insect cell types in an attempt to find a marker for the exit gate or gates from the ER. We have found that the smooth surface of the rough endoplasmic reticulum near Golgi complex transitional elements has beadlike structures arranged in rings at the base of transition vesicles. They occur in all insect cell types and a variety of other organisms. The beads can be seen only after staining in bismuth salts. They are 10-12 nm in diameter and are separated from the membrane and one another by a clear halo giving them a center to center spacing of about 27 nm. The beads are not sensitive to nucleases under conditions which disrupt ribosomes or remove all Feulgen staining material from the nucleus. Under conditions similar to those used to stain tissue, bismuth does not react in vitro with nucleic acids. The component of the beads that stains preferentially with bismuth is therefore probably not nucleic acid.
Effect of fibroblast growth factor on the division and fusion of bovine myoblasts.
Authors: Gospodarowicz D , Weseman J , Moran J S , Lindstrom J
Published: May 2004

The effect of fibroblast growth factor (FGF) on the rate of proliferation and fusion of bovine myoblast has been examined. Addition to the cultures of 0.1 mug-1 mug/ml of FGF stimulates the rate of proliferation and delays the fusion of primary cultures of bovine myoblasts cultured in 10% serum. Final cell densities reached in the presence of 0.1 mug/ml of FGF were fivefold higher than in controls; with 1 mug/ml, they were 10-fold higher. Increases in cell density were paralleled by increases in acetylcholine receptor sites as measured by the binding of 125I-alpha-bungarotoxin. Both fusion and the appearance of acetylcholine receptor sites were delayed in the presence of FGF. Growth hormone, insulin and testosterone, which have been reported to be mitogenic for rat and chick embryo myoblasts, did not have significant effects on DNA synthesis in bovine myoblasts when compared to the FGF. Conversely, FGF did not stimulate the proliferation of chick embryo myoblasts, indicating that it is not active in all vertebrate species.
Replication of kinetoplast DNA of Crithidia acanthocephali. I. Density shift experiments using deuterium oxide.
Authors: Manning J E , Wolstenholme D R
Published: May 2004

The protozoan Crithidia acanthocephali contains, within a modified region of a mitochondrion, a mass of DNA known as kinetoplast DNA (kDNA). This DNA consists mainly of an association of approximately 27,000 covalently closed 0.8-mum circular molecules which are apparently held together in a definite ordered manner by topological interlocking. After culturing of C. acanthocephali cells for 25 generations in medium containing 75% deuterium oxide, both nuclear DNA (rhonative, nondeuterated=1.717 g/cm3) and kDNA (rhonative, nondeuterated=1.702 g/cm3) increased in buoyant density by 0.012 g/cm3. The replication of the two DNAs was studied by cesium chloride buoyant density analysis of DNAs from exponentially growing cells taken at 1.0, 1.4, 2.0, 3.0, and 4.0 cell doublings after transfer of cells from D2O-containing medium into medium containing only normal water. The results obtained from analysis of both native and denatured nuclear DNAs indicate that this DNA replicates semiconservatively. From an analysis of intact associations of kDNA, it appears that this DNA doubles once per generation and that the newly synthesized DNA does not segregate from parental DNA. Fractions of covalently closed single circular molecules and of open circular and unit length linear molecules were obtained from associations of kDNA by sonication, sucrose sedimentation, and cesium chloride-ethidium bromide equilibrium gradient centrifugation. Buoyant density profiles obtained from these fractions indicate that: (a) doubling of the kDNA results from the replication of each circular molecule rather than from repeated replication of a small fraction of the circular molecules; (b) replication of kDNA is semiconservative rather than conservative, but there is recombination between the circles at an undefined time during the cell cycle.
Low resistance junctions in crayfish. Structural changes with functional uncoupling.
Authors: Peracchia C , Dulhunty A F
Published: May 2004

Electrical uncoupling of crayfish septate lateral giant axons is paralleled by structural changes in the gap junctions. The changes are characterized by a tighter aggregation of the intramembrane particles and a decrease in the overall width of the junction and the thickness of the gap. Preliminary measurements indicate also a decrease in particle diameter. The uncoupling is produced by in vitro treatment of crayfish abdominal cords either with a Ca++, Mg++-free solution containing EDTA, followed by return to normal saline (Van Harreveld's solution), or with VAn Harreveld's solution containing dinitrophenol (DNP). The uncoupling is monitored by the intracellular recording of the electrical resistance at a septum between lateral giant axons. The junctions of the same septum are examined in thin sections; those of other ganglia of the same chain used for the electrical measurements are studied by freeze-fracture. In controls, most junctions contain a more or less regular array of particles repeating at a center to center distance of approximately 200 A. The overall width of the junctions is approximately 200 A and the gap thickness is 40-50 A. Vesicles (400-700 A in diameter) are closely apposed to the junctional membranes. In uncoupled axons, most junctions contain a hexagonal array of particles repeating at a center to center distance of 150-155 A. The overall width of the junctions is approximately 180 A and the gap thickness is 20-30 A. These junctions are usually curved and are rarely associated with vesicles. Isolated, PTA-stained junctions, also believed to be uncoupled, display similar structural features. There are reasons to believe that the changes in structure and permeability are triggered by an increase in the intracellular free Ca++ concentration. Most likely, the changes in permeability are caused by conformational changes in some components of the intramembrane particles at the gap junctions.
Radiation-induced delay of nuclear pore formation.
Authors: Szekely J G , Copps T P
Published: May 2004

We have shown that radiation affects the nuclear envelope, a membrane structure-closely associated with DNA. The density of nuclear pores visible on freeze-etch surfaces decreased at a rate of 0.042 (pores/mum2)/100 rad with respect to unirradiated cells. This is interpreted as a radiation-induced delay in development of the nuclear envelope.
Lipid vesicle-cell interactions. III. Introduction of a new antigenic determinant into erythrocyte membranes.
Authors: Martin F J , MacDonald R C
Published: May 2004

The introduction of a new antigenic determinant, 2,4-dinitrophenyl-aminocaproyl-phosphatidylethanolamine (DNP-Cap-PE), into the surface membranes of intact human erythrocytes is described. Fresh cells were incubated in the presence of liposomes composed of 10% DNP-Cap-PE, 5% stearylamine, 20% lysolecithin, and 65% lecithin. Such liposome-treated erythrocytes are shown to be susceptible to immune lysis by anti-DNP serum in the presence of complement. Uptake of DNP-Cap-PE by erythrocyte membranes is also demonstrated by immunofluorescence using indirect staining with rabbit anti-DNP serum followed by fluroescein-conjugated goat anti-rabbit IgG and by electron microscopy using ferritin-conjugated antibody. Antigen uptake did not occur at low temperatures or from vesicles lacking lysolecithin and stearylamine. Fluorescence microscopy shows that the antigen-antibody complexes are free to diffuse over the cell surface, eventually coalescing into a single area on the cell membrane. Electron microscopy suggests that a substantial proportion of the lipid antigen is incorporated by fusion of vesicles with the cell membrane. There are indications that vesicle treatment causes a small proportion of cells to invaginate.
Cytoplasmic zone analysis. RNA flow studied by micromanipulation.
Authors: Edström J E , Lönn U
Published: May 2004

A technique is described, cytoplasmic zone analysis, by which it is possible to study the flow of different RNA-containing components in the cytoplasm after their release from the nucleus. After a pulse of RNA precursors, the salivary glands of the insect Chironomus tentans are fixed and microdissected for the isolation of three zones of cytoplasm situated at increasing distances from the nucleus. The RNA from each zone is isolated and analyzed by gel electrophoresis. The three ribosomal RNA components, 18 S, 28 S and 5 S RNA, appear in steep, specific radioactivity gradients (exit gradients) during the time interval 2-3 h after a precursor injection, the 18 S RNA gradient lying 30-50 mum peripheral to that of the 28 S or 5 S RNA gradient. Administration of puromycin led to the complete disappearance of the 28 S RNA and most of the 28 S RNA gradient within 45 min, suggesting that the gradients are caused by an engagement of the ribosomal subunits into polysomes close to the nucleus immediately or soon after their exit from the nucleus. The gradients may offer a unique model for the study of polysome formation and maintenance in vivo.
Mobility restriction in vivo of the heavy ribosomal subunit in a secretory cell.
Authors: Lönn U , Edström J E
Published: May 2004

Analysis in insect (Chironomus tentans) salivary gland cells of labeled RNA as a function of time after precursor injection and its distance to the nuclear membrane, cytoplasmic zone analysis, could previously be used to demonstrate the presence of short-lasting gradients in newly labeled ribosomal RNA. Since the gradients were sensitive to puromycin, they are likely to be a result of diffusion restriction due to an engagement of the subunits into polysomes. In the present paper the possibility was explored of recording gradients that were caused by labeled subunits in puromycin-resistant associations, which, in all probability, involve the endoplasmic reticulum. It was found that labeled 28 S and 5 S RNA but not 18 S RNA were present in radioactivity gradients lasting for at least 2 days but less than 6 days. The gradients also remained during inhibition of RNA synthesis by actinomycin, and they were completely resistant to puromycin whether given in vivo or in vitro. The semipermanent gradients formed fhere offer a unique parameter for the in vivo study of conditions for formation and maintenance of heavy subunits in puromycin-resistant bonds. An explanation for these and previous results is that the light subunit, although restricted in movement by engagement to polysomes, is nevertheless free to exchange and spread between rounds of translation, whereas at least part of the heavy subunit population is bound to the endoplasmic reticulum and less free to spread. These results offer a good in vivo correlate to previous results on in vitro exchangeability of subunits.
Galloylglucoses of low molecular weight as mordant in electron microscopy. II. The moiety and functional groups possibly involved in the mordanting effect.
Authors: Simionescu N , Simionescu M
Published: May 2004

Synthetic pentamonogalloylglucose applied to fixed tissues acts as a mordant, inducing high and diversified contrast similar to that obtained with natural gallotannins of low molecular weight (LMGG). By the separate use of each of the two moieties of the galloylglucose molecule, it was found that gallic acid is the mordanting agent. Glucose may contribute, however, to the effect by increasing the solubility and cross-linking potential of the compound, since the mordanting induced by gallic acid alone is weaker than that produced by its hexose esters. As suggested by results obtained with various phenolics and benzoic acid derivatives, the functional groups required for the mordanting effect of such agents are the carboxyl group, and at least one hydroxyl group concomitantly present on the benzene ring. In the case of galloylglucoses, it is assumed that the effect is due to hydrolysis products (gallic, digallic, or trigallic acids) or to the multiple hydroxyl groups of the intact molecule. Esters of gallic acid (propyl- and methylgallate), as well as pyrogallol, produce a "reversed staining" of all membranes, except for those of communicating (gap) junctions.
Cytotoxicity for tumor cells of cationic proteins from human neutrophil granules.
Authors: Clark R A , Olsson I , Klebanoff S J
Published: May 2004

Cationic proteins purified from human polymorphonuclear leukocyte granules exert a cytotoxic effect on mammalian tumor cells. This effect is time and concentration dependent, is inhibited by the anionic agent heparin, and is enhanced by preheating the cationic proteins. Other strongly basic proteins (histone, protamine) also exhibited cytotoxic activity. Myeloperoxidase isolated from human leukocytes is cytotoxic when combined with H2O2 and chloride. Under these conditions, the potency of the myeloperoxidase-mediated system is greater than that of the cationic proteins.
Microtubules and control of insect egg shape.
Authors: Tucker J B , Meats M
Published: May 2004

This study evidence for tension transmission by microtubules and desmosomes in the follicular epithelium during anisometric growth of certain insect eggs. Most insect oocytes, and the follicles which surround them, grow anisometrically as they assume shapes which approximate to those of long prolate spheroids. Surface growth is most rapid in directions which parallel the polar axis of an oocyte and slowest in circumferential directions at right angles to this axis. The longitudinal axes of microtubule bundles in follicle cells of the gall midge Heteropeza and the cockroach Periplaneta are oriented circumferentially with respect to the surfaces of developing eggs and at right angles to the polar axes of eggs. At cell boundaries, the tubules appear to be attached to spot desmosomes. It is suggested that microtubules and desmosomes form a mechanical continuum throughout a follicular epithelium which transmits tensile forces around the circumference of a growing egg. Follicular resistance to circumferential expansion may be largely responsible for defining the elongate form of insect eggs.
Causal relations among cell cycle processes in Tetrahymena pyriformis. An analysis employing temperature-sensitive mutants.
Authors: Frankel J , Jenkins L M , DeBault L E
Published: May 2004

Utilization of temperature-sensitive mutants of Tetrahymena pyriformis affected in cell division or developmental pathway selection has permitted elucidation of causal dependencies interrelating micronuclear and macronuclear replication and division, oral development, and cytokinesis. In those mutants in which cell division is specifically blocked at restrictive temperatures, micronuclear division proceeds with somewhat accelerated periodicity but maintains normal coupling to predivision oral development. Macronuclear division is almost totally suppressed in an early acting mutant (mola) that prevents formation of the fission zone, and is variably affected in other mutants (such as mo3) that allow the fission zone to form but arrest constriction. However, macronuclear DNA synthesis can proceed for about four cycles in the nondividing mutant cells. A second class of mutants (psm) undergoes a switch of developmental pathway such that cells fail to enter division but instead repeatedly carry out an unusual type of oral replacement while growing in nutrient medium at the restrictive temperature. Under these circumstances no nuclei divide, yet macronuclear DNA accumulation continues. These results suggest that (a) macronuclear division is stringently affected by restriction of cell division, (b) micronuclear division and replication can continue in cells that are undergoing the type of oral development that is characteristic of division cycles, and (c) macronuclear DNA synthesis can continue in growing cells regardless of their developmental status. The observed relationships among events are consistent with the further suggestion that the cell cycle in this organism may consist of separate clusters of events. with a varying degree of coupling among clusters. A minimal model of the Tetrahymena cell cycle that takes these phenomena into account is suggested.
Interactions of actin, myosin, and an actin-binding protein of rabbit pulmonary macrophages. III. Effects of cytochalasin B.
Authors: Hartwig J H , Stossel T P
Published: May 2004

Low concentrations (greater than or equal to 10(-7) M) of cytochalasin B reversibly inhibit the temperature-dependent gelation of actin by an actin-binding protein. The cytochalasin B concentrations which maximally inhibit actin gel formation are 10-fold lower than the concentrations which maximally impair phagocytosis by intact macrophages. Cytochalasin B also prevents the polymerization of monomeric actin in sucrose extracts of macrophages in the absence but not the presence of 0.1 M CKl. 10(-6) M cytochalasin B dissolves macrophage extract gels and gels comprised of purified actin and actin-binding protein by dissociating actin-binding protein from actin filaments. This concentration of cytochalasin B, however, does not depolymerize the actin filatments.
Retention of mRNA on the endoplasmic reticulum membranes after in vivo disassembly of polysomes by an inhibitor of initiation.
Authors: Adesnik M , Lande M , Martin T , Sabatini D D
Published: May 2004

Membrane-bound ribosomes and messenger RNA remained associated with the microsomal membranes of human fibroblasts after cultures were treated with Verrucarin A, an inhibitor of initiation which led to extensive run-off of ribosomes from polysomal structures. When a membrane fraction from Verrucarin-treated cells containing such inactive ribosomes and mRNA was suspended in a medium of high salt concentration, extensive release of ribosomal subunits occurred without the need for puromycin. The mRNA nevertheless remained associated with the membranes. These results add support to the conclusion that, in human fibroblasts, mRNA is bound directly to ER membranes, independently of the ribosomes and nascent polypeptide chains.
Vitreous body collagen. Evidence for a dual origin from the neural retina and hyalocytes.
Authors: Newsome D A , Linsenmayer T F , Trelstad R L
Published: May 2004

Two different cells types have been shown to synthesize embryonic chick vitreous collagen (vitrosin) at different stages of development. Identification of vitrosin was established by labeling the embryos in ovo [3H]proline at stages 23 and 28 and separating the extracted vitreous collagen alpha-chains by carboxymethylcellulose chromatography. The labeled collagen consisted predominately of alpha 1 chains, indicating a molecule in the form of a trimer of identical chains designated (alpha 1)3. The molecular weight of the labeled chains measured approximately 95,000 daltons by molecular sieve chromatography, and contained 41% of their imino acid as 4-hydroxyproline. To establish which eye tissues synthesize vitrosine, the collagens produced in organ culture by the isolated neural retina, lens and vitreous body from stages 26-27, 29-30, and 40 were examined. At the two earlier stages, only the neural retina synthesized large quantities of (alpha 1)3 collagen whereas the lens and the cells within the vitreous body itself synthesized relatively small amounts of collagen characterized by an alpha 1:alpha 2 ratio of about 2:1. At stage 40, however, the cells of the vitreous body itself synthesized the greatest quantities of collagen, which now was predominantly an (alpha 1)3 type molecule. Stage 40 neural retina and lens synthesized lesser amounts of collagen with an alpha 1:alpha 2 ratio of 2 to 3:1. Chick vitrosin thus appears to be synthesized by the neural retina in early embryonic stages, whereas the major contribution derives from cells within the vitreous body in later development.
Immunofluorescence evidence for the absence of histone H1 in a mitotically dividing, genetically inactive nucleus.
Authors: Johmann C A , Gorovsky M A
Published: May 2004

Antibodies directed against whole histone and purified lysine-rich histone H1 extracted from isolated macronuclei of the ciliate Tetrahymena were obtained and conjugated to fluorescein isothiocyanate. The fluorescein-antibody conjugates were used to directly label Tetrahymena cells. Both macro- and micronuclei were visibly fluorescent in cells stained with anti-whole histone conjugate. However, the anti-H1 conjugate only labeled macronuclei. This in situ demonstration of the lack of positive immunofluorescent staining of micronuclei with anti-H1 conjugate provide further evidence for the absence of H1 in the genetically inactive, mitotically dividing Tetrahymena micronucleus.
A quantitative description of the extension and retraction of surface protrusions in spreading 3T3 mouse fibroblasts.
Authors: Albrecht-Buehler G , Lancaster R M
Published: May 2004

We suggest a method of quantitating the motile actions of surface protrusions in spreading animal cells in culture. Its basis is the determination of the percentage of freshly plated cells which produce particle-free areas around them on a gold particle-coated glass cover slip within 50 min. Studying 3T3 cells with this assay, we found that the presence of Na+, K+, Cl-, and Mg++ or Ca++ in a neutral or slightly alkaline phosphate or bicarbonate buffered solution is sufficient to support the optimal particle removal by the cells for at least 50 min. Two metabolic inhibitors, 2,4-dinitrophenol and Na-azide, inhibit the particle removal. If D-glucose is added along with the inhibitors, particle removal can be restored, whereas the addition of three glucose analogues which are generally believed to be nonmetabolizable cannot restore the activity. Serum is not required for the mechanism(s) of the motile actions of surface protrusions in spreading 3T3 cells. However, it contains components which can neutralize the inhibitory actions of bovine serum albumin and several amino acids, particularly L-cystine or L-cystein and L-methionine. Furthermore, serum codetermines which of the major surface extension, filopodia, lamellipodia, or lobopodia, is predominantly active. We found three distinct classes of extracellular conditions under which the active surface projections are predominantly either lamellipodia, (sheetlike projections), lobopodia (blebs), or filopodia (microspikes). The quantitated dependencies on temperature, pH and the inhibition by cytochalasin B or the particle removal are very similar in all three cases. Preventing the cells from anchoring themselves for 15-20 min before plating in serum-free medium seems to stimulate particle removal threefold.
A partial map of the circular mitochondrial genome of Drosophila melanogaster. Location of EcoRI-sensitive sites and the adenine-thymine-rich region.
Authors: Wolstenholme D R , Fauron C M
Published: May 2004

The mitochondrial genome of Drosophila melanogaster is a circular DNA molecule of mol wt 12.35 X 10(6) daltons. A single region accounting for approx. 25% of this molecule can be reproducibly differentially denatured presumably because it is rich in adenine and thymine. We have mapped on the circular mitochondrial genome of D. melanogaster the relative positions of this adenine-thymine (A-T) rich region and the sites sensitive to cleavage by the restriction endonuclease EcoRI, using agarose gel electrophoresis and electron microscopy. Digestion of mitochondrial DNA (mtDNA) molecules to completion with EcoRI resulted in the production of four fragments, A, B, C, and D which represent (+/- SD) 58.9 +/- 1.1%, 27.5 +/- 0.8%, 8.9 +/- 0.5%, and 4.5 +/- 0.3%, of the circular genome length, respectively. Fragments produced by EcoRI digestion and circularized by incubation at 2 degrees C also fell into four distinct length groups with means (+/- SD) of 59.1 +/- 0.5%, 27.5 +/- 0.5%, 9.2 +/- 0.3%, and 4.6 +/- 0.2% of the circular genome length. From a consideration of the lengths of fragments resulting from incomplete EcoRI digestion, it was determined that the arrangement of the fragments in the circular genome was A-C-B-D. By electron microscope examination of partially denatured EcoRI fragments, the A-T-rich region was shown to be located in the A fragment closer to one end than to the other. By similar partial-denaturation studies of fragments resulting from incomplete EcoRI digestion, it was determined that, in the circular genome, of the two EcoRI sites which define the limits of the A fragment, the site between the A and D fragment lies nearest to the A-T-rich region.
[Ciliogenesis in the mucous cells of the quail oviduct. I. Ultrastructural study in the laying quail]
Authors: Sandoz D , Biosvieux-Ulrich E
Published: May 2004

The luminal epithelium of the oviduct (magnum) of laying quails is composed of ciliated cells and mucous cells. Ciliogenesis was observed in some of the mucous cells. Both centrioles of the diplosome migrate to the top of the cell, and one of them induces the formation of a rudimentary cilium. In some of the other cells, that are filled with mucous granules, the formation of basal bodies by an acentriolar pathway was observed. In these cells, numerous, dense fibrous masses are associated with the forming face of the Golgi apparatus. In the Golgi zone, generative complexes composed of a deuterosome and some forming procentrioles were found. Cilia develop from completed basal bodies. During ciliogenesis, the Golgi apparatus is disorganized, and generally the production of mucous granules is arrested. The nucleus is also modified: it becomes larger and the chromatin is dispersed. It is assumed that mucous cells are able to be transformed into ciliated cells in the oviduct of laying quails.
[Ciliogenesis in the mucous cells of the quail oviduct. II. Hormonal control]
Authors: Sandoz D , Biosvieux-Ulrich E , Laugier C , Brard E
Published: May 2004

The hormonal control of ciliogenesis and transformation of mucous cells was studied in the oviduct (magnum) of ovariectomized quails. Estradiol benzoate induces ciliogenesis with doses varying from 10 mug/day to 100 mug/day after 6 days of treatment. With 100 mug/day, differentiation of some mucous cells is also induced as well as the formation of transitory "mixed cells" which are in the process of ciliogenesis and contain mucous granules. Associated with progesterone (1 mg/day), estradiol benzoate (10 mug/day) induces the differentiation of mucous cells and ciliated cells. The luminal epithelium of quails injected with this mixture is similar to the luminal epithelium observed in the oviduct of laying quails. With the same dose of progesterone (1 mg/day) and 20 mug/day of estradiol benzoate for 6 days, ciliogenesis is completely inhibited. All epithelial cells are secretory cells. Transformation of 50% of the mucous cells into ciliated cells is obtained by following the previous estradiol-progesterone treatment with the injection of estradiol benzoate (20 mug/day) for 3 days. Divisions of mucous cells were also observed. It is also possible to induce ciliogenesis in some mucous cells by withdrawing both hormones for 3 days. In this case, no cell divisions were observed.
Adenosine 3':5'-monophosphate content and actions in the division cycle of synchronized HeLa cells.
Authors: Zeilig C E , Johnson R A , Sutherland E W , Friedman D L
Published: May 2004

The involvement of adenosine 3':5'-monophosphate (cAMP) in the regulation of the cell cycle was studied by determining intracellular fluctuations in cAMP levels in synchronized HeLa cells and by testing the effects of experimentally altered levels on cell cycle traverse. Cyclic AMP levels were lowest during mitosis and were highest during late G-1 or early S phase. These findings were supported by results obtained when cells were accumulated at these points with Colcemid or high levels of thymidine. Additional fluctuations in cAMP levels were observed during S phase. Two specific effects of cAMP on cell cycle traverse were found. Elevation of cAMP levels in S phase or G-2 caused arrest of cells in G-2 for as long as 10 h and lengthened M. However, once cells reached metaphase, elevation of cAMP accelerated the completion of mitosis. Stimulation of mitosis was also observed after addition of CaCl2. The specificity of the effects of cAMP was verified by demonstrating that: (a) intracellular cAMP was increased after exposure to methylisobutylxanthine (MIX) before any observed effects on cycle traverse; (b) submaximal concentrations of MIX potentiated the effects of isoproterenol; and (c) effects of MIX and isoproterenol were mimicked by 8-Br-cAMP. MIX at high concentrations inhibited G-1 traverse, but this effect did not appear to be mediated by cAMP. Isoproterenol slightly stimulated G-1 traverse and partially prevented the MIX-induced delay. Moreover, low concentrations of 8-Br-cAMP (0.10-100 muM) stimulated G-1 traverse, whereas high concentrations (1 mM) inhibited. Both of these effects were also observed with the control, Br-5'-AMP, at 10-fold lower concentrations.
Analytical study of microsomes and isolated subcellular membranes from rat liver. VI. Electron microscope examination of microsomes for cytochrome b5 by means of a ferritin-labeled antibody.
Authors: Remacle J , Fowler S , Beaufay H , Amarcostesec A , Berthet J
Published: May 2004

The distribution of cytochrome b5 in rat liver microsomes, and in two microsomal subfractions isolated by density equilibration in a linear sucrose gradient, was studied under the electron microscope by means of a ferritin-labeled hybrid anti-cytochrome b5/anti-ferritin antibody. Results of this study show that cytochrome b5 is present in essentially all microsomal vesicles derived from endoplasmic reticulum (ER), whether rough or smooth. Thus, the dissociation of ER constituents into two groups (b and c), achieved by subfractionating microsomes by isopycnic centrifugation (Beaufay, H., A. Amar-Costesec, D. Thines-Sempoux, M. Wibo, M. Robbi, and J. Berthet. 1974. J. Cell Biol. 61:213-231), does not reflect the association of each group with distinct microsomal particles but reflects rather an enzymatic heterogeneity of the ER: the ratio of group c to group b enzymes increasing with the density and ribosome load of the particles.
Loss of endocytic capacity in aging Paramecium. The importance of cytoplasmic organelles.
Authors: Smith-Sonneborn J , Rodermel S R
Published: May 2004

Aged cells have significantly fewer food vacuoles and ingest fewer bacteria than young cells. Loss of food vacuoles was explained by a decreasing difference in the food vacuole formation and excretion rates; the formation rate declined more rapidly than the excretion rate, approaching equivalence at 160 fissions, when the proportion of cells with no food vacuoles, in the presence of excess food, abruptly increased. A model for cellular aging is presented in which control of organelle numbers and cyclical interactions between the nucleus and cytoplasm may be of critical importance.
Splayed Tetrahymena cilia. A system for analyzing sliding and axonemal spoke arrangements.
Authors: Sale W S , Satir P
Published: May 2004

This study makes use of a procedure designed to illustrate, without serial section analysis, the three-dimensional changes in the ciliary axoneme produced by microtubule sliding, and to confirm essential features of the sliding microtubule hypothesis of ciliary movement. Cilia, isolated from Tetrahymena pyriformis by the dibucaine procedure, are attached to polylysine substratum, and treated with Triton X-100. Critical point drying maintains three-dimensional structure without embedding. The detergent removes the membrane and many axonemes unroll, always in an organized fashion so that doublets follow one another in sequence, according to the enantiomorphic form of the cilium. The central pair of microtubules fall to the side as a unit. The parallel doublet microtubules retain relative longitudinal positions in part by interdoublet or nexin links. Spoke organization and tip patterns are preserved in the opened axonemes. We generalize the work of Warner and Satir (Warner, F. D., and P. Satir, 1976. J. Cell Biol. 63:35-63) to show that spoke group arrangements are maintained for all doublets in straight regions, while systematic displacements occur in bent regions. The conclusion that local contraction of microtubles is absent in the axoneme is strengthened, and direct graphic demonstrations of sliding at the ciliary tip are shown. A morphogenetic numbering scheme is presented which results in a quantitative fit of the tip images to the images predicated by the equation for doublet sliding, and which makes possible new comparisons of structural parameters between axonemes and with cilia of other organisms.
The light-harvesting chlorpohyll-protein complex of photosystem II. Its location in the photosynthetic membrane.
Authors: Miller K R , Miller G J , McIntyre K R
Published: May 2004

We have investigated the structure of the photosynthetic membrane in a mutant of barley known to lack a chlorophyll-binding protein. This protein is thought to channel excitation energy to photosystem II, and is known as the "light-harvesting chlorophyll-protein complex." Extensive stacking of thylakoids into grana occurs in both mutant and wild-type chloroplasts. Examination of membrane internal structure by freeze-fracturing indicates that only slight differences exist between the fracture faces of mutant and wild-type membranes. These differences are slight reductions in the size of particles visible on the EFs fracture face, and in the number of particles seen on the PFs fracture face. No differences can be detected between mutant and wild-type on the etched out surface of the membrane. In contrast, tetrameric particles visible on the etched inner surface of wild-type thylakoids are extremely difficult to recognize on similar surfaces of the mutant. These particles can be recognized on inner surfaces of the mutant membranes when they are organized into regular lattices, but these lattices show a much closer particle-to-particle spacing than similar lattices in wild-type membranes. Although several interpretations of these data are possible, these observations are consistent with the proposal that the light-harvesting chlorophyll-protein complex of photosystem II is bound to the tetramer (which is visible on the EFs face as a single particle) near the inner surface of the membrane. The large tetramer, which other studies have shown to span the thylakoid membrane, may represent an assembly of protein, lipid, and pigment comprising all the elements of the photosystem II reaction. A scheme is presented which illustrates one possibility for the light reaction across the photosynthetic membrane.
Gap junctions between the oocyte and companion follicle cells in the mammalian ovary.
Authors: Anderson E , Albertini D F
Published: May 2004

Tracer and freeze-fracture electron microscopy of the ovaries of neonatal rat and adult mouse, rat, rabbit, and primate have revealed the presence of gap junctions between follicle cells and oocytes. The junctional connections are found at the ends of follicle cell projections which traverse the zona pellucida and terminate upon microvilli and evenly contoured nonmicrovillar regions of the oolemma. Gap junctions are often seen associated with a macula adherens type of junction. The gap junctions occasionally consist of minute ovoid plaques, but nore frequently appear as rectilinear single- or multiple-row aggregates of particles on the P-face or pits on the E-face. The functional significance of follicle cell-oocyte gap junctions is discussed with respect to the regulation of meiosis and luteinization.