bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of low molecular weight human serum factors and human somatomedin peptides on human lymphocyte cultures
Authors: Heulin M. H. , Artur M. , Straczek J. , Belleville F. , Nabet P. , Hermann A. , Lebeurre M. D. , Schimpff R. M.
Published: April 2021

Using [3H]thymidine incorporation into DNA of human lymphocytes in culture, we have shown that human serum contains an ultrafiltrable factor(s) that sensitizes the activation of lymphocytes by phyto haemagglutinin. This (these) factor(s) can replace either human serum or foetal calf serum in the culture. In addition, it permits the expression, and therefore the assay, of human somatomedin A peptides. In somatomedin assays we have shown that the assay using lymphocytes is a much more sensitive test than the assay using sulphation of chick embryo cartilage.
Carbon dioxide induced disassembly of gap-junctional plaques
Authors: Lee William M. , Cran David G. , Lane Nancy J.
Published: April 2021

When sheep ovarian follicle cells are maintained in an O2-rich environment their cells are metabolically coupled, as monitored by observing the exchange of [3H]choline ; choline metabolites were detected up to 4 mm from the explant under these control conditions. When the tissues were placed in a CO2,-rich environment the cells became uncoupled physiologically and choline metabolites were no longer exchanged. The cells in these two states, coupled and uncoupled, were examined by freeze-fracture. The initial controls were characteristic of ovarian follicular tissue exhibiting large macular plaques with regular outlines composed of PF intra-membranous particles (IMPs), which were arrayed in rows with IMP-free aisles. With uncoupling, the junctional plaques became irregular at the periphery, they became loosely packed and IMPs began to ‘stream’ out laterally across the membrane. Ultimately they were reduced to negligible IMP clusters or free IMPs. Analyses of the IMPs with an image analyser confirmed that in the uncoupled state the gap-junctional IMPs were dispersed over the membranes. On return to an O2-rich environment, the cells became recoupled as monitored by physiological criteria and in freeze-fracture replicas IMPs reclustered into macular, albeit smaller, plaques. These results support the contention that with uncoupling, gap-junctional particles are free to move and hence may become dispersed over the membrane face, with the possibility of being re-utilized to form junctions anew when conditions for coupling are re-established.
Migration of lymphocytes across specialized vascular endothelium : V. Production of a sulphated macromolecule by high endothelial cells in lymph nodes*
Authors: Andrews P. , Milsom D. W. , Ford W. L.
Published: April 2021

High endothelial cells lining the post capillary venules in the paracortical areas of rat lymph nodes were found by autoradiography to incorporate [35S]sulphate, whether it was injected into the footpad to reach the draining popliteal lymph node or added to short-term cultures of cervical lymph node slices. The early localization of [35S]sulphate was confined to the Golgi apparatus, but before it disappeared from the cell radioactivity was associated with cytoplasmic vesicles. Sulphated material in macromolecular form was extracted from lymph nodes that had been labelled in vivo and was also found in the supernatant of lymph node cultures. The labelled material was not proteoglycan in nature. High endothelial cells apparently secrete a sulphated macromolecule but its relationship to the only known function of high-walled endothelium -the selective extraction of lymphocytes from the blood -remains to be clarified.
Downward regulation of cell size in paramecium Tetraurelia: Effects of increased cell size, with or without increased dna content, on the cell cycle
Authors: Rasmussen Colin D. , Berger James D.
Published: April 2021

Two temperature-sensitive cell-cycle mutants were used to generate abnormally large cells (size estimated by protein content) with either normal or increased DNA contents. The first mutant, ccl, blocks DNA synthesis, but allows cell growth at the restrictive temperature. The cells do not progress through the cell cycle while at the restrictive temperature, but do recover and complete the cell cycle when returned to permissive conditions. The progeny have increased cell size and normal DNA content.

Downward regulation of cell size occurs during the ensuing cell cycle at permissive temperature. Two processes are involved. First, the G1 period is reduced or eliminated. As initial cell size increases there is a progressive shortening of the cell cycle to 75% of normal. This limit cell-cycle duration is reached when the initial mass of the cell is equal to or greater than that of normal cells at the time of DNA synthesis initiation (0·25 of a cell cycle). Cells with the limit cell cycle begin macronuclear DNA synthesis immediately after fission. The durations of the S period and fission are normal. Second, the rate of cell growth is unaffected by the increase in cell size, and results in the partitioning of excess cell mass between the daughter cells at the next fission.

The second mutant, cc2, blocks cell division, but allows DNA synthesis to occur at a reduced rate so that cells with up to about 14c% of the normal initial DNA content and twice the normal cell mass can be produced. The pattern of cell-cycle shortening is the same as in ccl. The rates of growth and both the rate and amount of DNA synthesis are proportional to the initial DNA content. This suggests that the rates of growth and DNA synthesis are limited by the transcriptional activity of the macronucleus in both ccl and cc2 cells when they begin the cell cycle with experimentally increased cell mass. Increases in both cell size and initial DNA content are required to bring about increases in the rates of growth and DNA accumulation.
Effects of vitamin A on the behaviour of migratory neural crest cells in vitro
Authors: Thorogood Peter , Smith Linda , Nicol Alastair , Mcginty Rose , Garrod David
Published: April 2021

It has been proposed elsewhere that the teratogenic effects of retinoids on craniofacial morphogenesis are caused by a disturbance of the migration of cranial neural crest cells. The effects of 3·5 × 10−6 M and 3·5 × 10−6 M-retinol on the migration of avian neural crest cells in vitro have been investigated by monitoring cell morphology, locomotory behaviour, fibronectin distribution and actin-microfilament organization. Retinol retards migration by affecting cell-to-substratum adhesiveness. Cells exposed to medium containing retinol are less adherent to the substratum, and although the cell surface is very mobile, are unable to extend or maintain lamellipodia. As a consequence the cells do not actively translocate. Fibronectin distribution at the cell surface is sparse, possibly as a result of shedding, and actin distribution remains diffuse.

At the retinol molarities used all these effects are reversible. Thus cells allowed to recover in normal medium flatten out, display lamellipodia and commence active translocation. Fibronectin becomes organized into a fibrillar array and actin microfilaments become organized into cables. The period needed for this recovery is directly related to the molarity of retinol during the initial exposure ; after recovery the retinol-treated cells are virtually indistinguishable from control cells.

We propose that in vivo the effects of retinoids might be to impair cell-extracellular matrix interaction, thus impeding a cell’s ability to migrate through that matrix. Contrary to previous suggestions, the in vivo effects are probably not in any way ‘specific’ to neural crest cells but are more accurately considered as ‘selective’, in that any cell undergoing migration would be similarly affected.
On mitosis in the multicellular alga Ulva mutabilis føyn
Authors: Løvlie A. , Bråten T.
Published: April 2021

Mitosis has been studied in the multicellular green alga Ulva mutabilis by light microscopy and by electron microscopy. Mitosis seems to be of the classical type with regard to spindle, centrioles and continuous and chromosomal microtubules. The nuclear membrane, however, disappears only at the poles and persists as a boundary around the mitotic apparatus. In this respect the Ulva cell seems to be in an intermediate position between those species which have intranuclear mitosis and the forms where the nuclear membrane breaks down. A hypothesis which involves localized synthesis of membranes explains partly the intracellular rearrangement of nucleus, Golgi region and chloroplast after mitosis.
Observations on the fine structure and development of the spindle at mitosis and meiosis in a marine centric diatom (Lithodesmium undulatum): III. the later stages of meiosis i in male gametogenesis
Authors: Manton Irene , Kowallik K. , Von Stosch H. A.
Published: April 2021

Numerical information with respect to spindle microtubules in serial sections of 3 cells at metaphase of the first meiotic division has been compiled and illustrated sufficiently to supplement the previous accounts with respect to both longitudinal and transverse views. At the equator the microtubules of the spindle are united laterally into bundles, the number of bundles being of the same order as that encountered at a premeiotic mitosis, though there is slight variation from cell to cell. The number of microtubules is greater than that at mitosis in a normal spermatogonium, though the distribution in different parts of the spindle is qualitatively similar. Stages of anaphase have been illustrated for the first time and shown to involve at least 3 types of physical forces mediating chromosome movements of various kinds. The later stages of cytokinesis have been timed and are illustrated from living cells and from sections. The relation of the spindle to the cord which unites the separating protoplasts towards the end of cytokinesis has been traced in outline. The cord itself is shown to contain microtubules in limited number and it is therefore not the whole spindle. The interpretation of these findings is discussed in a preliminary way.
An estimate of the amount of microtubule protein in the isolated mitotic apparatus
Authors: Cohen W. D. , Rebhun L. I.
Published: April 2021

The microtubule content of the isolated mitotic apparatus of sea-urchin eggs (Arbacia punctulata) has been investigated by electron microscopy. Cross-sections were made through asters or spindles of flat-embedded mitotic apparatuses of known mitotic stage and specific orientation in the block. Cross-sections between chromosomes and poles of five metaphase half-spindles revealed approximately 2000–2300 sectioned microtubules. The number was somewhat higher in three anaphase half-spindles examined, approximately 2400–2600.

A method was devised for calculating the total number of microtubules in an aster, based upon the number of microtubules appearing in cross-sections. Application of this method to selected mitotic apparatuses enabled calculation of the total number of microtubules in meta-phase mitotic apparatuses of average dimensions. Using a 13-protofilament model of the micro- tubule and existing data on possible monomer sizes and molecular weights, the total amount of microtubule protein in the isolated mitotic apparatus was calculated. The values obtained are in the range of about 1—2 × 10 −8 mg microtubule protein per isolated mitotic apparatus. These values are close to those reported for the 4–5 S protein of the isolated mitotic apparatus, but are considerably lower than the amount of 22s protein. The results are discussed with respect to cellular factors which determine microtubule number, and the possible sources and origin of mitotic microtubule protein.
Development, organization, and degeneration of the Drosophila sperm flagellum
Authors: Kiefer B. I.
Published: April 2021

The development and degeneration of sperm from Y-mutant, sterile Drosophila melanogaster were studied with emphasis on the differences among the various flagellar microtubules and the physical linkages among the components of the axial fibre complex.

During the degenerative process the axoneme is disrupted by the breaking of connexions between adjacent peripheral groups (doublet + satellite) and between the secondary and centralfibres, and the microtubules are lost in a definite sequence: (1) inner portion of B-tubule, (2) outer portion of A-tubule, (3) inner portion of A-tubule, (4) outer portion of B-tubule, (5) central and accessory tubules. The observations support the conclusion that the various microtubules are compositionally different and, further, that the A- and B-tubules are, in turn, composed of differing outer and inner halves.

Observations on the development and subsequent breaking apart of the various flagellar structures demonstrate the presence of the following physical linkages: (1) satellite-to-satellite, (2) A-tubule to adjacent B-tubule, (3) A-tubule to adjacent satellite (accessory tubule), (4) A-tubule to secondary fibres, (5) secondary fibres to central tubules, and (6) a connexion between the two central fibres.
The influence of fixation upon the fine structure of the z-disk of rat striated muscle
Authors: Landon D. N.
Published: April 2021

The fine structure of the Z-disk in rat striated muscle has been found to be dependent upon the manner of its fixation. Material primarily fixed in osmium tetroxide shows a square or ‘woven’ lattice in transverse sections, with a spacing of around 22 ran, and with its axes off-set by 45° from the axes of alignment of the files of I-filaments prior to their entry into the Z-disk. In longitudinal sections the disk may have a zig-zag appearance with individual I-filaments of one sarcomere apparently linked obliquely to 2 or more I-filaments of the next. Transverse sections of Z-disks in muscle primarily fixed in glutaraldehyde show a square-lattice pattern with a spacing of about 11 nm, its axes coinciding with the axes of alignment of the adjacent I-filaments. In longitudinal sections oblique linkages of the ends of the I-filaments are not seen, and they appear either to interdigitate, or to be longitudinally continuous with those of the next sarcomere. This second fine structure is interpreted as being the consequence of the superimposition of 2 basic square lattices, each of 22-nm period, 50 % out of register along each axis, and each formed from the lateral linkage of the ends of the interdigitating I-filamente with the ends of adjacent filaments from their own sarcomere. The relationship of this postulated structure to the lattice patterns previously described, the nature of the cross-linking material, and some possible functional implications are briefly discussed.
A progressive change in the electrophoretic mobility of preaggregation cells of the slime mould, Dictyostelium discoideum
Authors: Garrod D. R. , Gingell D.
Published: April 2021

The electrophoretic mobility of slime-mould preaggregation cells has been found to decrease progressively as they near the chemotactic aggregation stage. This appears to be a spontaneous event dependent on some aspect of cell metabolism. Its possible relevance to cell adhesion and morphogenesis is discussed.
Intranuclear accumulation of rna resembling the smaller ribosomal rna component
Authors: Bramwell M. E.
Published: April 2021

A study was made of the nuclear RNA in HeLa cells with particular reference to the rapidly labelled fractions. It was found that if cells were incubated at a high density, that is, under ‘step-down’ conditions, there was a rapid accumulation of RNA in the nucleus. The fraction of the nuclear RNA which includes rapidly labelled RNA and which binds tightly to columns of methylated albumin on kieselguhr increased in amount and reached levels which permitted enough of the material to be isolated for direct measurement of its base composition. This was found to be very similar to that of 16s ribosomal RNA.

When cells growing logarithmically were treated with low concentrations of actinomycin D and then incubated in the presence of [“[3H]uridine it was found that an RNA fraction which bound tightly to methylated albumin on kieselguhr again accumulated in the nucleus. This fraction resembled that which accumulated under ‘step-down’ conditions. It contained over 85 % of the total radioactivity in the nuclear RNA and again had a base composition very similar to 16s ribosomal RNA. Since nucleolar RNA synthesis was inhibited by the concentrations of actinomycin D used, it appeared that an RNA closely resembling 16s ribosomal RNA was synthesized outside the nucleolus.

Sedimentation patterns on sucrose density gradients and thermal denaturation profiles lent support to the view that the RNA which binds tightly to columns of methylated albumin on kieselguhr probably represents ‘nascent’ 16s ribosomal RNA.
Temperature-dependent functional structures in the polytene chromosomes of Phaseolus, with special reference to the nucleolus organizers
Authors: Nagl W.
Published: April 2021

During the endopolyploidization of the suspensor cells of Phaseolus coccineus and P. vulgaris, polytene chromosomes and an important nucleolar apparatus develop within the nuclei. The nucleolus-associated regions of the four nucleolus-organizing chromosomes and the regions of the secondary constrictions (intranucleolar chromatin threads) show a temperature-dependent, reversible variability in their structure. They split up and are dispersed at optimal temperatures, and they are compact and partly banded at too low or too high ones. Many nucleolar extrusions, and additional nucleoli which originate on distended elements of the heterochromatic parts of different giant chromosomes, occur at temperatures higher than 15° C.

The polytene chromosomes of P. coccineus are able to form lateral loops projecting at right angles to their axes, shortly after temperature elevation. This occurs by the uncoiling of the superficial chromomeres. Several loops synthesize droplets and, moreover, they form nucleolus-like bodies in a hitherto unknown manner. The duration of the lampbrush state is about 3–4 h.

Cytochemical staining methods indicate the presence of DNA in all parts of the polytene chromosomes, including the intranucleolar secondary constriction and the lateral loops, and the presence of RNA in all types of nucleoli and nucleolus-like bodies.

The structural modifications described are compared with the structure of salivary gland chromosomes of Diptera and lampbrush chromosomes in oocytes and spermatocytes. It is suggested that the structural changes are an expression of temperature-dependent changes in gene activity.
Increased contractile strength and tightened adhesions to the substratum result from reverse transformation of cho cells by dibutyryl cyclic adenosine monophosphate
Authors: Leader W. Mark , Stopak David , Harris Albert K.
Published: April 2021

We have examined the changes in cellular contractility and adhesive morphology that accompany the reverse transformation of CHO cells caused by dibutyryl cyclic adenosine monophosphate. The ability of these cells to distort elastic silicone rubber substrata was found to increase markedly over the 5 h period following addition of cyclic AMP and testosterone to the medium, and to relax again following hormone removal. Parallel changes were observed in the interference reflexion image of the adhesion of these cells to glass substrata; broad grey-appearing ‘close’ contacts characteristic of the transformed state were gradually replaced by numerous small black-appearing ‘focal contacts’. These changes in adhesive morphology required considerably longer (20–25 h) to be completed or to revert, however.
Endocytosis of the symbiotic dinoflagellate Symbiodinium microadriaticum freudenthal by endodermal cells of the scyphistomae of Cassiopeia xamachana and resistance of the algae to host digestion
Authors: Fitt William K. , Trench Robert K.
Published: April 2021

The ingestion and fate of four types of particles by endodermal cells of the scyphistomae of Cassiopeia xamachana were investigated by scanning and transmission electron microscopy. Ferritin was endocytosed pinocytotically by invagination of the plasmalemma. These small pinocytotic vesicles fuse with other similar vesicles to form larger ferritin-containing vacuoles, which eventually fuse with lysosomes. Such secondary lysosomes exhibit acid phosphatase activity. The cooccurrence of acid phosphatase activity and ferritin in secondary lysosomes achieved maximum frequency within 2 h of uptake of ferritin and was evident for at least 4 h following uptake. Artemia particles, live freshly isolated symbiotic algae (Symbiodinium microadriaticum), and heat-killed S. microadriaticum are phagocytosed by endodermal cells.

Ferritin-labelled lysosomes fused with food vacuoles containing particles of Artemia. Vacuoles containing heat-killed S. microadriaticum also showed evidence of phago—lysosome fusion. S. microadriaticum in situ (i.e. in host cells) after 3 days exposure to the photosynthetic inhibitor, 3-(3-4-dichlorophenyl)-l, 1 -dimethylurea, appeared degenerate, and were found in loose-fitting host vacuoles, many in mid and apical portions of the host cell. More than 70% of these vacuoles with moribund algae contained the ferritin label, indicating that lysosome fusion had occurred. In contrast, live S. microadriaticum in control animals were almost always found at the base of the host cell in individual tight-fitting vacuoles with no evidence of lysosome fusion.

Live S. microadriaticum apparently escape host digestion by prohibiting the fusion of lysosomes with the vacuole in which they reside. Vacuoles containing defunct algal symbionts, in contrast, were subject to lysosomal attack.
Ultrastructure, organization and cytochemistry of cytoplasmic crystalline inclusions in Origanum dictamnus l. leaf chlorenchyma cells
Authors: Bosabalidis A. M. , Papadopoulos D.
Published: April 2021

In the cytoplasm of chlorenchyma cells in primary Origanum dictamnus leaves, rectangular prism-like crystals occur, which, as shown by pepsin digestion, are proteinaceous. In sections they usually show either a square lattice or striations running parallel to the short or long axis. In both cases the interspacings are estimated to be about 100 A, suggesting that the arrangement of the crystallographic planes possesses tetragonal symmetry. High magnifications of the crystalline inclusions together with analysis of their diffraction patterns showed that the striations are composed of double helices of protein macromolecules. In leaves 3—4 mm long, eroded crystals are often observed. When leaves are larger than 5 mm, no crystalline bodies can be identified in chlorenchyma cells. It is possible that they represent a storage form of protein, which is used later by the developing cells.
Investigation of the cell cycle response of normal and fanconi’s anaemia fibroblasts to nitrogen mustard using flow cytometry
Authors: Dean S. W. , Fox Margaret
Published: April 2021

Cell survival has been measured in normal and Fanconi’s anaemia (FA) human fibroblasts after treatment with the bifunctional alkylating agent, nitrogen mustard (HN2). Two FA cell lines exhibited 6-to 10-fold greater sensitivity than the normal cell line.

Flow cytometry was used to investigate the effects of HN2 on cell cycle progression of normal and FA cells. After 0·1 μg/ml HN2 (surviving fraction, s.f. = 0·8) normal cells exhibited an S phase accumulation within 6 h, followed by a transient G2 delay. At higher doses of HN2, the S phase delay became more pronounced and there was considerably greater accumulation of cells in G2. HN2 at 0·01 μg/ml (s.f. = 0·8) induced no detectable S or G2 delay in FA cells. A higher dose, 0·1 μg/ml (s.f. = 0·13 and 0·29), again induced no S phase delay, but a gradual accumulation of cells in G1 was observed up to 78 h after treatment.

The presence of an S phase delay in normal cells after HN2 treatment may be important in allowing time for DNA repair before completion of DNA synthesis. The absence of such a delay in FA cells suggests that an inability to delay S phase traverse in response to DNA damage from bifunctional alkylating agents may contribute to the sensitivity of FA cells to such drugs.
Effect of tunicamycin, an inhibitor of protein glycosylation, on division of tumour cells in vitro
Authors: Savage K. E. , Baur P. S.
Published: April 2021

We determined the effect tunicamycin (TM), an inhibitor of protein glycosylation, had on cells in vitro that were derived from solid and ascites variants of a chemically induced rat hepatoma. Using flow microfluorometry (FMF), labelling index (LI), and population-doubling time assays, we monitored the progression of cells through the cell cycle after treatment with TM. Cells in monolayer culture were first incubated in 0·05 or 0·10 μg TM/ml medium for 24 h then analysed or given fresh medium without TM and allowed to recover for 6—24 h. Exposing cells to 0·05—0·50 μg TM/ml medium did not affect the percentage of viable cells as determined using the Trypan Blue exclusion procedure. However, continuous exposure to 0·05μgTM/ml medium did affect the population-doubling times of both the ascites and solid variants, and the ascites tumour cells were more sensitive than the solid tumour cells. TM reversibly inhibited hepatoma cells from entering

5 phase of the cell cycle. After exposure to TM for 24 h, the percentage of solid tumour cells in vitro in S phase decreased to 19%, as determined by autoradiography of tritiated-thymidine-labelled cells, and to 21% as determined by FMF; 49% of untreated solid tumour cells were in S phase. The percentage of ascites tumour cells in vitro decreased to 12% after exposure to TM for 24 h; 37% of untreated cells were in S phase. We concluded that TM can inhibit division of rat hepatoma cells in vitro by blocking them in G1 phase of the cell cycle.
Isolation and ultrastructural characterization of secretory mutants of Tetrahymena thermophila
Authors: Orias E. , Flacks M. , Satir B.H.
Published: April 2021

Isolation of 14-secretory mutants (exo-) of Tetrahymena thermophila and ultrastructural characterization (freeze-fracture and thin-section) of two of these (SB255 and SB258) are described. The site of secretion is marked by an intramembrane particle array, the rosette, beneath which the secretory organelle rests. Using Alcian Blue (8GS) as a secretagogue, a screening procedure for exo- cells was developed. Of the resulting 14 clones isolated, 10 are stable and have a tight mutant phenotype. Two of these, SB255 and SB258, lack assembled rosettes. Electron microscopy shows that SB255 has a reduced total number of mucocysts, whereas SB258 appears to have the normal number. This study demonstrates a useful eukaryotic model with which to study by genetic dissection the regulatory mechanisms involved in membrane events in secretion.
Structural and biochemical differentiation of the mammalian small intestine during foetal development
Authors: Bailey David S. , Cook Alastair , Mcallister George , Moss Margaret , Mian Nasi
Published: April 2021

Microscopical studies showed that initial differentiation of the guinea-pig small intestine occurs between days 35 and 55 of foetal development. Changes observed at this time include formation of villi (by day 42), elaboration of submucosal duodenal Brunner’s glands (by day 49) and the appearance of a well-developed microvillus membrane (by day 56).

Different microvillus membrane-associated hydrolases appear at different stages of foetal and postnatal development. The ‘early’ enzymes such as aminopeptidase, alkaline phosphatase and sucrase show a sharp increase and reach their maximal levels between days 35 and 50, whereas the late enzymes such as dipeptidyl peptidase IV and lactase increase gradually between days 35 and 50, and reach maximal activity between days 50 and 60.

A combination of techniques involving precipitation with Mg2 + followed by fractionation on sucrose density gradients has enabled us to prepare, for the first time, a 21-fold enriched microvillus membrane fraction from the foetal intestine.

Polypeptide analysis of this membrane fraction by sodium dodecyl sulphate/polyacrylamide gel electrophoresis showed the presence of developmentally specific polypeptides at different stages of foetal and postnatal development. Three polypeptides of molecular weights 205 000, 80 000 and 47 000 are major microvillus membrane components at the 40-day foetal stage. Two other polypeptides of molecular weights 60 000 and 131 000 are major microvillar components at 56-day and older foetal stages as well as at the 3-day neonatal stage. The adult microvillus membrane contained 112 000 and 122 000 Mr polypeptides as major components. The above results were confirmed using two-dimensional isoelectric focussing-sodium dodecyl sulphate/polyacrylamide gel electrophoretic techniques.
Dna replication and repair in Tilapia cells i. the effect of ultraviolet radiation
Authors: Yew F. H. , Chang L. M.
Published: April 2021

The effect of ultraviolet radiation on a cell line established from the warm water fish Tilapia has been assessed by measuring the rate of DNA synthesis, excision repair, post-replication repair and cell survival. The cells tolerate ultraviolet radiation better than mammalian cells with respect to DNA synthesis, post-replication repair and cell survival. They are also efficient in excision repair, which in other fish cell lines has been found to be at a low level or absent. Their response to the inhibitors hydroxyurea and 1-β-D-arabinofuranosylcytosine is less sensitive than that of other cell lines, yet the cells seem to have very small pools of DNA precursor.
Biochemical and ultrastructural studies of human eccrine sweat glands isolated by shearing and maintained for seven days
Authors: Lee Catherine M. , Jones Christopher J. , Kealey Terence
Published: April 2021

A new method of isolating human eccrine sweat glands by the repeated dissection of skin biopsies with scissors is described. The success of the technique is attributed to a potential line of weakness between the investing capsule and the surrounding connective tissue, which parts under shear forces. The yield is 20-50 glands per biopsy (5 cm×O·5 cm). The glands are judged to be viable by: (i) light and electron microscopy; (ii) ATP, ADP and AMP contents of 81 ·0 ± 12 ·7, 13 ·8 ± 3 ·3 and 3 ·8 ± 1 ·0pmol/gland, respectively (mean ± S.E.M.), which gave an energy charge of 0 ·90; (iii) the 28-fold rise in cyclic GMP content and the sevenfold rise in cyclic AMP content effected by treatment for 2min with 10−5 M-acetylcholine and for 10min with 10−5 M-isoprenaline, respectively; (iv) the rate of [3H]leucine uptake into protein; and (v) the concentration of Neutral Red by the collecting duct. Glands were maintained for 7 days on polycarbonate filters floating on RPMI 1640 tissue-culture medium. After this time the ATP, ADP and AMP contents were 63 ·2 ±7 ·3, 8 ·5 ± 2 ·2 and 3 ·5 ± 0 ·8 pmol/gland, respectively (mean ±S.E.M.), which gave an energy charge of 0’90. During maintenance a dilatation of the intercellular spaces developed in both secretory coil and collecting duct. Following maintenance there was a significant rise in the rate of [3H]leucine uptake into protein. Maintained glands demonstrated a fivefold greater accumulation of cyclic AMP in response to isoprenaline than did freshly isolated glands, but there was no comparable maintenance hypersensitivity of cyclic GMP to acetylcholine. This pattern of adrenergic, but not cholinergic, maintenance hypersensitivity matches the known lack of denervation hypersensitivity of human eccrine sweat glands to acetylcholine in vivo.
Studies on the cytoskeletal and nuclear architecture of Xenopus erythrocytes
Authors: Gambino John , Weatherbee James A. , Gavin R. H. , Eckhardt Ronald A.
Published: April 2021

A proteinaceous cytoskeletal network is present in nucleated erythrocytes, which is obscured ultrastructurally in whole cells due to the presence of haemoglobin. Lysis of Xenopus erythrocytes in solutions containing Triton X-100 reveals a cytoskeleton that contains a centrally positioned nucleus, which is linked to the cell surface-associated cytoskeleton by intermediate filaments. The marginal band microtubules are also preserved in these structures. In addition, a single or a pair of perinuclear centrioles is frequently observed in thin sections. These structures are surrounded by a mass of intermediate filaments and fibrogranular material. In contrast to the centrioles in invertebrate erythrocytes those in Xenopus erythrocytes are not associated with the marginal band.

Cytonuclear skeletons were obtained by DNase I digestion and subsequent high-salt extraction of cytoskeletons. The resulting structures were chromatin-depleted and consisted of a nuclear lamina that was maintained in the same overall shape and position as that of intact nuclei. With the exception of the marginal band, the remaining cytoskeletal elements persisted after these treatments. Although marginal bands were not detectable by electron microscopy, the cytonuclear skeletons contained roughly the same amount of tubulin as cytoskeletons, as indicated by immunoblotting with affinity-purified anti-tubulin antibodies.

When intact erythrocytes were exposed to the ionophore A23187 in the presence of calcium, the cell shape and centric nuclear position were altered. Nuclear dislodgement may be attributable to the disruption of intermediate filament associations with the subsurface cytoskeletal shell. Indirect immunofluorescent staining of cytoskeletons lysed in buffers containing either EGTA or calcium indicates that in the absence of calcium, the intermediate filament network extends to the cell periphery. In structures lysed in calcium, however, the filaments are restricted to the vicinity of the nucleus.
The subcellular concentration of ions and elements in thin cryosections of onion root meristem cells an electron-probe eds study
Authors: Cameron Ivan L. , Hunter Keithley E. , Smith Nancy K. R.
Published: April 2021

Quantitative electron-probe energy dispersive X-ray microanalysis has, for the first time, been accomplished at a subcellular level in plant tissue using cryofixed and thin freeze-dried cryosections. The subcellular concentrations of Na+, Cl−, K+, P, S, Mg2+ and Ca2+ were measured in mol/kg dry weight in two types of root meristematic cells of the onion, Allium cepa. The cell wall of the meristematic cells had much higher concentrations of K+ and Ca2+ than was found in the intracellular compartments. Storage granules in the protoderm cells were about 6-12 times lower in P and were about four times higher in S as compared to other intracellular compartments. Comparison between the concentrations of ions and other elements in meristematic plant cells and in mouse cardiac myocytes confirms that major differences in cytoplasmic Na+ and Cl− concentrations do indeed exist between these cell types.
Ultrastructure of the fusion cell inFaucheocolax attenuatasetch. (rhodophyta, rhodymeniales)
Authors: Delivopoulos Stylianos G. , Kugrens Paul
Published: April 2021

The fusion cell in Faucheocolax attenuata Setch. is a highly lobed, thicSk-walled, multinucleate and irregularly shaped cell originating from the basal cell of the auxiliary cell branch. The formation of the fusion cell occurs by an incorporation of vegetative cells into the basal cell, after dissolution of septal plugs between these cell types. Thus the fusion cell is a syncytium containing only haploid nuclei, as well as unusual mitochondria and plastids. Mitochondria lack cristae and instead contain a tubular helical structure. Plastids are atypical with regard to thylakoid organization in red algae, because they lack the peripheral thylakoid and their photosynthetic thylakoids are aggregated to one side. In addition, they contain large osmiophilic bodies. Nuclear envelopes appear to produce large quantities of membrane cisternae. Floridean starch is absent and the cytoplasm contains few ribosomes. The plasma membrane is irregular and endoplasmic reticulum cisternae are situated parallel to it. Bundles of putative microfilaments were commonly found in nuclei and the cytoplasm. Structural evidence does not support any meristematic, nutritive or secretory functions previously ascribed to fusion cells in other genera.
Xeroderma pigmentosum d-hela hybrids with low and high ultraviolet sensitivity associated with normal and diminished dna repair ability, respectively
Authors: Johnson R. T. , Squires Shoshana , Elliott G. C. , Koch G. L. E. , Rainbow A. J.
Published: April 2021

Fusion between HeLa and fibroblasts from complementation group D xeroderma pigmentosum (XPD) followed by challenge with small doses of ultraviolet light (u.v.) results in the production of hybrid cells expressing either HeLa (HD1) or XPn-like (HD2) sensitivity to u.v. and related repair capacity. Assays used include unscheduled DNA synthesis (UDS), DNA break accumulation in the presence of inhibitors of DNA repair synthesis and host cell reactivation of irradiated adenovirus. Complementation assay in heterokaryons reveals limited ability of HD2 to restore UDS in XPD nuclei. We believe this complementation is more apparent than real since proliferating hybrids of HD2 and XPD parentage are without exception u.v.-sensitive and express limited excision repair. On the other hand hybrids between HD2 and XPc, XPE or XPR fibroblasts show true complementation resulting in a return to normal u.v. sensitivity and elevated repair ability.
Bone cells predispose bone surfaces to resorption by exposure of mineral to osteoclastic contact
Authors: Chambers T. J. , Fuller K.
Published: April 2021

The cell-free endocranial surface of young adult rat parietal bones was used as a substrate for osteoclastic bone resorption, either without prior treatment, or after incubation of the parietal bones with collagenase or neonatal rat calvarial cells. Untreated, the endocranial surface consisted of unmineralized organic fibres; incubation with calvarial cells or collagenase caused disruption and removal of these fibres, with extensive exposure of bone mineral on the endocranial surface, without morphologically detectable mineral dissolution. Neonatal rabbit osteoclasts resorbed bone to a greater extent from parietal bones pre-incubated with calvarial cells or collagenase than from untreated bones; mineral exposure and subsequent osteoclastic resorption were both increased if calvarial cells were incubated with parathyroid hormone ; removal of bone mineral after incubation with calvarial cells removed the predisposition to osteoclastic resorption. These experiments demonstrate that calvarial cells are capable of osteoid destruction, and indicate that one mechanism by which osteoblasts induce osteoclastic bone resorption may be through digestion of the un-mineralized organic material that covers bone surfaces, to expose the underlying resorptionstimulating bone mineral to osteoclastic contact.
Infection and maintenance of Holospora obtusa, A macronucleus-specific bacterium of the ciliate Paramecium caudatum
Authors: Fujishima Masahiro , Fujita Miho
Published: April 2021

The gram-negative bacterium Holospora obtusa is a macronucleus-specific symbiont of the ciliate Paramecium caudatum, which invades the host cell via a food vacuole, infects its macronucleus and grows exclusively in the nucleus. From infection experiments, we showed that a property of the macronucleus that is necessary for it to be recognized and infected by H. obtusa is commonly provided by P. caudatum, P. multimicronucleatum and 14 species of the P. aurelia complex, but not by P. jenningsi, P. burearia, P. trichium, P. duboscqui, Didinium nasutum, Blepharisma japonicum, Pseudourostyla levis, seven species of Euplotes or Tetrahymena thermophila. Further-more, it was also shown that the bacteria that infect the macronuclei of P. multimicronucleatum and the P. aurelia species complex always disappear from the nuclei within 5 days and the infected bacteria are maintained stably in the host nuclei in only 13 out of 22 strains of P. caudatum. The results indicate that the species specificity of the habitat of H. obtusa is not simply a matter of its ability to penetrate the host nuclear membrane but depends on unknown factors that exist only in certain strains of P. caudatum.
Divergent expression of laminin and fibronectin in non-tumorigenic and transformed liver epithelial cells
Authors: Junker J. L. , Wilson M. J.
Published: April 2021

The immunocytochemical expression of laminin and fibronectin by non-transformed liver epithelial cells and by transformed cells derived from the same cell line, TRL1215, was examined in ethionine-transformed cells (ETC), untreated control cells at the same high passage level (HPC), and untreated, low passage cells (LPC). At confluence, a divergent expression of laminin and fibronectin was observed in the three sublines. In flat areas of polygonal cells, LPC showed abundant laminin staining and sparse fibronectin staining; HPC had intermediate expression of both; and ETC had sparse laminin staining and abundant fibronectin. Specifically, the laminin network was often found at intercellular junctions, outlining individual LPC, outlining groups of HPC, and having a focal expression in ETC. A fine reticulum of laminin was seen in large areas of LPC, in relatively small areas of HPC, and in multilayered areas of ETC. Fibronectin was visible as thick, matted fibrils, which were sparse in LPC, loosely arranged in HPC and dense in ETC. Prior studies had shown that the increased fibronectin expression in the transformed cells was associated with increased expression of actin stress fibres, increased cell spreading and increased numbers of focal contacts between cell and substrate. The divergent expression of laminin and fibronectin shown here indicates that these two matrix proteins need not be expressed in a parallel manner during trans-formation, and that increased fibronectin, but not laminin, is associated with maximal cell spreading and adhesion.
Duchenne muscular dystrophy: studies of cell motility in vitro
Authors: Witkowski J. A. , Dubowitz V.
Published: April 2021

Duchenne muscular dystrophy (DMD) is a severe degenerative disorder of skeletal muscle. It has been suggested that an abnormality of the plasma membrane may be responsible for the pathogenesis of DMD, and a number of cell surface changes have been described in DMD muscle fibres and other cell types. Alterations in cell-to-cell and cell-to-substratum adhesiveness have been reported for DMD cells and we have determined whether these alterations in cell adhesiveness affect migration of cells from DMD muscle explants. DMD cells move more rapidly and spend less time at rest than do normal or DMD carrier cells, although the differences were statistically significant only for the latter cells. An inverse relationship between cell speed and contact with surrounding cells was not observed. All cells tended to persist in their direction of movement, and there were no differences between the types of cells studied. Our results support the view that there may be a cell surface defect in DMD.
Nifedipine-sensitive calcium channels are involved in polar growth of lily pollen tubes
Authors: Reiss Hans-Dieter , Herth Werner
Published: April 2021

Pollen germination and tube growth of Liliunt longiflorwn in vitro are affected by 10−5 M-nifedipine. Germinating ‘tubes’ form broad protuberances along the whole colpus. Short tubes show a high tendency to grow ‘amoeboid-like’ and to branch; or a second tube emerges in another region of the colpus. Longer tubes (≧ 100 μm) broaden irregularly or swell at their tips. The diameter of the tube can vary drastically within the same tube. With increasing time of treatment many tubes burst. Normal tip growth stops within 10min, but protoplasmic streaming continues even after 15 h. More or less regularly, wall thickenings are formed along the whole tube or on the flanks of the germinating region after some hours. The internal calcium gradient, visualized by chlorotetracycline (CTC) fluorescence, is also disturbed. Nifedipine treatment results in uniform or irregular CTC fluorescence. Branching tubes temporarily show a new subapical CTC gradient. After 6–8 h of nifedipine treatment many cells are no longer stainable with CTC. The results indicate the presence of nifedipine-sensitive calcium channels in pollen tubes.
Actin synthesis in tumorigenic and non-tumorigenic human hybrid cells
Authors: Gowing Linda R. , Tellam Ross L. , Banyard M. R. C.
Published: April 2021

We have previously shown that the total actin content of tumorigenic HeLa/fibroblast somatic cell hybrids is significantly lower than that of the non-tumorigenic hybrid cells. A measure of actin synthesis, relative to total protein synthesis, was obtained for these cells to determine whether the reduced actin content of the tumorigenic cells is due to specific suppression of actin synthesis. Actin synthesis was measured in cells labelled with [35S]methionine using DNase I affinity chroma-tography to isolate the actin quantitatively. The results show that actin synthesis is not specifically suppressed, since the relative amount of actin synthesized is constant for the tumorigenic and non-tumorigenic cell lines. The reduced actin content of the tumorigenic cells is therefore most likely to be the result of increased degradation of actin.
The effect of partial protein synthesis inhibition on cell proliferation in higher plants
Authors: Cuadrado Antonio , Navarrete Matilde H. , Cánovas José L.
Published: April 2021

Meristematic cells from Allium cepa L. roots can attain a steady state of growth in the presence of anisomycin at concentrations that effectively reduce the rate of protein synthesis. Under these conditions the lengths of cell cycle periods increase but not in the same proportion as the generation time (t). Mitosis is hardly affected and S period is slightly lengthened. G2 increases less in proportion to t, while G1 is extended much higher in proportion to t. Natural synchronous populations have been used to study cell cycle parameters during transition from the physiological steady state to the new one created by the presence of the drug. G2 was the same during transition as during steady-state growth. G1 was much shorter during transition. Average cell mass at division was reduced, and a negative correlation was observed between the length of G2 and the size of the cell at termination of DNA synthesis. We propose that in higher plants, G2 length is regulated by cell mass at completion of DNA synthesis (G2 being shorter in big cells than in small cells), though there is no cell size requirement for mitosis.