bluuebunny/crossref_metadata_2025 huggingface dataset:
Checkpoint signals in grasshopper meiosis are sensitive to microtubule attachment, but tension is still essential
Authors: Nicklas R. Bruce , Waters Jennifer C. , Salmon E. D. , Ward Suzanne C.
Published: April 2021

The spindle checkpoint detects errors in kinetochore attachment to microtubules and delays anaphase if attachment is improper. The checkpoint is activated by attachment-sensitive components including Mad2 and certain phosphorylated proteins detected by the 3F3/2 antibody. We have studied Mad2 and 3F3/2 immunofluorescence in grasshopper spermatocytes. As in other cells, unattached kinetochores are loaded with Mad2 and are highly phosphorylated, whereas after proper attachment, Mad2 is lost and kinetochores are dephosphorylated. What is it about proper attachment that produces these changes – is it microtubule attachment itself or is it the tension from mitotic forces that follows proper attachment? Using micromanipulation, we created an intermediate state, weak attachment, that provides an answer. Weakly attached kinetochores are not under tension and have few kinetochore microtubules. Despite the absence of tension, many weakly attached kinetochores lose their Mad2 and become dephosphorylated. Therefore we conclude that microtubule attachment determines both Mad2 binding and phosphorylation. Nevertheless, tension plays an absolutely essential role. Tension elevates the number of kinetochore microtubules to the level necessary for the complete loss of Mad2 and dephosphorylation from all kinetochores. This gives a reliable ‘all clear’ signal to the checkpoint, allowing the cell to progress to anaphase.
Cell cycle arrest allows centrin translation but not basal body formation during spermiogenesis inMarsilea
Authors: Tsai Chiawei W. , Wolniak Stephen M.
Published: April 2021

Spermiogenesis in the water fern Marsilea vestita is a rapid process that requires the de novo formation of basal bodies in a cytoplasmic particle known as a blepharoplast. Spermiogenesis is activated by placing dry spores into water and is dependent upon the translation of new proteins from stored mRNAs with little, if any, new transcription. We looked at the necessity of cell division cycles in the gametophyte as a prerequisite for the activation of centrin translation and for the consequent formation of blepharoplasts. Cell cycle arrest was induced by treatments of gametophytes with hydroxyurea, with olomoucine, or after RNAi, employing dsRNA derived from Marsilea cyclin A or cyclin B. In all cases, centrin is translated from stored mRNA at the normal time, approximately 4 hours after imbibition, and it accumulates to maximal levels ∼6 hours after imbibition. In spite of the fact that centrin is translated at essentially normal times and accumulates to nearly normal levels, no blepharoplasts form in the gametophytes where division cycles have been disrupted. These results provide a clear demonstration that the new translation of centrin, by itself, is insufficient for blepharoplast formation, the de novo formation of basal bodies, and the assembly of a motile apparatus.
Nuclear envelope defects associated withLMNAmutations cause dilated cardiomyopathy and Emery-Dreifuss muscular dystrophy
Authors: Raharjo Wahyu Hendrati , Enarson Paul , Sullivan Teresa , Stewart Colin L. , Burke Brian
Published: April 2021

Nuclear lamin A and C alleles that are linked to three distinct human diseases have been expressed both in HeLa cells and in fibroblasts derived from Lmna null mice. Point mutations that cause dilated cardiomyopathy (L85R and N195K) and autosomal dominant Emery-Dreifuss muscular dystrophy (L530P) modify the assembly properties of lamins A and C and cause partial mislocalization of emerin, an inner nuclear membrane protein, in HeLa cells. At the same time, these mutant lamins interfere with the targeting and assembly of endogenous lamins and in this way may cause significant changes in the molecular organization of the nuclear periphery. By contrast, lamin A and C molecules harboring a point mutation (R482W), which gives rise to a dominant form of familial partial lipodystrophy, behave in a manner that is indistinguishable from wild-type lamins A and C, at least with respect to targeting and assembly within the nuclear lamina. Taken together, these results suggest that nuclear structural defects could contribute to the etiology of both dilated cardiomyopathy and autosomal dominant Emery-Dreifuss muscular dystrophy.
Cell agglutination mediated by concanavalin a and the dynamic state of the cell surface
Authors: Inoue M.
Published: April 2021

The binding of 131I-labelled concanavalin A (131I-Con A) to the cell surface has been studied in Ehrlich ascites tumour cells (EATC) and beef erythrocytes under various conditions. The binding of concanavalin A (Con A) to the cell surface was very specific and the available binding sites were saturated within a few minutes. The amount of 131I-Con A bound to EATC was 4·14 × 107 molecules/cell at 37 °C and 2·12 × 107 molecules/cell at o °C. Under these conditions, cell agglutination was observed only at 37 °C and not at o °C. However, the binding sites measured at o °C were also effective for agglutination at 37 °C. Beef erythrocytes were agglutinated by Con A only after treatment of cells with papain. The number of binding sites for Con A on the cell surface was decreased by this treatment to about half the number present on untreated cells. Various reagents such as colchicine, monoiodoacetic acid, dinitrophenol, rotenone, sodium azide and carboxyl cyanide-m-fluorophenylhydrazone (FCCP) had no effect on Con A-mediated cell agglutination. In contrast, periodate treatment produced a remarkable decrease in the agglutinability of cells. From these data, it is concluded that the cell agglutination induced by Con A was due to the topographical distribution of the surface receptors for the lectin, and not the result of energy-dependent or microtubule-dependent reaction processes. The number and the state of Con A receptors on the cell surface were in a dynamic condition, their conformation, orientation, and/or topographical distribution changing under different conditions.
Cell wall formation by soybean callus protoplasts
Authors: Hanke D. E. , Northcote D. H.
Published: April 2021

Protoplasts isolated from soybean (Glycine max (L.) Merr.) callus and cultured for 40 h developed a wall which could be seen on plasmolysis. They changed shape, producing buds, and became osmotically stable. Analysis after feeding radioactive glucose showed that the regenerated wall was devoid of pectin which was in the medium. Budding occurs because of the loss of pectin and the observations assist understanding of wall expansion and growth in normal plant cells. The complete molecule of weakly acidic pectinic acid was secreted, precluding the possibility of its assembly in the wall.
Incorporation of [3H]uridine and [3H]thymidine during the phase of nucleolar multiplication in Xenopus laevis oogenesis: A high-resolution autoradiographic study
Authors: Gansen P. Van , Schram A.
Published: April 2021

The nucleoli of the premeiotic, pachytene andyoung diplotene(A, B, C, upto 100μm diameter) oocytes are heavily labelled after 7 h of [3H]uridine incorporation, which is in good agreement with the hypothesis that nucleolar multiplication occurs throughout all these early stages of oogenesis. The total labelling of the nucleolar, nuclear and cytoplasmic volumes has been calculated from the uridine high-resolution autoradiograms and the estimated amounts are discussed. The chromatin of several premeiotic oocytes and the cap of all the pachytene oocytes are strongly labelled after 7 h of [3H]thymidine incorporation. We did not find any thymidine incorporation in the young A, B or C diplotene oocytes.
Furrow formation on a piece of cortex transplanted to the cleavage plane of the newt egg
Authors: Sawai Tsuyoshi
Published: April 2021

As part of an investigation of cleavage furrow formation in the egg of the urodele, Cynops pyrrhogaster, transplantation of the cortex was tried. A piece of the cortex with as little cytoplasm and yolk as possible, derived from various stages, was transplanted to the cleavage plane of another egg, using a fine glass needle.

Concerning the position on which grafting was carried out when transplantation was made to the future site of the host furrow, the cleavage furrow of the host travelled across the graft. When the site of transplantation was on the already formed furrow, the result was positive at the animal half, but negative at the vegetal hah. With regard to the graft itself, transplantation was successful regardless of the stage and of the position on the egg from which the graft was taken.

In grafts of the cortex of Xenopus egg on to Cynops eggs, only one successful result was obtained in about twenty trials.
The transition from tadpole to frog haemoglobin during natural amphibian metamorphosis: i. protein synthesis by peripheral blood cells in vitro
Authors: Benbassat J.
Published: April 2021

The transition from larval to adult haemoglobin during natural metamorphosis of Rana catesbeiana tadpoles was studied by polyacrylamide gel electrophoresis of either untreated or reduced and alkylated haemolysates in 8 M urea. The capacity of the peripheral red cells to synthesize haemoglobin in vitro declined in the course of the development of tadpoles prior to metamorphosis. The beginning of the metamorphosis climax, characterized by emergence of the front legs, was associated with an abrupt increase in the capacity of the circulating cells to synthesize haemoglobin. The protein synthesized at this stage consisted mainly of frog haemoglobin and of smaller amounts of tadpole haemoglobin.

The observed changes in haemoglobin synthesis during metamorphosis are compatible either with the appearance of a new cell line synthesizing adult haemoglobin, or with the renewed proliferation of the tadpole erythroid cell line which eventually produces cells capable of synthesis of frog haemoglobin.
The chloroplast nucleoid inOchromonas danica: I. three-dimensional morphology in light and dark-grown cells
Authors: Gibbs Sarah P. , Cheng D. , Slankis T.
Published: April 2021

The 3-dimensional structure of the plastid nucleoid was determined from serial sections of the plastid of dark-grown, greening, and light-grown cells of Ochromonas danica. In light-grown and greening cells, the chloroplast nucleoid forms a continuous cord or ring which closely follows the rim of each lateral lobe of the chloroplast and is continuous across the top and bottom of the bridge connecting the 2 chloroplast lobes. The nucleoid always lies just inside the chloroplast girdle bands where they loop around the rim of the plastid. It was demonstrated by electron-microscopic autoradiography of greening cells labelled with [3H]-thymidine that all the plastid DNA is localized in this peripheral ring-shaped nucleoid. In the proplastid of dark-grown cells, the nucleoid also forms a ring-shaped structure lying just inside the single girdle thylakoid, although frequent irregularities, such as gaps, are present. It is postulated that the girdle bands determine the shape of the chloroplast nucleoid, possibly by having specific attachment sites for the plastid DNA molecules. A survey of the literature shows that a peripheral ring-shaped chloroplast nucleoid is a characteristic feature of the 5 classes of algae whose chloroplasts possess girdle bands, namely the Raphidophyceae, Chrysophyceae, Bacillariophyceae, Xanthophyceae, and Phaeophyceae, and has never been observed in plants whose plastids lack girdle bands.
Ontogeny of hamster haemoglobins determined by isoelectric focusing in polyacrylamide gel
Authors: Boussios Thalia , Bertles J.F.
Published: April 2021

Haemoglobin ontogeny in an inbred strain of the golden hamster was determined from 12 days in gestation to adulthood. Haemoglobins, separated by isoelectric focusing in poly-acrylamide gel in a linear pH gradient (7·0 to 8·0), were quantified by optical density scanning (420 nm) of the unstained gels. Three species (adult haemoglobins) increase in proportion, one (15% at 12 days gestation) becomes dominant (85% in adults), and two (nearly absent at 12 days gestation) increase and exist as minor species in adults. Two species (foetal haemoglobins) decrease rapidly, one (37% at 12 days gestation) to trace levels, the other (24% at 12 days gestation) to a persistent 3% in adults.

Isoelectric-focused haemoglobins were eluted individually and re-identified by isoelectric focusing, disk-gel electrophoresis, and vertical gel electrophoresis. Gel exclusion studies ruled out the possibility that any one haemoglobin species is a polymer of another.

Haemoglobin proportions determined by the technique used here, isoelectric focusing, are very reproducible, both from sample to sample and from hamster to hamster of any specific age. The presence of a foetal haemoglobin fraction persisting at significant levels into adulthood suggests that this small laboratory animal is a suitable model for studies on foetal haemoglobin synthesis.
Electron-microscopic mapping of at-rich regions and of E. Coli RNA polymerase-binding sites on the circular kinetoplast DNA of Trypanosoma Cruzi
Authors: Brack Christine , Delain Etienne
Published: April 2021

Partial alkaline denaturation of the circular kinetoplast DNA (kDNA) of Trypanosoma cruzi has shown the existence of 4 small, well-defined AT-rich regions with an average size of about 200 base pairs. They are almost equally distributed, separated by approximately 90 degrees on the circular molecule. All minicircles, whether free or linked in networks, have the same denaturation pattern and, therefore, seem to contain the same information. The long linear molecules present in low amounts in the kDNA samples do not show the same denaturation pattern. Partial denaturation of molecules in larger associations indicates that the circular units may be linked to each other by one strand only.

kDNA can be transcribed in vitro by the RNA polymerase of E. coli. RNA polymerase-kDNA complexes have been studied in the electron microscope. By spreading the DNA-protein complexes by adhesion to positively charged carbon films and dark-field observation, it was possible to show the existence of 4 specific binding sites of the E. coli RNA polymerase on the kDNA circles. Comparing the position of the polymerase-binding sites and the AT-rich melted zones, it is suggested that a correlation exists between the two.

As had been shown in earlier work, the replication of circular kDNA can be blocked by treating the trypanosomes with the trypanocidal drug Berenil. The comparison of the relative position of the Berenil-blocked replication forks with the position of the 4 denaturation loops shows that the DNA replication is stopped at these AT-rich regions. Since there is evidence that Berenil binds preferentially to AT-rich DNA and seems to be involved in inhibition of DNA replication, the following hypothetical model can be proposed. The replication of the circular kDNA molecules is discontinuous and involves the synthesis of RNA primers; when Berenil is bound to the AT-rich regions, synthesis of new RNA primers is inhibited and replication is blocked at these points, leading to the accumulation of replicating intermediates with defined branch lengths.
The synaptinemal complex in Rhoeo spathacea
Authors: McQuade H. A. , Wells B.
Published: April 2021

The synaptinemal complex in meiocytes of Rhoco spathacea is described.

Unpaired zygotene chromosomes do not exhibit well defined axial cores under the ordinary fixations of electron microscopy and appear diffuse. However, the axial core is defined by ethanolic phosphotungstic acid (PTA) although it docs not respond to uranyl-EDTA-lead. Thus the core appears to contain histone but not RNA and presents a condition which is modified later in pairing when lateral elements of the synaptinemal complex respond positively to both tests.

The total number of attachments of synaptinemal complexes to the nuclear envelope was determined in several nuclei from serial sections. Eleven of the twelve possible attachments were found in one nucleus. It thus seems certain that all must be so attached. In the same manner all chromosomes can be seen to have an attachment to a chromocentre.

Chromocentres are often very large and compound in that two kinds of heterochromatin can be distinguished. These states of chromatin within the chromocentre are considered to be a function of the degree of condensation.

Segments of synaptinemal complexes are distributed randomly through sections of pachytene nuclei and long uncoiled segments of complexes are frequently found in or near the centres of median nuclear sections. Synaptinemal complexes are also found in chromocentres.

Our findings suggest that on completion of pairing, which begins distally, homologous chromosomes in Rhoeo are paired throughout their entire lengths, rather than in small terminal segments only.
The quantitative requirements of human diploid cells (Strain MRC-5) for amino acids, vitamins and serum
Authors: Lambert Kathleen , Pirt S. J.
Published: April 2021

The uptakes of all essential amino acids, vitamins (except riboflavin), glucose and serum during growth of human diploid cells (MRC-5) were determined. The amino acid uptakes varied considerably with the conditions of culture. The glucose requirement is several times greater than that for mouse LS or human HeLa cells. These analytical results were used to modify the medium so as to ensure that an excess of all defined medium constituents was present and pH was not limiting during study of the scrum requirement. It was then found that maximum cell populations were directly proportional to the serum concentration. Hence the growth was limited by the supply of an unknown growth factor in serum. The scrum growth factor was not replaced by a mixture of over 60 vitamins, co-enzymcs, hormones and other organic and inorganic compounds considered to be possible growth factors, although this mixture did not lower the growth rate and somewhat (22 %) increased the yield from the serum growth factor. The unit of scrum growth factor is precisely defined in terms of the amount in a standard batch of calf scrum. This standard contains 10 units/ml whereas the other batch of serum used contained only 5 units/ml.
Haemoglobin synthesis in fused cells
Authors: Davis T. J. , Harris H.
Published: April 2021

When primitive erythroid cells from 5-day-old chick embryos are exposed to inactivated Sendai virus they do not undergo haemolysis but fuse with other cells by the normal process of cytoplasmic coalescence. In this way cells actively engaged in the synthesis of haemoglobin may be fused with others that are not. In heterokaryons formed by the fusion of such erythroid cells with cells from established mouse or hamster lines, haemoglobin synthesis initially continues at a high level, but then declines and ceases altogether within a period of about 60 h. This decline affects the synthesis of both haem and globin and reflects the activity of a specific regulatory mechanism, for under these conditions other chick proteins continue to be synthesized. The haemoglobin synthesized in the heterokaryons is entirely chick, and not mouse or hamster, haemoglobin.
Calcium regulation of the contractile state of isolated mammalian fibroblast cytoplasm
Authors: Izzard C. S. , Izzard Sally L.
Published: April 2021

Calcium-dependent contractions have been induced in fresh, naked cytoplasm of L-929 fibroblasts using physiological solutions (rigor, relaxing and contracting) similar to those designed to control the contractile state of vertebrate striated muscle. Free access of solutions to the cytoplasm was achieved by popping and stripping the plasma membrane from cells using 7-10 strokes of a Dounce homogenizer. Contracting solution (free Ca2+ 7 ×10−5 M; with added MgATP) applied locally from a micropipette to cells popped in rigor (free Ca2+ < 10−8 M) or relaxing (free Ca2+ < 10−8M; with added MgATP) solutions induced symmetrical contractions of unstretched cytoplasm and directional shortening of stretched cytoplasm. The contractions produced 12–18 % shortenings and were complete in 1·38. The cytoplasm could be cycled repeatedly through the contracted state from the relaxed state.

Exogenous MgATP was required for the Ca2+-dependent contractions. At low free Ca2+ concentrations (< 10−8 M), MgATP had a marked plasticizing effect on the cytoplasm. Thus cytoplasm prepared in relaxing solution was less cohesive and more easily deformed than cytoplasm prepared in rigor solution. When induced to contract, relaxed cytoplasm showed a loss of plasticity. Using this criterion, the threshold concentration of free Ca2+ for contraction was determined to lie between 7 × 10−8 and 5 ×10−7 M.
Autoradiography of soluble [2-14C]thymidine derivatives during meiosis and microsporogenesis in Lilium anthers
Authors: Heslop-Harrison J. , Mackenzie A.
Published: April 2021

A dry autoradiographic method suitable for locating soluble tracers has been used to follow the fate of [2-14C]thymidine supplied to detached buds and inflorescences of Lilium henryi and a related cultivar. During the interval from the archesporial phase until pachytene, the derivative (or derivatives) reaching the anther loculi moved freely into the meiocytes. Subsequently, the tracer was excluded from the mother cells until the dissolution of the tetrads. The young spores readily took up tracer in the thecal fluid upon their release, and yielded strongly localized autoradiographs. These observations are interpreted as indicating that access of materials to the meiocytes is related to the formation of cytoplasmic links between mother cells in the early meiotic prophase, and the later severance of these links through the growth of the isolating callose wall which comes to invest the tetrads. Judged from the tracer retained in preparations extracted with trichloroacetic acid, thymidine incorporation occurs mostly in the premeiotic and early leptotene period, although there is some slight evidence of incorporation later in prophase. In the tapetal cells, incorporation occurred in most of the stages tested, but there was no indication of a transfer of labelled materials from tapetum to spores in the post-meiotic period.
The fibrillar flight muscles of giant water-bugs: An electronmicroscope study
Authors: Ashhurst Doreen E.
Published: April 2021

The fibrillar flight muscles of several species of tropical water-bugs of the family Belosto-matidae have been examined in the electron microscope. The myofibrils are very similar to those of the other fibrillar flight muscles which have been studied. The membrane systems, however, display features which appear to be peculiar to this family. The sarcoplasmic reticulum can be divided into three parts : a series of interconnecting vesicles surrounding the Z-lines, randomly scattered small vesicles around the myofibrils, and flattened cisternae which lie along the transverse tubular system, and form the dyads. These three components of the sarcoplasmic reticulum do not appear to be interconnected. The cisternae of the dyads contain an electron-dense substance. The narrow tubules of the transverse tubular system or T-system penetrate deep into the fibre from the cell mémbrane. They follow a course roughly perpendicular to the myofibrils at the level of the M-lines. The dyads are scattered along their length, and may not be near a myofibril. Another system of very large vesicles is found in the muscle fibres, interspersed among the mitochondria. These vesicles usually appear to be empty; their nature and function are not at present known. Numerous mitochondria are present among the myofibrils.

The peculiarities of the water-bug fibrillar flight muscle are discussed in relation to the flight muscles of other insects and the physiological properties of fibrillar flight muscle.
Invertebrate gap junctions
Authors: Flower N. E.
Published: April 2021

Both glycerol and glutaraldehyde, the two most commonly used chemical aids in freeze-fracture studies, have been shown individually to affect the structure of certain membranes as observed in freeze-fracture replicas. The present investigation studied the effect of glycerol on the gap junctions found in a number of tissues from several invertebrate phyla. Glycerol was shown, in some of these tissues, to affect both the spatial arrangement of the particles within the membrane and their fracturing properties if the tissue had not been prefixed with glutaraldehyde. It is suggested that the effect of glycerol on invertebrate gap junctions may be of diagnostic use in enabling them to be separated into a number, or spectrum, of types.

Previously B-type gap junctions have been reported only in Arthropoda. This study has extended knowledge of their occurrence into the phyla Coelenterata, Platyhelminthes and Annelida. The B-type gap junctions appear consistently to have a 12-nm particle separation, which is larger than the 10-nm separation found in vertebrate and molluscan A-type gap junctions.
Gene transfer by means of cell fusion : I. statistical mapping of the human X-chromosome by analysis of radiation-induced gene segregation
Authors: Goss S. J. , Harris H.
Published: April 2021

Hybrid cells were obtained by virus-induced fusion of hamster cells with irradiated human cells. The analysis of such hybrids permits a study of the effects of lethal doses of radiation on human cells and provides a method of sub-chromosomal genetic mapping that is independent of karyological analysis. Radiation-induced chromosome exchanges are shown to be extremely localized, and a map of 4 X-linked genes is presented.
Experimental results on mammalian cells growing In Vitro in deuterated medium for neutron-scattering studies
Authors: Murphy J. , Desaive C. , Giaretti W. , Kendall F. , Nicolini C.
Published: April 2021

SV-40 virus-transformed human diploid fibroblasts (2RA) were grown in a monolayer on plastic Petri dishes in an aqueous medium deuterated to different concentrations of deuterium oxide: 10, 20, 30, up to 60%. The cells must be acclimatized to concentrations higher than 20% D2O by stepping them from a lower initial concentration during their exponential growth. The increase of cell doubling time with increasing deuterium concentrations seems to correlate, at least at 20% D2O, with an initial period of suspended cell growth (lag-phase), and is qualitatively similar to that previously reported for Escherichia coli.
Influence of the time in culture on cellular and neuronal properties of neuroblastoma X glioma hybrid cells
Authors: Heumann R. , Valet G. , Maison D. , Kemper J. , Reiser G. , Hamprecht B.
Published: April 2021

The stability of a clonal mouse neuroblastoma × rat glioma hybrid cell line was examined. Cell volume and cellular content of DNA and protein were measured as functions of the passage number. They decreased with the number of serial subcultivations. Cellular volume was linearly related to cellular DNA and protein. Thus, measurements of cell volume can be used to monitor the loss of DNA from hybrid cells. After about 60 passages a stable population of hybrid cells arose, as judged by the constancy of cellular volume and by the decreased coefficient of variation of the cell volume distribution. A mathematical model for the kinetics of the simultaneous loss of cellular volume, DNA and protein is introduced. Several neuronal properties were investigated. The specific activity of the neurotransmitter enzyme choline acetyltransferase decreased by more than 50 % during 56 passages. After 70 subcultivations, the hybrid cells were still capable of extending processes, action potentials could still be elicited electrically or by iontophoretic application of acetylcholine, and the cells still responded to prostaglandin E1 as they do at low passage number.
Autoradiographic evidence for the effects of light on rna and dna synthesis during chloroplast replication in spores of Polytrichum
Authors: Kass L. B. , Paolillo D. J.
Published: April 2021

Light stimulates the incorporation of [3H]uridine and [3H]thymidine in addition to plastid replication in germinating Polytrichum spores. Significant amounts of [3H]uridine and [3H]-thymidine are incorporated in darkness but not to the same level as in light. Plastids continue to produce nucleic acids when their capacity to multiply is suspended due to the absence of light. However, a higher amount of DNA synthesis in the light is correlated with the result that chloroplast replication begins again in the light after prolonged dark incubation. An imperfect association of plastid replication and nucleic acid synthesis is suggested by the lack of stimulation of DNA synthesis by light during plastid replication in the first 8 h of incubation. A temporal separation can be demonstrated for chloroplast and nuclear DNA synthesis at the beginning of germination in Polytrichum spores, with DNA synthesis in the chloroplasts preceding that in the nucleus. The mitotic S phase is longer than 16 h for at least half of the nuclei.
Genetic analysis of developmental mechanisms in hydra. ii. isolation and characterization of an interstitial cell-deficient strain
Authors: Sugiyama Tsutomu , Fujisawa Toshitaka
Published: April 2021

A mutant strain (nf-I) of Hydramagmpapillata isolated that contained no interstitial cells, nerve cells or nematocytes. This strain appeared spontaneously in a sexually inbred clone of hydra, and it was recognized by its inability to eat. When force-fed, however, it grew, multiplied by budding and regenerated. In this and in many other respects, nf-I was very similar to the interstitial cell-deficient strain produced by Campbell (1976) by means of colchicine.

A chimera strain was produced by the reintroduction of interstitial cells from another strain into nf-I. The properties of nf-I, the chimera and other related strains were examined, and the possible roles that the interstitial cells and the nerve cells play in growth and morphogenesis of hydra are discussed.
Radioautographic and chemical studies of incorporation into sycamore vascular tissue walls
Authors: Wooding F. B. P.
Published: April 2021

Chemical and radioautographic studies on sycamore seedling stems have shown an involvement of the Golgi body in cell-wall polysaccharide synthesis from tritiated glucose. Tritiated phenylalanine is shown to be incorporated only into lignin after short incubation times. The patterns of labelling are compared and discussed for the two precursors.
The ultrastructure and ontogeny of pollen in Helleborus Foetidus l. II. pollen grain development through the callose special wall stage
Authors: Echlin P. , Godwin H.
Published: April 2021

During the early stages of microsporocyte ontogeny in Helleborus foetidus L. there is protoplasmic continuity between the cells of the tapetum and between the individual sporogenous cells, but not between the two tissues. The plasma canals and plasmodesmata are progressively sealed off by the deposition of thick callose walls, so that by the first meiotic division, each pollen mother cell is isolated from its neighbours and from the surrounding tapetum. Callose is formed by dictyosomes in the individual pollen mother cells. The four meiocytes are separated by the deposition and coalescence of masses of çallose forming in the cell plate area. The exine pattern is initiated at the surface of the young microspores while they are still invested with a thick wall of callose. Periclinally arranged endoplasmic reticulum lying just below the microspore cell membrane corresponds with the position of the furrows. The cell membrane in the interfurrow region thickens and becomes highly convoluted. A fibrous layer appears between the outer part of the convolutions and the callose, and locally it becomes less electron-dense at places that become filled with material of moderate electron density corresponding to the probacula; these in turn will become the bacula of the mature exine. In spite of an extensive examination of material prepared by a variety of techniques, no organelle or cytoplasmic component may be consistently associated with the positioning of the first signs of exine patterning.
The topographical relationship between the plane of the central pair of flagellar fibrils and the transverse axis of the head in guinea-pig spermatozoa
Authors: Fawcett D. W.
Published: April 2021

Earlier studies on the arrangement of sperm-tail components have suggested that a line through the central pair of fibrils is always perpendicular to the broad face of the flattened sperm head. The principal plane of bending of proximal regions of the tail was therefore assumed to coincide with the transverse axis of the head.

The heads of guinea-pig epididymal sperm are flexed 45-50° from the long axis of the tails and are stacked one upon the other in coherent packets. The parallel arrangement of the heads ensures that all of the associated tails will be similarly oriented, and certain planes of section transect heads and tails of the same sperm packet. Taking advantage of this circumstance, it was possible to demonstrate that in quiescent sperm of this species the plane of the central pair is not at 90o to the transverse axis of the head, but is inclined 20-30° off the perpendicular and always in the same direction.

Attention is drawn to examples from the literature on cilia and flagella, where there appears to be a similar inclination of the axis of the central pair with respect to external landmarks.
Freeze-etched surfaces of membranes and organelles in the cells of pea root tips
Authors: Northcote D. H. , Lewis D. R.
Published: April 2021

The structure of the inner and outer surfaces of the plasmalemma, the tonoplast and the membranes of the nucleus and endoplasmic reticulum have been investigated. The structure of the plasmalemma probably varies with the metabolic state of the cell, in particular with the synthesis and transport of material for cell-wall formation. The organization of the plasmalemma during the deposition of material in the wall by reverse pinocytosis is shown, and evidence is presented for the possible synthesis of the microfibrillar structure of the wall by synthetic units arranged as particles on and near the plasmalemma surface. A clear indication of substructure along the length of microtubules has been shown, and since views of large surface areas are possible the distribution of the microtubules at the cytoplasmic surface inside the plasmalemma has been revealed; they bound the cell by running around the circumference in one direction only. A definite organization of nuclear pores has been observed and the structure and shape of the pores is described. By the freeze-etch technique it is possible to investigate crystal-containing bodies, amyloplasts with starch grains and bundles of fibres in addition to mitochondria and Golgi bodies. The method also distinguishes certain spherical organelles by their characteristic surface appearance.
Cytological and cytochemical studies on cell death and digestion in the foetal rat foot: The role of macrophages and hydrolytic enzymes
Authors: Ballard Kathleen J. , Holt S. J.
Published: April 2021

Physiological cell death and degeneration in the interdigital mesenchyme of the hind foot of the rat foetus have been studied using classical staining methods and staining methods for enzyme localization. Individual mesenchymal cells die and shrink as the result of some unknown mechanism. Their acid phosphatase and esterase activities are not significantly different from those of viable loose mesenchymal cells. The dead cells are engulfed by viable neighbouring cells which resemble other loose mesenchymal cells in their morphology and in their acid phosphatase and esterase activities. These phagocytes then differentiate and become typical macrophages. Expressions of this process are the altered appearance of their nuclei and the increase in cytoplasm and in acid phosphatase and esterase activities. Many dead cells may be engulfed by a single macrophage and are then digested by its acid hydrolases. No evidence was found suggesting that cell death might be initiated by the intracellular release of lysosomal enzymes.
Mitosis and the cell cycle in the metamorphic moult of the milkweed bug, Oncopeltus Fasciatus. A radioautographic study
Authors: Lawrence P. A.
Published: April 2021

A simple method of whole-mount radioautography is devised to investigate aspects of the cell cycle during metamorphosis in the epidermis of the milkweed bug, Oncopeltus. Tritiated thymidine is used to indicate DNA synthesis. As the label only lasts in the insect for about 2 h, a wave of labelled cells passes through the different phases of the cell cycle. The S period is found to overlap with an exceptionally long prophase and there is thus no G2 period. The length of prophase (408 ±10 min) is estimated from a plot of the fraction of labelled prophases against time after injection of label. By an equivalent method the length of the 5 period is found to be 289 ± 12 min. No labelled cells divide again until about 24 h after the previous mitosis, when some cells embark on a second mitosis. The minimum interphase (G1) period is approximately 16 h. In the area studied, the cell number more than doubles during the proliferative mitoses; and it is thus possible, but not certain, that every cell divides at least once.

Fifth-stage larvae injected during the differentiative divisions (which are involved in the development of dense hairs) show that each of the three kinds of differentiative divisions has its own peculiar timing. The timing of the very first division, that of the epidermal cell which will become the hair mother cell, suggests that the cell is already different from its progenitors prior to prophase.
Cytochemical adenosinetriphosphatase in plant root meristem
Authors: Shifrin Norma , Levine L.
Published: April 2021

Root tip meristems were stained to demonstrate ATPase activity by two different methods, with general agreement in localization but not specificity, and with emphasis on mitotic cells.

In interphase, ATPase was localized in nucleoli and nuclear membranes, with lesser activity in the nuclear substance. In prophase, chromosomes were outlined by ATPase stain which gradually declined in intensity at prometaphase, becoming least evident in metaphase. Staining activity increased again in anaphase, and remained high in telophase. In prometaphase, anaphase and late anaphase-early telophase, the ATPase was concentrated in a fibril which appeared to coil around the chromosomes. The ATPase fibril was thinnest at metaphase and shorter and thicker at telophase. In addition, granules farmed in association with the coils of the fibril in late anaphase and early telophase. Later on, these granules may have fused and contributed to nucleolar reformation.

The ATPase never localized in the chromosomal fibre nor in any other region of the spindle. RNA generally localized like ATPase, but ATPase loci were unchanged after ribonuclease (RNase) treatment.

Because of certain similarities between ATPase and argentaffin localization, some relationship between the nucleolus and ATPase is suggested. A mechanochemical transducing role is postulated for the ATPase, because cytochemical properties were like those of ATPase in the A-band of myofibrillae, and because other changes in it could be correlated with chromosome movement.
Surface features of striated muscle: II. guinea-pig skeletal muscle
Authors: Rayns D. G. , Simpson F. O. , Bertaud W. S.
Published: April 2021

A study of the structure of the terminal part of the T-tubule system and the distribution of subsarcolemmal caveolae was undertaken in guinea-pig psoas muscle. The results were correlated with the array of cell surface features as revealed by frozen-etched, shadowed replicas of the cell membrane.

Freeze-etching revealed numerous small rounded objects overlying the Z- and I-bands and the A-I junction regions of the sarcomeres. These objects appeared as pits or excrescences, depending on whether the cell membrane was viewed from outside or inside the cell, and were interpreted as apertures in the membrane.

Conventional thin sections demonstrated the presence of numerous subsarcolemmal caveolae with a similar distribution to the rounded features seen in the replicas. Such sections also showed that the T-tubules, lying at the A-I junctions, seem to change direction when approaching the cell surface and may occasionally appear to branch in the subsarcolemmal region. The T-tubules often terminated in caveolae. Caveolae were sometimes seen in direct communication with the extracellular space. No simple direct communications of T-tubules with the cell surface were observed.

After treatment of the muscle with lanthanum during fixation, thin sections revealed apparently continuous dense deposits from the cell surface, through the caveolae to the T-tubule proper. It thus appears that each T-tubule communicates indirectly with the extracellular space via one or more subsarcolemmal caveolae.
Displacement of valine from intact sea-urchin eggs by exogenous amino acids
Authors: Piatigorsky J. , Tyler A.
Published: April 2021

Unfertilized and fertilized eggs of the sea urchin Lytechinus pictus were preloaded with [14C]valine and exposed to individual solutions of each of the twenty ‘coded’ [14C]amino acids in artificial sea water. After 1 h incubation the amount of radioactivity in the medium was determined. The radioactivity was effectively displaced by most of the other neutral [14C]amino acids that are known to compete with valine for uptake. A chromatographic test with fertilized eggs showed the displaced radioactivity to be [14C]valine and not some metabolic product. Addition of acidic, basic or some neutral amino acids that are known to be poor inhibitors of valine uptake did not cause significant quantities of label to appear in the medium. For the unfertilized eggs, the concentration of acid-soluble label remained many hundreds of times greater in the egg fluid than in the sea water.

Tests indicated that efflux of [14C]valine and subsequent competition for re-entry is a primary factor responsible for the displacement phenomenon. That this may not be the sole factor is suggested by the fact that some amino acids that are known to be powerful inhibitors of valine uptake were found to be only weak displacers of [14C]valine. Neither [14C]arginine nor [14C]glutamic acid were displaced in significant amounts from preloaded unfertilized or fertilized eggs by any of the tested [14C]amino acids.

Attempts were made to utilize the displacement of [14C]valine to elevate the incorporation of [14C]valine and of other labelled amino acids into protein by intact eggs. Unfertilized and fertilized eggs were pretreated with related [14C]amino acids and then exposed to [14C]valine or a mixture of [14C]amino acids. The results varied in the different tests, ranging from no significant increase to 2-fold.
Translational movements of macrophages through media of different viscosities
Authors: Folger R. , Weiss L. , Glaves D. , Subjeck J. R. , Harlos J. P.
Published: April 2021

The extent of the migration of guinea-pig peritoneal macrophages from capillary tubes over the surfaces of plastic Petri dishes, was quantitated by planimetry. It was observed that the amount of migration decreased as the viscosity of the medium was increased by the addition of agarose.

An essential component of translational movement is the formation of adhesions between cells and their substrata. It is suggested on the basis of the present migration and adhesion experiments, that the increased viscosity reduces migration by retarding the formation of adhesions between the cells and their substrata. The experiments do not support the suggestion that agarose adsorbed to the dish surface affects the adhesion-dependent arm of migration or that viscous ‘drag’ on whole cells (over the viscosity range of 0·71 to 3·9 × 10−3; N s m-2) reduces their movements.
Cell interactions in the developing somite; in vivo comparisons between Amputated (am|am) and normal mouse embryos
Authors: Flint O. P. , Ede D. A.
Published: April 2021

Light and electron microscopy coupled to a quantitative analysis form a powerful technique for the analysis of cell behaviour in mutant and normal tissues. Using this approach the morphology of the cells and their contacts are examined in the somites of a recessive mouse mutant, amputated, and of its normal littermates. The results of the analysis show that cell density is the same in both mutant and normal sclerotome but that mutant cells tend to form small clumps whereas normal cells disperse individually. There is a correspondingly greater area of cell contact per cell in the mutant. Filopodia are equally numerous in the mutant and normal but where in the normal they stretch across wide intercellular spaces to make contact at their tips with other cells, in the mutant they form a tangled web sticking back on to the surface of the cell of origin and adjacent cells. The appearance of mutant and normal sclerotome is compared with presomitic cells and with the cells of other mutants whose abnormal development has been shown to depend on cell contact morphology and behaviour.
Electrical control of flagellar activity in impaled bull spermatozoa
Authors: O’Day Peter M. , Rikmenspoel Robert
Published: April 2021

The control of bull spermatozoon flagellar activity has been investigated using direct current injection into the cells through an impaling glass microelectrode. Negative current injection results in a decrease in the flagellar frequency. Flagellar frequencies can be decreased to zero with high negative currents. This current injection response is dependent on the magnesium concentration available to the spermatozoon interior. The current injection response is nearly independent of ATP concentrations. Resistance measurements indicate that the current injection pathway has a resistance of about 200 ± 300 kΩ, and that the current flowing through the cell membrane is not exceedingly large. Measurements of the induced potentials indicate transmembrane potentials during current injection of about —35 ± 30 mV per μA of injected current. The results are compatible with an active transport process in bull spermatozoa that controls the flagellar activity in response to current injection by decreasing the internal Mg2+ concentrations during the injection of current.
Plasma membrane vesiculation in 3T3 and SV3T3 cells: II. factors affecting the process of vesiculation
Authors: Scott Robert E. , Maercklein Peter B.
Published: April 2021

Plasma membrane vesicles are shed from monolayer cell cultures during incubation in low concentrations of formaldehyde and other sulphydryl blocking reagents. In both 3T3 and SV3T3 cells disulphide reducing agents, including dithiothreitol and mercaptoethanol, potentiate formaldehyde-induced vesiculation. Plasma membrane vesiculation is shown to be a temperature-dependent phenomenon which occurs optimally between 22 and 37 °C and at pH 7·0 to 7·5. Membrane shedding is an energy-dependent phenomenon, requiring monovalent and divalent cations and slightly hypertonic medium. Plasma membrane vesiculation is not affected by pretreatment of cells with inhibitors of protein synthesis, i.e. cycloheximide, nor by agents which disrupt the cytoskeleton.