bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyteny and the functional significance of the polytene cell cycle
Authors: Pearson M. J.
Published: April 2021

Polyteny is a special nuclear differentiation reported in larval and adult Diptera, Collembola, Protista and angiosperm ovular nuclei. In not all cases, however, do discrete giant chromosomes represent homologous pairs as in the salivary gland nuclei of Drosophila or Chironomus larvae, and in Calyptratae (e.g. Calliphora) a degree of homologue separation and dissociation of the constituents results in a reticular chromosomal organization within which banded polytene regions are prominent. The correlation previously shown between the polytene cycle of replication without mitosis and the growth habit of larval Calliphora suggests that the significance of the polytene phenomenon may lie, not in a special physiology of discrete giant chromosomes, but in the cell cycle responsible for the polytene condition; chromosome morphology may not be functionally significant. The significance of polyteny versus endopolyploidy is considered in terms of the cell cycle. Whereas the endopolyploid cycle is endonuclear and thus non-disruptive of cytoplasmic syntheses, the polytene cycle further departs from a normal mitotic cycle in that there is no M-phase: the nucleus is in permanent ‘interphase’, and clearly the cycle should not be referred to as ‘endomitotic’. The physiology of polytene chromosomes is discussed: there is no evidence that the intense activities of hypertrophied salivary cells in Diptera depend on continuous monitoring at transcription level. The aceticorcein squash technique has been used to describe the chromosomal organization in two cell types known to hypertrophy without sign of an M-phase: oenocytes of the locust Schistocerca gregaria, and the giant trophoblast cells of mouse concepti. In both cases, there is cytological evidence of polytene lateral pairing over short regions. In Schistocerca oenocytes, this organization is similar to the reticular fibrillation of polytene chromosomes seen in calyptrate epidermal and salivary nuclei. The functional significance of the polytene cell cycle is discussed in the light of its known incidence among eukaryotes, and the use of terminology examined.
The abdominal epidermis of Calliphora Erythrocephala (diptera): I. polyteny and growth in the larval cells
Authors: Pearson M. J.
Published: April 2021

The extremely rapid growth of feeding larvae of Calliphora is achieved with a hypertrophy of larval epidermal cells and concomitant polytene specialization of their nuclei. Within the epidermis of each abdominal segment are differentiated sense organs of the campaniform and a more complexpossibly chemosensory-kind in a constant pattern; there is no post-embryonic differentiation of new sense organs before metamorphosis, while the cuticlesecreting cell of these sense organs also becomes polytene.

The polytene organization of epidermal nuclei differs from the classical giant chromosome structures of lower dipteran larval cells. Calliphora epidermal polytene chromosomes irregularly fragment into oligotene or smaller fibrils which, through apparently non-specific reassociations, form a nuclear reticulum of which the banded polytene regions are a part. This loose reticular organization is unlikely to reflect a condition of genetic activity.

Photometric densitometry shows the period of polytene DNA replication in general epidermal nuclei is closely correlated with the period of larval growth. At hatching, epidermal nuclei are diploid, with the zC DNA content. Through a series of endoreduplications, such that at any stage nuclei tend to fall into a series of DNA classes with a percentage falling in between, the largest polytene nuclei reach about 256C by the end of the feeding stage. During the feeding stage, whole mount autoradiography shows a very slow continuation of DNA synthesis in some epidermal nuclei; that is, after cessation of larval growth. DNA synthesis in cupologen nuclei of the campaniform organs ceases after secretion of the third instar cuticle at the end of the second instar.

The polytene cycle responsible for nuclear DNA increase is discussed in the context of these data, and a functional correlation drawn for the rate of polytene increase in the epidermal nuclei and the cupologen nuclei. This correlation suggests active control of the cycle, and raises the question of the significance of the polytene cell cycle.
Cell border demarcation in the scanning electron microscope by sil ver stains
Authors: Bruijn W. C. De , Mourik W. Van , Bosveld I. J.
Published: April 2021

Silver nitrate and silver proteinate were both successfully used as electron stains for the demarcation of the aortic endothelial cell borders in the scanning electron microscope.

By energy-dispersive X-ray analysis it was demonstrated that silver was present in the demarcation lines around the endothelial cells. The presence of silver closely coincided with the places where secondary electrons were produced.

Judged by the quality of the aortic tissue in the transmission electron microscope, the method using silver proteinate was preferable to those using silver nitrate. The limited resolution of the method is demonstrated.

The role of the dextran solution in such procedures was investigated, and it was shown that the presence of such a dextran solution, or its particle size or charge, does not contribute to the formation of these silver lines around the endothelial cells. In ultrathin sections of such material the cell surface-contrasting capacity of colloidal thorium dioxide solutions was com pared to the cell border-contrasting capacity of silver proteinate. It was found that prior aldehyde fixation abolished the cell border demarcation by silver proteinate, but only reduced the cell surface demarcation by thorium dioxide particles.
Study of nucleolar vacuolation and rna synthesis in embryonic root cells of zea mays
Authors: Barsy TH. De , Deltour R. , Bronchart R.
Published: April 2021

The process of nucleolar vacuolation has been quantitatively studied in root cells of the embryo of Zea mays. During germination, we have estimated the percentage of vacuolated nucleoli, the number of vacuoles per nucleolus and the volume density of the vacuoles, the latter by application of the stereological principles of morphometry. In the dormant embryo, no vacuoles can be detected in the nucleolus. When germination occurs at 22 or 16 °C, there is a rapid increase in the percentage of vacuolated nucleoli and in the volume density (VA), with a maximum after 4 and 8 h. At 6 °C, a temperature which does not permit emergence of the root, the percentage of vacuolated nucleoli increases regularly but never reaches the level observed at 16 and 22 °C. In parallel with the appearance of nucleolar vacuoles, the size of the nucleolus decreases statistically and shows a minimum when vacuolation is maximum. This suggests that the appearance of vacuoles within the nucleolus is the result of loss of material from this organelle. Indeed, electron micrographs show that granular components are lost from the nucleolus during the first 8 h of germination at 16 °C. According to the literature, these granular components are probably ribosomal subunits.

An autoradiographic study of tritiated uridine incorporation shows that the nucleolus does not synthesize rRNA at the early beginning of germination. Hence the nucleolus is unable for several hours to rebuild the lost granular elements.

Application of actinomycin D, 5-fluoro-uracil and 2-thio-uracil to the seeds, during the first 48 h of soaking, inhibits rRNA synthesis, the vacuolation process, the loss of granular components and the reduction in size of the nucleolus.

These results allow us to determine some of the physiological conditions characterizing the appearance of the nucleolar vacuoles.
Electron-microscope observations on the organization of the nucleus in chicken erythrocytes and a superunit thread hypothesis for chromosome structure
Authors: Davies H. G. , Murray A. B. , Walmsley M. E.
Published: April 2021

Previously it was shown that when condensed chromatin from several different types of cell is stained with uranyl-lead and examined in thin sections in the electron microscope, the stain is distributed into a dot-dash pattern arising from threads, with lesser-staining intermediate areas. We now show that when a section through chicken erythrocyte chromatin is stained with ethanolic phosphotung3tic acid (PTA) the stain distribution is homogeneous. This shows that the lesser-staining regions after uranyl-lead, cannot be an overlap artifact. We conclude that the stains and hence the molecules in chromatin are distributed between 2 phases, an 0- and an e-phase, so called because the structural units in chromatin are arranged in an orderly way at the surface of the nucleus and give rise to oddly (o) and evenly (e) numbered bands. Measurements of electron density per unit thickness, proportional to the number of stain molecules per unit volume, are made in thin sections through erythrocytes and reticulocytes from adult hen, 4-day-old chicks and 17-day embryos. The results indicate differences in the packing of the molecules in chromatin and further show that the e-phase is quite likely to have a higher DNA to protein ratio than the o-phase. After uranyl-lead stain the visibility of the dot-dash pattern in cells from adult hen is relatively low due, we propose, to closer packing. In micrographs through condensed chromatin treated with uranyl-lead the eye selects out only the densely stained dots and dashes, width 17 nm. When erythrocyte chromatin is partially or completely disrupted in various ways, threads 25–30 nm then become visible. We propose that condensed chromatin in intact cells contains structural units which consist of a central element, width 17 nm previously referred to as the unit thread, forming the e-phase, surrounded by a cylindrical shell forming the o-phase. This socalled superunit thread is similar in width, about 25–30 nm, to that reported by other workers in preparations of chromosomes spread on water surfaces. The hypothesis therefore helps explain what appeared to be discrepancies in thread dimensions. Certain other ultrastructural features of erythrocyte nuclei are also reported which are either pertinent to the general aim of this study, namely the way in which nucleoproteins fold up in chromosomes, or to biochemical studies, to be reported shortly, in which attempts are made to locate the proteins removed from isolated erythrocyte nuclei during subsequent washing in salt solutions.
Inhibition of growth and dna synthesis in cell cultures by cyclic amp
Authors: Eker P.
Published: April 2021

Cyclic AMP (0·1 to 1 mM) was found to inhibit the growth of human liver cells in monolayer cultures. Significant amounts of degradation products were not detected in the medium indicating that the growth-inhibiting effect was associated with the intact cyclic nucleotide. DNA synthesis in the liver cell cultures, as measured by thymidine incorporation into acid-insoluble material, was markedly inhibited by cyclic AMP. RNA and protein synthesis were not significantly affected. Cyclic AMP induced a considerable increase in the cellular uptake of thymidine and uridine from the medium.

When the liver cells were incubated in medium containing radioactive cyclic AMP, no labelled cyclic AMP could be detected in the acid-soluble cell fraction by chromatographic analysis. It is suggested that cyclic AMP does not enter the liver cells, but that its action on growth and DNA synthesis is somehow mediated through an interaction with the cell surface.
Cell cycle kinetics and development of Hydra attenuata: III. nerve and nematocyte differentiation
Authors: David C. N. , Gierer A.
Published: April 2021

The differentiation of nerve cells and nematocytes in Hydra attenuata has been investigated by labelling interstitial cell precursors with [3H]thymidine and following by autoradiography the appearance of labelled, newly differentiated cells. Nematocyte differentiation occurs only in the gastric region where labelled nematoblasts appear 12 h and labelled nematocytes 72—96 h after addition of [3H]thymidine. Labelled nerves appear in hypostome, gastric region, and basal disk about 18 h after addition of [3H]thymidine. The lag in the appearance of labelled cells includes cell division of the precursor as well as differentiation since nerves and nematocytes have 2n postmitotic nuclear DNA content.

A cell flow model is proposed for interstitial cells and their differentiated products. Stem cells occur as single interstitial cells or in pairs. Per cell generation about 60 % of the daughter cells of stem cell divisions remain stem cells and about 40 % differentiate nerves and nematocytes. Nerves differentiate directly from stem cells in about 1 day. Nematocyte differentiation requires 5-7 days including proliferation of a cluster of 4, 8, 16 or 32 interstitial cells and differentiation of a nematocyst capsule in each cell. The numbers of interstitial cells and nematoblasts predicted by the cell flow model from the rates of nerve differentiation (900 nerves/day/ hydra), nematocyte differentiation (1760 nematocyte nests/day/hydia) and stem cell proliferation (stem cell cycle = 24 h), agree with the numbers of these cells observed in hydra. The number of stem cells per hydra is 3000-6000 depending on assumptions about the time of determination. The ratio of nematocyte to nerve differentiation averaged over the whole hydra is 3:1. In the hypostome and basal disk interstitial cell differentiation occurs exclusively to nerve cells while in the gastric region the ratio of nematocyte to nerve differentiation is about 7:1.
Limpet haemocytes: III. effects of cytochalasin b and colchicine on cell spreading and aggregation
Authors: Jones G. E. , Partridge T.
Published: April 2021

Limpet blood cells are suitable for the study of a number of interdependent features of cell behaviour; microspike formation, spreading and locomotion on a solid substrate, and aggregation. The effects of cytochalasin B (CCB) and colchicine on each of these activities is studied with a view (a) to determining with which functions these 2 reagents interfere; and (b) to gaining information on the relationships between these functions in normal cell behaviour.

Rapid spike formation and fast aggregation in a shaker system, which are normal features of the behaviour of amoebocytes in limpet blood or in seawater, are totally but reversibly inhibited by the presence of low concentrations of CCB (e.g. 0·5 μg/cm3). Similarly, the spreading of amoebocytes on to a solid substrate is greatly inhibited by CCB, both in rate and extent, and the rapid locomotion on a solid substrate of normal amoebocytes is completely abolished by CCB. The first observable effects of CCB on spread amoebocytes are loss of optical integrity of the spikes and retraction of parts of the anterior cell margin. The loss of distinctive cell shape, the inhibition of spreading on to a glass surface and the lack of motility on such a surface may all be immediate consequences of the disruption of spike structure.

CCB inhibits aggregation but does not disrupt preformed contacts between cells, which suggests that it acts on an early stage in the formation of stable contact rather than on the adhesiveness per unit area of contacting cell surface. A possible link between the effects of CCB on spikes and on aggregation is the proposal that low-diameter projections are needed to establish initial contact between cells. Alternatively, the spikes may be required for the rapid spreading of cells, not only on to glass but also over the surfaces of other cells, enabling them to increase their mutual contact area very rapidly and thus stabilize an adhesion.

Amoebocytes maintained in the presence of 50 μg/cm3 colchicine for a number of hours gradually lose their bipolar form and the entire cell margin becomes occupied by the spike-supported lamella which normally constitutes the leading edge of the cell. Thus microtubules are probably not necessary for the skeletal functions of spikes or for their roles in spreading and aggregation, but they do appear to play a part in the control of spike orientation.

Macrophages, cells lacking obvious spikes and showing little sign of bipolarity, appear unaffected by CCB or colchicine and spread normally on to a glass slide in the presence of either reagent. This, together with the limited spreading of amoebocytes in CCB, suggests that at least 2 distinct mechanisms may operate in the spreading of cells on to a solid substrate.
Contact inhibition of overlapping and differential cell adhesion: A sufficient model for the control of certain cell culture morphologies
Authors: Martz E. , Phillips H. M. , Steinberg M. S.
Published: April 2021

Using intuitive arguments, several investigators have proposed that the relative strengths of adhesion of cell to cell and of cell to substratum could determine whether or not monolayering – and specifically contact inhibition of cell overlapping – will occur. In the present communication, these ‘strengths of adhesion’ are given precise physical definitions, and the adhesive relationships which would promote spontaneous cell monolayering are rigorously derived, using the thermodynamic approach embodied in the differential adhesion hypothesis. This analysis verifies that contact inhibition of overlapping could, in principle, be a result solely of differential adhesion. In addition, it is demonstrated that for homogeneous populations of uniform cells cultured on a solid, uniform substratum, eleven distinct equilibrium configurations (cell population morphologies) could be generated merely by varying the relative values of cell-to-cell and cell-to-substratum adhesiveness. Most of these configurations have been observed previously in actual cell cultures.
Effects of hormones on the polysaccharide-synthesizing membrane systems of lettuce pith
Authors: Wright K. , Bowles D. J.
Published: April 2021

Changes have been induced in the polysaccharides laid down in the cell walls of lettuce pith by administration of the hormones auxin and zeatin. This polysaccharide derives from the membrane systems of the cells and radioactive precursor has been used to follow the accompanying changes which occurred in the polysaccharide contained within isolated Golgi and endoplasmic reticulum fractions. Zeatin-induced division and differentiation was accompanied by up to 12-fold increases in the amount of radioactivity in polysaccharide of isolated membrane fractions, and the pattern of distribution of label between the sugars of this polysaccharide was qualitatively different in the presence of zeatin. The change in this pattern was evident in the Golgi fraction at an earlier stage in the induction of the response than that in the endoplasmic reticulum.
Distribution of microtubules and microfilaments in developing vestibular sensory epithelium of mouse otocysts grown in vitro
Authors: Heywood P. , Van De Water T. R. , Hilding D. A. , Ruben R. J.
Published: April 2021

Otocysts explanted from 12th-gestation-day mice and maintained in organ culture under went a series of developmental changes which paralleled those that occurred in vivo and which resulted in the formation of a sensory epithelium of the vestibular type. At the time of explantation presumptive vestibular sensory epithelium consisted of cells that were undifferentiated, pseudostratified and rapidly proliferating. The only microtubules present were those of the mitotic apparatus. After 4 days of in vitro development cells comprising the presumptive vestibular sensory epithelium were less pseudostratified and more elongate; their nuclei had assumed a basal orientation and there was a clear marginal velum. Longitudinally oriented cytoplasmic microtubules were present at the apices of some cells; they were often grouped around a centriole which may have served as a nucleation centre for their assembly. After 7 days of in vitro development mitosis had ceased and supporting cells and innervated hair cells were present: both types of cells were always longer than they were broad and were often highly asymmetrical. Hair cells were flask- or columnar-shaped, with a nucleus situated in the basal third of the cell. Most mitochondria in hair cells were located in the apical third of the cell. The same distribution of mitochondria and nuclei was evident in supporting cells. Microtubules occurred throughout the length of the supporting cell and were always parallel to its longitudinal axis. In hair cells microtubules were more frequent than in supporting cells: the majority were parallel to the longitudinal axis of the cell but there were two exceptions. First, at the apex of hair cells some microtubules were oriented transversely and diagonally: these were probably involved in the development and maintenance of the constricted apex of these cells. Secondly, microtubules appeared to be randomly arranged in the narrow region of the cytoplasm between the ventral surface of the nucleus and the base of the hair cells. Microfilaments were confined to the basal third of hair cells where their orientation paralleled that of the microtubules. The possible functions of microtubules and microfilaments in the development of hair cells and supporting cells of the mouse vestibular epithelium are discussed.
Observations on the ultrastructure of the choanoflagellate Codosiga botrytis (Ehr.) saville-kent with special reference to the flagellar apparatus
Authors: Hibberd D. J.
Published: April 2021

The ultrastructure of the choanoflagellate Codosiga botrytis is described with particular reference to the flagellar appendages, the flagellar rootlet system, the transition zone, the basal body and accessory centrioles, and the stalk. The controversial early reports of flagellar appendages in this species have been confirmed and they have been detected in 2 further species, Salpingoeca frequentissima and Monosiga sp. The appendages consist of a delicate bilateral vane 2 am wide on either side of the axis, composed of extremely fine overlapping or interwoven fibrils.

The flagellar root system consists of a large number of radiating microtubules associated with bands of electron-dense material near the basal body; striated roots are absent. The microtubules extend from several separate foci, those in any one group originating near a composite electron-dense band, and for a distance of 300 nm from the basal body they are separated by blocks of interstitial material.

The flagellar basal body forms one of a diplosome pair of centrioles. The triplet microtubules of the accessory centriole are embedded in amorphous electron-dense material and the whole is enveloped in a sheath of similar appearance. The existence of a third centriole close to the diplosome pair is also reported. The relatively complex structure of the flagellar transitional zone is described.

The stalk is composed of a core of circular lacunae, which may or may not contain finger-like protoplasmic extensions of the posterior end of the cell, surrounded by a continuation of the sheath material which encloses the remainder of the protoplast. In the stalk only there is a further closely sheathing layer about 15 nm thick which is regularly striated, the spacing of the striations in shadowcast material and sections being about 3 times that measured by negative staining.

The structure of choanoflagellates differs widely from that of the algal class Chrysophyceae, the group in which they are included in some classifications, and from the remainder of the algae; they do not appear to have a place in either the algae or the plant kingdom. The structure of Codosiga botrytis is briefly compared with that of sponge choanocytes and collared cells in the Metazoa and some of the possible phylogenetic implications of this are indicated.
Linkage of the loci for glucose-6-phosphate dehydrogenase and for inosinic acid pyrophosphorylase to the x chromosome of the field-vole Microtus agrestis
Authors: Cook P. R.
Published: April 2021

It has been proposed that there are strong selective pressures which have acted during the evolution of mammals to conserve the linkage of genes on the X chromosome. If so, loci that are known to be X-linked in one mammalian species should be X-linked in others. The loci for glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49) and for inosinic acid pyrophosphorylase (E.C. 2.4.2.8) are known to be X-linked in a variety of mammals. The linkage of these loci to the X chromosome of the field-vole, Microtus agrestis, is indicated by the pattern of segregation of these loci in hybrid cells derived by fusion of mouse cells with vole lymphocytes.
Drosophila cell fusion induced by wheat germ agglutinin
Authors: Rizki Rose M. , Rizki T. M. , Andrews C. A.
Published: April 2021

The effects of wheat germ agglutinin on Drosophila embryonic cell lines growing on coverglasses was examined by scanning electron microscopy. At low concentrations of the lectin (5-10 μg/ml), cells spread against the glass surface and fused to form syncytia. At high concentration, damage to the cell surface was evidenced as extensive membrane shrivelling and loss of surface microfilaments. Fusion also occurred under these conditions. There was some indication that the morphology of cells in division remains undisturbed by wheat germ agglutinin. The coalescence of cells and morphologic distortion induced by wheat germ agglutinin were not inhibited by N-acctylglucosamine, the hapten inhibitor of the lectin, under the conditions utilized in this study.
Insect peripheral nerves: Accessibility of neurohaemal regions to lanthanum
Authors: Lane Nancy J. , Leslie R. A. , Swales Lesley S.
Published: April 2021

During incubation in vivo, exogenously applied ionic lanthanum comes to surround the numerous neurosecretory terminals which are found lying within or immediately beneath the acellular neural lamella ensheathing the nerves from fifth instar and adult specimens of Rhodnius prolixus. The lanthanum does not penetrate beyond the cellular perineurium, which completely surrounds the non-neurosecretory axons in these nerves and constitutes a form of ‘blood-brain barrier’. In some cases, however, lanthanum is found in the vicinity of a neurosecretory axon lying beneath the perineurium, where it can be assumed to have leaked in from the neurosecretory terminal lying free in the neural lamella.

When nerves are incubated in calcium-free media, regions with an attenuated perineurium become ‘leaky’, in that lanthanum is found lying in those extracellular spaces between axons and glia which lie immediately below the thin part of the perineurial layer. Bathing solutions made slightly hyperosmotic to the haemolymph with sucrose have no apparent disruptive effects on the barrier. When the tissues are incubated in more hypertonic solutions, the perineurial barrier becomes ‘leaky’ throughout, and tracer pervades beyond its cells into all the intercellular spaces between glia and axons.

The possible role of the zonulae occludentes in both the maintenance of the perineurial barrier and in the formation of interglial occlusions to local penetration of exogenous substances is considered.
Fine structure of the cytoplasm in salivary glands of simulium
Authors: Macgregor H. C. , Mackie J. B.
Published: April 2021

The salivary glands of 3rd or 4th instar larvae of Simulium mditifrons are about 5 mm long and up to 400 μ wide. They have a capacious lumen which is normally filled with secretion.

The apical (luminal) plasmalemma of the gland cells is thrown into numerous microvilli. The basal plasmalemma is usually straight but is infolded in places. The infoldings may be complex near to cell junctions. There is a thick, uniform basement membrane. Contact surfaces of adjacent cells often interdigitate. A septate junction extends inwards from the lumen for one-quarter the depth of the cells. Rough endoplasmic reticulum is distributed evenly throughout the cytoplasm. Many Golgi complexes with dark membrane-bounded granules are scattered throughout the cytoplasm. Solitary granules, often more than 1 μ in diameter, lie in the apical cytoplasm, especially near the apical border of the cell. These granules resemble the larger Golgi granules and the contents of the lumen. Solitary granules consisting of 2 components have been seen in various stages of passage through the cell membrane. The 2 components are present in roughly constant proportions and can be identified in the larger Golgi granules and in the secretion in the lumen. The nucleus is spherical. The nuclear envelope is smooth in the larger cells of a gland but may be folded in the smaller cells. There are 80–100 pores/μ2 of nuclear envelope. Each pore appears to have a small granule at its centre. Microtubules, about 180 A thick, are numerous in the apical cytoplasm, particularly near the luminal border. Tubules which lie deep in the cytoplasm are flanked by a clear area 100–200 Å wide.

The fine structure of a salivary gland cell of Simulium appears to indicate that the major components of the salivary secretion are synthesized in association with the ribosomes on the rough endoplasmic reticulum, concentrated in the Golgi regions, formed into secretion granules, and passed out of the cell into the lumen of the gland by reverse phagocytosis.
The reactivation of the red cell nucleus
Authors: Harris H.
Published: April 2021

When the nucleus of a mature hen erythrocyte is introduced into the cytoplasm of a HeLa cell it resumes the synthesis of RNA and DNA. This reactivation of the red cell nucleus in the heterokaryon is associated with a marked increase in its volume. There is a direct relationship between the volume of the nucleus and the amount of RNA which it makes. The nuclear enlargement is not a consequence of increased RNA synthesis, or of DNA synthesis : enlargement is the primary event, and the increase in RNA synthesis is determined by it. The possibility is considered that changes in nuclear volume may regulate not only the amount of RNA made in the nucleus but also the areas of chromatin on which it is made.
Mast cell proliferation in adult rats
Authors: Blenkinsopp W. K.
Published: April 2021

Mast cell proliferation was investigated in adult male rats using continuous infusions of tritiated thymidine to label deoxyribonucleic acid. The results indicate that the total number of mast cells increases as body weight increases (though at a lower rate) and that there is no mast cell turnover in the sense of discard and replacement. No evidence was found of mast cell formation from ‘stem’ cells.
The influence of indol-3yl acetic acid and sugar on the pattern of induced differentiation in plant tissue culture
Authors: Jeffs R. A. , Northcote D. H.
Published: April 2021

The induction of vascular differentiation in callus tissue of Phaseolus vulgaris by the application of indol-3yl acetic acid (IAA) and sucrose has been studied by cytological methods. The application of radioactive IAA and sucrose in the induction experiments has enabled the concentration of these substances, which move through the callus tissue mass by simple diffusion, to be estimated.

Various monosaccharides, disaccharides, trisaccharides and sugar derivatives have been used instead of sucrose in order to study the biological role of the sugar molecule in the induction process. The results indicate that sucrose and certain other α-glucosyl disaccharides have a specific action in inducing differentiation into nodules containing xylem, phloem and meristematic activity.

Evidence is also presented to show that possibly only very young cells, immediately following division, can be induced to differentiate.
Cytoplasmic streaming and microtubules in the coenocytic marine alga, Caulerpa prolifera
Authors: Sabnis D. D. , Jacobs W. P.
Published: April 2021

Two distinct patterns of cytoplasmic streaming in the leaf of Caulerpa prolifera are described. Broad, longitudinally running, two-way streams are restricted to the endoplasm of one leaf surface. Also present are large numbers of narrow, two-way streams that coil helically through-out the endoplasm surrounding the central vacuole. Numerous unique bundles of aggregated, evenly spaced, oriented microtubules are distributed within the inner cytoplasm some distance from the cell wall. Cortical microtubules, as described for other plant material, have been only very infrequently encountered in Caulerpa and appear to be sparsely distributed. Apart from the prominent bundles of oriented microtubules, no other significant ultrastructural differences were noted between the stationary ectoplasm and streaming endoplasm. The possible cyto-skeletal role of the oriented microtubules in the development and maintenance of asymmetries in organ differentiation is discussed in relation to their direct or indirect influence on the directional migration of cytoplasmic components.
Sites of protein synthesis in nucleoli of root meristematic cells ofAllium cepaas shown by radioautography with [3H]arginine
Authors: Chouinard L. A. , Leblond C. P.
Published: April 2021

The interphase nucleolus in root meristematic cells of Allium cepa may be divided into four regions, three of which are always present: the fibrillar, granular and lacunar regions, while the fourth or vacuolar region may be missing. The sites of protein synthesis in nucleoli were investigated by means of light and electron-microscope radioautography after a 5-min immersion of the roots in a solution of [3H]arginine.

The radioautographs of interphase nucleoli showed many silver grains over both the fibrillar and the granular regions. Occasional silver grains were also recorded over, or close to, the lacunar regions, but none were over the vacuolar regions. A 15-min chase period did not change the radioautographic pattern. It is concluded that the three permanent regions of the interphase nucleoli, namely the fibrillar, the granular and the DNA-containing lacunar regions, are sites of protein synthesis.
Photoinduction of plastids and of chlorophyll in a Chlorella mutant
Authors: Bryan G. W. , Zadylak Arlene H. , Ehret C. F.
Published: April 2021

Stage-characterized populations of dark-grown heterotrophs of an asexually reproducing, unicellular alga, Chlorella mutant C-10, have been studied to determine light-induced ultra-structural changes in plastids and in chlorophyll synthesis. C-10 requires light to synthesize chlorophyll and to produce a photosynthetically potent chloroplast. Thylakoid development is followed through a series of stages from prethylakoidal tubules to primary thylakoids which produce blebs. The blebs expand and slide over the primary thylakoid, and then form a secondary thylakoid; the process continues until the characteristic stacks of tertiary thylakoids are present in the mature chloroplast. A dramatic decrease in the rate of chlorophyll synthesis (‘ early-rate-decline’) is observed approximately 1 h after the onset of induction. This early-rate-decline correlates with the appearance of blebs on the primary thylakoid. Twelve hours after the onset of induction, the photosynthetically impotent proplastid develops into a mature plastid containing stacks of disc-like thylakoids. The application of chloramphenicol, puromycin and actinomycin D suggests that the early-rate-decline is associated with an insufficient rate of synthesis of the holochrome proteins.
The structure and development of the spermatozoon of Aspiculuris tetraptera (nematoda)
Authors: Lee D. L. , Anya A. O.
Published: April 2021

The mature spermatozoon of Aspiculuris tetraptera has a distinct head-like structure and a tail-like structure. The tail contains a long mitochondrion which extends from within the head almost to the posterior end of the tail. Two bundles of microtubules oriented parallel to the longitudinal axis also extend the length of the tail on either side of the mitochondrion. The head of the spermatozoon contains abundant cytoplasm but no nucleus. The DNA of the spermatozoon is in the tail-like structure where it is associated with an electron-dense sheath and the two bundles of microtubules. The head can put out pseudopodia and it is suggested that they may be involved in locomotion or may be acrosome-like. The tail, which structurally resembles a motile appendage, has not been seen to move. This spermatozoon differs markedly in its structure from all others which have been described.
Cytoplasmic microtubules in the leaf glands of Phaseolus vulgaris
Authors: O’Brien T. P.
Published: April 2021

Preliminary observations on the fine structure of the club-shaped glands on Phaseolus vulgaris leaves are reported. The perinuclear cytoplasm of the apical cells of these glands contains an abundance of microtubules. These occur either as aggregates of 2–8 or more tubules, or they may be organized around a central core of material to form a fibre-like structure. The cells also contain cortical microtubules and are rich in rough endoplasmic reticulum and dictyosomes. The nuclei of these cells also contain a proteinaceous fibre, visible in the light microscope. The possible significance of these structures is discussed in relation to cytoplasmic streaming, maintenance of cellular asymmetry, and reaction to virus infection.
An electron-microscope study of subcellular fractions of Octopus brain
Authors: Jones D.G.
Published: April 2021

Using subcellular fractionation techniques the primary fractions (P1 P2 and P3) have been prepared from homogenates of the supraoesophageal lobes (brain) of Octopus vulgaris. A morphological study of the fractions was made, particular emphasis being placed upon the synapto-somes (nerve-ending particles), and the agranular and granular vesicles they contain. The acetylcholine levels in the fractions were determined by bioassay.

Synaptosomes and isolated mitochondria are present in all the fractions examined. In addition, the remains of blood vessels are found in P1 nuclei, vesicular structures and lamellated bodies in Px and P2, and microsomes in P3 and the final supernatant. The synaptosomes are similar to those isolated from mammalian nervous tissue. The remains of the post-synaptic endings are seen as recognizable processes around their periphery. They are more extensive than the post-synaptic membranes of mammals, and thickenings on them are seen in tissue stained with phosphotungstic acid. The number of mitochondria outside synaptosomes varies with the fixative used, being far greater with formalin than with permanganate. The agranular vesicles vary in diameter from 150 to 1200 Å; over 70 % of them are between 250 and 500 Å. In formalin-fixed preparations, the synaptosomes can be separated into two types: those containing mainly rounded vesicles, and those with many ellipsoidal vesicles. About 4 % of all the vesicles are granular; they have an average diameter of 720 Å, with few of them measuring over 1000 Å.

Acetylcholine is distributed throughout the fractions, the highest level being in P2, with appreciable levels in the others. The total recovered for the combined fractions of the supra-oesophageal lobes was 104·6 mμmole/g tissue. For the combined fractions of the optic lobes, which are also rich in synaptosomes, the total was 32·3 mμmole/g. tissue.
The ultrastructure of the olfactory epithelium of the lamprey Lampetra fluviatilis
Authors: Thornhill R. A.
Published: April 2021

In common with those on other vertebrate olfactory receptors, the short cilia on the sensory cells are arranged in a ring on the tip of the dendrite. The cilia have two distinct regions—a proximal region, having a typical ciliary structure, and a distal region in which only single peripheral fibres are present. One or more basal feet are present, projecting from the basal body of the olfactory cilium. A 40–50 Å subunit structure in the peripheral fibres of the olfactory cilium is described. Numerous microtubules are present in the dendrite and in the basal cells, but are absent from the supporting cells. The supporting cells contain an extensive system of tonofilaments. Junctional complexes are situated between the plasma membranes at the apex of supporting cells and between supporting cells and neurons. Degenerating neurons and supporting cells are present as well as possible regenerating cells. On the basis of this evidence it is postulated that limited cell replacement may occur. It is also postulated that the arrangement of olfactory nerve fibres within the Schwann cell may allow some processing of information to take place at this level by means of electrotonic field effects.
Similarities of the golgi apparatus membrane and the plasma membrane in rat liver cells
Authors: Hodson S. , Brenchley G.
Published: April 2021

A Golgi apparatus-rich fraction and a plasma membrane-rich fraction were isolated from a common homogenate of rat liver. Their respective buoyant densities, appearances in the electron microscope and 5′-nucleotidase and UDP-galactose ovalbumin galactosyltransferase activities were in accord with published data on separately isolated Golgi apparatus-rich and plasma membrane-rich fractions. Contamination by endoplasmic reticulum and mitochondria was low.

Gel electrophoresis of the membrane proteins of the Golgi apparatus-rich and plasma membrane-rich fractions (separately and mixed) showed a close similarity. After Neville’s demonstration that electrophoretic patterns of membrane protein subunits from different subcellular fractions are easily distinguishable, the present work demonstrates an unusually close relationship between the Golgi apparatus membrane and the cell membrane. It is possible that membrane similarity may be mediated by the transfer of membrane-bound vesicles from the Golgi apparatus to the cell membrane.
Template activity of unfixed metaphase chromosomes
Authors: Cohen B. B. , Deane D. L.
Published: April 2021

Unfixed metaphase and non-metaphase cells were tested for their template activity with RNA polymerase. A device was used which disrupts the cell membrane by centrifugation, and which also ensures that the cells do not continue with their mitotic cycle during the transcription process. The template activity of acid/methanol fixed cells was also tested.

None of the unfixed metaphase cells transcribed RNA whereas most of the non-metaphase cells did. In contrast, using fixed cells both classes of cells were transcribed equally well and to a much greater extent. It was concluded that metaphase chromosomes in vivo cannot act as templates for RNA synthesis.
Regulation of interstitial cell differentiation in Hydra attenuata: I. homeostatic control of interstitial cell population size
Authors: Bode H. R. , Flick Kristine M. , Smith G. S.
Published: April 2021

Mechanisms regulating the population size of the multipotent interstitial cell (i-cell) in Hydra attenuata were investigated. Treatment of animals with 3 cycles of a regime of 24 h in 10−2 M hydroxyurea (HU) alternated with 12 h in culture medium selectively killed 95—99% of the i-cells, but had little effect on the epithelial cells. The i-cell population recovered to the normal i-cell: epithelial cell ratio of 1:1 within 35 days. Continuous labelling experiments with [3H]thymidine indicate that the recovery of the i-cell population is not due to a change in the length of the cell cycle of either the epithelial cells or the interstitial cells.

In control animals 60% of the i-cell population undergo division daily while 40% undergo differentiation. Quantification of the cell types of HU-treated animals indicates that a greater fraction of the i-cells were dividing and fewer differentiating into nematocytes during the first 2 weeks of the recovery after HU treatment. Therefore, the mechanism for recovery involves a shift of the 60:40 division: differentiation ratio of i-cells towards a higher fraction in division until the normal population size of the i-cells is regained. This homeostatic mechanism represents one of the influences affecting i-cell differentiation.
The influence of gibberellic acid and abscisic acid on cell and tissue differentiation of bean callus
Authors: Haddon Lindsay , Northcote D. H.
Published: April 2021

Bean callus was induced to form roots (tissue differentiation) and vascular nodules (cell differentiation) by lowering the ratio of auxin to cytokinin in the growth medium. Both types of differentiation were inhibited by the addition of abscisic acid (at concentrations greater than 1 μM) to induction medium. Initiation of differentiation was inhibited, but its subsequent development was not, and the inhibition was not affected by the addition of gibberellic acid. Addition of gibberellic acid (GA) alone to induction medium stimulated tissue differentiation, although cell differentiation was unaffected (30 μM GA) or inhibited (45 μM GA) and its onset was delayed at both concentrations. Root initiation was also stimulated by gibberellic acid (0·1-45 μM) at an auxin-to-kinin ratio 10 times that normally optimal for cell differentiation.

The phenylalanine ammonia lyase (PAL) activity of the calluses was closely correlated with the amount of cell differentiation which had occurred, and measurement of this confirmed that gibberellic acid delayed the initiation of cell differentiation. The increase and subsequent decline of PAL and βI → 3 glucan synthetase activities, normally induced by transfer to induction medium, was abolished by abscisic acid. Addition of gibberellic acid did not affect the βI → 3 glucan synthetase activity.
Two ultrastructurally distinct tubulin paracrystals induced in sea-urchin eggs by vinblastine sulphate
Authors: Starling D.
Published: April 2021

Two types of ultrastructurally distinct tubulin paracrystals have been induced in sea-urchin eggs with vinblastine sulphate (VLB) under different sets of conditions. One type of paracrystal appears to consist of hexagonally-close-packed microtubules and closely resembles paracrystals present in mammalian cells treated with vinblastine or vincristine sulphate, but not previously reported in sea-urchin eggs. The other type is also made up of tubulin subunits, but these do not seem to have polymerized into microtubules.

Both types of paracrystal are induced in sea-urchin eggs in the presence of VLB at a time when tubulin subunits would not normally polymerize. Possible mechanisms for tubulin activation and the induction of paracrystal formation are discussed in respect to the available information on the binding sites of the tubulin subunits.
The effects of mitotic inhibitors on the structure of vinblastine-induced tubulin paracrystals from sea-urchin eggs
Authors: Starling D.
Published: April 2021

Vinblastine sulphate (VLB) is known to induce in vivo formation of tubulin paracrystals in sea-urchin eggs. Corresponding paracrystals have been prepared in the presence of both vinblastine sulphate and other mitoclasic agents. Careful standardization of conditions was required to restrict the formation of alternative forms of the paracrystals induced by vinblastine alone. Comparisons were made between preparations in terms of paracrystal shape, size, proportion of eggs containing paracrystals, number per egg and their relative times of first appearance. A correlation between such properties was established. Comparison of paracrystals at the ultrastructural level showed them all to be similar regardless of the drugs present during their formation. The implications of tubulin polymerization in the presence of mitoclasic agents are discussed and mechanisms for paracrystal enhancement by combinations of such drugs are suggested. Some similarities of paracrystal and microtubule seeding are discussed together with the activation of tubulin in the pool.