bluuebunny/crossref_metadata_2025 huggingface dataset:
Proportional regulation of body form and cortical organelle pattern in the ciliate Dileptus
Authors: Golinska Krystyna , Kink Jolanta
Published: April 2021

Morphometric and ultrastructural studies of shape and pattern regulation were performed on Dileptus anser. In this cihate 2 body regions can be distinguished: proboscis and trunk. When a large portion of the trunk is excised, shape regulation occurs and the proper proboscis/trunk ratio is restored through elongation of the remnant of the trunk and shortening of the proboscis. When there is nothing but proboscis left, the trunk is formed from the proximal portion of proboscis and again the right proportion is restored.

Regulation of the ciliary pattern is based mainly on resorption of some ciliary elements. The resorption of somatic ciliature is especially intense within narrowing regions, where otherwise overcrowding of cilia would occur. The resorption of oral ciliature was found to occur within an area located at the apex of the proboscis. Oral structures when damaged by cutting may be repaired in situ. Changes in the microfibrillar system of the cell were found during regulation of shape of the posterior region of the cell, as well as during regulation of size of oral structures.

Regulatory processes in Dileptus are compared to those known for other ciliates, and possible differences between the regulation of shape and the regulation of pattern are discussed.
Extensive pairing of the xy bivalent in mouse spermatocytes as visualized by whole-mount electron microscopy
Authors: Tres Laura L.
Published: April 2021

Autosomes and sex chromosomes of mouse spermatocytes were examined during zygotene, pachytene, and diplotene by a whole-mount electron-microscope technique after cell dispersion in a detergent solution (Nonidet-P40). Zygotene, pachytene, and diplotene stages can be adequately identified in the preparations. Thus, asynchronous side-by-side pairing of homologous autosomes, some of them displaying attached nucleoli, defines zygotene. Pachytene is identified by complete pairing of homologues. Diplotene is characterized by disjunction of bivalents (autosomes and sex chromosomes), lack of autosomal-attached nucleoli, divergent expansions observed at lateral element endings of disassembled synaptonemal complexes, end-to-end association of the XY pair and well defined outward deformations (‘bulges’) along sex chromosomal axial cores. X and Y chromosomes display at pachytene an extensive side-by-side pairing segment which decreases in length as meiotic prophase advances. Each sex chromosomal axial core appears double and is formed by close apposition of 2 nearly parallel elements displayed separately along the entire length of the chromosomal core. This double structural feature suggests that each sex chromosomal axial core is presumably composed of 2 chromatid axial cores, each of which, in turn, constitutes the respective lateral elements of short synaptonemal complexes observed at the unpaired segment.
Analysis of contractile vacuole pore morphogenesis in Tetrahymena Pyriformis by 180° rotation of ciliary meridians
Authors: Ng Stephen F.
Published: April 2021

The contractile vacuole pores (CVPs) in Tetrahymena pyriformis are usually found to the left of ciliary meridians (CVP meridians). When the CVP meridians are experimentally rotated 180° (‘inverted’), the CVPs are now found to the right of the rotated CVP meridians. In other words, the CVP is almost invariably found on the same side with respect to the CVP meridian. Thus, the 2 sides of the CVP meridian have different morphogenetic properties and such differences are determinative in the asymmetrical fine-positioning of the CVP.

The number of CVPs per animal and their general placement on the animal (i.e. with which ciliary meridians the CVPs are associated) are known to be a function of the total number of ciliary meridians possessed by the animal. Rotation of the CVP meridians affects both the number of CVPs per animal and their general placement. The specificity of such effects appears to depend on whether both, or one, or which one, of the CVP meridians is rotated. Rotation of ciliary meridians may be used as a tool in analysing the mechanism determining the number of CVPs per animal and their general placement.
Studies of anionic sites on the cell surface of the amoeba Naegleria gruberi using cationized ferritin
Authors: King C. A. , Preston T. M.
Published: April 2021

Interaction of cationized ferritin with the anionic groups on the cell surface of Naegleria was studied using transmission electron microscopy in conjunction with fluorescence microscopy. Most of the experiments involved the use of fluorescein-labelled cationized ferritin (FITC-CF) incubated with living amoebae. Initially the FITC-CF was located over the posterior two-thirds of the amoebae but the label was rapidly redistributed to form a cap at the posterior end in the region of the uroid; frequently this cap was shed. Pinosomes containing FITC-CF were clearly visible within the amoebae. Amoebae prefixed in glutaraldehyde were uniformly stained and did not show redistribution of the label. Exposure of live amoebae, previously incubated with cationized ferritin and allowed to cap, to fresh FITC-CF failed to produce fluorescent staining of the general cell surface, i.e. depletion of binding sites had occurred. The binding of the FITC-CF was not affected by pretreatment of the amoebae with neuraminidase or pronase. The possible nature of the anionic sites on the membrane is discussed.
Membranes in lupin root nodules: I.the role of golgi bodies in the biogenesis of infection threads and peribacteroid membranes
Authors: Robertson J.G. , Lyttleton P. , Bullivant S. , Grayston G. F.
Published: April 2021

The process of infection of lupin nodule cells by rhizobia was examined using thin-section and freeze-fracture electron-microscopic techniques to characterize the properties of different membranes and to establish relationships between them. The membranes of the Golgi bodies and the endoplasmic reticulum stained with zinc iodide-osmium tetroxide but not with phos-photungstic acid or silver. By contrast the infection thread membranes, peribacteroid membranes, plasma membranes and membranes of cytoplasmic vesicles did not stain with zinc iodide-osmium tetroxide but stained with phosphotungstic acid and silver. The peribacteroid membranes and plasma membranes are, however, different from each other since the particle density on the E face of freeze-fracture replicas of plasma membranes was twice that on the E face of the peribacteroid membranes.

An examination of the tips of the infection threads in the cytoplasm of the plant cells, showed that the rhizobia bud off from the infection threads enclosed in the infection thread membranes. The rhizobia continue to divide still surrounded by membranes of plant origin, namely the peri-bacteroid membranes. Cytoplasmic vesicles are observed in both thin-section and freeze-fracture preparations of nodule tissue closely associated with, and apparently produced by, Golgi bodies. Formation of the walls and membranes of the infection threads and of the peribacteroid membranes involves fusion of the cytoplasmic vesicles with these membranes. It is proposed that the process of infection of plant cells in lupin nodules involves a change in the function of the Golgi body system for the biogenesis of plant cell walls and plasma membranes to include the synthesis of the walls and membranes of the infection threads and also the peribacteroid membranes.
Ultrastructural localization of cationic proteins in human polymorphonuclear leukocytes
Authors: Brown William J. , Wood Eunice M.
Published: April 2021

The present investigation is concerned with the use of the post-formalin ammoniacal silver reaction to detect the arginine-rich cationic proteins in human polymorphonuclear leukocytes at the ultrastructural level. These proteins appear to function as neutral proteases in antibacterial action and as mediators of inflammation. Originally, the ammoniacal silver reaction relied upon primary fixation in dilute formalin which prevented optimum fixation of tissues. This study shows that by using the proper sequence of glutaraldehyde fixation and the ammoniacal silver solution in conjunction with osmium tetroxide treatment, better fixation of the tissue and localization of the ammoniacal silver reaction can be achieved. Also, the ammoniacal silver reaction in human polymorphonuclear leukocytes is exclusively located in the large, crystalline cytoplasmic granules of eosinophils. All other cytoplasmic granules of neutrophils, eosinophils, and basophils were found to be devoid of the ammoniacal silver reaction product. These results are contrary to previously published experimental data. Possible explanations for this discrepancy are discussed.
Supercoiling of dna and nuclear conformation during the cell-cycle
Authors: Warren A. C. , Cook P. R.
Published: April 2021

When cells are lysed in solutions containing high concentrations of salt and a non-ionic detergent, structures are released which retain many of the morphological features of nuclei. These nucleoids contain superhelical DNA but are depleted of nuclear protein. We have analysed DNA conformation in nucleoids derived from HeLa cells synchronized at different stages in the cell cycle. The gross differences in nuclear morphology seen during the cell cycle are reflected in the morphology of the nucleoids; for example, the individual chromosomes of mitotic cells remain identifiable and aggregated within the mitotic nucleoid. The sedimentation rate of nucleoids in sucrose gradients reflects the gross nuclear morphology; the small S-phase nucleoids sediment 9 times faster than the large mitotic nucleoids. Despite these large differences at the gross level of organization, both the degree of supercoiling and the size of the units in which supercoiling is maintained are roughly similar in the nucleoids derived from cells in the different phases. The protein content of the various nucleoids is also very similar. Like the nucleoids made from randomly growing cultures of cells, mitotic nucleoids are excellent templates for the RNA polymerase of Escherichia coli.
Cellular actin and junction formation during re aggregation of adult rat hepatocytes into epithelial cell sheets
Authors: Miettinen A. , Virtanen I. , Linder E.
Published: April 2021

Aggregation of adult rat hepatocytes, isolated by the collagenase perfusion technique, was studied by ultrastructural methods and the indirect immunofluorescence technique using anti-actin antibodies. In a primary culture the cells rapidly made contact with each other by filopodia-like structures, as seen by scanning electron microscopy. In a few hours this led to stable adhesion of the cells. No identifiable junction formation occurred during the first 17 h in culture. Within 48 h the cells had formed epithelial cell sheets with junctional complexes consisting of tight junctions, bile canaliculus-like structures and zonula adhaerens-type junctions.

The distribution of cytoplasmic actin fluorescence remained homogeneous in the contacting cells during the first 24 h in culture, as seen with anti-actin antibodies by the indirect immunofluorescence technique. The first short, fluorescent actin filaments appeared in the periphery of the developing lamellipodia of the spreading cell islands. In organized epithelial cell sheets these filaments were seen as long fibres ending at the perinuclear region of the marginal cells. In the submarginal cells fluorescent actin fibres were distinct at the junctional regions of the cells. This filamentous fluorescence seemed to extend throughout the entire cell sheet in an organized manner and correspond to the apical layer of parallel microfilaments seen in transmission electron microscopy. Our results suggest that filamentous actin plays a role in the contact-induced spreading of the cells and in the maintenance of the internal organization of the epithelial cell sheets.
Insect axopods
Authors: Bradley Timothy J. , Satir Peter
Published: April 2021

Using the electron microscope we have found axopods, a cell organelle previously undescribed in multicellular animals, in the lower Malpighian tubule of the insect, Rhodnius prolixus. The axopods, which are 0 · 2 to 0 · 8 μm in diameter and 10 or more μm in length, derive from the luminal surface of the tubule and contain an array of 1 to about 46 microtubules each. These microtubules arise within the cell near the cell junctions or near clumps of mitochondria.

Uric acid crystals which occur naturally in the lower tubule have been observed to move down the tubule under experimental conditions where peristalsis and fluid secretion can be ruled out. We suggest that the axopods are motile and serve to transport the crystals along the narrow tubule lumen. Since cilia are not found on somatic cells of arthropods, we suggest that axopods have evolved in the lower tubule to perform a function analogous to a ciliated epithelium in other animals.
The role of algal antigenic determinants in the recognition of potential algal symbionts by cells of Chlorohydra
Authors: Pool R. R.
Published: April 2021

Algal cells grown in the green hydra Chlorohydra viridissima were shown to possess characteristic antigenic determinants not found in algae cultured in vitro. These antigenic determinants, including those localized on the algal cell surface, were shown to be responsible for the phagocytic recognition of potential algal symbionts by digestive cells of Chlorohydra. The results of this study indicate the existence of two systems governing phagocytosis in Chlorohydra, one specific for algal cells grown in hydra, another governing the uptake of other particles by the hydra digestive cells.
The association of chloroplast dna with photosynthetic membrane vesicles from spinach chloroplasts
Authors: Rose R. J.
Published: April 2021

To investigate the association between chloroplast DNA (cp DNA) and the photosynthetic membranes of spinach chloroplasts, previously suggested by electron-microscope autoradiography, use has been made of vesicles formed by isolating chloroplasts directly in 3·5 Mm Mg2+. These chloroplast vesicles consist of photosynthetic membranes, separate from chloroplast envelope membranes. Light and electron microscopy confirm that the vesicles consist of swollen stroma lamellar membranes with some peripheral grana lamellae that are much less swollen. Vesicles labelled with [3H]thymidine were obtained from [3H]thymidine-labelled chloroplasts from spinach disks in which chloroplast division and cp DNA synthesis and segregation were occurring. The chloroplast vesicle fraction retains about 45 % of the cp DNA as determined by liquid scintillation counting. The cp DNA-membrane associations do not appear to be dependent on the presence of Mg2+. The chloroplast vesicles can be autoradiographed for light microscopy if they are fixed in formaldehyde and no centrifugation steps are used. Lightmicroscope autoradiography is consistent with a preferential labelling of grana as opposed to stroma membranes, and long lengths of membrane are labelled. It appears that in spinach chloroplasts cp DNA is associated with granal thylakoids at intervals along the length of a continuous photosynthetic membrane system. Such an organization would facilitate cp DNA segregation during chloroplast division.
Marginal bands in camel erythrocytes
Authors: Cohen William D. , Terwilliger Nora Barclay
Published: April 2021

The elliptical, anucleate erythrocytes of camels have been examined for the presence of marginal bands and their constituent microtubules. Lysis of erythrocytes under microtubulestabilizing conditions readily revealed marginal bands in at least 3 % of the cells, as observed by phase-contrast and darkfield light microscopy. Microtubules plus a marginal bandencompassing network of material are visible in lysed cell whole mounts with transmission electron microscopy. Marginal band microtubules are also evident in electron micrographs of thin-sectioned camel erythrocytes identifiable as reticulocytes on the basis of submaximal electron density (reduced haemoglobin iron content) and presence of polysomes. The results suggest that marginal bands may be involved in morphogenesis of camel erythrocytes but are not required for maintenance of their ellipticity after cells are fully differentiated.
Blue light-induced, intrinsic vacuolar fluorescence in onion guard cells
Authors: Zeiger Eduardo , Hepler Peter K.
Published: April 2021

Guard cells of onion irradiated with broad-band blue light display a green intrinsic fluorescence. The fluorescence has been found in eleven species of Allium, but it has not been observed in any other monocot or dicot examined. The fluorescence occurs only in guard cells and is absent in neighbouring epidermal cells. During development it is first apparent in guard mother cells soon after the asymmetric division. Microscopic observation reveals that the fluorescence is associated with the vacuole and examination of vacuoles isolated from guard cell protoplasts suggests that it may be localized on the tonoplast. Microspectrophotometric analysis of single cells reveals an emission peak at around 520 nm. Our results are consistent with the view that this blue light receptor is a flavin or flavoprotein and that it might be related to the blue light-enhanced stomatal opening observed in onion.
Colchicine-induced paracrystals in the tapetum of wheat anthers
Authors: Bennett M. D. , Smith J.B.
Published: April 2021

Prolonged colchicine treatment induced the formation of numerous cytoplasmic para crystals in tapetal cells of wheat anthers containing germ line cells at pre-meiotic mitosis or early pre-meiotic interphase. Such paracrystals were up to 8 μm long and 0·7 μm in diameter, and filled up to about 8% of the volume of the cytoplasm. Paracrystals were not bounded by a membrane. A paracrystal consisted of tubules running in parallel with its long axis. Paracrystals cut at right angles to their long axes revealed hexagonal arrays of circles with a maximum diameter of about 35 nm and electron-dense walls 6-7 nm in thickness. Similar paracrystals were not seen in any cell type of untreated anthers, or in germ line cells of treated anthers, containing stages between pre-meiotic mitosis and first metaphase of meiosis inclusive. The possible significance of the paracrystals in relation to the function of the tapetum is discussed.
Specific end-to-end attachment of chromosomes in Ornithogalum virens *
Authors: † Terry Ashley
Published: April 2021

C-banding of nonhomologous chromosomes in haploid generative nuclei of Ornithogalum virens (n = 3) reveals a high degree of specificity with respect to end-to-end connexions. The centromeric end of chromosome 2 preferentially associates with the centromeric end of chromosome 3 and the telomeric end of chromosome 3 associates preferentially with the telomeric end of chromosome 1. This same association of nonhomologous chromosomes persists in prophase nuclei of diploid root tips. In addition, the telomeric ends of the 2 chromosome 2s are connected to one another as are the centromeric ends of the chromosome is. This results in a ring of chromosomes in which homologues lie opposite one another. Centromeric ends lie on one side of the nucleus and telomeric ends on the other. It is proposed that this specific association of chromosome ends reflects an order which was probably established at the preceding anaphase or telophase and which persists throughout interphase. The suggestion is made that the proximity of homologous ends and consequently homologous alignment may facilitate initiation of pairing at meiosis.
Isolation of a residual protein structure from nuclei of the myxomycete Physarum polycephalum
Authors: Mitchelson K. R. , Bekers A. G. M. , Wanka F.
Published: April 2021

A nuclear framework structure has been obtained from isolated interphase nuclei of Physarum polycephalum by extraction with 2·5 M NaCl and subsequent digestion with DNase. Wholemount electron micrographs showed a nuclear lamina containing residual pore structures associated with the fibrous internal matrix. The matrix was continuous with fibrillar remnants of the nucleolus. The structure was shown to consist of 2 major polypeptides of 23000 and 36 500 Daltons as well as 30 to 40 minor polypeptides of various molecular weight classes. The 2 major polypeptides were also prominent in preparations of the residual nucleolar material, suggesting that matrix proteins are common to both structures. The predominance of low-molecular-weight polypeptides in Physarum nuclear matrix suggests that there may be significant differences in composition of nuclear structural proteins between lower and higher eukaryotes.
Immunoelectron-microscopic studies of endoplasmic reticulum-golgi relationships in the intracellular transport process of lipoprotein particles in rat hepatocytes
Authors: Matsuura Shiro , Tashiro Yutaka
Published: April 2021

Endoplasmic reticulum (ER) –Golgi relationships in the intracellular transport process of secretory proteins in rat hepatocytes have been studied using lipoprotein particles as a marker for the secretory protein and cytochrome P-450 as a marker enzyme for the ER membranes. Ferritin immunoelectron-microscopic observation revealed that, while almost all the microsomal vesicles derived from ER membranes are heavily labelled with ferritin anti-cytochrome P-450 antibody conjugates, labelling of the small peripheral vesicles containing lipoprotein particles, the stacks of Golgi saccules, especially the outermost saccule which is sometimes fenestrated, condensing vacuoles in the trans-Golgi region and the secretion droplets of lipoprotein were scanty and at the control level. Such a characteristic pattern of labelling was especially evident when these structures were prepared from phenobarbital-treated rats.

These findings indicate that the membranes of the small peripheral vesicles do not contain cytochrome P-450 and that the cytochrome is probably not transferred to Golgi saccules in the transport process of lipoprotein from ER to Golgi. It is suggested, therefore, that the small peripheral vesicles are formed by budding of the special regions of ER membrane where microsomal marker proteins such as cytochrome P-450 are excluded and the membrane proteins destined to the Golgi complexes are clustered.

It is also shown that lysosomal membranes are not labelled with the anti P-450 antibody conjugates.
Rhizoplast and rootlet system of the flagellar apparatus of Chlamydomonas moewusii
Authors: Katz Kenneth R. , McLEAN Robert J.
Published: April 2021

The ultrastructure of the flagellar apparatus of Chlamydomonas moewusii was examined in detail. Two rhizoplasts were found associated with the basal bodies of this biflagellate and were observed to extend to the central area of the cell. A segment of smooth endoplasmic reticulum ran parallel to each rhizoplast. These 2 segments anastomose beneath the basal bodies and the tubule proceeds over the top of the distal connecting fibre. A functional role for the smooth endoplasmic reticulum in these locations is discussed. Four sets of rootlet microtubules emanate from a region between the 2 basal bodies and the distal connecting fibre. Two sets have a three-over-one arrangement and the other 2 sets are doublets. Cytoplasmic microtubules were seen associated with possible nucleating sites on the rootlet microtubules. The associations of the observed structures are discussed and compared to the flagellar apparatus of C. reinhardtii.
The structure and some properties of the isolated mitotic apparatus
Authors: Goldman R. D. , Rebhun L. I.
Published: April 2021

The morphology of the isolated sea-urchin mitotic apparatus (MA) was examined by light and electron microscopy. With the polarization microscope and the Nomarski differential interference microscope, the isolated MAs appeared to be similar to in vivo MAs. Electron microscopy of the isolated MAs revealed the presence of microtubules, ribosome-like particles and vesicles. A close association between the ribosome-like particles and the MA microtubules resulted in the appearance of chains of particles running along the length of the microtubules.

Isolated MAs washed two to three times in isolation medium showed fine-structural changes in the electron microscope, which were reflected by lower retardation values obtained with the polarization microscope. The addition of magnesium and calcium or sucrose to the washing medium prevented these structural changes. Varying the pH of the isolation medium also resulted in changes in birefringence and ultrastructure of unwashed MAs.

Isolated MAs stored in the original isolation medium gradually became less birefringent and lost their microtubules. At pH 6·1 and pH 6·2 a residual birefringence was retained, even after several weeks of storage. Electron microscopy of these MAs revealed the presence of linear aggregates of ribosome-like particles oriented parallel to the long axis of the spindle. On the other hand, at pH 6·3 and pH 6·4, MAs lost their birefringence completely, and the ribosome-like particles became more randomly dispersed. 2M sucrose or 0·003 M Mg2+ greatly retarded the loss of birefringence in stored MAs.

Glutaraldehyde-fixed MAs stained intensely with azure B bromide, demonstrating the presence of RNA. Treatment with RNase resulted in a loss of this staining. RNase-treated MAs examined with the electron microscope, revealed changes in the ribosome-like particles.

The results are discussed in the light of recent biochemical analyses of the isolated MA, structural similarities to in situ MAs and the interpretation of the birefringence of the MA.
The sperm centriole persists during early egg cleavage in the insect Chrysopa carnea (neuroptera, chrysopidae)
Authors: Friedlander Michael
Published: April 2021

The giant centriole of the sperm of Chrsyopa carnea persists in the fertilized egg. The giant centriole appears together with a regular small centriole at one pole of the first cleavage spindle; two small centrioles are found at the other pole. During the subsequent divisions, the giant centriole appears either at one pole of one of the spindles, as in the first cleavage, or close to one inter-kinetic nucleus. All the other centrioles are regular in size. Therefore, the assumption that the mature spermatozoa of insects contain no true centrioles is not valid, at least for Chrysopa.
Organotypic cultures of the avian salt gland: Biosynthesis of membrane proteins
Authors: Mazurkiewicz Joseph E. , Barrnett Russell J.
Published: April 2021

The salt glands of control and salt-stressed ducklings were dissociated with collagenase to produce cell aggregates or ‘minilobules’ which were cultured. The fine-structural organization of freshly isolated and cultured (up to 72 h) aggregates were examined and showed surprisingly intact fine-structural organization with minimal changes from untreated glands. Incorporation of [3H]leucine into total protein, membrane protein and immunoprecipitable Na+ ATPase was determined in cultures at various time points, by pulse or pulse-chase experiments. Incorporation of label was linear for 4 h in protein, but higher in cultures of salt-stressed glands than in controls. Na+ ATPase was synthesized throughout the time of the experiment, the rate being highest during the first 4 h, reaching a plateau by 24 h. Up to 10% of the total label was present in Na+ ATPase. These results are discussed with reference to the use of minilobule culture to analyse further synthesis and assembly during biogenesis and control of these processes.
Megasporogenesis in a heterosporous fern: features of the organelles in meiotic cells and young megaspores
Authors: Bell P. R.
Published: April 2021

Megasporogenesis in the heterosporous fem Marsilea (Hydropterideae) shows features intermediate between sporogenesis in homosporous fems and that in heterosporous seed plants. The plastids in the dyads and young spores were associated with tubules 30–35 nm in diameter, probably a specialized form of endoplasmic reticulum. No consistent differences in size or cytoplasmic components could be found between the megaspores of a tetrad that might account for differential survival. The view that megaspore viability within the tetrad is genetically determined is thereby strengthened.
Hordeum and Secale mitotic genomes: Lie apart in a hybrid
Authors: Finch R. A. , Smith J. B. , Bennett M. D.
Published: April 2021

In both unpretreated root tip metaphases and pretreated mitoses of Hordettm vulgare L. cv. Sultan × Secale africanum Stapf F1 hybrids, Hordeum chromosomes tended to be nearer the centre of the mitosis than Secale chromosomes. This was clear in 4 serially sectioned cells examined in the electron microscope. In Feulgen squashes of 38 of 40 cells studied in the light microscope, the mean distances in each cell from the mean centromere position for the cell was less for Hordeum centromeres than for Secale centromeres.

Such spatial separation of parent genomes might prevent pairing of homoeologues in hybrids.
Substratum wettability and charge influence the spreading of Dictyostelium amoebae and the formation of ultrathin cytoplasmic lamellae
Authors: Gingell David , Vince Sheila
Published: April 2021

Amoebae of Dictyostelium discoideum attach and spread on strongly hydrophobic methylated glass and polystyrene as well as the hydrophilic surfaces of clean glass, polylysine adsorbed on glass and acid-treated polystyrene.

On polylysine-treated glass, spreading is rapid and the edges of the fully spread cells withdraw, forming a wide ∼ 0·1 μm thick lamella, which gives a very dark image in the interference reflection microscope. The optical properties of the lamella have been analysed in detail using finite aperture theory and can be distinguished from dark images generated by a small aqueous cell-substratum separation. The formation of the lamella is discussed in terms of the mechanics of cell movement.
Cell-glass separation depends on salt concentration and valency: Measurements on Dictyostelium amoebae by finite aperture interferometry
Authors: Gingell David , Vince Sheila
Published: April 2021

Using pre-aggregation amoebae of the cellular slime mould Dictyostelium discoideum we have investigated the influence of cation concentration and valency on cell–glass separation. For computing the separation we used interference reflection microscopy and converted measured image irradiance to distance by finite aperture theory.

Alterations in ionic strength caused virtually instantaneous reversible changes in the inter-ference image due to changes in cell membrane–glass separation. In solutions containing monovalent cations, a change in ionic strength from 20 mM to ∼ 0·5 mM increased the separation of the plasmalemma from the glass by 60 nm. Divalent cations were better than monovalent cations at maintaining a small separation. Our results show that both divalent and trivalent cations adsorb to one or both of the interacting surfaces, in addition to acting as electrostatic double-layer counterions. The optical measurements also show that the cell membrane–glass gap is not reduced to zero by counterion screening ; this is apparently due to the presence of a cell surface glycoprotein coat.
Flagellar membrane specializations and their relationship to mastigonemes and microtubules in Euglena gracilis
Authors: Melkonian M. , Robenek H. , Rassat J.
Published: April 2021

The flagellum of Euglena gracilis has been studied comparatively, using the freeze-fracture technique and with thin sections involving a tannic acid staining procedure. The flagellar membrane exhibits specializations in the form of two groups of intramembrane particle rows (IMP rows; mean IMP diameter, 6 nm) and single clusters of larger IMPs (mean IMP diameter, 10 nm) associated with the edge of one of the two groups of IMP rows. The IMP rows are helically arranged. The two groups of IMP rows are separated from each other by two membrane areas (measuring 170 and 300 nm in length) devoid of IMP arrays. The IMP rows are arranged in a four-start helix around the flagellum. A comparative morphometric analysis of IMP arrays and the arrangement of the two types of non-tubular mastigonemes (evaluated from tannic-acid-stained thin sections) reveals that the two groups of IMP rows correspond to the attachment points of the short non-tubular mastigonemes, whereas the cluster of three to seven larger IMPs corresponds to the attachment points of a group of the long non-tubular mastigonemes.

Flagellar membrane specializations also occur with respect to sterols, since filipin-sterol complexes are absent from all plasma membrane regions except the flagellar membrane. On the flagellar membrane filipin-sterol complexes occur predominantly in a membrane area free of IMP-arrays and are probably related in location to a prominent microtubule-membrane linkage. Details of the linkage between axonemal microtubules and the flagellar membrane have been evaluated, individual microtubule doublets have been numbered and the absolute configuration of the Euglena flagellum has been established.

In the reservoir region the flagellar membrane of the emergent flagellum is not covered by mastigonemes, but exhibits IMP arrays in the form of IMP rows and IMP clusters. In contrast to specializations on the free part of the emergent flagellum, in the reservoir region IMP rows are not regularly spaced, are distributed on opposite membrane halves (in the reservoir region on the E-face, in the free flagellum on the P-face) and often not associated closely with the clusters of larger IMPs. An hypothesis is presented explaining how mastigonemes might attach to the flagellar membrane and finally become oriented in their characteristic arrays. It is suggested that the observed IMP specializations in the flagellar membrane are (a) responsible for attachment of mastigonemes to the flagellar membrane, (b) responsible for linkage of mastigonemes to intraflagellar structures associated with axonemal microtubules, and (c) play an important role as a template for the development of the characteristic mastigoneme arrays.
Acquisition of β-glucuronidase activity by deficient fibroblasts during direct contact with lymphoid cells
Authors: Olsen I. , Dean M. F. , Muir H. , Harris G.
Published: April 2021

Fibroblasts deficient in β-glucuronidase acquired high levels of this enzyme when they were co-cultured with concanavalin A-stimulated lymphocytes. Acquired enzyme activity, determined using a single-cell cytochemical assay, was directly proportional to the number of lymphocytes added and persisted for several days in fibroblasts maintained at high density.

Lymphocytes did not secrete significant levels of β-glucuronidase into their culture medium, and did not release other substances able to induce synthesis of the enzyme by the deficient fibroblasts. Nor did β-glucuronidase acquisition result from concanavalin A-mediated uptake of enzyme, since a-methylmannoside did not reduce acquired activity. Moreover, lymphocytes from various sources, whether unstimulated or activated by a different mitogen, bacterial lipopolysaccharide, were equally effective in promoting the appearance of β-glucuronidase.

Deficient fibroblasts did not acquire β-glucuronidase by active endocytosis when co-cultured with lymphocytes, since enzyme extracted from lymphocytes was not itself effective in this respect. Furthermore, mannose 6-phosphate, which did inhibit endocytosis by deficient fibroblasts of exogenous β-glucuronidase prepared from 3T3 cells, had no effect on enzyme acquisition by fibroblasts during their co-culture with lymphocytes. Conversely, inhibitors of protein synthesis and energy metabolism, which did not interfere with endocytosis of exogenous enzyme, abolished the acquisition of βglucuronidase during co-culture.

Deficient fibroblasts did not acquire β-glucuronidase when they were cultured together with lymphocytes but separated from them by Millipore membranes permeable to exogenous enzyme. Thus, although the mechanism of acquisition is still unclear, the present results suggest that β-glucuronidase is transferred from lymphocytes to deficient fibroblasts by a process in which direct cell-to-cell contact is obligatory.
Enzymic dissection of embryonic cell adhesive mechanisms: III. *Immunological identification of a component of the calcium-dependent adhesive system of embryonic chick neural retina cells
Authors: Grunwald Gerald B. , Pratt Rodney S. , Lilien Jack
Published: April 2021

Immunological probes and cell-surface biochemical analysis are combined to identify a cellsurface glycoprotein, which appears to be involved in the formation of calcium-dependent adhesions among embryonic chick neural retina cells. Comparison of radioiodinated cells shows that adhesive-competent cells have at their surface two glycoproteins not present on nonadhesive cells. These two components (with M, 130 × 103, pl 4·8 and Mr 70 × 103, pl 4×8) are immunoprecipitable with adhesion-blocking antisera. A fraction derived from retina-conditioned medium, containing one major immunoprecipitable component, neutralizes the inhibitory activity of aggregation-inhibiting Fab’ fragments and competes in immunoprecipitation for the two glycoprotein components. The evidence suggests that one or both of these components is involved in the formation of calcium-dependent adhesions among embryonic chick neural retina cells.
Polyacrolein microspheres as a new tool in cell biology
Authors: Margel S. , Beitler U. , Ofarim M.
Published: April 2021

Polyacrolein (PA) microspheres in sizes ranging from 0·04 μm to 40 μm were synthesized. Magnetic and fluorescent PA microspheres were formed by carrying out the polymerization process in the presence of appropriate ferrofluidic or fluorochromic compounds, respectively. The microspheres carry reactive aldehyde groups, through which various ligands, containing primary amino groups, were covalently bound at physiological pH values.

The potential use of these microspheres was demonstrated by the specific labelling of fresh human red blood cells (RBC) and by the separation of human RBC from turkey RBC by means of a magnetic field. PA microspheres were also bound covalently to the anti-allergic drug disodium chromoglycate (DSCG) and the conjugate was used for the labelling of rat basophilic leukaemia cells.
High-resolution scanning electron microscopy of human metaphase chromosomes
Authors: Harrison Christine J. , Allen Terence D. , Britch Martin , Harris Rodney
Published: April 2021

Human metaphase chromosomes, prepared for light microscopy, were examined by scanning electron microscopy. Use of an osmium impregnation technique eliminated the need for sputter-coating and allowed high-resolution visualization of uncoated specimens. Chromosomes were of three-dimensional cylindrical profile, with well-defined chromatids and centromeres. Prior to Giemsa-banding a smooth surface morphology was observed. Relaxation of chromosome integrity by Giemsa-banding pretreatment allowed resolution of several orders of chromosome structure not previously demonstrated by scanning electron microscopy. The observed organization of the chromatin fibres allowed parallels to be drawn with the radial loop model of chromosome construction as described by Marsden and Laemmli.
Structure and behaviour of the sperm terminal filament
Authors: Omoto C. K. , Brokaw C. J.
Published: April 2021

Light- and electron-microscopic observations of Ciona and Lytechinus spermatozoa show a thin terminal filament at the distal end. The terminal filament is 5·6 μm long and contains the two central microtubules and a variable number of A-tubule extensions of the peripheral doublet microtubules. The transition from the 9 + 2 region to the terminal filament is tapered more gradually in Lytechinus than in Ciona. Photographs of the movement of beating spermatozoa do not show any obvious discontinuity in curvature at the transition region. Bends are propagated smoothly off the end of the flagellum with no decrease in curvature. However, spermatozoa in which the terminal filament has been removed show a clear * end effect ‘. This end effect involves a rapid unbending of bends that have reached the distal end of the flagellum. Computer simulations of flagellar models lacking a terminal filament show a similar end effect. Addition of a terminal filament to the end of the computer model can eliminate the end effect. Realistic bending behaviour of the model is obtained by using a terminal filament with a tapered elastic bending resistance in the basal portion of the terminal filament and a value of 0·03 × 109 pN nm* in the remainder of the terminal filament. This leads to estimates of 0·01 × 109 pN nm2 for the elastic bending resistance of an individual microtubule, and 0·2 × 109 pN nm2 for the elastic bending resistance of the 9 + 2 region of the flagellum. An improvement in propulsive effectiveness by addition of a terminal filament remains to be demonstrated.
Coated and smooth vesicles in the biogenesis of cell walls, plasma membranes, infection threads and peribacteroid membranes in root hairs and nodules of white clover
Authors: Robertson John G. , Lyttleton Pamela
Published: April 2021

Involvement of coated and smooth vesicles in the infection by rhizobia of root hairs and nodule cells of white clover was examined using electron microscopy of thin sections. Coated vesicles, about 100 nm in diameter including coat, were observed free in the plant cell cytoplasm and associated with root hair plasma membranes, infection thread membranes and peribac-teroid membranes. The number of coated vesicles seen associated with segments of the plasma membrane at the tip of the root hair was about 20-fold greater than the number associated with the plasma membrane towards the base of the root hair. Similarly, the number seen associated with segments of the infection thread membrane near the tip of the thread was about 20-fold greater than the number associated with the membrane towards the base of the thread. The number seen associated with segments of the peribacteroid membranes in recently infected nodule cells was comparable to the number associated with the plasma membrane towards the base of the root hair or with the infection thread membrane towards the base of the thread.

Coated vesicles were observed in the vicinity of and associated with both proximal and distal faces of the Golgi bodies; they often possessed, while still attached to the Golgi cistemae, shorter coats than those observed on coated vesicles free in the cytoplasm. Coated vesicles contained electron-dense material that did not stain positively with Thiéry stain for polysaccharides, and which appeared to have been released into the region of the cell wall or peribacteroid space as a result of fusion of the vesicles with plasma membranes or peribacteroid membranes.

Smooth vesicles were also observed in the vicinity of and associated with Golgi bodies, and in association with root hair plasma membranes, infection thread membranes and peribacteroid membranes. The smooth vesicles commonly contained material of varying electron density, which sometimes occurred in the form of droplets. Similar droplets seen in the region of the cell wall and in the peribacteroid space appeared to have resulted from the fusion of smooth vesicles with these membranes.

It is proposed that both smooth and coated vesicles derived from Golgi bodies are involved in the biogenesis of cell walls, plasma membranes, infection threads and peribacteroid membranes in root hairs and nodules of white clover.
Spindle microtubules in the dividing nuclei of trypanosomes
Authors: Vickerman K. , Preston T. M.
Published: April 2021

Stages in nuclear division have been identified in sections of bloodstream and cultured trypanosomes examined with the electron microscope

In the sleeping sickness trypanosome Trypanosoma rhodesiense at division the nuclear envelope and nucleolus-like endosome persist and become stretched along an axis. An acentric spindle of microtubules encases the elongating endosome As division proceeds the endosomal material fragments In bloodstream forms condensed chromatin (chromosomal material) appears to be associated with the nuclear envelope during the phase of nuclear elongation but to fall away from the envelope late in the phase of nuclear constriction. In culture forms the chromatin is not so abundant The discrete chromosomes envisaged by some light microscopists in stained preparations have not been identified using the electron microscope. The spindle may contain only continuous microtubules. It is suggested that the spindle serves to push the two halves of the nucleus apart, and that the nuclear envelope of each half may act as a vehicle in separation of the daughter genomes.

In culture forms of the elasmobranch parasite T. raiae, the endosome appears to disintegrate as the spindle is formed, and from then onwards it becomes difficult to distinguish endosomal material from what might be chromatin. There is no noticeable association between chromatin-like material and the nuclear envelope. Some of the spindle tubules converge on kinetochore-like plaques and the presence of chromosomal microtubules cannot be ruled out.

These preliminary studies indicate that the nuclear division process of trypanosomes is not closely akin to eukaryote mitosis, though it may bear some resemblance to nuclear division in Euglena. Within the genus Trypanosoma, moreover, the nuclear division process may vary from species to species and, possibly, even from one strain to another within a species.
Effect of microtubules and intermediate filaments on mitochondrial distribution
Authors: Summerhayes Ian C. , Wong David , Chen Lan Bo
Published: April 2021

The laser dye rhodamine 123 specifically stains mitochondria in living cells and facilitates the observation of changes in mitochondrial distribution in single cells under a variety of experimental conditions. Visualization of mitochondria in a number of cell lines followed by processing of these cells to study different cytoskeletal elements by indirect immunofluorescence, revealed good but not absolute correlation between mitochondria and microtubules or intermediate filaments. Mitochondria and microfilament distribution within the same cell did not show such a correlation. On the basis of observations made by various experimental approaches, we suggest that mitochondrial distribution is under the strong influence of the two systems, microtubules and intermediate filaments. Neither plays an absolute role but one seems able to play a more dominant role in the absence of the other.
C value and cell volume: Their significance in the evolution and development of amphibians
Authors: Horner Heather A. , Macgregor Herbert C.
Published: April 2021

Cell volume has been determined in 18 species of amphibian, ranging in C value from 1·4 pg to 62 pg DN A. There is a strong linear relationship between C value and both erythrocyte volume and erythrocyte nuclear volume. We have collected data on the timing of early embryogenesis from fertilization of the egg to the hatching tadpole in some amphibians ranging in C value from 1·4 pg to 83 pg. The species with large genomes take up to 24 times longer to reach a comparable state of development. Polyploid species develop faster than closely related diploid species. These data are discussed in relation to genome expansion and increase in cell cycle time as factors in the evolution of the Amphibia.