bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of mitosis in the chloromonadophycean algaVacuolaria virescens
Authors: Heywood Peter
Published: April 2021

During preprophase in the chloromonadophycean alga Vacuolaria virescens microtubules are present around the flagellar basal bodies and extend over the anterior surface of the nucleus. These microtubules assist in the separation of the flagella and later enter the nucleus through polar gaps. During prophase the nucleoli begin to disperse and the chromosomes become condensed. At metaphase the nucleus assumes an elliptical shape and an equatorial plate of chromosomes becomes aligned across the long axis of the nucleus; kinetochores are recognizable on some of the chromosomes. The nuclear envelope remains intact over most of the surface and in places it forms folds. During anaphase chromosomes are less distinct and vesicles are present in the elongating nucleus. Most of the new nuclear envelope around the progeny nuclei is formed by coalescence of these membrane vesicles during late anaphase and telophase, although some of the original nuclear envelope may also become incorporated. During telophase disintegration of the original nuclear envelope becomes pronounced and portions of this structure are recognizable in the cytoplasm after completion of mitosis.

It is suggested that this unusual type of nuclear envelope behaviour may be important in ensuring the segregation of the Golgi apparatus and contractile vacuole to progeny cells. Interphase cells contain a single extensive Golgi apparatus which is located between the anterior surface of the nucleus and the contractile vacuole. The Golgi apparatus and contractile vacuole act as an osmoregulatory system and their presence is presumably essential to the existence of the organism. Formation of a new contractile vacuole and division of the Golgi apparatus occur early in mitosis and thereafter a Golgi apparatus and contractile vacuole become associated with each of the poles of the nucleus. They retain this location throughout mitosis and during cytokinesis, with the result that an osmoregulatory system is present in each of the daughter cells. In a similar manner, microbody-like organelles are associated with the nuclear envelope during mitosis but not at interphase. Growth of the nuclear envelope during mitosis may serve as the means of partitioning these organelles to the progeny cells. Thus mitosis in Vacuolaria virescens is responsible not only for the equal segregation of the genetic material but also for the correct distribution of some of the cytoplasmic components.
The histochemical localization of acrosin in guinea-pig sperm after the acrosome reaction
Authors: Green D. P. L. , Hockaday A. R.
Published: April 2021

The protease acrosin is widely considered to be an essential component of a zona lysin which enables sperm to penetrate the zona pellucida of the egg. Sperm form a characteristic penetration slit little wider than the sperm head itself and this has long suggested that any zona lysin is attached to the sperm surface after an acrosome reaction. This paper provides the first ultrastructural evidence that this is the case.

The protein acrosin inhibitor, Kunitz soybean trypsin inhibitor, has been covalently attached to the electron-dense marker, ferritin, and the conjugate incubated with guinea-pig sperm which have undergone an Az3i87-induced acrosome reaction. Electron microscopy shows that ferritin is distributed unevenly over the outer surface of the newly exposed inner acrosomal membrane but does not extend to the equatorial segment. This is further evidence that acrosin can be considered as a candidate for the role of zona lysin. The mechanism of sperm penetration of the zona is discussed in the light of these observations.
Meiosis in Coprinus: IX. the influence of premeiotic s-phase arrest and cold temperature on the meiotic cell cycle
Authors: Lu B. C. , Chiu S. M.
Published: April 2021

Arrest of premeiotic 5 phase by high temperature and light causes the meiotic cell cycle time to become shortened by 4 h after release of the arrest. Genetical and cytological evidence shows that diplotene is drastically reduced from 4·5 h to less than 1 h. Cycloheximide (50 μg/ml) treatment of early and late diplotene cells in normal cultures prevents the meiotic divisions even though the chromosomes are condensed. The same treatment given within 1 h of metaphase I allows both divisions to be completed but fails to allow sporulation. This is interpreted to mean that the cellular programme for meiotic division (division programme) is made during diplotene. In the arrest-release cultures, however, the division programme is made during pachytene. This finding is interpreted to mean that the cellular programme in meiosis is prepared one step at a time. When the nuclear cycle is arrested, the cytoplasmic programmes continue. As a result, the division programme is precociously induced at pachytene. Since the diplotene programme is complete, the cells proceed directly from pachytene into metaphase I with the diplotene stage drastically reduced. Cold treatment at 5 °C at pachytene temporarily suspends the progress of meiosis and hence prolongs the pachytene stage. This prolongation causes an increase in recombination frequency. This finding supports the argument that recombination frequency is a function of time.
The role of golgi bodies in polysaccharide sulphation in Fucus zygotes
Authors: Callow Maureen E. , Coughlan S. J. , Evans L. V.
Published: April 2021

The cell wall of 24-h zygotes of Fucus serratus is composed of 3 layers -an inner fibrillar layer (sulphated fucan), an outer fibrillar layer (alginic acid/cellulose) and an exterior amorphous layer (sulphated fucan, alginic acid). The 2 layers containing sulphated fucan are preferentially thickened at the rhizoid pole.

Light- and electron-microscope autoradiographic pulse-chase experiments on 22-h zygotes using 56SO3-show the Golgi bodies to be the sites of fucan sulphation. The isolation and characterization of isolated organelle fractions from 22-h zygotes is described. Biochemical analysis of isolated Golgi-rich fractions from 22-h zygotes shows that the first detectable labelled macromolecule is associated with these fractions 2 min after addition of 56SO24-. The sulphate acceptor molecule has been partially characterized. 56S-APS and 56S-PAPS are detectable in the soluble fraction 0·5 min after addition of 56SO24-.

The results are discussed in relation to other published work on the differentiation of Fucus embryos and on polysaccharide sulphation.
Structural differences contrast higher plant and animal golgi apparatus
Authors: Mollenhauer Hilton H. , Morré D. James
Published: April 2021

The intercistemal spacings between cistemae of dictyosomes of higher plants differ from those of mammalian dictyosomes. In plants, the spacings increase from an average of about 8·0 nm at the forming face to about 14·0 nm at the maturing face. The increase in spacing coincides with the appearance within the intercistemal space of parallel filaments called intercistemal elements. In mammals, the intercistemal spacings are more nearly constant, and intercistemal elements have not been observed. Plant and animal dictyosomes may differ as well in the relative widths of the cisternal lumina, the widths of the intercistemal spacings, and in more subtle ways involving the appearance of the membranes. These structural differences may be indicative of some functional differences that contrast higher plant and animal Golgi apparatus.
Non-reciprocal contact inhibition of locomotion of chick embryonic choroid fibroblasts by pigmented retina epithelial cells
Authors: Parkinson E. K. , Edwards J. G
Published: April 2021

Using light and electron microscopy, we have confirmed an earlier observation that chick embryonic pigmented retina epithelial cells (PRE cells) seeded in vitro on cultured sheets of choroid fibroblasts, are able to spread. Spreading is as rapid (and shows the same dependence on lateral contact between PRE cells) as on a serum-coated culture substrate. After 1 h most cells are spreading on the upper surface of the choroid sheet, but after 4 h, some PRE cells can be found sandwiched between overlapping choroid cells, and thus have invaded the sheet. Choroid fibroblasts underlie PRE in vivo, but the ability of PRE cells to spread on cultured fibroblasts is not specific for choroid, since PRE cells spread also on BKH21 hamster kidney fibroblasts, and on fibroblasts from chick embryonic heart.

As reported by others for various fibroblastic cells, choroid cells seeded on to choroid sheets or on to cultured PRE are unable to spread. A possible explanation is that spreading of adherent cells is contact-inhibited by the cells in the sheet, just as their leading edges are paralysed on contact, and thus locomotion is inhibited, when fibroblasts collide on a plane substratum. If spreading of seeded cells and cell locomotion are inhibited by the same mechanism, PRE cells should contact-inhibit choroid fibroblasts with which they collide, but not themselves be so inhibited. Using time-lapse cinemicrography, we have found this to be the case.

We first established that in homotypic collisions, choroid fibroblasts do show contact inhibition of locomotion, despite the criss-cross (not well monolayered) appearance of confluent cultures. In heterotypic collisions between choroid and PRE we found the predicted nonreciprocal behaviour: the choroid leading edge is paralysed on collision, and the cell subsequently retracts, whereas the active PRE margin appears to be completely unaffected. Speed measurements from a series of such collisions show that the speed of choroid cells is markedly reduced on collision with PRE, whereas the slight slowing of PRE is not statistically significant.

We have observed similar behaviour in heterotypic collisions between various epithelial and fibroblastic cells, and so it seems possible that non-reciprocity may prove general for this interaction. If so, it has important implications for the role of contact inhibition of locomotion in phenomena such as morphogenesis, wound healing and the invasiveness of carcinoma cells. On the one hand, non-reciprocal contact-inhibition of locomotion may permit the spreading of epithelia over mesenchymal cells, thus generating or restoring an epithelial bounding membrane. On the other hand, in the absence of other interactions, it would fail to inhibit the invasion of mesenchymal territory by aberrant epithelial cells, or presumably by epithelial free edges.
Cyclic production of tension force in the plasmodial strand of Physarum polycephalum and its relation to microfilament morphology
Authors: Nagai Reiko , Yoshimoto Yasuaki , Kamiya Noburô
Published: April 2021

Cyclic contraction and relaxation of plasmodial strands of Physarum polycephalum were measured under both isotonic and isometric conditions, and their relation to changes in microfilament (MF) morphology was investigated. The contraction-relaxation rhythm of a strand segment was insignificant and irregular immediately after isolation from the mother plasmodium. It became regular half an hour later when local minute rhythms were synchronized spontaneously. If a strand kept under isotonic conditions was loaded with a heavier weight or a strand kept under isometric conditions was stretched a few times, the amplitude of each contraction wave was enhanced. After a strand had been thus conditioned, it was fixed at a selected phase of the contraction-relaxation cycle under both isotonic and isometric conditions.

The state of MFs changed strikingly according to the phase of the contraction cycle. In the shortening phase of the strand under isotonic contractions, MFs with a diameter of 6-7 nm were arranged parallel to each other to form large compact bundles in which adjacent filaments were bridged with cross linkages. Among these MFs, thicker filaments were sporadically scattered. At about the phase of minimal strand length, most of the MFs became kinky and formed networks. In the elongating phase, new loose bundles of MFs developed from the network. These loose bundles became compact again when the strand reached its maximal elongation phase. In the isometric contraction, MFs in the increasing tension phase were nearly the same as those in the shortening phase in isotonic contraction. Around the maximal tension phase, dense areas of MFs appeared along the bundles in place of the network formed in the isotonic contraction phase. These areas were closely packed, with MFs arranged parallel to each other. In the decreasing and minimal tension phases in isometric contraction, MFs were arranged similarly to those in the elongating and maximally elongated phases, respectively, in isotonic contraction. Alternation between the straight bundle and fine network configuration of the MFs observed in isotonic contraction was inconspicuous in isometric contraction. This was probably due to spatial restriction of shortening under isometric contraction. The results are interpreted in terms of cyclic changes of the aggregation pattern of the MFs in the form of F-actin, as opposed to the possibility that the contraction-relaxation cycles depend on cyclic G-F transformation of actin.
Isolated flagellar apparatus of Chlamydomonas: characterization of forward swimming and alteration of waveform and reversal of motion by calcium ions in vitro
Authors: Hyams Jeremy S. , Borisy Gary G.
Published: April 2021

The control of flagellar activity in the biflagellate green alga, Chlamydomonas reinhardtii was investigated by the in vitro reactivation of the isolated flagellar apparatus (the 2 flagella attached to their respective basal bodies plus accessory structures). The waveform and beat frequency of the isolated apparatus in the presence of 1 mM adenosine triphosphate (ATP) were comparable to those recorded for living cells. Equimolar concentrations of adenosine diphosphate (ADP) could be substituted for ATP with little change in beat frequency and no apparent change in waveform, suggesting that the latter is converted to ATP by axonemal adenylate kinase. No reactivation occurred in adenosine monophosphate (AMP). Beat frequencies in cytidine, guanosine and uridine triphosphates (CTP, GTP and UTP) were approximately 10% that obtained in ATP. Reactivation was optimal over a broad pH range between pH 6·4 and pH 8 9 in both ATP and ADP.

Isolated flagellar apparatus could be induced to change from forward to reverse motion in vitro by manipulation of exogenous calcium ions. The 2 types of motion were directly comparable to recorded responses of living cells. Forward swimming occurred at levels of calcium below 10−6 M, the isolated apparatus changing to backward motion above this level. Motility was inhibited at concentrations above 10−3 M. The threshold for reversal of motion by calcium was lowered to 10−7M when the flagellar membranes were solubilized with detergent, indicating that the flagellar membranes are involved in the regulation of the level of calcium within the axoneme. The reversal of motion by calcium was itself freely reversible. The relationship of these observations to the known tactic responses of Chlamydomonas is discussed.
Carbon dioxide evolution during the cell cycle of the fission yeast Schizosaccharomyces pombe
Authors: Creanor James
Published: April 2021

The rate of CO2 evolution was measured in synchronous cultures of the fission yeast Schizosaccharomyces pombe growing in a minimal medium. The rate of CO2 evolution was found to double sharply at about the time of nuclear division (0·75 of the way through the cell cycle). For the remainder of the cell cycle the rate remained constant.

Addition of inhibitors of DNA synthesis or nuclear division did not affect the pattern of CO2 evolution in synchronous cultures. Similarly, in an induced synchronous culture, in which DNA synthesis, nuclear division and cell division -but not growth, were synchronized, CO2 evolution showed a continuous pattern and not the step-wise increase associated with the normal synchronous cultures.

When S. pombe was grown in a complete medium, the evolution of CO2 in synchronous cultures was shown to increase in a continuous manner but at a rate faster than the growth of the culture.
Nuclear volume control by nucleoskeletal DNA, selection for cell volume and cell growth rate, and the solution of the DNA C-value paradox
Authors: Cavalier-Smith T.
Published: April 2021

The 40000-f0ld variation in eukaryote haploid DNA content is unrelated to organismic complexity or to the numbers of protein-coding genes. In eukaryote microorganisms, as well as in animals and plants, DNA content is strongly correlated with cell volume and nuclear volume, and with cell cycle length and minimum generation time. These correlations are simply explained by postulating that DNA has 2 major functions unrelated to its proteincoding capacity: (1) the control of cell volume by the number of replicon origins, and (2) the determination of nuclear volume by the overall bulk of the DNA; cell growth rates are determined by the cell volume and by the area of the nuclear envelope available for nucleocytoplasmic transport of RNA, which in turn depends on the nuclear volume and therefore on the DNA content. During evolution nuclear volume, and therefore DNA content, has to be adjusted to the cell volume to allow reasonable growth rates.

The great diversity of cell volumes and growth rates, and therefore of DNA contents, among eukaryotes results from a varying balance in different species between r-selection, which favours small cells and rapid growth rates and therefore low DNA C-values, and K-selection which favours large cells and slow growth rates and therefore high DNA C-values. In multicellular organisms cell size needs to vary in different tissues: size differences between somatic cells result from polyteny, endopolyploidy, or the synthesis of nucleoskeletal RNA. Conflict between the need for large ova and small somatic cells explains why lampbrush chromosomes, nurse cells, chromatin diminution and chromosome elimination evolved. Similar evolutionary considerations clarify the nature of polygenes, the significance of the distribution of haploidy, diploidy and dikaryosis in life cycles and of double fertilization in angiosperms, and of hetero-ploidy despite DNA constancy in cultured cells, and other puzzles in eukaryote chromosome biology.

Eukaryote DNA can be divided into genic DNA (G-DNA), which codes for proteins (or serves as recognition sites for proteins involved in transcription, replication and recombination), and nucleoskeletal DNA (S-DNA) which exists only because of its nucleoskeletal role in determining the nuclear volume (which it shares with G-DNA, and performs not only directly, but also indirectly by coding for nucleoskeletal RNA). Mechanistic and evolutionary implications of this are discussed.
Membrane recycling at the cytoproct of Tetrahymena
Authors: Allen Richard D. , Wolf R. W.
Published: April 2021

Exocytosis and membrane recycling at the cytoproct (cell anus) of Tetrahymena pyriformis were studied using thin-section electron microscopy. Single cells were fixed at specific times relative to the elimination of the vacuole’s contents —before elimination, at elimination, 3–5 s and 10–15 8 following elimination. The closed cytoproct is distinguished from other pellicular regions by a single membrane at the cell surface which is circumscribed by an electron-opaque flange that links or welds the plasma membrane to the underlying alveolar margins. Microtubules originating in the flange pass inward where they lie over, and possibly guide, the approaching food vacuoles to the cytoproct. Food vacuoles near the cytoproct are also accompanied by coats of microfilaments. These microfilaments appear to be active in the channelling and endocytosis of food vacuole membrane. Upon cytoproct opening the plasma membrane and food vacuole membrane fuse. Elimination seems to be essentially passive and is accomplished by re-engulfment of the old food vacuole membrane which is constantly associated with microfilaments. Re-engulfment of all the food vacuole membrane requires 10–15 s and results in a closed cytoproct. The membrane remnants embedded in microfilaments form a cluster under the closed cytoproct. At the periphery of this cluster remnants take the shape of 70–130-nm spherical vesicles or 0 · 2-μm-long flattened vesicles.
Production of serum proteins in normal diploid fibroblast-hepatoma cell hybrids and in A9-normal liver cell hybrids
Authors: Szpirer J. , Szpirer C.
Published: April 2021

Two series of interspecific hybrids have been generated between liver cells (which actively secrete several serum proteins) and fibroblasts (which do not). In each series, one of the parental cells was a normal diploid cell: mouse hepatoma cells were fused with normal diploid rat fibroblasts, and normal rat liver cells were fused with mouse fibroblasts of the permanent line A9. The production of albumin, alpha-fetoprotein (AFP) transferrin and the third component of complement (C3) was analysed in these hybrids. Most hepatoma cell hybrids exhibit extinction of albumin, AFP and (to a lesser extent) transferrin; they retain the capacity to secrete C3. Normal liver cell hybrids are also characterized by the absence of albumin and transferrin production and by retention of C3 secretion. These results, when compared to previous results obtained with hybrids derived exclusively from different differentiated cells of permanent and transformed lines show that the phenotype of such hybrids is not determined by the abnormal character per se of the aneuploid parental cells. Amongst the rat fibroblast-mouse hepatoma cell hybrids, a few clones retain the capacity to actively secrete mouse albumin, AFP and transferrin, without the concomitant production of the rat serum proteins. These hybrids have lost more rat (fibroblast) chromosomes than the other clones and also have an increased number of mouse (hepatoma) chromosomes. Thus, their phenotype must result from either the complete loss of ‘extinguisher’ chromosomes, or gene dosage effects. The significance of the lack of rat serum protein production is also discussed, and it is suggested that retention, without concomitant activation, could be explained in terms of diffusible regulators and heritable differences in chromatin conformation.
Extent and rate of chromosome segregation in two intraspecific mouse cell hybrids: A9 × diploid foetal erythrocyte and A9 × B82
Authors: Russell M. H. , McGEE B. J. , Engel E.
Published: April 2021

Patterns of chromosome segregation were studied in 2 different intraspecific mouse cell hybrids: (1) A9 × B82, formed by fusing 2 cell lines of heteroploid fibroblasts, and (2) UWE, originating from the fusion of A9 cells with euploid foetal erythrocytes. Detailed analyses of Giemsa (G)-banded chromosomes and chromosome arms of both parental and hybrid cells were made for each hybrid type, in order to determine the specificity of the losses and to assess the influence of ploidy and cell differentiation.

Unlike the A9 × B82 hybrids, which revealed a significant chromosome loss under selective tissue culture pressures only after 9 months, the UWE hybrids showed a sharp reduction in the total chromosome number during the initial 2 months under similar pressures. However, with no additional cloning, UWE remained karyotypically stable after that time. This rapid chromosomal segregation in UWE hybrids may be caused by properties of the parental foetal erythrocytes.

In UWE cells, the majority of the chromosome arms were retained or duplicated. Less than a quarter of the total number of chromosome arms were segregated or lost, and these were all chromosome arms with abnormal mouse G-banding patterns, present only in the heteroploid A9 parental cells. In two of the four A9 × B82 hybrid lines, there was marked segregation of chromosome arms whose banding patterns were identical to those of wild type mouse telocentric chromosomes. For both types of intraspecific cell hybrids, two thirds or more of the chromosome arms had banding patterns which were the same as those of the wild type genome.
Cell-associated proteases affect tumour cell migration in vitro
Authors: Varani J. , Orr W. , Ward P. A.
Published: April 2021

The in vitro migratory activity of mouse fibrosarcoma cells in medium containing either foetal calf serum or normal human serum was studied. These 2 sera were studied because foetal calf serum contains high levels of protease inhibitor activity while human serum contains much less. The cells migrated actively in medium with foetal calf serum but migration was greatly inhibited in human serum-containing medium. When protease inhibitors such as soybean trypsin inhibitor, lima bean trypsin inhibitor and bovine pancreas trypsin inhibitor were added to human serum-containing medium cell migration was supported almost as effectively as in medium with foetal calf serum. Addition of є-amino-n-caproic acid to human serum or depletion of the plasminogen from human serum did not enable it to support enhanced migration, є-amino-n-caproic acid actually inhibited migration. A variant cell population with elevated levels of caseinolytic activity and elevated levels of activity against the substrate n-acetyl-DL-phenylalanine-β-naphthyl ester (a substrate specific for chymotrypsin-like enzymes) was isolated from the parent cells. When the variant cells were compared to the parent cells regarding migratory activity in foetal calf serum or human serum-containing medium, the variant cells showed much less activity. Only a few, widely scattered variant cells migrated in the human serum-containing medium. These data suggest that a cell-associated factor interferes with the migration of the cells in medium with human serum. This factor apparently is neutralized in medium containing human serum to which protease inhibitors with antitrypsin activity have been added.
The evolution of excitable behaviour in Dictyostelium
Authors: Lax Alistair J.
Published: April 2021

Aggregation of Dictyostelium discoideum amoebae is effected by relayed cyclic AMP (cAMP) signals. The period of this wave propagation drops abruptly at the transition from aggregative to post-aggregative development. In this paper I demonstrate that the light-scattering response induced by a low concentration pulse of cAMP evolves from one lasting 5 min to one lasting 2 min. The definitive establishment of the 2-min response coincides with the beginning of post-aggregative gene expression. Amoebae at the aggregative stage are unable to respond to a second cAMP pulse delivered less than 4 min after the first, whereas at the post-aggregative stage they can respond to 2 pulses separated by 1 min or longer. Addition of cAMP phosphodiesterase to amoebae at the aggregative stage can in part mimic the change in excitable behaviour: the response is shortened and the amoebae can respond more frequently. However the shortened response is not post-aggregative in shape and the prolonged presence of cyclic nucleotides induces different responses at the aggregative and post-aggregative stage. Both these results suggest that the rate of destruction of the relayed signal is not solely responsible for the change in excitability.
Studies of membrane fusion.: III. fusion of erythrocytes with polyethylene glycol
Authors: Knutton S.
Published: April 2021

Freeze-fracture electron, microscopy has been used to investigate the mechanism of polyethylene glycol-induced cell fusion. Interaction of cells with the high concentrations of polyethylene glycol required for cell fusion results in cell agglutination with large planar areas of very close contact between adjacent cell membranes. An aggregation of intramembrane particles into large patches at the sites of cell-cell contact accompanies cell agglutination. Fusion occurs following the removal of most of the PEG when cells only remain in close contact at small (∼ 0·1 μm diameter) plaques of smooth particle-denuded membrane. Membrane fusion occurs at these plaques of smooth membrane resulting in cells connected by one (or more) small cytoplasmic connexions. Expansion to form spherical fused cells occurs by a process of cell swelling.
Actin in spindles of Haemanthus Katherinae endosperm : II. distribution of actin in chromosomal spindle fibres, determined by analysis of serial sections
Authors: Forer Arthur , Jackson W. T. , Engberg A.
Published: April 2021

We have studied the arrangements of actin-containing filaments in 13 bundles of kinetochore microtubules in glycerinated, heavy meromyosin-treated Haemanthus endosperm cells : 7 bundles were in a cell at anaphase, and 6 were in a cell at metaphase. Actin-containing filaments were present in each of the 13 bundles of kinetochore microtubules : they were in amongst the microtubules in the bundle and seemed to be associated with the microtubules. Actin-containing filaments in each bundle seemed to terminate at the kinetochores. Actin-containing filaments associated with the kinetochore microtubules were of consistent polarity (the arrowheads pointed towards the kinetochores) whereas those associated with other microtubules and those not associated with microtubules did not have consistent polarity (some pointed towards the spindle pole, others pointed away from it). Roughly, there were as many individual stretches of actin-containing filaments identified per bundle of kinetochore microtubules as there were microtubules which terminated at the kinetochore. These data suggest that actin-containing filaments in spindles have a functional role.

We used 2 glycerination procedures in our studies (one for each cell), and neither seemed to disrupt the basic microtubule arrangements : the arrangements of spindle microtubules seen after glycerination of Haemanthus endosperm were identical to those described previously by others in non-glycerinated glutaraldehyde-fixed Haemanthus endosperm. Thus we argue that spindle structure is not disrupted by the procedures, and therefore that the arrangements of actin-containing filaments are not artifacts of the glycerination procedures. The only difference between microtubules in glycerinated cells and microtubules in untreated cells is that there seem to be fewer in the glycerinated cells.

The possible role of actin-containing filaments in the spindle is discussed.
An abnormality of cell behaviour in human dystrophic muscle cultures: A time-lapse study
Authors: Yasin Rose , Beers G. Van , Riddle P. N. , Brown D. , Widdowson G. , Thompson E. J.
Published: April 2021

The initiation of monolayer mass cell cultures from adult human biopsies has revealed a striking abnormality in the growth and development pattern of muscle cultures from Duchennetype dystrophy. This abnormality in cell behaviour was seen as early as 4 days in culture, well before myotubc formation or confluence, and consisted of areas where cells clustered together in a multilayered mass rather than showing the typical monolayer distribution normally ob served.

To gain some insight into the mechanism of cell cluster development, we have examined such a culture by time-lapse cinematography and also the cell behaviour of other control cultures. The results of this study show that the clusters enlarged primarily by cell division and, to a lesser extent, by the acquisition of neighbouring cells. Furthermore, none of the single cells surrounding the clusters exhibited contact inhibition of movement. This behaviour was not observed in the other cultures examined. These findings could be indicative of an abnormality in the cell surface or cell-locomotory machinery of dystrophic cells.
The time course of male meiosis in the red-backed salamander, Plethodon cinereus
Authors: Morgan Garry T.
Published: April 2021

Tritiated-thymidine autoradiography was used to follow the progress of cells through meiosis in male P. cinereus at 20 °C. Spermatocytes spend 7 days in leptotene, 5 days in zygotene and 3 days in pachytene before entering the diffuse stage. Diffuse lasts for 8 days and is followed by a diplotene of 2 days. First and second meiotic metaphase occur a total of 26 days after the end of premeiotic S.

Considering the information for P. cinereus together with that for 3 other species, it appears that in amphibians the duration of meiosis does not show the linear relation with C-value that has been described for other groups of organisms.
Effect of temperature on dry mass of polytene nuclei in Drosophila
Authors: Hartmann-Goldstein Ingeborg J. , Goldstein D. J.
Published: April 2021

Nuclei were isolated by an aqueous detergent method from Drosophila prepupal salivary glands, and measured by integrating interference microscopy. There was a highly significant correlation between nuclear volume and dry mass. Dry masses fell into 2, 3 or 4 distinct groups corresponding to polytene replication classes; the mean of a given dry mass group was between 8 and 30% less than twice that of the group below, indicating that the ratio of DNA:dry mass increases during polytenic growth.

The proportion of nuclei in the higher mass groups, the mean dry mass of nuclei within a given mass group, and the percentage loss of nuclear dry mass in the first hour after isolation were all higher when animals were reared at 150 instead of 25 °C. Nuclear dry mass in prepupae was affected by the temperature during both the embryonic and larval periods, and also to some extent by the nutrition and degree of crowding of the cultures.
The effect of cell mass on the cell cycle timing and duration of S-phase in fission yeast
Authors: Nasmyth Kim , Nurse Paul , Fraser R. S. S.
Published: April 2021

Two isotopic methods for measuring DNA replication in the fission yeast Schizosaccharomyces pombe are described. The first is a method for measuring the total quantity of [3H]uracil incorporated into DNA after pulse labelling. The second is a means of detecting DNA replication in single cells by autoradiography. Both of these techniques have been used to investigate the timing and duration of S-phase in a series of mutant strains whose cell mass at division varies over a 3-fold range. The results support the hypothesis that in S. pombe there are 2 different controls over the timing of S-phase: an attainment of a critical cell mass and a dependency upon the completion of the previous mitosis coupled with a short minimum time in G1. Strains whose cell mass at birth is above this critical level initiate DNA replication almost immediately after septation, that is, very soon after the previous mitosis. Strains whose cell mass at birth is below the critical level do not initiate replication until the critical cell mass is attained. The duration of S-phase has been estimated from the proportion of cells whose nuclei are labelled after a pulse of given duration. S-phase is short in S. pombe, lasting only about 0·1of a cell cycle in wild type. Cell mass at S-phase does not have any consistent effect on this length. We have also investigated the degree of synchrony of S-phase initiation in daughter cells, and have found that, in a cell cycle 240 min long, their S-phases are initiated within 1-2 min of each other. This result indicates that between sisters variability in the duration of the G1 phase is small compared with variability in the total cell cycle time, and argues against the hypothesis that the rate of cell cycle traverse is determined by a random transition in G1.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: III. radioautographic distribution of [14C]sucrose
Authors: Appleton T. C. , Pelc S. R. , Dingle J. T. , Fell Honor B.
Published: April 2021

Earlier experiments have shown that when limb-bone rudiments from day embryonic chicks are cultivated in medium containing an indigestible sugar, the perichondrial cells become intensely vacuolated, but this vacuolation does not appear in the chondrocytes, except in the articular region. Appleton’s radioautographic method for demonstrating water-soluble materials was used to study the uptake, distribution and loss of 14C-labelled sucrose in day limb-bone rudiments cultivated in a chemically denned medium (BGJ5).

After 48 h exposure to [14C]sucrose, both perichondrium and cartilage were heavily labelled. When such explants were either washed for 1 h in BGJ5 or cultivated for a further 24 h in non-radioactive medium, labelling was almost unaffected in the perichondrial cells but was greatly reduced in the cartilage, the cells of which were almost devoid of radioactivity.

The presence in the medium of 0·08 M ‘cold’ sucrose did not alter the perichondrial grain counts in the washed explants. This finding supports the view that in the perichondrial cells sucrose is taken up non-specifically by endocytosis, and that the intense vacuolation of the cytoplasm is due to abnormal persistence of the pinocytotic vesicles in the presence of the sugar.

It is concluded that failure of the chondrocytes to take up sucrose is due, not to lack of penetration of the sugar into the cartilage, but to a weak endocytotic activity of the cells.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: IV. lysosomal and other biochemical effects. general discussion
Authors: Dingle J. T. , Fell Honor B. , Glauert Audrey M.
Published: April 2021

Cultivation of limb-bone rudiments in medium containing various non-metabolizable or poorly metabolizable sugars caused vacuolation of the perichondrial and articular cells and was accompanied by an increased synthesis and profuse secretion of lysosomal enzymes. Experiments with [14C]dextran indicated that the cytoplasmic vacuolation was due not to a higher rate of endocytosis, but rather to an abnormally long persistence of the pinocytotic vacuoles. Meta-chromatic material was lost from the cartilage only in the immediate vicinity of the vacuolated articular chondrocytes and the amount of hexosamine and hydroxyproline released into the medium was not much increased. However, the hexosamine and hydroxyproline of the sucrosetreated rudiments was much more susceptible to extraction with neutral salt than those of paired controls.

Sucrose taken up by the cells was liberated when the rudiments were returned to normal medium; this release, unlike the secretion of lysosomal enzymes, was unaffected by the presence of hydrocortisone. It is probable that the primary lysosomes, formed in the enlarged Golgi region, are the vehicles for the secretion of lysosomal enzymes. No appreciable amount of enzymic activity was released into the medium from rudiments grown in the presence of 0·08 M sucrose, before 36 h; at, or just before this time, however, a net increase in synthesis of enzyme was observed. The role of endocytosis in the resorption of skeletal matrix is discussed.
The effect of enucleation on flagellar regeneration in the protozoon Peranema trichophorum
Authors: Tamm S. L.
Published: April 2021

A rotocompressor was used to enucleate the flagellate protozoon Peranema trichophorum at known stages in the mitotic cycle. This new enucleation technique, combined with recently devised methods for amputating the flagellum and recording its regeneration in single living cells, permitted the investigation of the role of the nucleus in flagellar regeneration at different cell ages.

The flagellar regeneration capacity of an enucleate Peranema depended on the stage in the cell cycle when the nucleus was removed. Post-division enucleate cells regenerated about half the length reached by sham-operated controls, and at slower rates, while predivision enucleate cells regenerated flagella equally as well as the controls.

Therefore, the nucleus is making an immediate contribution to flagellar regeneration early in the cell cycle, but not late in the cell cycle.
Nuclear morphology and the ultra-structural localization of deoxyribonucleic acid synthesis during interphase
Authors: Milner Gillian R.
Published: April 2021

The ultrastructural localization of deoxyribonucleic acid (DNA) synthesis was studied by electron-microscope autoradiography in human transforming lymphocytes, embryonic lung fibroblasts, epithelial cells and normoblasts. Euchromatin was found to be active in DNA synthesis in all cell types studied, whereas heterochromatin was inactive. However, DNA synthesis was also prominent in the regions where heterochromatin was thought to be decondensing to form euchromatin. Analysis of sequential changes in nuclear morphology of the transforming lymphocyte suggested that there is decondensation of heterochromatin during the S-phase until none is left. In nuclei with no heterochromatin a prominent localization of DNA synthesis was at the nuclear membrane. This sequence of complete decondensation of hetero-chromatin also seemed likely for fibroblasts and epithelial cells. Normoblasts however showed no stage where the nucleus was wholly euchromatic and it is suggested that in this cell decondensation of heterochromatin for replication is localized and transient.
Natural segregation of the ribonucleoprotein components of the nucleoli of chloragogen cells in Tubifex
Authors: Djaczenko W. , Grabska J. , Filadoro F.
Published: April 2021

Nucleolar ribonucleoprotein (RNP) components of the chloragogen cells of normal untreated specimens of Tubifex tubifex (Mull.) were found to be segregated, there being separate zones for each RNP species. There were external and internal zones, containing granular RNP, and a fibrillar zone located between them in which only filamentous RNP components were’found. The innermost part of the nucleolus was formed by one or more vacuole-like structures which occasionally contained 350-A granules of high electron opacity. In the vicinity of the nucleolus a spherical mass, called the ‘paranucleolar body’ and composed of densely packed granules and filaments, was constantly encountered.
The uptake and localization of catecholamines in chick embryo sympathetic neurons in tissue culture
Authors: England J. M. , Goldstein M. N.
Published: April 2021

The uptake of exogenous [3H]dopamine, [3H]norepinephrine, and [3H]epinephrine by dissociated chick embryo sympathetic neurons growing in tissue culture was studied by autoradiography. The neurons, growing in a medium containing nerve growth factor, rapidly and specifically took up all three catecholamines for at least 60 days, while no uptake was observed in several other cell types, including satellite cells and chick dorsal-root ganglion cells. The uptake was dependent on the concentration of the catecholamine and the duration of the pulse and was inhibited by cocaine and several sympathomimetic amines.

Labelling was visualized only with fixatives which react with catecholamines to form waterinsoluble compounds.

Autoradiographs showed that the label was much denser over the axons than the cell bodies. The label was distributed uniformly along the axons and did not seem to be preferentially localized at the axon terminals or varicosities which contain aggregates of dense core granules. These observations indicate that a large portion of the exogenous 3[H]catecholamine is localized in an extragranular compartment and suggest that the differentiated function of the sympathetic neuronal cell membrane, which plays an important role in uptake, is retained after prolonged tissue culture.
Control of nerve cell formation from multipotent stem cells in hydra
Authors: Berking Stefan
Published: April 2021

Feeding of starved animals provides a very short signal which determines stem cells to differentiate into nerve cells after the next mitosis. Only those stem cells become determined which are just in the middle of their S-phase at the time of feeding. Stem cells of any other stage of the cycle do not become determined. Nerve cell determination is suppressed by very low concentrations of an endogenous inhibitor. The inhibitor exerts its effect only during the first half of the S-phase, not before and not after this period. Based on these findings it is proposed that stem cells are susceptible to 2 different signals during the first half of their S-phase; one signal allows the development into nerve cells, the other prevents this development. Within this period the decision whether to become a nerve cell or not is reversible. It becomes fixed at the end of this period.
Intercellular transfer of β-glucuronidase in chimeric mice
Authors: Herrup Karl , Mullen Richard J.
Published: April 2021

Chimeric mice were produced by aggregating 2 embryos, each of which was homozygous for a different structural allele of the enzyme β-glucuronidase. The two alleles used were Gusb, the ‘wild-type’ allele, and Gutk, an allele whose gene product shows decreased activity in all tissues as well as decreased heat stability. Staining of untreated adult chimeric livers for glucuronidase activity revealed a mosaic of high (Gusb) and low (Gusk) activity cells. The boundaries between cells of different activity were sharp and revealed no diffusion of enzyme or reaction product.

Treating sections at 73 °C before staining led to a decay of staining activity in normal (non-chimeric) Gusk/Gusk and Gusb/Gusb tissue. The rates of activity loss under the conditions used differed by 10-fold. Of the 2 genotypes in the chimera, the dark-staining, Gusb, cells decayed in a fashion similar to that of the Gusb/Gusb control. The light-staining, Gusk, cells of the chimera lost their staining in a unique fashion. Within 20 min they quickly lost a majority of their staining activity but that which remained was relatively heat stable. The second Gusb Mike phase of the decay, seen both photographically and photometrically, suggests that Gusb gene product has been transferred to cells of Gusk/GusK genotype.
The effects of egta and trypsin on the serum requirements for cell attachment to collagen
Authors: Schor Seth L.
Published: April 2021

Cells growing on plastic or glass surfaces in vitro may be brought into suspension by proteases (e.g. trypsin) or chelating agents (e.g. EGTA). Trypsin and EGTA remove different quantities and types of molecules from cell surfaces. Previous studies have revealed that when confluent cultures of either BHK or PyBHK cells are brought into suspension by exposure to trypsin, foetal calf serum (or fibronectin) is required for cell attachment to films of denatured type I collagen, but not to 3-dimensional gels of native collagen fibres. In this communication the scrum requirements for the attachment of BHK and PyBHK cells to collagen substrata have been examined as a function of (a) the method used to prepare the cell suspension (EGTA or trypsin), and (b) cell density. Data are presented consistent with the view that cell surface-associated fibronectin is able to mediate cell attachment directly to films of denatured collagen.
Abnormal microtubule deployment during defective macronuclear division in a Paramecium mutant
Authors: Cohen J. , Beisson J. , Tucker J. B.
Published: April 2021

The tam 8mutant of Paramecium tetraureliais a representative of a class of mutants characterized by abnormal nuclear divisions during binary fission and the failure of trichocysts to attach to the plasma membrane. Compared with wild-type organisms the following abnormalities occur in tam 8individuals. (1) The spherical interphase macronucleus is not positioned near the oral apparatus; it is randomly located in the cytoplasm of interfission organisms. (2) The macronucleus does not migrate towards the anterior dorsal cortex as its division starts, nor is it dorsally and subcortically positioned as it elongates. (3) Elongating macronuclei exhibit variable and irregular shapes. (4) This elongation is delayed and reduced. (5) Longitudinally oriented microtubules assemble in the nucleoplasm of dividing macronuclei but their spatial deployment is abnormal. (6) Unequal segregation of micronuclei between daughter organisms occurs during binary fission. The abnormal arrangement of nucleoplasmic microtubules provides support for the proposal that a microtubule sliding mechanism is involved during the elongation of dividing macronuclei. The extent to which macronuclear division may be controlled by the cell cortex is considered in relation to the pleiotropic effects of the tam 8mutation.