bluuebunny/crossref_metadata_2025 huggingface dataset:
The translaminal fibrils of the human amnion basement membrane
Authors: Campbell S. , Allen T. D. , Moser B. B. , Aplin J. D.
Published: April 2021

The organisation of extracellular matrix beneath the human amniotic epithelium was investigated in order that the co-ordinate synthesis of basal lamina and stroma by these cells could be better understood. Transmission electron microscopy of intact tissue confirmed that stromal matrix fibrils are located between the cell surface and the basal lamina, and also penetrate the lamina. The distribution of the supralaminal fibrils and their association with the lamina was further investigated by scanning electron microscopy (SEM) after removal of the overlying epithelium. Five complementary procedures were used to remove the cells from the underlying lamina. Trypsin–EDTA treatment caused the epithelial cells to retract or detach from the lamina. SDS or ammonium hydroxide was used to extract the epithelium, which was then removed by physical shearing. Transmission electron microscopy (TEM) confirmed that the lamina densa and supralaminal fibres were present after extraction by these agents. Incubation in CHAPS, a zwit terionic detergent, did not remove the epithelium but permitted exposure of the basal lamina by mechanical scoring. Extraction with boric acid followed by osmium tetroxide produced epithelial disruption and revealed the lamina and stroma in different areas. Although the extraction pattern was different in each case, all of the five methods confirmed that individual fibrils and fibril bundles are present on the apical surface of, and enter, the lamina densa. Examination of the stromal surface of the basal lamina after fracture revealed fibrils passing from the stroma into the lamina densa. We therefore suggest that, in this tissue, newly synthesised stromal matrix components appear in an assembled fibrillar form between the basal cell surface and the basal lamina before becoming associated with the sublaminal stroma.
Onset of expression of peanut lectin-binding glycoproteins is correlated with stratification of keratinocytes during human epidermal development in vivo and in vitro
Authors: Watt Fiona M. , Keeble Stella , Fisher Chris , Hudson David L. , Codd Jane , Salisbury Jonathan R.
Published: April 2021

During gestation the epidermis develops from a single layer of ectoderm into a layer of keratinocytes overlaid by a layer of periderm; this is followed by a progressive increase in the number of layers of keratinocytes, until finally the distinct granular and cornified layers characteristic of mature epidermis are formed. As part of our investigation into the function of the peanut lectin-binding glycoproteins of cultured human keratinocytes, we have examined their expression at different stages of human epidermal development. We found that the onset of expression of the glycoproteins coincided with the transition from a two-to a threelayered epidermis, both in vivo and in organ culture. In adult epidermis, the patterns of binding of peanut lectin and Limax flavus lectin are complementary, with peanut binding more strongly to suprabasal keratinocytes and Limax βavus lectin binding more strongly to cells in the basal layer. We found that the complementary pattern of binding of the two lectins was established at, or shortly after, the onset of stratification and retained throughout development. In contrast, expression by keratinocytes of involucrin, a protein precursor of the cornified envelope, occurred after stratification had begun. Finally, we identified the peanut lectin-binding glycoproteins of adult epidermis by immunoblotting with an antiserum raised against the glycoproteins of cultured neonatal keratinocytes. In conclusion, expression of the peanut lectin-binding glycoproteins is an early eve>Summarynt in epidermal development, and this would be consistent with a role for the glycoproteins in stratification.
Commentary how is microtubule-based organelle translocation regulated?
Authors: STEBBINGS HOWARD
Published: April 2021

It has long been appreciated from light-microscopical studies that components move in a directed fashion within cells, and this is particularly obvious in cells showing high degrees of asymmetry. The correlation between such movements and the presence of orientated aggregations of microtubules, first observed by electron microscopy and subsequently at the light-microscopic level using immunological techniques, pointed to the involvement of these linear organelles in this intracellular translocation (see Hyams and Stebbings, 1979). Many different cellular organelles, including endosomes, lysosomes, mitochondria and various types of secretory vesicles, show directed translocation along microtubules, and their movement is clearly crucial to normal cell physiological function. The most extensively studied example has been the axonal processes of neurones, but various protozoa, fish pigment cells and insect ovaries also show exaggerated forms of intracellular translocation, and have proved valuable in studying the phenomenon.
Serum enhancement of human endothelial cell attachment to and spreading on collagens I and IV does not require serum fibronectin or vitronectin
Authors: Norris William D. , Steele John G. , Johnson Graham , Underwood P. Anne
Published: April 2021

The initial attachment and spreading of endothelial cells from human umbilical artery onto type i collagen, type IV collagen or gelatin substrata was shown to be enhanced by inclusion of serum in the culture medium. To test whether this serum effect was mediated by adsorption of serum fibronectin or vitronectin onto the collagen, these adhesive glycoproteins were selectively removed from the serum prior to addition to the culture medium. The stimulatory effect of serum on human endothelial cell spreading on collagens I and IV was also observed with serum from which either fibronectin or vitronectin, or both, had been selectively removed. The stimulatory effect for cell spreading on gelatin was diminished by selective removal of serum fibronectin, but unaffected by removal of vitronectin. Hu man endothelial cell attachment and spreading onto tissue culture plastic was abolished by removal of vitronectin from the serum in the culture medium. These results emphasize that the native structure of collagens is required for serum-enhancement of human endothelial cell attachment and spreading on native collagen types I and TV, and show that on these substrata the stimulated adhesion and spreading are not dependent upon adsorption of serum fibronectin or vitronectin onto the collagen substratum.
Contact activation in Chlamydomonas gametes by increased binding capacity of sexual agglutinins
Authors: Tomson A. M. , Demets R. , Musgrave A. , Kooijman R. , Stegwee D. , Ende H. Van Den
Published: April 2021

When the flagella of compatible gametes of Chlamydomonas eugametos contact one another, the capacity for sexual adhesion is rapidly increased. It is shown that during this so-called contact activation the amount of adhesion molecules, or agglutinins, on the flagellar surface remains relatively constant, indicating that the increase in sexual adhesiveness is mainly the result of an enhancement in binding capacity of the agglutinins. Contact activation coincides with an apparent aggregation of agglutinins in association with a weakening of the agglutinin binding to the membrane. Artificial clustering of the agglutinins, using the lectin wheat germ agglutinin, also leads to an increase in sexual adhesiveness. In the presence of anti-tubulin drugs compatible gametes make contact with one another but fail to increase their adhesiveness. It is proposed that micro-aggregation of agglutinin molecules, mediated by tubulin, underlies the enhancement of sexual binding capacity.
The circadian bioluminescence rhythm of Gonyaulax is related to daily variations in the number of light-emitting organelles
Authors: Fritz Lawrence , Morse David , Hastings J. W.
Published: April 2021

The number of scintillons, which are cellular organelles responsible for light emission in the marine alga Gonyaulax, were counted by both immunofluorescence and electron microscopic methods and found to vary tenfold between subjective day and subjective night. The number of scintillons peaks during the subjective night, as does stimulated bioluminescence (flashing). Furthermore, the number drops sharply at the time of the maximal spontaneous bioluminescence (glow), which occurs at the end of the night phase, suggesting that the breakdown of scintillons may be responsible for this mode of emission.
In situanalyses reveal that the two nuclei ofGiardia lambliaare equivalent
Authors: Kabnick Karen S. , Peattie Debra A.
Published: April 2021

The protozoan parasite Giardia lamblia has the unusual morphology of bearing two equalsized nuclei. This organism probably represents the earliest diverging lineage of eukaryotes, suggesting that its biological tactics may be transitional. To begin to understand the role played by the two equalsized nuclei in this organism, and perhaps the role this organism has played along the path to higher eukaryotes, we have analyzed the structure and function of these two nuclei. We show that the two nuclei are equivalent with respect to the amount of DNA harbored in each nucleus, the presence of ribosomal DNA sequences, and the transcriptional activity. We begin also to address the question of how these bilaterally symmetrical ancestors divide, by illustrating the mitotic plane of division.
Telomere cloning and mammalian chromosome analysis
Authors: Brown William R. A. , Dobson Melanie J. , Mackinnon Philip
Published: April 2021

Although eucaryotic chromosomes vary in size over five orders of magnitude and are constituents of diverse genetic systems the fundamental features of their telomeres appear to be almost completely conserved. This can be exploited to enable molecular cloning of human telomeres in yeast and suggests that many of the ideas that will arise from studies of telomeres in the experimentally tractable ciliates and yeasts will hold true of mammalian telomeres. The particular value of cloned mammalian telomeres is that they contribute reagents for mapping mammalian chromosomes and that they provide one set of elements for the construction of artificial mammalian chromosomes.
Cell proliferation in the repairing adult insect central nervous system: incorporation of the thymidine analogue 5-bromo-2-deoxyuridine in vivo
Authors: Smith P. J. S. , Howes E. A. , Treherne J. E.
Published: April 2021

Uptake of the thymidine analogue 5-bromo-2-deoxyuridine into non-neuronal cells of the insect central nervous system has been examined following a controlled lesioning of the glial elements. The pattern of BUdR labelling along the penultimate abdominal connective was examined over a period of 17 days. Cell proliferation occurred in and immediately around the site of damage in both perineurial and subperineurial glial cells but at different times post-lesion for the two regions. Proliferation in the perineurial zone was maximal at 6-8 days post-lesion but continued for at least 17 days. Subperineurial proliferation was less dramatic and peaked between days 8-11 post-lesion. In both areas division appears to be confined to the reactive glial cells. These results are discussed in the context of past research on this system, particularly with regard to the restoration of the bloodbrain barrier.
Pseudo-self-compatibility in ultraviolet-irradiated plants of Primula acaulis (‘pin’ morph)
Authors: Carraro Luisa , Gerola P. D. , Lombardo Giuliana , Gerola F. M.
Published: April 2021

Apoplastic peroxidase distribution in transmitting tissue of the stylar ‘neck’ was investigated using the DAB cytochemical reaction applied to electron microscopy in non-, self- and cross-pollinated pistils of Primula acaulis (‘pin’ morph) exposed or not to ultraviolet (u.v.) irradiation. In non-irradiated flowers, apoplastic peroxidase activity, which is present in non-pollinated pistils, is increased by self-pollination, whereas cross-pollination causes its disappearance from the central portion of the transmitting tissue. Apoplastic peroxidases localized in the central portion of the transmitting tissue are supposed to play a role in the predisposition of the pistil to reject incompatible pollen tubes and in the rejection mechanism itself. Pistil irradiation with u.v., which induces pseudo-self-compatibility, modified the aforementioned apoplastic peroxidase distribution. Shortly after u.v. irradiation of nonpollinated styles, apoplastic peroxidase activity was absent from the central portion of the transmitting tissue; some hours later peroxidase activity was restored, and 40 h after treatment, the ‘normal’ peroxidase distribution was observed. Our data suggest an u.v.-induced temporary removal of the ‘predisposition’ for incompatible pollen tube rejection. Moreover, soon after irradiation, the usually observed peroxidase production due to self-pollination was inhibited. Pseudo-self-compatibility, observed when self-pollination was carried out immediately after u.v. irradiation, was due to incompatible pollen tube elongation in a transmitting tissue devoid of apoplastic peroxidases and hindered in the rejection mechanism. However, pseudo-self-compatible pollen tube growth was not accompanied by the dramatic changes in transmitting tissue ultrastructure observed after compatible cross-pollination. The data indicate that, even if incompatible pollen tubes are not ‘rejected’, they are still ‘recognized’ and hindered in their absorption of cellular reserves from the transmitting tissue.
Polarity of endogenous and exogenous glycosyl-phosphatidylinositol-anchored membrane proteins in madin-darby canine kidney cells
Authors: Wilson Jean M. , Fasel Nicolas , Kraehenbuhl Jean-Pierre
Published: April 2021

Madin-Darby canine kidney cells (MDCK) were transfected with a cDNA encoding the glycosyl-phosphatidylinositol (GPD-anchored protein mouse Thy-1 in order to study the steady-state surface distribution of exogenous and endogenous GPI-linked proteins. Immunofluorescence of transfected cells grown on collagen-coated coverslips showed that expression of Thy-1 was variable throughout the epithelium, with some cells expressing large amounts of Thy-1 adjacent to very faintly staining cells. Selective surface iodination of cells grown on collagen-coated or uncoated transwell filters followed by immunoprecipitation of Thy-1 demonstrated that all the Thy-1 was present exclusively in the apical plasma membrane. Although cells grown on uncoated filters had much smaller amounts of Thy-1, it was consistently localized on the apical surfaces. Immunofluorescent localization of Thy-1 on 1 pm frozen sections of filter-grown cells demonstrated that all the Thy-1 was on the apical surface and there was no detectable intracellular pool. Phosphatidylinositolrspecific phospholipase C digestion of intact iodinated monolayers released Thy-1 only into the apical medium, indicating that Thy-1 was processed normally in transfected cells and was anchored by a GPI-tail. In agreement with previous findings, endogenous GPI-linked proteins were found only on the apical plasma membrane. These results suggest that there is a common mechanism for sorting and targeting of GPI-linked proteins in polarized epithelial cells.
Commentary How mobile are active RNA polymerases?
Authors: Cook P. R.
Published: April 2021

The photographs of ‘genes in action’ taken by Miller et al. (1970) are some of the most evocative in molecular biology. When bacteria are burst osmotically to spread their DNA, RNA polymerases can be seen frozen in the act of transcription as they processed along the template; the resulting nascent transcripts are covered with ribosomes, which are also caught in the synthetic act. These beautiful images adorn standard texts and we are all familiar with the model for transcription that they apparently confirm so powerfully. The model underlies our terminology - the ‘processivity’ of polymerases, nuclear ‘run-ons’, ‘upstream’ and ‘downstream’. But this model is usually a two-dimensional one. I will argue that recent data on the three-dimensional organisation of DNA ill-fit this accepted model and can be accommodated by an alternative model derived from studies on eukaryotes. The essential element of the alternative is the immobilisation of the polymerase so that the DNA moves past the fixed polymerase, rather than vice versa.
Tetrins: polypeptides that form bundled filaments in Tetrahymena
Authors: Honts Jerry E. , Williams Norman E.
Published: April 2021

The cortex of the ciliated protozoan Tetrahymena contains a number of fibrous elements, including a network of filaments that pervades the feeding organelle of this organism. The cluster of polypeptides (79–89K; K=103MT) in Tetrahymena pyriformis GL-C that constitute these filaments has been purified by in vitro assembly after solubilization in 1.0 M KI. Four distinct sets of these polypeptides, designated ‘tetrins’, have been shown to be distinguishable from each other by immunochemical and biochemical criteria. The smallest filaments reassembled in vitro were 3–4 nm in diameter and these fine filaments were seen to be bundled together into thicker strands of varying diameters, similar to those within the cell. The thicker filament bundles were clearly distinguishable from intermediate filaments, but fine filaments in these bundles were superficially similar to the 2–5 nm filaments described as microtubule-associated proteins in other organisms. The ultrastructure of the tetrin filaments localized within the feeding organelle reveals a substantial presence of these filaments apart from microtubules. In addition, circular dichroism measurements indicate a relatively low a-helical content for these filaments and suggest that the tetrins may be substantially different from other fine filament proteins such as the tektins and giardins.
Changes in the rate of oxygen consumption in synchronous cultures of the fission yeast Schizosaccharomyces Pombe
Authors: Novak B. , Mitchisonf J. M.
Published: April 2021

Oxygen consumption was measured with an oxygen electrode in synchronous cultures of S. pombe. There were changes during the cell cycle in the rate of oxygen uptake, which are most clearly shown as oscillations in acceleration curves (rate of the rate of uptake). Under various conditions of selection and induction synchrony the acceleration curves are similar to those found earlier for CO2 production. As with CO2 production, the oscillations continued after a block to the DNA-division cycle. There were, however, two differences between oxygen uptake and CO2 production. The oxygen oscillations were more marked and also were out of phase by half a cycle. The respiratory coefficient therefore changes through the cycle.
Adaptation to non-ammoniagenic medium and selective substrate feeding lead to enhanced yields in animal cell cultures
Authors: Hassell T. , Butler M.
Published: April 2021

Methods for the adaptation of three animal cell lines to media in which glutamine is replaced with either glutamate or 2-oxoglutarate are described. The cell Unes differ in their rate of adaptation. The consequences of the adaptation of the McCoy cell line to a glutamate-based medium was measured in terms of: cell yield (increased by 17%), ammonia accumulation (reduced by 70%), glucose consumption (decreased by >70%) and lactate accumulation (decreased by >75%).

The value of such adaptation and concomitant changes in energy metabolism lies in the potential for increased cell yields. Batch feeding of adapted cells in a microcarrier culture with a cocktail of glucose and amino acids resulted in increases in cell yields of 80% compared to unfed controls.
Effect of temperature on the assembly of tight junctions and on the mobility of lipids in membranes of ht29 cells
Authors: Cohen E. , Ophir I. , Henis Y. I. , Bacher A. , Shaul Y. Ben
Published: April 2021

In the human colon adenocarcinoma cell line HT29, tight junctions can be induced by treatment with appropriate proteases or salt solutions. The temperature dependence of induced tight junction formation is characterized by a marked sigmoidal behavior. The different methods of induction used in this study were characterized by threshold temperatures ranging from 15 to 32°C. Fluorescence photobleaching recovery measurements of the lateral diffusion of a fluorescent phospholipid probe in the cellular plasma membrane gave no evidence for a phase transition or for alteration in the organization of membrane lipids in lateral domains in the temperature range between 0 and 37°C. Moreover, dynamic parameters of the probe in the plasma membrane did not change substantially on mild treatment with trypsin. Thus, the temperature dependence of tight junction formation is not dictated by the bulk properties of the cytoplasmic membrane lipids. The observed temperature dependence suggests that the assembly of tight junctions is a cooperative process, which may involve conformational rearrangement in a protein precursor subsequent to its proteolytic activation.
Gene expression pattern of chicken erythrocyte nuclei in heterokaryons
Authors: Bergman Mathias , Ringertz Nils
Published: April 2021

Expression of erythro-specific chick genes was studied in heterokaryons prepared by fusing chick erythrocytes (CE) with rat myoblasts. In this type of heterokaryon the inactive erythrocyte nucleus takes up nuclear proteins of myoblast origin and undergoes transcriptional reactivation. In order to study the stability of the genetic programming of the reactivated CE nucleus, chick gene expression was examined by analysis of RNA from the heterokaryons. Probes for several erythro- and chick-specific genes were used. The heterokaryons showed strong expression of the chick histone H5 and adult β-globin genes, while other genes, e.g. the transcription factor Eryf1 gene, normally expressed during erythroid differentiation, were not transcribed. Although the CE used were of the definitive lineage, the heterokaryons showed activation of the chick embryonic β-globin gene, i.e. a gene normally expressed only in CE of the primitive lineage.

We conclude that the reactivation of the mature CE nucleus in a rat cytoplasm resulted in a more immature erythroid gene expression pattern. The activation of the embryonic β-globin gene indicated a switch of the lineage-specific gene expression pattern. This switch occurred in the absence of DNA replication. The strong expression of the globin and H5 genes in heterokaryons, in the absence of expression of the regulatory factor Eryf1, suggested the existence of Eryf1-independent regulatory mechanisms for erythroid gene expression in these cells.
Peroxisomes induced in Candida Boidinii by methanol, oleic acid and d-alanine vary in metabolic function but share common integral membrane proteins
Authors: Goodman Joel M. , Trapp Steven B. , Hwang Harold , Veenhuis Marten
Published: April 2021

Peroxisomes massively proliferate in the methylotrophic yeast Candida boidinii when cultured on methanol as the only carbon and energy source. These organelles contain enzymes that catalyze the initial reactions of methanol utilization. The membranes contain abundant proteins of unknown function; their apparent molecular masses are 20, 31, 32 and 47×10 3M r and are termed PMP20, PMPs31-32 and PMP47. Recently, we reported that peroxisomes in this yeast are also induced by oleic acid and D-alanine as carbon sources, and that these peroxisomes contain increased concentrations of the enzymes of fatty acid β-oxidation or D-amino acid oxidase, respectively. Tliis report extends these findings and further compares the enzyme composition from peroxisomes induced by methanol, oleic acid and D-alanine. The patterns of matrix proteins represented on SDS-polyacrylamide gels from peroxisomes induced by oleic acid or D-alanine were found to be very different from those of peroxisomes induced by methanol. In order to differentiate between membrane proteins that have specific functions in pathways of substrate utilization from those with more generalized functions, peroxisomal membranes from cultures grown on methanol, oleic acid or D-alanine were purified. Analysis of these fractions demonstrated that while PMP20 is found only in peroxisomes induced by methanol, the PMPs31-32 and PMP47 were the abundant peroxisomal membrane proteins (PMP) regardless of inducing substrate. The data strongly suggest that the function of PMP20 is related to methanol metabolism. In contrast, the functions of PMPs31-32 and PMP47 are ‘substrate-nonspecific’. We speculate that they may relate to the structure, assembly or general function of the organelle.
Antibody markers of basal cells in complex epithelia
Authors: Purkis P. E. , Steel J. B. , Mackenzie I. C. , Nathrath W. B. J. , Leigh I. M. , Lane E. B.
Published: April 2021

In the course of immunohistochemical studies it has become apparent that there is a distinct phenotype of keratin expression that is shared by basal epithelial cells in a variety of different tissues. A basal cell can be defined as a cell in contact with a basal lamina but with no free luminal surface; this distinguishes it from a simple epithelial cell, which has a free luminal surface as well as basal lamina contact, and from stratifying suprabasal kératinocytes, which have neither basal lamina contact nor free luminal surface. All basal cells, whether they are in glandular ductal or secretory epithelia, or in stratified squamous epithelia, express the keratin pair K5 and K14. In this paper we describe monoclonal and polyclonal antibodies that are monospecific for both keratins 14 and 5 or are specific for denaturationsensitive epitopes unique to basal cells, including five new monoclonal antibodies: LL001 and LL002 (to keratin 14), 2.1.D7 (to keratins 5, 6 and 8), and LH6 and LH8 (conformation-specific basal cell markers). These antibodies have been used to monitor the distribution of the basal cell phenotype and to demonstrate the expression of keratins 5 and 14 in this cell type, in both stratified epithelia and mixed epithelial glands. The consistent association of this keratin pair with basal cells suggests a possible specific function for these keratin in reinforcing epithelia under physical stress, whilst expression of these keratins may conflict with the differentiated functions of most simple epithelial cells.
Characteristics of cells that give rise to the central nervous system
Authors: Temple Sally
Published: April 2021

Neural induction by the axial mesoderm designates a population of embryonic ectoderm cells to give rise to the central nervous system (CNS). The cells of the neural rudiment are overtly similar and are distributed in a single cell layer that folds up to become the neural tube. The nuclei of the neural tube cells undergo a ‘to and fro’ migration in synchrony with their cell cycles, and the mitotic phase occurs at the border of the neural tube lumen that comprises the early ventricular system (Sauer, 1935). As development proceeds, neurons and glioblasts migrate away from this ventricular zone and begin to form the mature CNS. Different classes of CNS cells arise on well-defined time-schedules (see Jacobson, 1978, for a review) and the precise timing of cell differentiation is likely to be important in generating CNS cytoarchitecture and appropriate cell–cell interactions.
A centrosomal antigen localized on intermediate filaments and mitotic spindle poles
Authors: Buendia Brigitte , Antony Claude , Verde Fulvia , Bornens Michel , Karsenti Eric
Published: April 2021

A monoclonal antibody (CTR2611) raised against centrosomes isolated from human lymphocytes (KE37) stains the pericentriolar material and intermediate filaments in the same cells. In MDCK cells, where most of the microtubules do not originate from the pericentriolar region during interphase, the antigen is distributed along intermediate filaments. At the onset of mitosis, a large fraction of the CTR2611 antigen associates with the minus-end domain of the microtubules of the mitotic spindle but not with the pericentriolar region itself. Treatment of mitotic MDCK cells with taxol leads to the assembly of many microtubule asters in the cytoplasm at the expense of the mitotic spindle. The CTR2611 antigen is present in the center of each of these asters. Similar asters can also be produced in vitro by adding taxol to concentrated Xenopus egg mitotic cytoplasm. Again, the antigen is found close to the center of the asters. These results suggest that CTR2611 antigen is associated with a material involved in microtubule nucleation or microtubule minus-end stabilization. The monoclonal antibody recognizes a 74×103Mr polypeptide and other polypeptides at 120×103Mrand 170×103Mr. The 74×103Mr polypeptide is found in all species examined so far, suggesting that it contains a highly conserved epitope.
Subpopulations of chondrocytes from different zones of pig articular cartilage: Isolation, growth and proteoglycan synthesis in culture
Authors: Siczkowski Martin , Watt Fiona M.
Published: April 2021

Articular cartilage varies in ultrastructure and composition with distance from the articular surface. We have cultured chondrocytes from different zones of pig articular cartilage and investigated whether there are intrinsic differences in their behaviour that might account for the variation observed in intact tissue. On isolation, cells from the upper third of the cartilage were smaller than those of the lower third, but this difference was not maintained in culture. Upper zone cells attached and spread more slowly than lower zone cells; morphological differences between the two populations could be seen for several weeks. The growth rates of the two populations were similar, but upper zone cells reached a lower confluent density. Levels of protein synthesis were similar for both populations, but upper zone cells deposited less proteoglycan in the cell layer. On isolation, the percentage of upper zone cells that stained positive with MZ15, a monoclonal antibody to keratan sulphate, was smaller than the percentage of lower zone cells, but this difference was lost after several days in culture. Nevertheless, the keratan sulphate content of proteoglycan synthesised by lower zone chondrocytes at high density was greater than of that synthesised by upper zone cells. The proportion of nonaggregating proteoglycan was greater in upper than lower zone cartilage and this difference was also observed in long-term cultures. Proteoglycans were further characterised by composite and polyacrylamide gel electrophoresis and by immunoblotting; differences detected in cartilage extracts were not, however, maintained in culture; instead, the small proteoglycans synthesised by both upper and lower zone cells varied with plating density. Finally, alkaline phosphatase, a marker of hypertrophic, calcifying cartilage, was only expressed in lower zone cultures. We conclude that some of the observed heterogeneity of articular cartilage reflects intrinsic differences between the cells of different zones, whereas some may reflect the response of chondrocytes to different environmental conditions.
Modulation of native chondroitin sulphate structure in tissue development and in disease
Authors: Caterson Bruce , Mahmoodian Fatemeh , Sorrell J. Michael , Hardingham Tim E. , Bayliss Michael T. , Carney Stephen L. , Ratcliffe Anthony , Muir Helen
Published: April 2021

Chondroitin sulphate proteoglycans are synthesised by different tissues and cell types, and the chondroitin sulphate chains are variably sulphated. Three monoclonal antibodies 3B3, 7D4 and 6C3 that recognise different native chondroitin sulphate epitopes have been used to investigate changes in structure during embryonic tissue development in the chick and in the response of mature canine articular cartilage during experimental osteoarthritis. Strong focal expression of the epitopes was seen during development of chick bursa, which was different for the three epitopes and which changed during 5 days of development. In embryonic chick limb, although chondroitin sulphate is present throughout the cartilage, the 3B3 epitope, which is at the non-reducing terminus of chains, was only expressed on chondroitin sulphate within one region of the sub-articular cartilage. In mature canine articular cartilage the expression of this epitope on proteoglycans was very low, but when determined 3 or 6 months after induction of experimental osteoarthritis the level was greatly increased in all joints tested (23/23). The abundance of the other two native chondroitin sulphate epitopes was also increased in this experimental disease. The results show that expression of the chondroitin sulphate epitopes detected by the monoclonal antibodies changes during cellular differentiation and development and suggests that it is closely controlled by the cells synthesising chondroitin sulphate chains.
A vibrating electrode analysis of extracellular ion currents in Acetabularia acetabulum
Authors: O’shea Paul , Goodwin Brian , Ridge Irene
Published: April 2021

An investigation of extracellular ionic currents in Acetabularia acetabulum is presented. Utilising the vibrating electrode technique it is shown that there are large (up to 380μAcm-2) light-dependent and small (up to lOμAcm-2) light-independent extracellular ionic currents around Acetabularia. The current density was greatest at the rhizoid and diminished towards the developing apex where there was no measurable current.

Ion-replacement and ion-transport inhibitor studies indicated that Cl-was the main constituent of the light-dependent and light-independent currents. Calcium ions were found to contribute about 5–15% of the light-independent current and <1% of the light-dependent current, as deduced from cobalt inhibition studies. Possible mechanisms responsible for these phenomena are discussed briefly.
The three-dimensional arrangement of chromosomes at meiotic metaphase I in normal and interchange heterozygotes of Briza humilis
Authors: Moss Janet M. , Murray Brian G.
Published: April 2021

Pollen mother cells at metaphase I have been reconstructed from serial sections in normal and interchange heterozygotes of Briza humilis. The pollen mother cells have an irregular shape with a prominent projection from the tangential face into the anther loculus. The seven bivalents of the normal plant are usually arranged with one bivalent in a central position surrounded by a ring of the remaining six or as a ring of all seven bivalents. The centrahperipheral distribution of quadrivalents is different in two different interchange plants; in a sector analysis, where cells are divided into fourquarters relative to the tangential face of the pollen mother cell, the two plants also show differences in quadrivalent distribution, indicating that individual chromosomes occupy different positions in the cell. The relevance of these results to the positioning of quadrivalents in lateral squashes of meiotic metaphase I are discussed.
Broad spectrum pan-cadherin antibodies, reactive with the C-terminal 24 amino acid residues of N-cadherin
Authors: Geiger Benjamin , Volberg Tova , Ginsberg Dorit , Bitzur Sigal , Sabanay Ilana , Hynes Richard O.
Published: April 2021

We describe here the preparation and application of antibodies directed against a synthetic, 24 amino acid long, peptide corresponding to the conserved cytoplasmic C terminus of N-cadherin. We demonstrate here that the antibodies to the synthetic peptide react extensively with all known members of the cadherin family and, in addition, recognize novel cadherins in a variety of cells and tissues, suggesting that these antibodies indeed exhibit pan-cadherin reactivity. By Western blot screening of chicken tissues at least 4 different immunoreactive bands were resolved, commonly disclosing 2–3 distinct bands within the same tissue. The pan-cadherin antibodies also displayed a broad interspecies cross reactivity, recognizing cadherins in man, bovine, canine, avian, amphibian and teleost cells. This property renders these antibodies excellent reagents for the cloning and identification of novel cadherins. Immunocytochemical labelling with the pan-cadherin antibodies, at the light- and electron-microscope levels, revealed an extensive reactivity with intercellular adherens junctions in cardiac muscle and in various epithelia. We thus propose that the pan-cadherin antibodies may be used as ubiquitous cadherin probes and serve as markers for adherens junctions.
Subcellular distribution of hepatic alanine:glyoxylate aminotransferase in various mammalian species
Authors: Danpure Christopher J. , Guttridge Keith M. , Fryer Patricia , Jennings Patricia R. , Allsop Jennifer , Purdue P. Edward
Published: April 2021

The subcellular distribution of alanine:glyoxylate aminotransferase 1 (AGT1) enzyme activity and immunoreactive protein has been determined in the livers of a variety of mammalian species (marmoset, baboon, cat, rabbit, pig, sheep) using the techniques of post-embedding protein A-gold immunoelectron microscopy and isopycnic density gradient centrifugation. In baboon and rabbit livers, AGT1 was exclusively peroxisomal. Morphometric analysis of the distribution of immunoreactive AGT1 protein in cat liver showed that 91–92% was located in the mitochondria with 8–9% in the peroxisomes. In marmoset liver, 59% of AGT1 was found in the mitochondrial matrix and 41% in the peroxisomal matrix. The results from pig and sheep were ambiguous, because of the low levels of expression of AGT1. The implications of these data in terms of the metabolic roles of AGT1 (gluconeogenesis and glyoxylate detoxification) and in terms of the evolutionary acquisition and loss of functional mitochondrial and peroxisomal targeting sequences are discussed.
Kinetochore fiber formation in dividing generative cells of Tradescantia Kinetochore reorientation associated with the transition between lateral microtubule interactions and end-on kinetochore fibers
Authors: Liu Bo , Palevitz Barry A.
Published: April 2021

Division of the generative cell of Tradescantia virginiana is unusual in that a typical bipolar spindle is not present Instead, the cell contains an axial system of microtubule (Mt) bundles, with kineto-chores distributed along the length and depth of the cell. Kinetochore fibers appear to be derived from and remain attached to the Mt bundles. Localizations with both anti-tubulin and CREST serum were performed in order to probe this relationship further. Pairs of CREST-positive, fluorescent dots presumed to be kinetochores are initially oriented transverse to the cell axis and appear to be associated with the Mt bundles via latéral interactions. Adjacent pairs are often joined to the same bundles, like rungs on a ladder. Lateral interactions are then converted intoor replaced by end-on kinetochore fibers similar in morphology to those seen in other cells. This conversion is accompanied by a realignment of the kinetochore pairs along the long axis of the cell. In addition, the center-to-center spacing between filial kinetochores doubles. Interconnections between kinetochore fibers and surrounding Mts appear to be maintained during the transition. These results may provide a general insight into the manner in which kinetochores interact with the division apparatus in eukaryotes.
BWTG3 hepatoma cells can acquire phenylalanine hydroxylase, cystathionine synthase and CPS-I without genetic manipulation, but activation of the silent OTC gene requires cell fusion with hepatocytes
Authors: Farmer A. A. , Goss S. J.
Published: April 2021

The mouse hepatoma BWTG3 has been tested for its ability to grow in three different media that select for traits normally expressed in adult liven homocysteine medium to select for cystathionine synthase (CS), tyrosine-free medium for phenylalanine hydroxylase (PH), and ornithine medium for carbamylphosphate synthetase-I (CPS-I) and ornithine transcarbamylase (OTC). In no case were the cells immediately capable of bulk growth, showing that all these traits were in some degree deficient. However, the cultures in homocysteine medium and in tyrosine-free medium both gave rise, spontaneously, to growing clones with frequencies of approximately 10−3 and 10−B, respectively. The deficiencies of CS and PH were accordingly excluded from further study, in view of their inherent instability. In contrast, no colonies ever formed in ornithine medium. Though neither CPS-I nor OTC were detectable in stock BWTG3 cells, it was found that CPS-I was readily inducible by hormones. The deficiency of OTC, however, appeared to be totally stable, showing no reversion in response either to hormones or to azacytidine treatment. This deficiency was investigated by fusing the hepatoma to OTC+ liver cells prepared from normal or sparse-fur (spf) mice. Sparse-fur mice were used because their OTC is mutant and has a distinctive pH-dependence. OTC+hybrids were readily produced, without the need for any specific selection for OTC, and, in one case at least, with only minimal chromosome segregation. In all the OTC+ hybrids made with spf cells, there was clear reactivation of the wild-type, hepatoma-derived OTC gene. The properties of the OTC in these hybrids varied according to the dosage of genes contributed by the hepatoma and the spf liver cells. The most likely explanation of these results is that the hepatoma lacks some activator of OTC expression, and that this deficiency is corrected in the hybrids, presumably by activator supplied by the liver cells.
Mechanism of collagen phagocytosis by human gingival fibroblasts: importance of collagen structure in cell recognition and internalization
Authors: Knowles G. C. , McKeown M. , Sodek J. , McCulloch C. A. G.
Published: April 2021

Phagocytosis of extracellular collagen by fibroblasts appears to be the principal pathway of collagen degradation in the physiological turnover of connective tissues. To study the mechanism of collagen phagocytosis, subconfluent gingival fibroblasts were serum-starved and incubated for up to 16 h with collagen-coated fluorescent latex beads. Internalization of beads was measured either by flow cytometry or by image analysis. Phagocytosis was blocked by inactivation of protein kinase C with staurosporin, and was also decreased significantly (32%) when cells were pre-incubated for 6h with cycloheximide. Phagocytosis of collagen-coated beads appeared to be receptor-mediated, since internalization was inhibited threefold by the cellattachment blocking peptide (GRGDSP). The process of internalization was influenced by the type of collagen and its molecular structure. Thus, internalization was decreased in the order: type I>V>III collagen, and internalization of type I collagen was reduced significantly by digestion with either bacterial (45%) or vertebrate (38%) collagenase. However, collagen denaturation, which facilitates binding to fibronectin, did not effect internalization. Although concanavalin A stimulated both phagocytosis (71 %) and collagenase synthesis, PM A and IL-1, which also increase collagenase expression, did not affect phagocytosis, indicating that phagocytosis of collagen-coated beads does not require collagenase. Moreover, analysis of tissue inhibitor of metalloproteinase expression revealed no difference between phagocytic and non-phagocytic cells. Collectively, these results demonstrate that collagen phagocytosis is regulated through protein kinase C and is also dependent upon cellular recognition and collagen structure, but not on the expression of collagenase.
Distinguishing the sites of pre-rRNA synthesis and accumulation in Ehrlich tumor cell nucleoli
Authors: Thiry Marc , Goessens Guy
Published: April 2021

The precise location of transcribing rRNA genes within Ehrlich tumor cell nucleoli has been investigated using two approaches: high-resolution autoradiography of cells pulse-labelled with tritiated uridine, varying the exposure time, and in situ-in vitro transcription coupled with an immunogold labelling procedure.

When autoradiographic preparations are exposed for a short time, silver grains are found associated almost exclusively with interphasic cell nucleoli. Labelling of extranucleolar areas requires longer exposure. Within the nucleolus, the first sites to be revealed are in the dense fibrillar component. Prolonging exposure increases labelling over the dense fibrillar component, with label becoming more and more apparent over the fibrillar centers. Under these conditions, however, labelling does not extend into the granular component, and no background is observed.

Initiation of transcription on ultrathin cell sections occurs preferentially at the borders of condensed chromatin blocks and in their close vicinity. The condensed chromatin areas themselves remain unlabelled. Inside most nucleoli, gold-particle clusters are mainly detected in the fibrillar centers, especially at their periphery, whereas the dense fibrillar component and the granular component remain devoid of label.

These results, together with previous observations made on the same cell type, clearly indicate that the fibrillar centers are the sites of rRNA gene transcription in Ehrlich tumor cell nucleoli, while the dense fibrillar component is the site of pre-rRNA accumulation.
Lectures on histology, delivered at the Royal College of Surgeons of England in the Session 1851-52.
Authors: Quekett John
Published: April 2021

In pursuance of the plan laid down in his first volume, Professor Quekett has in this work presented us with another instalment of the histology of organic beings. The subject here taken up is the structure of the skeleton of plants and invertebrate animals. Although we hope Mr. Quekettt may be encouraged to proceed with the publication of his lectures, we think he has very judiciously selected his present subject as supplying a want of the physiologist and the microscopic inquirer. The fact is, at the present day, there is little to be added to our knowledge of the histology of the human body, and what we really want to complete our knowledge of the structure of organized beings, is more extended researches upon the lower animals. Our knowledge of vegetable structure, also, is much more extensive than it is of the lower animals. To all inquirers, then, in the field of comparative histology, this volume of Mr. Quekett’s lectures will be found very acceptable. We cannot commend Mr. Quekett’s volume as a comprehensive treatise upon all that is known with regard to the hard parts of plants and invertebrate animals ; but, like that which renders all his other writings valuable, it bears the impress of original observation, and in all cases the reader may rely upon the accuracy of the author. Mr. Quekett nowhere commits himself to physiological inferences or speculations, leaving those who follow him to form their own opinions with regard to the functions and relations of the parts he describes.