bluuebunny/crossref_metadata_2025_split huggingface dataset:
The initiation of new gene transcription duringXenopusgastrulation requires immediately preceding protein synthesis
Authors: Cascio S. , Gurdon J. B. 
Published: April 2021

ABSTRACTThe incubation of Xenopus embryo fragments in cycloheximide at 5 or 10μgml−1 rapidly inhibits protein synthesis to 10 % or less of control levels. In most batches of embryos, treatment with cycloheximide for up to 1 h causes no obvious cellular damage and protein synthesis is fully restored to normal levels 5h later. Transcript analysis with RNA probes shows that the inhibition of protein synthesis at late blastula or early gastrula stages completely suppresses the normal initiation of actin gene transcription at the mid-late gastrula stage. This applies to muscle-specific actin genes, whose transcription is initiated by induction, as well as to cytoskeletal actin genes not activated by induction. Two-dimensional gel protein analysis shows that cycloheximide irreversibly inhibits only 10 % of all genes normally expressed at a postneurula stage and that all of these are genes whose expression is normally initiated during or soon after gastrulation. Cycloheximide treatment causes a limited reduction of DNA synthesis, and no reduction of overall RNA synthesis. We conclude that the initiation of new gene transcription during gastrulation in Xenopus is dependent on the immediately preceding synthesis of certain proteins.
The pattern of innervation in serially duplicated axolotl limbs: further evidence for the existence of local pathway cues
Authors: Stephens Nigel , Holder Nigel 
Published: April 2021

ABSTRACT
The innervation of the biceps muscle was examined in regenerated and vitamin A-induced serially duplicated axolotl forelimbs using retrograde transport of horseradish peroxidase. The regenerated biceps muscle becomes innervated by motor neurones in the same position in the spinal cord as the normal biceps motor pool. In previous experiments in which the innervation of a second copy of a proximal limb muscle was examined in serially duplicated limbs (Stephens, Holder & Maden, 1985), the duplicate muscle was found to become innervated by motor neurones that would normally have innervated distal muscles. In the present study, the innervation of the second copy of biceps was examined under conditions designed to encourage nerve sprouting from ‘correct’ biceps axons. Following either partial limb denervation or denervation coupled with removal of the proximal biceps, the second copy of the muscle was still innervated by inappropriate motor neurones, which again would normally innervate distal limb muscles. These results are interpreted as evidence for the necessity for an appropriate local environment for axonal growth to allow reformation of a correct pattern of motor innervation in the regenerated limb.
Mode of action of ammonia and amine on rRNA synthesis in Xenopus laevis embryonic cells
Authors: Shiokawa Koichiro , Fu Yuchang , Kawazoe Yuichi , Yamana K. 
Published: April 2021

ABSTRACT
Recently, we found that rRNA synthesis in dissociated embryonic cells of Xenopus laevis is selectively inhibited by ammonium salts added to their surrounding medium. Similar effects were also observed in cells treated with amines. In this report, we analysed in more detail the effects of an ammonium salt and trimethylamine on rRNA synthesis in Xenopus embryonic cells cultured under several different conditions.
Results obtained showed that ammonia and trimethylamine inhibit formation of 40S pre-rRNA, without inducing breakdown (wastage) or aberrant processing of the 40S pre-rRNA. Such inibitory effects were also shown not to be due to interference with cellular ATP level. Furthermore, we found that the effects of both ammonium salt and trimethylamine were completely abolished when Na+ in the culture medium of the testing cells was replaced by choline ions. These results favour the view that the inhibition of rRNA synthesis by ammonia and amine is realized at the transcriptional level or at the step before the formation of 40S pre-rRNA, most probably via a slight increase of intracellular pH, but not via an inhibition in energy-generating systems.
Differentiation and innervation of the atrioventricular bundle and ventricular Purkinje system in sheep heart
Authors: Canale E. , Smolich J. J. , Campbell G. R. 
Published: April 2021

ABSTRACTThe development of the atrioventricular bundle (AVB) and ventricular Purkinje system and their innervation have been studied in fetal sheep from 27 to 140 days gestation (term is 147 days). The AVB initially consisted of a primordium, which lacked innervation and was composed of small, relatively undifferentiated myocytes. Differentiation of Purkinje-like cells within the AVB began near its distal end and extended towards the atrioventricular node (AVN). Differentiation of the ventricular Purkinje system extended distally from the region of bifurcation of the AVB from cells that were indistinguishable from the working myocardium and continuous with the AVB primordium. Differentiation of Purkinje-like AVB cells was complete by 46 days gestation but Purkinje fibres were still differentiating within the ventricular wall at 60 days gestation. The main morphological changes included a large increase in cell size and organization into strands, development of characteristic glycogen-filled regions containing many intermediate filaments and early development of myofibrillar M lines compared to the working myocardium.The differentiation of AVB cells and the ventricular Purkinje system preceded their innervation. The AVB became innervated earlier than ventricular Purkinje fibres, intimate contacts between proximal AVB cells and nerve axons being present at 60 days gestation. Nerve fibres were present in the septomarginal band at this time, however, en passant associations with ventricular Purkinje fibres were rarely observed until 140 days gestation and intimate contacts were not present at any stage.Although the AVB and ventricular Purkinje system of adult sheep are composed of morphologically similar cells, the present study demonstrates that they differ in origin and their mode of differentiation as well as timing and intimacy of innervation. Innervation is not part of the developmental mechanism leading to the differentiation of Purkinje fibres. No primordium of the ventricular Purkinje system could be identified, suggesting that the mechanism of differentiation of ventricular Purkinje fibres involves recruitment from early working myocardium.
Retinal axons with and without their somata, growing to and arborizing in the tectum of Xenopus embryos: a time-lapse video study of single fibres in vivo
Authors: Harris William A. , Holt Christine E. , Bonhoeffer Friedrich 
Published: April 2021

ABSTRACT
Time-lapse video recordings were made of individual retinal ganglion cell fibres growing to and terminating in the optic tectum of Xenopus embryos. The fibres were stained by inserting a crystal of the lipophilic fluorescent dye, Dil, into the developing retina. Growth cones were observed in the optic tract and tectum using 20 ms flashes of light to induce fluorescence approximately once every minute. Fluorescent images were captured with a SIT camera, processed and saved on a time-lapse video recorder. The main conclusions from observing normal growing fibres are as follows. (1) Axons in the optic tract grow at a steady rate directly toward their targets without retracting or branching. (2) As axons approach the tectum they slow down and their growth cones become more complex. (3) Most terminal branches in the tectum are formed by back branching rather than by bifurcation of leading growth cones.
In a second experiment, labelled growing axons were separated from their cell bodies by removing the retina. Such isolated axons continued to grow for up to 3h in vivo and were capable of recognizing the tectum and arborizing there. This result shows that growth cones must contain the machinery needed to sense and respond to their specific pathways and targets.
Factors controlling induction of commitment of murine erythroleukemia (TSA8) cells to CFU-E (colony forming unit-erythroid)
Authors: Noguchi Tsuyoshi , Fukumoto Hiroaki , Mishina Yuji , Obinata Masuo 
Published: April 2021

ABSTRACT
On addition of DMSO, the MEL cell line TSA8 becomes committed into erythroid progenitor cells (CFU-E) which can form differentiated colonies in the presence of erythropoietin. To understand the mechanism of cellular commitment, the number and the affinity of the receptors for erythropoietin were estimated. The affinity of the receptors did not change before or after induction. The number of receptors changed depending on the growth phase, but was not dependent on the addition of the inducer. Thus, the presence of the receptors for erythropoietin may be required, but are not essential for responsiveness to erythropoietin.
Further examination of the optimum conditions for commitment suggests that the concomitant actions of induced factor(s) with the receptors may control commitment of TSA8 cells to CFU-E.
Inhibitory and stimulatory influences on mesodermal erythropoiesis in the early chick blastoderm
Authors: Kessel Joan , Fabian Barry 
Published: April 2021

ABSTRACT
We use a standing-drop culturing method to investigate the effect on mesodermal erythropoiesis of ectoderm and endoderm from the .area opaca vasculosa (AOV) and area pellucida (AP) of stage-4 chick blastoderms. We find that ectoderm from the AOV and ectoderm and endoderm from the AP exert an inhibitory influence on mesodermal erythropoiesis. This inhibitory influence is coupled with the tendency of the explants to spread out and become flattened in culture. In contrast, endoderm from the AOV is found to be stimulatory, in agreement with previous studies. We correlate these in vitro inhibitory and stimulatory influences with the morphogenetic patterns that occur during normal development.
Evidence against electrophoresis as the principal mode of protein transport in vitellogenic ovarian follicles of Drosophila
Authors: Bohrmann Johannes , Gutzeit* Herwig 
Published: April 2021

ABSTRACT
Charged cell constituents in polytrophic insect follicles are thought to be transported in the nurse celloocyte syncytium by way of electrophoresis. This concept, proposed by Woodruff & Telfer (1980) was based on electrophysiological data and microinjection of heterologous proteins using Hyalophora follicles. By microinjecting fluorescently labelled acidic and basic proteins into the nurse cells or oocyte of vitellogenic Drosophila follicles, we failed to obtain evidence for charge-dependent migration of these molecules. We have also analysed the proteins of nurse cells and oocyte on isoelectric focusing gels, by means of twodimensional gel electrophoresis, and by ion exchange chromatography to see if basic or acidic proteins accumulate in vivo in nurse cells and oocyte, respectively. For the bulk of the follicular proteins we found no accumulation. Further evidence against an electrophoretic transport system in Drosophila was obtained by estimating the intracellular pH from the colour of indicator dyes microinjected into the follicles; the results indicate that the pH in the nurse cell cytoplasm is lower than that in the ooplasm. According to the model developed for Hyalophora, electrophoretic transport would be favoured by high pH in the nurse cell cytoplasm.
Characterization of sea urchin primary mesenchyme cells and spicules during biomineralization in vitro
Authors: Decker Glenn L. , Morrill John B. , Lennarz William J. 
Published: April 2021

ABSTRACT
An in vitro culture system for primary mesenchyme cells of the sea urchin embryo has been used to study the cellular characteristics of skeletal spicule formation. As judged initially by light microscopy, these cells attached to plastic substrata, migrated and fused to form syncytia in which mineral deposits accumulated in the cell bodies and in specialized iilopodial templates. Subsequent examination by scanning electron microscopy revealed that the cell bodies and the filopodia and lamellipodia formed spatial associations similar to those seen in the embryo and indicated that the spicule was surrounded by a membrane-limited sheath derived by fusion of the filopodia. The spicules were dissolved from living or fixed cells by a chelator of divalent cations or by lowering the pH of the medium. However, granular deposits found in the cell bodies appeared relatively refractory to such treatments, indicating that they were inaccessible to agents that dissolved the spicules. Use of rapid freezing and an anhydrous fixative to preserve the syncytia for transmission electron microscopy and X-ray microprobe analysis, indicated that electron-dense deposits in the cell bodies contain elements (Ca, Mg and S) common to the spicule. Examination of the spicule cavity after dissolution of the spicule mineral revealed openings in the filopodia-derived sheath, coated pits within the limiting membrane and a residual matrix that stained with ruthenium red. Concanavalin A-gold applied exogenously entered the spicule cavity and bound to matrix glycoproteins. Based on these observations, we conclude that components of the spicule initially are sequestered intracellularly and that spicule elongation occurs in an extracellular cavity. Ca2+ and associated glycoconjugates may be routed to this cavity via a secretory pathway.
An ultrastructural and morphometric analysis of an in vivo contact guidance system
Authors: Wood Andrew , Thorogood Peter 
Published: April 2021

ABSTRACT
The pectoral fin bud of the developing teleost embryo contains a highly ordered extracellular matrix of collagenous fibrils, called ‘actinotrichia’. During invasion of the fin fold, mesenchymal cells, migrating distally from the base of the fin, become contact aligned by the actinotrichial fibrils. Behavioural aspects of this response have previously been studied using Nomarski differential interference contrast microscopy and time-lapse video recording (Wood & Thorogood, 1984). Here we present an ultrastructural description of these cells and their matrix associations and a computer-based morphometric analysis of selected parameters within the migration substratum, relevant to this in vivo ‘contact guidance’ phenomenon. The study shows that a differentiated and aligned matrix of actinotrichial fibrils can be detected before invasion of the fin fold, at levels up to 40/zm distal to the advancing mesenchymal cell margin. Subsequently, during invasion of the fin fold, aligned mesenchymal cells and processes are almost exclusively associated with actinotrichia and not the intervening surface of the epithelial basal lamina. However, aligned cell processes appear to avoid the smaller actinotrichia and at late stages of development 87·0 % of actinotrichia without cell process contacts are distributed at the lower end of the size range. Study of cell ultrastructure revealed a complete absence of cytoskeletal organization within this mesenchymal cell population, although cytoskeletal components are clearly visible in adjacent epithelia. The computer-based morphometric survey of the migration substratum has shown a gradual but progressive increase in the mean diameter of actinotrichia at a level at which distal cell processes are first detectable in sections of fins. However, at similar levels over the same period the mean value for interactinotrichial spacings remained virtually constant. These results suggest that the spacing between actinotrichia is not significant in contributing to progressive changes in mesenchymal cell phenotype, but that the actinotrichia themselves are strongly implicated in providing the guidance cues to direct cell migration within the developing fin and the initiation of cell migration. These findings are discussed in the general context of cell movement and contact guidance both in vivo and in vitro.
Mechanical aspects of the mesenchymal influence on epithelial branching morphogenesis of mouse salivary gland
Authors: Nogawa Hiroyuki , Nakanishi Yasuo 
Published: April 2021

ABSTRACT
Three activities of mesenchymes from mouse embryonic submandibular gland, lung, stomach, mandible and skin were comparatively studied. The first ability was the induction of branching of submandibular epithelial lobes. Epithelial lobes branched well in recombination with submandibular or lung mesenchyme, less well with stomach mesenchyme, but never with mandibular or dermal mesenchyme. The second behavioural aspect studied was the contraction of collagen gels. When respective mesenchymal cells were dispersed at 2 0×105 cells ml−1 in collagen gels (1×5 mg ml−1) and incubated, dermal mesenchymal cells had the highest gel-contracting activity. The gelcontracting activity of submandibular or lung mesenchymal cells was two thirds as high as that of dermal cells and that of stomach or mandibular mesenchymal cells was much lower. The last activity was to separate three plastic beads that were recombined with mesenchymes in place of epithelial lobes. Salivary or lung mesenchyme effected a large separation of the beads, whereas dermal mesenchyme left beads contacting one another. There was a positive correlation between the branch-inducing activity and the beads-separating activity within the five kinds of mesenchymes. In timelapse cinematography of recombinates, cells of submandibular and lung mesenchyme were observed moving (or flowing) around, and their property was different from that of dermal mesenchyme. In the presence of cytochalasins, both the contraction of collagen gels and separation of plastic beads by submandibular mesenchymal cells were completely inhibited. These results suggest the importance of mechanical influences of the mesenchyme in salivary branching morphogenesis.
Corneal morphogenesis in the Mov13 mutant mouse is characterized by normal cellular organization but disordered and thin collagen
Authors: Bard Jonathan B. L. , Kratochwil Klaus 
Published: April 2021

ABSTRACT
This paper compares corneal development in the normal and in the Movl3 mutant mouse homozygote which does not synthesize type I collagen. During the period 12-14 days of development, there is no obvious difference between cellular organization in the normal and the mutant corneas or, indeed, elsewhere in the eye. In particular, there is normal colonization of the mutant cornea by the mesenchymal cells which will form the endothelium and the fibroblasts. In the early stages of stromal deposition (&lt;14 days), when relatively little collagen is normally laid down, mutant and wild-type corneas differ only in that mutant collagen fibrils are less uniform than normal ones. Later development in the Movl3 mutant cannot usually be studied because almost all mutant embryos are dead by 14 days, but we now have two homozygous embryos from a single, 16-day litter. Their stromas obviously differed from those of their normal littermates: there was markedly less collagen in the mutant cornea and the collagen that was deposited lacked orthogonal organization. Fibril morphology also differed: the diameters of fibrils in the normal corneas peaked sharply at about 20 nm, whereas the diameters of mutant fibrils were spread over the range 5-15 nm, with only a small percentage overlapping the normal distribution.
These results suggest that type I collagen is of negligible importance in controlling the cellular organization of the cornea, but has a dominant role in the formation of normal 20 nm fibrils and of normal stromal organization. They also show that, as collagen production is markedly lower in the mutant than in the wild-type cornea, the production of other collagens cannot compensate in any way for the lack of type I collagen. As the mutant cornea is likely to contain interstitial collagens II, III and V, the almost complete absence of normal fibrils in the mutant stroma is surprising because other workers have shown that each of these collagens forms normal fibrils in vitro.
Cell-cell interactions modulate the responsiveness of PC12 cells to nerve growth factor
Authors: Doherty Patrick , Mann Derek A. , Walsh Frank S. 
Published: April 2021

ABSTRACT
The growth of PC 12 cells on a collagen substratum or on monolayers of several non-neuronal cell types was studied by measuring nerve growth factor (NGF)- dependent increases in the expression of a 150 × 103(Mr) neurofilament protein subunit and the membrane glycoprotein Thy-1. Both responses were found to be greatly suppressed in cultures of fibroblasts as compared to the C2 and G8-1 muscle cell lines and the C6 glioma cell line. This suppression was associated with an inhibition of NGF-dependent neuritic outgrowth from PC12 cells grown on fibroblast monolayers. There was no evidence that fibroblasts secrete soluble molecules that directly inhibit these responses or neutralize NGF. In addition, there was no difference in the neurofilament protein response from PC 12 cells that had been treated with NGF prior to coculture, and the now primed PC12 cells readily extended axons over fibroblast monolayers. These data demonstrate that cell–cell and/or cell–matrix interactions can modulate biochemical responses to NGF and suggest that responsiveness of neuronal cells to environmental cues is not immutable. Control of the latter may be at the level of expression of receptor molecules for cell-surface- or matrix-associated macromolecules and a similar mechanism operating during development could play a role in growth cone guidance.
Vimentin expression in oocytes, eggs and early embryos ofXenopus laevis
Authors: Tang P. , Sharpe C. R. , Mohun T. J. , Wylie C. C. 
Published: April 2021

AbstractImmunocytochemical studies using a monoclonal antiporcine vimentin antibody reveal a well-organized pattern of staining in Xenopus laevis oocytes, eggs and early embryos. The positions of Xenopus vimentin and desmin in two-dimensional (2D) polyacrylamide gels were first established by immunoblotting of muscle Triton extracts with anti-intermediate filament antibodies (anti-EFA), which cross-react with all intermediate filament proteins (IFPs). The anti-porcine vimentin reacts with vimentin and desmin in muscle 2D immunoblots, but only reacts with one polypeptide in oocyte blots in the position predicted for vimentin (Mr55×103, pl 5·6).Using an anti-sense probe derived from a Xenopus vimentin genomic clone in RNase protection assays, we show that expression of vimentin begins in previtel-logenic oocytes. The level of expression remains constant throughout oogenesis and in unfertilized eggs. These data suggest that vimentin is expressed in oocytes and eggs. Most interestingly, the immunocytochemical results also show that vimentin is present in the germ plasm of oocytes, eggs and early embryos. It is therefore possible that vimentin has an important role in the formation or behaviour of early germ line cells.