bluuebunny/crossref_metadata_2025_split huggingface dataset:
Étude immuno-électrophorétique de l’apparition progressive de quelques constituants caractéristiques de l’adulte dans le foie embryonnaire du Poulet
Authors: Croisille par Yvon 
Published: April 2021

ABSTRACT
Dans le cadre des recherches consacrées à l’étude de l’apparition des constituants spécifiques de l’adulte au cours du développement embryonnaire, les méthodes immunochimiques ont trouvé un emploi toujours grandissant pendant les 15 dernières années. Le nombre de travaux, dont les principaux ont été récemment exposés (Croisille, 1958), permet de juger combien l’emploi de ces méthodes s’est révélé fructueux dans ce domaine. La plupart des auteurs ont utilisé les méthodes immunochimiques classiques: réaction à l’interface, épuisement des anti-sérums, techniques de précipitation en milieu gélifié et réaction de déviation du complément. Mais ces méthodes ne permettent souvent pas, malgré leur spécificité et leur sensibilité, de dénombrer et d’identifier correctement tous les constituants, surtout s’il s’agit de l’analyse d’un mélange complexe. Aussi y a-t-il des résultats contradictoires dus pour la plupart à des difficultés techniques ou d’interprétation, notamment en ce qui concerne l’identification certaine des constituants embryonnaires et adultes.
Acetylcholinesterase Activity in the Regenerating Forelimb of the Adult Newt, Triturus
Authors: Singer Marcus , Davis Marjorie H. , Arkowitz Eleanor S. 
Published: April 2021

ABSTRACT
Acetylcholinesterase activity in the regenerating forelimb of the adult newt, Triturus, was measured during various stages of development with the Hestrin colorimetric and the Warburg manometric method. The activity of the enzyme is low during the early formative phases of development. It then increases, the greatest rate of change being in the stage just preceding that of differentiation of muscle. At the time of muscle differentiation the activity levels off and then returns to normal as regeneration draws to a close. The variation in cholinesterase activity correlates well with the cycle of acetylcholine production during regeneration. The acetylcholine content is very high during early regeneration but then drops to a near normal level as esterase activity rises. Since the nerve is required for the regeneration process and since the nerve effect is most dramatic when the acetylcholine content is very high, the possibility that acetylcholine may be the agent of the nerve influence is assessed. The enzymatic activity during regeneration is compared to that observed in embryonic development.
Generation of spatially periodic patterns by a mechanical instability: a mechanical alternative to the Turing model
Authors: Harris Albert K. , Stopak David , Warner Patricia 
Published: April 2021

ABSTRACT
We have studied the generation of spatial patterns created by mechanical (rather than chemical) instabilities. When dissociated fibroblasts are suspended in a gel of reprecipitated collagen, and the contraction of the gel as a whole is physically restrained by attachment of its margin to a glass fibre meshwork, then the effect of the fibroblasts’ traction is to break up the cell-matrix mixture into a series of clumps or aggregations of cells and compressed matrix. These aggregations are interconnected by linear tracts of collagen fibres aligned under the tensile stress exerted by fibroblast traction. The patterns generated by this mechanical instability vary depending upon cell population density and other factors. Over a certain range of cell concentrations, this mechanical instability yields geometric patterns which resemble but are usually much less regular than the patterns which develop normally in the dermis of developing bird skin. We propose that an equivalent mechanical instability, occurring during the embryonic development of this skin, could be the cause not only of the clumping of dermal fibroblasts to form the feather papillae, but also of the alignment of collagen fibres into the characteristic polygonal network of fibre bundles -which interconnect these papillae and which presage the subsequent pattern of the dermal muscles serving to control feather movements.
More generally, we suggest that this type of mechanical instability can serve the morphogenetic functions for which Turing’s chemical instability and other reaction-diffusion systems have been proposed. Mechanical instabilities can create physical structures directly, in one step, in contrast to the two or more steps which would be required if positional information first had to be specified by chemical gradients and then only secondarily implemented in physical form. In addition, physical forces can act more quickly and at much longer range than can diffusing chemicals and can generate a greater range of possible geometries than is possible using gradients of scalar properties. In cases (such as chondrogenesis) where cell differentiation is influenced by the local population density of cells and extracellular matrix, the physical patterns of force and distortion within this extracellular matrix should even be able to accomplish the spatial control of differentiation, usually attributed to diffusible ‘morphogens’.
Retinoids and pattern formation in a hydroid
Authors: Müller W. A. 
Published: April 2021

ABSTRACT
The retinoids (retinol, retinal, retinoic acid) cause alterations in the pattern of limb elements in vertebrates (Summerbell & Harvey, 1983). As shown here, retinoids also influence pattern specification in hydroid polyps (Hydractinia echinata) in a way suggesting interference with the generation and transmission of signals responsible for the dimension and spacing of structures. A pulse-type application of low doses (e.g. retinoic acid 10−6 to 10−10 M, 4 h) causes metamorphosing primary polyps to develop more tentacles but fewer stolons per unit circumference, to shorten the length of the hydranth while the stolon elongates, and to bud secondary hydranths at high frequency 2–3 days after treatment (Fig. 3). Dose-response curves display optimum peaks. It is argued that the increase in budding rate is due to a reduction of the range of spacing signals emitted by the primary hydranth. In regenerating hydranths, low doses (10−10 to 10−9M) improve the rate of head formation, whilst medium doses (10−8 to 10−6M) result in more tentacles being regenerated. However, prolonged treatment with high doses (10−6 to 10−5 M) causes the animals to reduce all head structures and to transform eventually into stolons, in contravention of the rule of distal transformation that they normally obey (Fig. 8). The effects of the retinoids are counteracted by a putative morphogen, the endogenous inhibitor isolated from Hydra by Berking (1977). The Hydra-derived ‘head-activator’ displayed no stimulating effect on the number of tentacles and buds formed.
Effect of microtubule inhibitors on the expansion of hypoblast and margin of overgrowth of chick blastoderms
Authors: Mareel Marc , Bellairs Ruth , Bruyne Georges De , Van Peteghem Marie Christine 
Published: April 2021

ABSTRACT
The effect of the microtubule inhibitors, Nocodazole and taxol, was studied on the expansion of fragments of chick hypoblast (8 to 10 h incubation) and of margin of overgrowth (24 h incubation) cultured on artificial substrata and on the epiboly in intact blastoderms (24 h incubation).
Immunocytochemical staining of these cells with antiserum against tubulin showed that 1 μg Nocodazole/ml caused disassembly of microtubules, and that 1μg taxol/ml led to increased but unordered assembly. The solvent dimethylsulphoxide had no effect. At these concentrations both microtubule inhibitors led to rapid arrest of the expansion of fragments of hypoblast and of margin of overgrowth in culture, and of the epiboly in intact blastoderms. Time-lapse films showed that inhibition of expansion in both situations was reversible within 2 h after removal of the drugs. Phase-contrast microscopy showed remarkably little difference between the morphology of treated as compared to untreated cultures. Measurements of the height of the cells on sectioned fragments of margin of overgrowth showed no differences between treated and untreated cultures. These results suggest that the cytoplasmic microtubule complex is important both for epiboly and for the migration of hypoblast cells in the chick blastoderm. The mechanisms of this microtubule-related migration are not understood.
Histological studies of the effects of wounding vibrissa follicles in the hooded rat
Authors: Jahoda Colin A. B. , Oliver Roy F. 
Published: April 2021

ABSTRACT
The effects of wounding the lower region of rat vibrissa follicles with a sharp tungsten needle were examined histologically, both shortly after injury and up to one year postoperatively. Following cell damage in the dermal papilla component hair growth ceased, and resumption of fibre production was always preceded by dermal papilla reformation. This papilla healing and regeneration was not associated with the production of scar tissue. In follicles undergoing no cell displacement during wounding (an effect associated with the growth of longer than normal hairs) dermal papillae were reformed from the residual papilla cell population, with recruitment of cells from surrounding mesenchyme. Follicles plucked just prior to wounding revealed little or no original epidermal matrix three days later, confirming that dermal components were primarily affected. Papilla cell counts performed on follicles which had consistently produced longer hairs gave no indication of increased papilla cell numbers. Follicles which underwent displacement of cellular material and displayed distortion of normal follicle morphology shortly after wounding (effects associated with the production of shorter than normal hairs) also revealed abnormalities at long-term biopsy. Moreover these follicles often had a history of altered fibre characteristics from one postoperative generation to the next. It is concluded that gross morphological disruption of the normal cellular relationships in the lower follicle results in a series of reorganizational difficulties with each recurring phase of the hair cycle.
Gibberellins and gene control in cereal aleurone cells
Authors: Baulcombe David , Lazarus Colin , Martienssen Robert 
Published: April 2021

ABSTRACT
The production of hydrolytic enzymes in the germinating cereal grain is considered as a model for plant cell differentiation. Recent literature is reviewed which suggests that gibberellins are involved in this process, but in a less straightforward manner than considered previously. It seems likely that only a subfraction of gibberellin is active and that production of this gibberellin is actually in the hydrolase-producing cells. These include aleurone cells and also the scutellar epithelial cells.
At the intracellular level the action of gibberellin results in the accumulation of α-amylase mRNA and also mRNA for other unidentified proteins, referred to as gibb-ons. The α-amylase mRNAs are transcribed from two distinct gene families. The pattern of expression of α-amylase and gibb-on mRNAs is consistent with a common gibberellin-stimulated mechanism of control of for all of these genes. However it seems likely from experiments with ABA and from observations on gibb-on gene expression in non-aleurone cells that gibberellin does not have a role determining the specificity of gene expression, but rather acts as a general stimulator of mRNA accumulation.
Analysis of transcriptional regulation of the s38 chorion gene of Drosophila by P element-mediated transformation
Authors: Kalfayan Laura , Wakimoto Barbara , Spradling Allan 
Published: April 2021

ABSTRACT
Transcriptional regulation of the s38 chorion gene was studied using P element-mediated germline transformation. A 5–27 kb DNA fragment containing the s38 gene and 5′- and 3′-flanking sequences, was tested for its ability to be transcribed with correct developmental specificity. Five single-insert transformed lines were generated by microinjection of this DNA fragment cloned into a marked P element transformation vector. In each line, the transformed gene was transcribed according to the precise developmental pattern followed by the native s38 gene. The 1– 3 kb at the 5′ end of this tested fragment was fused to the E. coli lac z gene. This fragment was also capable of initiating transcription of E. coli lac Z RNA with the developmental profile of the native s38 gene. In vitro deletion studies are underway to determine which sequences in the 1–3 kb fragment are necessary for regulating the developmental expression of the gene.
Computer modelling of cell division during development using a topological approach
Authors: Ransom Robert , Matela Raymond J. 
Published: April 2021

ABSTRACT
Development in multicellular animals consists of a constant progression of cell division, differentiation and morphogenesis. Our understanding of the relationship between division and the acquisition of shape and form is not well understood, and this paper describes a computer representation of cell division processes with possible applications to the modelling of developmental events. This representation is not itself a model in the true sense, but is a scaffolding onto which a set of model assumptions and parameters can be built. We discuss one such set of assumptions, used to model cell sorting, describe the extension of the framework to represent sheets of cells in three dimensions, and make some observations on the incorporation of mechanical forces into the representation.
A mathematically modelled cytogel cortex exhibits periodic Ca++-modulated contraction cycles seen in Physarum shuttle streaming
Authors: Odell Garrett M. 
Published: April 2021

ABSTRACT
If each of many cells of an embryo (or different zones in a single cell) possess identical active cytogel machinery, having the ‘right’ mechanochemical response properties, then the collective interaction among those identical participants leads automatically to the globally coherent tissue deformations seen in embryogenesis, and to shuttle streaming in the plasmodial slime mould Physarum polycephalum.
Biologically plausible, and experimentally verifiable hypotheses are proposed concerning how the tension generated by a strand of cytogel is determined by the deformation it suffers and by the concentration of a contraction trigger chemical, Ca2+, whose kinetics involve coupling to mechanical strain. The consequences of these hypotheses, deduced by solving the appropriate differential equation systems numerically, and displayed in computer-animated films, closely imitate diverse tissue deformation events seen in developing embryos.
The same hypotheses on cytogel behaviour are used to model a thick-walled Physarum vein segment, and two such segments are set up to be able to pump endoplasm back and forth between them. Under certain conditions, this model exhibits spontaneous rhythmic mechanochemical oscillations, many features of which correlate well with shuttle streaming in Physarum.
Small gradual variations of parameters, presumably under genetic control, are shown to cause abrupt and biologically interesting bifurcations of the qualitative behaviour of the model.
Chromosomes and sex differentiation in eutherians
Authors: Müller Ulrich 
Published: April 2021

ABSTRACT
In order to learn more about the role of sex chromosome-dependent gene products in gonadogenesis, changes in protein patterns were studied during gonadal development. Two-dimensional gel electrophoresis analysis revealed specific proteins in both sexes at all developmental stages. Evidently the gonads are not indifferent by biochemical criteria at any developmental stage and express several specific genes from the onset of differentiation. To correlate these polypeptides with the sex chromosomes, proteins were investigated in human-rodent somatic cell hybrids and in genetically identical cell clones differing in one sex chromosome only. On two-dimensional gels one Y-dependent polypeptide was found with similar characteristics (relative molecular mass and isoelectric point) as an early testicular polypeptide. Its identity, however, remains to be proven.
Chromosome order – possible implications for development
Authors: Heslop-Harrison J. S. , Bennett M. D. 
Published: April 2021

ABSTRACT
Chromosomes are arranged in ordered haploid sets around the centre of the metaphase plate at mitosis in several grass species and hybrids. Each chromosome is in a fixed mean position relative to other, heterologous chromosomes, this order can be predicted using Bennett’s model, and is clearly demonstrated from reconstructions of electron micrographs of serial sections (see Heslop-Harrison & Bennett, 1983a,b,c).
The nucleus contains spatial domains of genes with similar functions. Chromosomes with major effects on nuclear behaviour - division or meiotic pairing - may be at special positions in the order. Changing spatial relationships of chromosomes with respect both to each other and the nuclear envelope (during the cell cycle and during development) may affect cell differentiation and gene activity.
Chromosome order may have implications for the control of development within the nucleus and the organism. Order may constrain karyotype and hence species evolution.
Accumulation and localization of troponin-T in developing hearts of Ambystoma mexicanum
Authors: Fuldner Rebecca A. , Lim Soo-Siang , Greaser Marion L. , Lemanski Larry F. 
Published: April 2021

ABSTRACT
Troponin-T (Tn-T) expression in developing hearts of axolotls, Ambystoma mexicanum, was studied with the use of polyclonal and monoclonal antibodies and SDS-polyacrylamide gel electrophoresis. In precontractile hearts (stage 32β3), Tn-T was present in addition to myosin, actin and tropomyosin as evidenced by the presence of the protein bands in SDS-gels and by indirect immunofluorescence. Tn-T was localized in amorphous collections at the peripheries of these precontractile cells. Hearts of normal and cardiac lethal mutant siblings were also analysed for Tn-T expression. No detectable differences in the quantity of protein present was observed by gel electrophoresis or by indirect immuno-fluorescence. The most striking difference concerned the localization of the protein. In normal hearts, Tn- T was primarily localized in the I-bands of organized myofibrils; however, in mutant cells the Tn-T was localized in amorphous collections at the cell peripheries suggesting a reduction of myofibrillar organization in these cells. No differences were observed in the contractile protein composition between normal and mutant em-bryonic hearts by gel electrophoresis experiments.
Differentiation markers in the Drosophila ovary
Authors: White Robert A. H. , Perrimon Norbert , Gehring Walter J. 
Published: April 2021

ABSTRACT
A library of monoclonal antibodies, raised against imaginal discs of Drosophila melano-gaster, was screened for binding to differentiation antigens in the adult ovary by immuno-fluorescence. Several lectins were similarly assayed. Two antibodies, DOV 1 and DOV 2, and wheat germ agglutinin exhibited binding which was restricted to particular stages of ovarian cell differentiation. DOV 2 also showed a marked preferential binding to the cell surface of germ line cells in the ovary. A differentiation of the portion of the tunica propria covering the anterior part of the germarium was revealed by the monoclonal antibody DOV 3. Another monoclonal antibody, DOV 4, identified a molecular specialization of the chorion at the tip of the micropyle. These markers should provide tools for the molecular analysis of oogenesis.
The acellular stroma of the chick cornea inhibits melanogenesis of the neural-crest-derived cells that colonize it.
Authors: Campbell Steven , Bard Jonathan B. L. 
Published: April 2021

ABSTRACT
Neural crest (NC) cells from the periorbital mesenchyme (POM) invade the acellular stroma of the chick cornea at stage 27 of development (∼6 days). The invading cells become collagen-producing fibroblasts while the NC cells remaining in the POM differentiate into a wide range of cell types, the most easily recognizable of which is the pigment-producing melanocyte. In this paper, we report observations on the differentiation in vitro of cells within and migrating from explants of corneal stroma and compare their behaviour with that of cells within and migrating from explants of the POM. In ∼70 % of cases, POM explants produced black, eumelanin pigmentation within 2–3 days in culture and gave rise to a mixed outgrowth of fibroblasts and melanoblasts that produced brown pigment. In no case, however, did a corneal explant produce black pigment (so demonstrating that any POM contamination was negligible). However, in 28 % of cultures from stage-27 and -28 corneas, some of the cells in the outgrowth contained brown pigment indistinguishable from that produced by the POM control, although the majority of the cells in each case were fibroblasts. Two lines of investigation demonstrated that this pigment was melanin: first, transmission electron microscopy showed that the pigment organelles were incompletely melanized, granular melanosomes; second, tests designed to demonstrate the presence of lipofuscin, an alternative pigment, proved negative. Migrating cells from older corneas, in contrast, showed no evidence of even the first stages of melanogenesis. These results show, first, that some of the NC cells that invade the cornea are at least bipotent and hence representative of the POM population rather than being a unique subgroup and, second, that the acellular stroma of the cornea determines the state of differentiation of the NC cells that colonize it. The results thus provide an unequivocal demonstration that extracellular matrix can induce postmigratory NC cells to differentiate into fibroblasts.
Influence of cyclic AMP and hydrolysis products on cell type regulation in Dictyostelium discoideum
Authors: Weijer Cornelis J. , Durston Antony J. 
Published: April 2021

ABSTRACT
We describe the effect of cyclic AMP on regulation of the proportion of prespore and prestalk cells in Dictyostelium discoideum. Prespore and prestalk cells from slugs were enriched on Percoll density gradients and allowed to regulate in suspension culture under 100 % oxygen. The transition of prespore to prestalk cells is blocked by cAMP, while cAMP phosphodiesterase and caffeine cause a decrease in the number of prespore cells. This suggests that extracellular cAMP plays a role in cell type proportioning by inhibiting the conversion of prespore to prestalk cells.
Low concentrations of cAMP prevent the conversion of prestalk to prespore cells; the same effect is seen with hydrolysis products of cAMP, 5 AMP, adenosine and also adenine. We suggest that, when low concentrations of cAMP are added to regulating cells, the cAMP itself is quickly broken down and the breakdown products thereafter inhibit the prestalk-to-prespore conversion.
The relevance of these findings is discussed in the context of an non-positional double-negative feedback model for cell type homeostasis.