bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neurulation in the Mexican salamander (Ambystoma mexicanum) : a drug study and cell shape analysis of the epidermis and the neural plate
Authors: Brun Rudolf B. , Garson John A. 
Published: April 2021

ABSTRACT
We analysed the neurulation movements in the Mexican salamander Ambystoma mexicanum. Embryos were exposed to colchicine or nocodazole prior to neural fold formation. Exposure to these drugs prevented the anterior neural folds from closing. Neurulation however proceeded normally in the posterior regions of the embryo. We were unable to find apically constricted cells in the neural plate of colchicine-blocked neurulae. Only rounded-up neural plate cells were present (semithin sections). This situation was typical in embryos exposed to colchicine prior to neural fold formation. Concentrations of colchicine up to 2 ·5 × 10-3 were not capable of blocking neurulation once the neural folds were formed. The wedge-shaped cells were present in similar numbers to those found in controls. We quantified the cell shape changes in the neural plate and in the epidermis in both controls and drug-arrested embryos. The comparison of these to classes of data shows that epidermal spreading is prevented by colchicine but only slightly affected by nocodazole. Embryos blocked in late neurulation by exposure to these drugs can resume neurulation following neural plate excision in nocodazole but not in colchicine. We conclude from this observation that the epidermis contributes to raising and closing of the neural folds. The presence of neural folds in absence of wedge-shaped cells in the neural plate is also taken as evidence that neurulation is not exclusively driven by forces generated in or acting on the neural plate. Our view on the concerted interplay of various embryonic components is illustrated in a summarizing diagram (Fig. 11).
Nuclear position in the cells of the mouse early embryo
Authors: Reeve W. J. D. , Kelly F. P. 
Published: April 2021

ABSTRACTThe nuclei of preimplantation mouse embryos were identified after labelling with either DAPI or Hoechst 33258. During the 4- and 8-cell stages the peripherally located nuclei become clustered nearer the centre of the embryo. This nuclear migration towards the base of each cell was also observed during the development of couplets of 2/4 and 2/8 cells. Most blastomeres isolated from compact 8-cell embryos contained a nucleus located in their basal half away from the microvillous pole. The displacement may be critical for the generation of a range of sizes of blastomeres in the 16-cell embryo.
Spreading of a sperm surface antigen within the plasma membrane of theeggafter fertilization in the rat
Authors: Gaunt Stephen J. 
Published: April 2021

ABSTRACTThe rat sperm surface antigen 2D6, located over the entire surface of the spermatozoon, is shown by use of a monoclonal antibody in indirect immunofluorescence experiments to spread laterally over the surface of the egg after fusion of sperm and egg plasma membranes at fertilization. Freshly fertilized eggs, obtained from superovulated rats 14h after hCG injection, showed the 2D6 antigen to have spread in a gradient over a discrete fan-shaped area of the egg surface anterior to the protruding sperm tail. Eggs at a later stage of sperm incorporation, obtained 20 h after hCG injection, showed that the spread of antigen had extended to cover most or all of their surfaces. By 40 h after hCG injection, the approximate time that fertilized eggs cleaved to form 2-cell embryos, most of the 2D6 antigen had been lost from the cell surface. Fertilized eggs, but not unfertilized eggs or 2-cell embryos, were lysed by 2D6 monoclonal antibody in the presence of guinea pig complement. A model for sperm-egg fusion is presented to account for the observed pattern of spreading shown by the 2D6 antigen. The possible role of sperm antigens on the egg surface is discussed.
Effect of glucose on beta cell proliferation and population size in organ culture of foetal and neonatal rat pancreases
Authors: Kaung Hue-Lee Cheng 
Published: April 2021

ABSTRACTThe effect of glucose on growth of the beta cell population was characterized in rat pancreatic organ culture. The effect was monitored by measuring [3H]thymidine labelling indices of beta cells during the culture period and by quantitation of beta cell population size at the end of the culture period. Foetal and neonatal pancreases and different glucose levels were compared.Glucose was found to be effective in stimulating the beta cell proliferation and beta cell population increase at 300 mg/100 ml in 18-day foetal pancreatic explants, but not in 3-day neonatal explants, when compared to the control level of 100mg/100ml. A higher level of glucose (500 mg/100 ml) was ineffective and may even inhibit beta cell population growth. The higher than control levels of glucose (300 mg/100 ml and 500 mg/100 ml) were able to stimulate insulin secretion in neonatal tissue, but not in foetal tissue, although foetal tissue may develop such response later in culture. These results suggest that glucose stimulates beta cell proliferation and insulin secretion through different mechanisms. They further show that the potentiality for beta cell proliferation under glucose stimulation decreases with age of the explants and that the capacity for beta cell to proliferate as a function of glucose stimulation is limited.
A study of the growth cones of developing embryonic sensory neurites
Authors: Roberts Alan , Taylor J. S. H. 
Published: April 2021

ABSTRACTThe scanning electron microscope was used to examine the growth cones of sensory neurites on the basal lamina of the trunk skin and on the myotomes in dissected embryos of the amphibian, Xenopus laevis. On the myotomes growth cones are large and flat with extensive lamellipodia and many filopodia. On the skin growth cones are smaller and have simpler processes particularly in more ventral positions. Where growth cones contact each other or other neurites they are very intimately apposed and show many indications of strong mutual adhesion. Fasciculation and separation of growing neurites is described and the conditions leading to fasciculation are considered. Measurements of growth cones on the myotomes and different dorsoventral regions of the skin are interpreted in terms of possible differences in the adhesiveness of these substrates. We conclude that many of our observations can be explained by differences in substrate adhesion to the growth cones but that the skin may have some special, unknown attraction for them.
Size dependence during the development of the amphibian foot. Colchicine-induced digital loss and reduction
Authors: Alberch P. , Gale Emily A. 
Published: April 2021

ABSTRACTLocalized treatment of the limb buds of the frog, Xenopus laevis, and the salamander, Ambystoma mexicanum, with the mitotic inhibitor colchicine results in limbs that, when compared with the contralateral control, are smaller in size and have lost skeletal elements. There is a very well defined pattern in terms of what elements are most likely to be lost. For example, frogs that have lost a toe always lose the first toe, while salamanders always lose the fifth. These differences correspond to qualitative differences in developmental sequence of digital differentiation in anurans as compared to urodeles. We propose a hypothesis in which the digital pattern is indirectly affected by reduction in the number of mesenchymal cells in the embryonic field.
Genetic and developmental characteristics of the homeotic mutationbx1 ofDrosophila
Authors: Sánchez-Herrero Ernesto , Morata Ginés 
Published: April 2021

ABSTRACTThe mutations at the bithorax locus produce a transformation of anterior haltere into anterior wing. The bx1 allele presents unusual features when compared with other bx alleles. The phenotype of bx1 homozygotes is temperature sensitive but only with regard to the distal and not to the proximal transformation, thus suggesting two different components in the bithorax transformation. The phenotype of bx1 homozygotes is stronger than that of bx1 over the deletion of the gene, suggesting a trans interaction of the bx1 chromosomes which results in mutual partial inactivation. We show by temperature shift and clonal analysis experiments that the decision on whether to differentiate haltere or wing structures is taken at the end of the proliferation period of the mutant disc.
Morphological and molecular modifications induced by heat shock in Drosophila melanogaster embryos
Authors: Graziosi Giorgio , Cristini Franco De , Marcotullio Angelo Di , Marzari Roberto , Micali Fulvio , Savoini Adriano 
Published: April 2021

ABSTRACT
The early embryo of Drosophila melanogaster did not survive treatment at 37°C (heat shock) for 25 min. The histological analysis of eggs treated in this way showed that the heat shock caused disintegration of nuclei and of cytoplasmic islands, displacement and swelling of nuclei and blocked mitoses. These effects were not observed in embryos treated after blastoderm formation. After this stage, we noticed that development was slowed down. The heat shock proteins (hsp 83,70 and 68) were, under shock, synthesized at all developmental stages. There was little or no synthesis of hsp 70 and 68 in unfertilized eggs, but synthesis increased in proportion to the number of nuclei present. Most probably, hsp 70 synthesis was directed by zygotic mRNA. DNA synthesis was not blocked by the heat shock though the overall incorporation of pH]thymidine was substantially reduced, presumably because of the block of mitoses. We did not find a direct relation between survival pattern and hsp synthesis. We concluded that some, at least, of the heat shock genes can be activated at all developmental stages and that heat shock could be used for synchronizing mitoses.
Regeneration of the retinotectal projection following compression onto a half tectum in goldfish
Authors: Schmidt John T. 
Published: April 2021

ABSTRACT
This study tested whether regeneration of the optic nerve following half-tectal compression in goldfish leads to the immediate reestablishment of the compressed projection or to an initial half map followed by the gradual compression. Half of the tectum was removed and the optic nerve crushed in large 12–18 cm goldfish which were kept at 20 °C and later mapped either in air or in water. At 35 to 41 days, the maps showed the presence of the nasal field projection and only the first 27 degrees of the temporal field. Most of the temporal field was represented after 200 days or more. After 253 to 343 days when the compression was largely complete, the optic nerve was recrushed. The projections mapped 35 to 41 days later were always compressed with up to 99 % of the temporal field represented, as were projections regenerated at 28°C and mapped at 23–25 days. Regeneration after compression restores the compressed projection, consistent with the concept of altered tectal markers.
Fine structure of the regressing interdigital membranes during the formation of the digits of the chick embryo leg bud
Authors: Hurle J. M. , Fernandez-Teran M. A. 
Published: April 2021

ABSTRACTThere is recent evidence showing that in addition to the well-known mesenchymal necrotic mechanism involved in the disappearance of the interdigital membranes, the ectodermal tissue may also play an active role in the formation of the free digits of most vertebrates. Ultrastructural study of the regressing interdigital membrane of the chick leg revealed significant changes at the epitheliomesenchymal interface. Disruptions of the ectodermal basal lamina and an intense deposition of collagenous material were the most conspicuous changes observed in the extracellular matrix. In addition the basal ectodermal cells showed prominent cell processes projected into the mesenchymal core of the membrane, and mesenchymal macrophages appeared to migrate through the epithelial tissue to be detached into the amniotic sac. It is concluded from our results that the elimination of the interdigital membranes is a complex process requiring the interaction of all the tissue components of the membrane.
The effects of the pink-eyed unstable gene on the retinal pigment epithelium of the mouse
Authors: Deol M. S. , Truslove Gillian M. 
Published: April 2021

ABSTRACTPink-eyed unstable (pun), an autosomal gene in the mouse, causes variegation of the coat. In some melanocytes it functions as the normal allele p+, producing dark pigment, and in others as the mutant p, producing light pigment. As a study of another unstable gene at a different locus had shown that the instability was strongly influenced by the tissue environment, it seemed desirable to find out whether this also applied to pun.An examination of the retinal pigment epithelium, the only structure in mammals in which it is practicable to determine the position of individual melanocytes, showed that the distribution of dark and light cells in punpun animals was not random. The dark cells increased in frequency with the distance from the optic nerve, suggesting that the tissue environment was a factor in the instability of the gene (i.e. in its rate of mutation), although the increase was less striking than in the other mutant.It is generally assumed that when pun behaves as p+ it is a case of reversion, and that reversion can also occur in germ cells, the revertant p+ allele subsequently behaving as a stable gene. It is here argued that it is unlikely to be a case of reversion, and that the evidence for the involvement of the germ line is inconclusive. Further, it is suggested that the phenotype of punpun animals is probably an instance of Position Effect variegation, the instability resulting from some chromosomal alteration, which is too small to be cytologically detectable.
Transcription and polyadenylation processes during early development of quail embryo
Authors: Olszańska B. , Kludkiewicz B. , Lassota Z. 
Published: April 2021

ABSTRACT
Transcription of tRNA and mRNA occurs in quail as early as during cleavage while rRNA transcription becomes measurable during blastulation. The polyadenylated fraction content in newly synthesized RNA amounting to 6 % during cleavage and blastulation decreases to 3 % during gastrulation. Up to 3/4 adenylic residues incorporated into RNA during cleavage are accumulated in the polyadenylated molecules mainly in the form of RNAse-resistant tracts.
Labelling of basement membrane constituents in the living chick embryo during gastrulation
Authors: Sanders Esmond J. 
Published: April 2021

ABSTRACT
The basement membrane of the living chick embryo epiblast has been labelled with ultrastructural markers in order to study the movement and turnover of this structure during gastrulation. Two problems were addressed in these experiments. Firstly, to what extent does the basement membrane move medially with the epiblast during morphogenesis? Secondly, what is the relationship to the basement membrane of the so-called interstitial bodies? The ultrastructural markers used were concanavalin A conjugated to ferritin and fibronectin antibodies conjugated to peroxidase. Embryos were cultured using the technique of New, and the label was applied to the periphery of the basal surface of the epiblast through a hole in the endoblast at the early primitive streak stage of development. The embryos were then allowed to develop to the full primitive streak stage in the presence of the label. When the position of the label was determined after incubation, it was found to have accumulated in large amounts at the edge of the primitive streak at the point where the basement membrane is disrupted. This indicates that constituents of the basement membrane are transported medially with the epiblast cells and are sloughed off as the latter pass through the primitive streak. This movement of basement membrane constituents is counter to the direction of migration of the underlying mesoderm cells. When embryos are exposed to label for only 1 h, then washed and incubated for a further three hours, the marker was found in the interstitial bodies and not distributed throughout the basement membrane itself. This suggests that the interstitial bodies, which have been implicated in influencing the migration of the mesoderm cells, are turnover products of the basement membrane to which they are attached.
Experimental analysis of control mechanisms in somite segmentation in avian embryos II. Reduction of material in the gastrula stages of the chick
Authors: Bellairs Ruth , Veini Marianne 
Published: April 2021

ABSTRACT
A new theory of control of somite segmentation in chick embryos is proposed. This supposses that tiny clusters of already programmed cells are present throughout the presumptive somite area at stage 4, but that in order to fulfill their destiny they probably depend on the addition of further cells from the primitive streak. Evidence is based on the two groups of experiments:
a) Experiments involving transection across the primitive streak at various stages, (which results in a ‘tail’ which possesses mesodermal derivatives) and across the segmental plate (which results in a ‘tail’ lacking mesodermal derivatives).
b) Experiments in which parts of embryos have been explanted with or without their primitive streak.
It is suggested that the initial clusters of pre-programmed cells move further and further posteriorly, developing into somitomeres (the precursors of true somites) only as they receive re-inforcements from the primitive streak or, ultimately, from the tail bud.
Differentiation of Argyrophil and Argentaffin Cells in Organotypic Cultures of Embryonic Chick Intestine
Authors: Monesi Valerio 
Published: April 2021

ABSTRACTArgyrophil, Bodian positive cells, and argentaffin, Masson-Hamperl positive cells differentiate in vitro in organotypic cultures of intestine of chick embryos explanted before argyrophil and argentaffin cells are known to differentiate, which is at the 14th and the day of incubation, respectively. During culture in vitro, argyrophil and argentaffin granules differentiate simultaneously; the number of cells demonstrable with either method does not show any significant difference throughout the duration of the cultures, which were incubated up to a maximum of 6 days. This result is at variance with what occurs in vivo, where argyrophil cells differentiate earlier than argentaffin cells and are in earlier stages 3 or 4 times as frequent as the latter, becoming only twice as numerous at a later stage. As in development in vivo, argyrophil and argentaffin cells differentiating in the intestine of the chick embryo are mainly situated in the epithelium. Only very few are found in the connective tissue of the lamina propria. Simard & van Campenhout (1932) and Ghidini (1940) showed that enterochromaffin granules differentiate in chorioallantoic grafts of intestine of chick embryos and they disproved in this way any kind of derivation of the enterochromaffin substance (enteramine) from the lumen of the gastrointestinal tract, as well as its formation under the influence of normal nervous connexions. It is now shown that the specific granules differentiate also in intestine cultivated in vitro and therefore in conditions which exclude any other possible mode of correlation with the whole organism, and particularly any uptake of enteramine from the blood, thus strongly supporting the conclusion that it is synthesized in situ.
Factors Responsible for the Abnormal Development of Embryos Obtained by Nuclear Transplantation inXenopus laevis
Authors: Gurdon J. B. 
Published: April 2021

ABSTRACTAn analysis has been made of factors which can cause abnormal development of embryos derived from transplanted nuclei in Xenopus laevis. A distinction is made between innate and technical factors, and between those which affect donor nuclei and recipient eggs. The innate developmental potentialities of endoderm donor nuclei do not appear to be limited, at least up to the early gastrula stage. Abnormalities known to be due to differentiated donor nuclei from later donor stages are described elsewhere. The technical treatment of donor nuclei can be carried out so as not to damage them, even if this is purposely made more severe than usual. The innate capacity for development of recipient eggs was found to vary considerably from one spawning to another; this variation seems to be due to an inability of the eggs of any one frog to withstand technical treatment which may be shown to be harmless to the eggs of other frogs. As the quality of recipient eggs can only be judged from results, experiments using Xenopus eggs should be accompanied by control transplantations, using donor nuclei the developmental capacity of which is already known. With these control transplantations for comparison, the technique is suitable for testing unknown developmental potentialities of different kinds of donor nuclei or recipient eggs.
The Development of Anucleolate Embryos ofXenopus laevis
Authors: Wallace H. 
Published: April 2021

ABSTRACTA Mutation of Xenopus has been found which reduces the maximum number of nucleoli per diploid nucleus from 2 in the wild-type to 1 in heterozygotes. Homozygous mutants possess no true nucleoli, hence being termed anucleolate. They do, however, possess pyronine-staining intranuclear organelles that are smaller and more numerous than typical nucleoli. The mutation can be considered as a recessive larval lethal, unlinked to sex: heterozygotes of both sexes are fully viable, but anucleolate larvae die at about the time their sibs begin to feed. These points have been recorded in two preliminary reports (Elsdale, Fischberg & Smith, 1958; Fischberg & Wallace, 1960). The development of anucleolate embryos is described here as a basis for the design of an experimental analysis of the ways in which the mutation acts. The description rests mainly on the progeny of a single mating of heterozygous toads, conforming with notes made on other such matings, from which additional data are drawn when required. As no developmental differences have been detected between the wildtype and heterozygotes, they are treated together as nucleolate (+n) controls, to which the anucleolate (On) embryos are compared. Nieuwkoop & Faber’s (1956) stages of normal development are used here to indicate age, made independent of temperature. After stage 40, the retarded On larvae are assigned to the stage of their controls.
Embryonic Responses to Structurally Related Inhibitors
Authors: Liedke Kathe , Gillespie H. B. , Graff Samuel 
Published: April 2021

ABSTRACTThe effects of variously substituted quinoxalines, benzimidazoles, and benzotriazoles on Rana pipiens embryos of 2-cell (S. 3), blastula (S. 8), neurula (S. 14) and tail-bud stage (S. 18) were studied. It was found that: Toxicity is variably increased by double substitution with two nitro groups (diN) or a nitro group and a chlorine atom (N+Cl). The relative toxicity of the single N-substituent is diminished by the addition of a hydroxy group, and generally also by a methoxy group, but not by addition of a methyl group; still greater is the diminishing effect of the carboxyl group which nullifies all activity. Cl-substitution in place of N is less toxic except at stages 3 and 8 with benzimidazoles.Susceptibility to benzo triazoles increases with age of embryo from 2-cell to tail-bud stage 18, while the reverse is true for quinoxalines and benzimidazoles. The diN-or N+Cl-substituted compounds are exceptions, as they are highly toxic at all developmental stages under the experimental conditions.In young tadpoles (S. 25) N-substitution increases the toxicity of quinoxaline or benzimidazole approximately 10 times, and of benzotriazole as much as 40 times.