bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell movement in intact and regenerating planarians. Quantitation using chromosomal, nuclear and cytoplasmic markers
Authors: Saló Emili , Baguñà Jaume 
Published: April 2021

ABSTRACT
One of the tenets of Wolff and Dubois’ ‘neoblast theory’ of planarian regeneration (Wolff & Dubois, 1948) is that blastema is mainly formed by the accumulation of undifferentiated parenchymal cells (neoblasts) that can migrate, if needed, over long distances to the wound. That neoblasts migrate was claimed by these authors after partial X-irradiation, and total X-irradiation and grafting using planarian strains of different pigmentation. From this they suggested that migration of neoblasts is stimulated by the wound and directed towards it.
To study the nature and extent of such ‘migration’ in intact and regenerating organisms, and in order to avoid the flaws of using pigmentation as a marker, we made grafts between sexual and asexual races of Dugesia(S)mediterranea that differ in a chromosomal marker, and between diploid and tetraploid biotypes of Dugesia(S)polychroa that differ in nuclear size. Also, fluorescent latex beads were used as cytoplasmic markers to follow ‘migration’ of differentiated cells. The hosts were irradiated or non-irradiated intact and regenerating organisms.
The results show that: 1) movement of graft cells into host tissues occurs in intact organisms at a rate of ≃40μm/day, and that this increases up to ≃75μm/day in irradiated hosts; 2) movement of cells occurs evenly in all directions; 3) regeneration does not speed up rate of movement nor drives cells preferentially to the wound; 4) spreading of cells is mainly due to the movement of undifferentiated cells (neoblasts) ; and 5) higher rates of movement are correlated with higher mitotic indexes. From this, it is concluded that the so-called ‘migration’ of neoblasts is not a true cell migration but the result of the slow, even and progressive spreading of these cells mainly caused by random movements linked to cell proliferation. The implications of these results for blastema formation and the origin of blastema cells are discussed.
Radiodestructions partielles chez l’embryon de Poulet aux stades jeunes et localisation des ébauches digestives
Authors: Douarin par Nicole Le 
Published: April 2021

ABSTRACT
La localisation des territoires présomptifs du tractus digestif de l’embryon de Poulet a été établie aux stades initiaux du développement. En particulier, les travaux de Hunt (1932), Dalton (1935), Rawles (1936) et Rudnick & Rawles (1937) ont montré qu’aux stades de la ligne primitive et du prolongement céphalique, ces territoires s’échelonnent le long de la ligne primitive. Au niveau de la première moitié de cette ligne se situe le territoire de l’intestin antérieur et de ses annexes. Le reste du tube digestif se trouve en arrière de cette zone.
Visual deprivation and the maturation of the retinotectal projection in Xenopus laevis
Authors: Keating M. J. , Grant S. , Dawes E. A. , Nanchahal K. 
Published: April 2021

ABSTRACT
There has been a resurgence of interest, recently, in the possible role of neural activity in the ordering of synaptic connections in the lower vertebrate retinotectal system. Blockade of all neural activity, by chronic administration of tetrodotoxin (TTX), during the regeneration of the optic nerve in goldfish has been found to prevent the re-emergence of a fully ordered retinotectal projection. We sought to determine the effects of visual deprivation, a less radical perturbation of neural activity than that produced by TTX, on the initial development of the retinotectal projection. The contralateral visuotectal projection was studied in Xenopus laevis which had been reared in darkness from before the onset of visual function. The projection mapped electrophysiologically at metamorphic climax, or in postmetamorphic juveniles, showed a normal retinotopic topography. The topographic precision of the projection, as revealed by the multiunit receptive field sizes, was the same in light- and dark-reared animals. The laminar distribution, in the superficial neuropil of the optic tectum, of terminals from different classes of retinal ganglion cells was also normal. It is concluded that the specific retinotectal connections underlying these features of the projection are generated by intrinsic developmental processes which do not require visual experience. Among these intrinsic processes might be ‘spontaneous’ neural activity.
Manipulation of gap junctional communication during compaction of the mouse early embryo
Authors: Goodall Harry 
Published: April 2021

ABSTRACT
Three treatments that prevent cell flattening during compaction of the mouse preimplantation embryo were assessed for their effects on the onset of gap junctional communication. Medium low in calcium (LCM) and an antiserum to an embryonal carcinoma cell line (anti-EC; Johnson et al. 1979) both prevented the establishment of coupling between blastomeres of the 8-cell embryo as assessed by transmission of carboxyfluorescein or by ionic coupling. Since neither of these agents prevents the contact-mediated induction of cell polarity that occurs at this stage, it is concluded that the induction of this process is not signalled via gap junctions. A monoclonal antibody (ECCD-1; Yoshida-Noro, Suzuki & Takeichi, 1984), that recognizes more specific components of the calcium-dependent cell adhesion system, failed to prevent the onset of junctional coupling. This suggests that the onset of junctional coupling is not dependent upon extensive cell apposition and that the requirement for extracellular Ca2+ resides at a level other than that of cell adhesion. Moreover, neither LCM nor anti-EC could reverse cell coupling once it had become established despite their complete reversal of cell flattening.
Changes in composition of the porcine zona pellucida during development of the oocyte to the 2-to 4-cell embryo
Authors: Brown C. R. , Cheng W. K. T. 
Published: April 2021

ABSTRACT
Our objective was to identify any changes that occur in the composition of the porcine zona pellucida during development of the 2-to 4-cell embryo from the oocyte. Oocytes, unfertilized eggs and single and 2-to 4-cell embryos have been recovered surgically and their zonae pellucidae 125I-labelled and analysed individually by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The zonae from ovulated eggs possessed two major glycoproteins Mr 250000 and 90000 which were absent from follicular oocytes but present in the fluid from the oestrus, but not luteal, oviduct. The glycoproteins remained on the zona pellucida of 2-to 4-cell embryos whose analysis showed the presence of additional polypeptides of Mr 150000, 57000, 50000 and 25000. It is concluded (i) that shortly after ovulation, and in spite of the presence around the egg of cumulus oophorus and corona radiata cells, significant amounts of oviducal glycoproteins are able to bind firmly to the zona pellucida, and (ii) that after contact with spermatozoa there is evidence of a limited hydrolysis of the structure by the sperm protease acrosin.
Ocular migration and the metamorphic and postmetamorphic maturation of the retinotectal system in Xenopus laevis \ an autoradiographic and morphometric study
Authors: Grant S. , Keating M. J. 
Published: April 2021

ABSTRACT
The growth of the retina and tectum during larval life in Xenopus has previously been studied extensively. These two structures continue to grow in metamorphosing and postmetamorphic animals. During these later stages there are marked changes in eye position. We have used histogenetic and morphometric techniques to monitor retinal and tectal growth in Xenopus aged from stage 58 of larval life to ten years postmetamorphosis. The relative eye migration was quantified with optical techniques. An attempt has been made to relate modes of retinal growth to problems associated with changing interocular geometry.
The predominant mode of growth during this period is hypertrophic, that is, it is due largely to an increase in size and complexity of existing elements, rather than the histogenetic creation of new elements. In the retina, however, tritiated thymidine autoradiography reveals that histogenesis does persist until at least six months after metamorphosis. The rate of histogenesis is much decreased compared with that of larval stages but, like that of larval stages, it takes place at the ciliary margin. It is asymmetrically distributed in the retina, most histogenesis occurring at the ventral retinal pole and very little at the dorsal retinal pole. Some histogenesis occurs at the nasal and temporal retinal poles. Thymidine autoradiography and cell counts indicated that little significant histogenesis occurs in the tectum after metamorphic climax.
Two possible biological reasons for the asymmetry of retinal histogenesis have been examined. The first was the suggestion that the asymmetry was related to the emergence, during this period, of a binocular visual field secondary to the relative migration of the two eyes. It is shown that the asymmetric pattern of histogenesis is not closely related to those retinal areas that come to view binocular visual space. It was found, however, that the asymmetry of retinal growth from metamorphic climax was that required to stabilize retinal visual field positions with respect to body position. It is suggested that this minimizes the requirements for visuomotor readjustments that would otherwise be necessary to compensate for a situation in which eye position, relative to the body, is changing.
Abnormal accumulation of sulphated materials in lens tissue of mice with the aphakia mutation
Authors: Webster Earl H. , Zwaan Johan , Cooper Philip 
Published: April 2021

ABSTRACT
Sulphated materials were tested for in the eyes of late gestational and postnatal normal mice and mice with the aphakia mutation using Spicer’s high iron diamine staining method. Qualitative identification of these materials was attempted with bovine testicular hyaluronidase and nitrous acid digestion methods. The grossly abnormal morphology of the aphakia lens made it necessary to confirm identification of lens-derived tissue by testing for lens crystallins using standard immunohistological methods. As seen in normal mouse lens maturation, accumulated inter- and intracellular sulphated materials were observed in aphakia lens tissue from just before birth through juvenile maturation. Large cyst-like structures consisting of lens-derived tissue were commonly seen in the eyes of young postnatal mutant mice. Sulphated materials formed basal lamina-like structures on many of these lens-derived units, but a well-defined lens capsule never formed. Abnormal fibrillar structures rich in sulphated materials were seen in the intraocular cavity in many older mutant specimens, most of which were largely resistant to both digestion methods. These results indicate that the potential to elaborate sulphated materials qualitatively similar to those seen in normal mouse lens maturation is present in the aphakia mutant, although the mode of accumulation is grossly disturbed.
Parthenogenesis and cytoskeletal organization in ageing mouse eggs
Authors: Webb Michelle , Howlett Sarah K. , Maro Bernard 
Published: April 2021

ABSTRACT
The cytoskeletal organization of the mouse egg changes during ageing in vivo and in vitro. The earliest change observed is the disappearance of the microfilament-rich area overlying the meiotic spindle. This is followed by the migration of the spindle towards the centre of the egg. Finally the spindle breaks down and the chromosomes are no longer organized on a metaphase plate. This spindle disruption may result from changes in the microtubule nucleating material found at the spindle poles and from an increase in the critical concentration for tubulin polymerization. It is possible to correlate the changes in the cytoskeletal organization of the egg occurring during ageing with the different types of parthenogenetic embryos obtained after ethanol activation. These observations strengthen the hypothesis that the actin-rich cortical area that overlies the meiotic spindle forms a domain to which the meiotic cleavage furrow is restricted and provides some insights into the mechanisms by which different types of parthenogenetic embryos are generated.
Protein synthesis and messenger RNA levels along the animal–vegetal axis during early Xenopus development
Authors: Smith Rosamund C. 
Published: April 2021

ABSTRACT
The patterns of proteins synthesized in animal and vegetal regions of Xenopus oocytes, eggs and embryos were examined by 2D gel electrophoresis. In oocytes and eggs, the only proteins synthesized asymmetrically along the animal–vegetal axis were a small number of proteins synthesized predominantly in the vegetal hemisphere. At the cleavage stage there were a total of four proteins synthesized unevenly in animal and vegetal regions: three synthesized predominantly in the vegetal hemisphere and one synthesized predominantly in the animal hemisphere. By the gastrula stage, when maternal messages have largely been replaced by embryonic transcripts, the number of differences in proteins synthesized in the animal-derived ectoderm and mesoderm, and the vegetal-derived endoderm started to increase rapidly with time of development with many more animal-characteristic proteins than vegetal-characteristic proteins appearing. Comparison of protein synthesis patterns with those obtained when extracted RNA was translated in vitro and run on 2D gels, showed that the asymmetry in protein synthesis along the animal–vegetal axis in the oocyte and early embryo reflected directly the distribution of their mRNAs along the axis. There was no evidence for localized ‘masked’ abundant messages along the animal–vegetal axis of oocytes and cleavage embryos.
Changes in the transferrin requirement of cultured chick embryo mesoderm cells during early differentiation
Authors: Sanders E. J. 
Published: April 2021

ABSTRACT
Mesodermal tissue from the chick embryo at various stages of early differentiation was cultured in hydrated gels of type I collagen in the presence and absence of transferrin. Primary mesoderm expiants from primitive-streak-stage embryos responded to the presence of avian transferrin by significantly improved outgrowth which appeared to be related to the ability of the cells to attach to, and migrate in, the collagen. No evidence was obtained which suggested that this observation was dependent on increased cell proliferation. This outgrowth enhancement was not duplicated by transferrin of human origin. The avian transferrin did not produce this effect on cells cultured on plastic substrata, suggesting that the species-specific effect involves modulation by the extracellular matrix. Mesoderm expiants from somite stages of development showed no increase in outgrowth in the presence of either avian or human transferrin as judged by counting the number of outwandering cells. Ultrastructural immunocytochemistry indicated surface binding of transferrin by cells in the gels, and the presence of endogenous transferrin on the surfaces of mesoderm cells in situ and in their extracellular environment. It is suggested that by binding to cell surface receptors, transferrin may be able to influence the strength of cellular adhesion to collagen and hence the capacity for cell locomotion.
Regulation of stalk and spore antigen expression in monolayer cultures of Dictyostelium discoideum by pH
Authors: Dominov Janice A. , Town Christopher D. 
Published: April 2021

ABSTRACT
The terminal differentiation of Dictyostelium discoideum cells plated as monolayers with cyclic AMP is dramatically affected by developmental buffer conditions. High pH and addition of weak bases induces spore differentiation while low pH and weak acids favour stalk cell formation. In order to analyse the timing and nature of this regulation we have raised and characterized an anti-stalk serum which we have used together with an anti-spore serum to monitor developmental progression in the monolayer system and to detect the phenotypic effects of pH at earlier stages of development. The stalk serum detects both polysaccharide and protein antigens expressed during the terminal stages of normal development. In monolayer culture, the stalk-specific protein antigen appears precociously, while the timing of prespore vacuole appearance is unaffected. Expression of stalk polysaccharide antigens in monolayer cultures occurs as early as 12 h and is localized in a single subset of cells or region of extracellular space within the small cell clumps that form. The effects of pH (and acid/base) on these phenotype-specific antigens can be detected early in development, shortly after their first appearance. In monolayers of wild-type V12 M2 cells, the low pH regimes appear to act more by suppressing the spore than enhancing the stalk pathway, while the high pH regimes both suppress stalk and enhance spore antigen expression. In monolayers of the sporogenous mutant HM29, low pH regimes both enhance stalk antigen and suppress spore antigen expression. These results show that extracellular pH regulates phenotypic expression during a large part of the differentiation process and is not simply restricted to terminal cytodifferentiation.
Cell–matrix interactions: influence of noncollagenous proteins from dentin on cultured dental cells
Authors: Lesot Herve , Smith Anthony J. , Meyer Jean-Marie , Staubli Aline , Ruch Jean Victor 
Published: April 2021

ABSTRACT
Matrix-mediated epitheliomesenchymal interactions control dental cytodifferentiations. Experiments were performed in order to study the effects of noncollagenous proteins extracted from dentin on cultured enamel organs and dental papillae.
Seven noncollagenous protein fractions were prepared from rabbit incisor dentin and used as substrates to coat Millipore filters. Embryonic mouse tooth germs were dissociated and the isolated tissues were cultured for 4 days on these different substrates as well as on noncoated Millipore filters.
When compared to control cultures, only two protein fractions affected the behaviour of epithelial cells. A slight elongation of the cell body and a preferential localization of the nuclei at the basal pole of the cells in contact with the filter was observed with protein fractions 5 and 6.
When dental papillae were cultured on Millipore filters coated either with protein fraction 2 or fraction 6, the mesenchymal cells in contact with the filter elongated, polarized and demonstrated a high metabolic activity. Such modifications in the cell organization, implying changes in the cytoskeleton organization and, or, activity, never occurred spontaneously or in the presence of isolated collagens (I-V), laminin or fibronectin.
Disruption of segmentation in a short germ insect embryo
Authors: Mee Jane E. , French Vernon 
Published: April 2021

ABSTRACT
The effect of heat shock (15 min at 48 °C) on segmentation has been investigated in the short germ embryo of the locust (Schistocerca gregaria). Prior to formation of the germ anlage and at the disc stage heat shock considerably reduced the survival of eggs but appeared to have little effect upon segmentation. At later stages heat shock had no effect on survival but resulted in disruptions of the segmental pattern. The location of abnormal segments depended upon the stage at heat shock and the number affected depended on its severity. A constant number of normal segments developed between the last segment visible at the time of heat shock and the first abnormal segment. These results are similar to the disruptions observed in amphibian somites following heat shock. However, different parts of the segment pattern varied in their response; the head segments were very rarely affected, and disrupted regions rarely started in the middle abdomen (segments A5 and A6).
The results are discussed in relation to two models (the clock and wavefront and progress zone models) that have been proposed as an explanation for the specification of the somite pattern in amphibians.
Electrical properties of the otic vesicle epithelium in the chick embryo
Authors: Represa J. J. , Barbosa E. , Giraldez F. 
Published: April 2021

ABSTRACT
The electrophysiological properties of the epithelium of the otic vesicle were studied in the chick embryo using conventional microelectrode techniques. A preparation is described that allows continuous recording of transmural potential and resistance during changes in the composition of the bathing fluid. Vesicles in stages 18 to 22 showed a spontaneous transmural potential (ET) that ranged from 2 to 6 mV, inner positive. This electrical potential difference was abolished after 2h incubation in K+-free strophantidin (10−4M) and it increased by about twofold immediately after addition of the cation ionophore Amphotericin B (250 μM) to the bath. The specific resistance of the wall (RT) was about 80 Ωcm2 between stages 18 and 22 indicating a low-resistance, noncellular, permeation pathway for current flow. The short-circuit current, calculated from ET and RT was about 50 × 10−6 A cm–2 throughout this period. This corresponds to a net flux of 187 ×10−8molcm–2h–1 of a single cation pumped towards the vesicular cavity. Diffusion potentials (salt gradients and single-ion substitutions) showed a selectivity ratio PK:PNa:PCl = 1:0 ·9:0 ·7, which is that of a weakly charged aqueous pathway. Measurements of vesicular volume and surface area showed an increase by a factor of ten in the size of the vesicle with maximal rates of change in volume of 5 μlcm–2h–1. The electrical properties reported here for the epithelium of the otic vesicle resemble very much those of ‘leaky’ epithelia which are known to transport ions and water at a very high rate.
Role of bilateral zones of ingressing superficial cells during gastrulation of Ambystoma mexicanum
Authors: Lundmark Cathy 
Published: April 2021

ABSTRACT
Vital dye staining and cell lineage tracers were used to mark superficial cells of early Ambystoma mexicanum gastrulae. Superficial marks placed between the equator and the blastopore, on the dorsal midline, stained notochord, whereas marks or injections made at similar animal–vegetal levels but 90° to either side of the dorsal midline were later found in somitic mesoderm. Notochord marks remained on the dorsal surface of the archenteron throughout gastrulation, though they became elongate and narrow by the morphogenetic movements of extension and convergence. Marked somitic mesoderm disappeared from the superficial epithelial layer soon after passing over the blastoporal lip and could not be found on the archenteron surface. A possible mechanism for this de-epithelialization is proposed on the basis of correlated SEM. The significance of a method of gastrulation so distinctly different from that of certain other amphibians is discussed in terms of amphibian phylogeny.
The regulation of dna synthesis and mitosis in multinucleate frog eggs
Authors: Graham C. F. 
Published: April 2021

Abstract
The timing of DNA synthesis and mitosis in normal eggs, in activated eggs, and in eggs containing several accessory nuclei has been studied in Xenopus. DNA synthesis was followed by injecting [3H] thymidine into the egg and detecting its subsequent incorporation into DNA by autoradiography.
It was found that the accessory nuclei which were introduced into the egg during different phases of the cell cycle incorporated label and entered mitosis in synchrony with the resident egg and sperm nuclei if the introduced nuclei were released from the intact sperm. In eggs activated by pricking, the egg nucleus had synthesized DNA at a time when it would have done so during normal fertilization.