bluuebunny/crossref_metadata_2025_split huggingface dataset:
The early development of the primary sensory neurones in an amphibian embryo: a scanning electron microscope study
Authors: Taylor J. S. H. , Roberts Alan 
Published: April 2021

ABSTRACT
We have described the development of the primary sensory system of the trunk region of Xenopus laevis embryos from larval stages 21 to 32. The system is based upon Rohon-Beard and extramedullary cells, which have central axons forming a dorsolateral spinal tract and peripheral neurites which innervate the skin. The pioneer axons of the central tract grow along the outer surface of the cord at stage 22. These pioneer axons may be used by secondary axons as a growth substrate. As the tract forms it is covered by the radially expanding distal processes, ‘end feet’, of the ependymal cells of the cord. Cell bodies of the extramedullary cells bulge out of the cord surface, and are first seen between the newly segmented myotomes, at stage 24. Peripheral neurites from these extramedullary cells grow out laterally from the cord. The Rohon-Beard cells, located within the cord, produce similar peripheral neurites which grow laterally with the extramedullary cell neurites, using them as a substrate. The neurites form bundles which coincide with the intermyotomes and are periodically spaced. The growth cones of these neurites contact the outer surface of the myotomes and proceed ventrally, first on the myotomes and then on the basal lamina of the skin. ‘Pioneer’ neurites are used by later neurites as a growth substrate, but not to the exclusion of all other substrates. The neurites form a plexus on the skin’s basal lamina and contact the underlying epidermal cells through holes in the basal lamina. These holes occur in positions over the intercellular boundaries of the epidermal cells.
Growth of 9·5-day rat embryos in human serum
Authors: Gupta M. , Beck F. 
Published: April 2021

ABSTRACT
Rat embryos were explanted at 9·5 days and cultured for 48 h in human serum supplemented with glucose. The embryos were anaemic and frequently malformed. The haemoglobin and DNA content of these embryos was less than those grown in pure rat serum. Addition of 10 % rat serum improved the embryonic growth as well as the haemoglobin and DNA content. This suggests that rat serum provides essential growth factors required by the embryos which are not present in human serum.
A test of the predictions of the boundary model regarding supernumerary limb structure
Authors: Maden M. 
Published: April 2021

ABSTRACT
The model proposed in the preceding paper (Meinhardt, 1983) makes specific predictions about the handedness of supernumerary limbs generated after 180° rotation of blastemas. These predictions are tested here by re-examining, in detail, the structure of 100 of these supernumeraries. Of the four predictions, only one was found not to hold. The other three are remarkably precise in their predictions and fit perfectly with the data. A possible reason for the failure of this one prediction is suggested.
Replacement of irradiated epidermis by migration of non-irradiated epidermis in the newt limb: the necessity of healthy epidermis for regeneration
Authors: Lheureux Emile 
Published: April 2021

ABSTRACT
An X-irradiated newt limb is able to regenerate if non-irradiated skin as well as non-irradiated muscle is transplanted to the stump. Non-irradiated epidermis is brought to the stump with a skin graft but not with a muscle graft. In order to know whether limb regeneration required healthy epidermis or not, a triploid skin cuff was set at the most proximal level of an irradiated limb and muscle was transplanted to the level of the midforearm. The forearm was then amputated through the muscle graft. A cytophotometrical analysis of DNA content of the epidermis cell nuclei sampled from the skin of the regenerate was undertaken to detect a migration of triploid epidermal cells. The result was a complete replacement of diploid irradiated epidermis by triploid epidermis, during the six weeks necessary for regeneration. Another investigation consisted of detecting a possible migration of non-irradiated triploid epidermis along an irradiated limb which had not been amputated. Healthy epidermis was found to migrate distally and replace irradiated epidermis in three weeks. Previous experiments involving transplantation of a non-irradiated skin cuff or muscle to an irradiated limb stump were carried out again but on animals which had been entirely irradiated to prevent any extra healthy epidermis cells from contaminating the regenerating limb epidermis. A regenerate developed from the skin graft but not from muscle graft. It is concluded that healthy epidermis must be present on the limb stump to permit the blastema to develop.
Membrane changes in neural target cells studied with fluorescent lectin probes
Authors: Gualandris L. , Rougé P. , Duprat A. M. 
Published: April 2021

ABSTRACT
The competent ectoderm of Pleurodeles waltl comprises two cell layers with characteristic differences in their morphology, their composition and the molecular arrangement of the various constituents.
The use of labelled lectin probes for observations of ectoderm tissue in vitro with u.v. microscopy (epi-illumination) and the quantification of the results show the following:- Differences in labelling according to the nature of the lectins (SBA, PSA, LCA and Con A). These differences provide information on the nature of the carbohydrates which are present at this stage and on the number of receptors.Differences in fluorescence intensity of the surfaces studied. The internal surface of the ectoderm is labelled more densely than the external surface.Rearrangement of the lectin receptors with a new molecular configuration, stressing the fluidity of the membrane (by the mobility of the receptors throughout the membrane) and its importance for the occurrence of neural induction.Existence of membrane glycoconjugate turnover.A difference in behavioural characteristics between the internal and the external surfaces with respect to the lectins and the formation of an extracellular matrix on the internal surface alone. The extracellular matrix seems to have a role in morphogenetic movements.
Expression of differentiation markers by chick embryo neuroretinal cells in vivo and in culture
Authors: Pomerai D. I. De , Kotecha B. , Flor-Henry M. , Fullick C. , Young A. , Gali M. A. H. 
Published: April 2021

ABSTRACT
Several markers of chick neuroretinal differentiation were monitored in vivo and in culture. All increase markedly between 7 and 20 days of embryonic development in vivo. In vitro, endogenous GABA levels decrease almost immediately, while other neuronal markers increase as in vivo for 2 to 5 days before declining (choline acetyltransferase, acetyl cholinesterase, glutamic acid decarboxylase). Neuronal cell surface markers (binding sites for tetanus toxin, α-bungarotoxin, muscimol), however, reach maximal levels only after 8 days in vitro. Glial markers such as carbonic anhydrase and hydrocortisone-induced glutamine synthetase activities are also expressed only transiently in culture.
Regeneration of adult newt skeletal muscle tissue in vitro
Authors: Schrag Joan A. , Cameron Jo Ann 
Published: April 2021

ABSTRACT
Explants and cells of forelimb muscle from adult Notophthalmus viridescens were cultured for periods up to 160 days in MEM-based medium supplemented with serum, hormones, and antibiotics. Explants which were not minced prior to culture contained muscle fibres with healthy myonuclei and no evidence of dedifferentiation after four weeks. Exlants which were minced prior to culture contained degenerated muscle fibres after 1 day and no evidence of dedifferentiation after four weeks. Mononucleated cells from both minced and non-minced explants proliferated. Cell proliferation and myotube formation was greater in the minced muscle cultures. Proliferation and fusion of myoblasts and subsequent formation of myofibrils were observed on the plate in primary cultures. Secondarily transferred cells proliferated and fused into myotubes. Although adult newt muscle does not contain satellite cells, myogenesis in this amphibian followed the same course as all other vertebrate skeletal muscle: proliferation of mononucleated myogenic cells, fusion of the myoblasts to form syncytia, and eventual accumulation of myofibrils. The ultimate source of the myogenic cells was not identified; however, the absence of dedifferentiation of the mature fibres and the occurrence of myogenesis in cultures of minced muscle explants demonstrated that the regenerated muscle developed from a population of mononucleated cells whose origin did not depend upon dedifferentiation of intact fibres.
The positional coding system in the early eye rudiment of Xenopus laevis, and its modification after grafting operations
Authors: Cooke J. , Gaze R. M. 
Published: April 2021

ABSTRACT
In a series of Xenopus embryos, 60–90 ° sectors at various positions distributed around the eye rudiment were replaced with sectors grafted from the opposite position in the rudiment on the same side of the head of a donor. The majority of the operations were carried out before stage 28 (Nieuwkoop & Faber, 1956), and many before stage 26. The patterns of retinotectal connectivity which then developed were assayed electrophysiologically soon after metamorphosis. The visuotectal maps were frequently compound, giving evidence that many parts of the rudiment had already been equipped with distinct tissue positional codes by the time operations were performed (i.e. before neurogenesis). Although graft-derived sectors of retina connected to tectal sectors that were more nearly appropriate for their original positions in the rudiment than for their translocated ones, the ‘handedness’ of these ectopic components of the compound maps tended to bear a mirror-image relation to the major map, rather than the point-symmetrical one to be expected from a complete autonomy of mapping functions in grafted tissue. The results are discussed in relation to possible modes of organization of the developing eye, considered as a pattern-forming system.
Normal and abnormal development of an identified leech motor neuron
Authors: Kuwada John Y. 
Published: April 2021

ABSTRACT
In embryonic and mature leeches, the identified L motor neuron, which innervates the longitudinal muscles of the contralateral half body segment, can be identified by the location and relatively large size of its cell body. Here the morphological and physiological development of the L motor neuron has been investigated by intracellular recording and dye-filling techniques in normal and abnormal embryonic leeches. Normally the L motor neuron growth cone projects from the cell body at about the same time as from many other neurons located in the lateral part of the ganglion, including the P mechanosensory neurons. The L motor axon, like many other leech axons, projects directly into the appropriate pathway. The L motor neuron does not initially extend an excessive number of axons followed by elimination of the inappropriate ones. Its growth cone is tapered and relatively free of filopodia and grows out of the ganglion in the contralateral posterior nerve behind the growth cone of the primary peripheral axon of the dorsal P mechanosensory cell, which is one of the earliest axons in the posterior root.
Occasionally the bilateral halves of the germinal plate fail to fuse resulting in an embryo with separated but intact half ganglia, body wall, and skin. In such embryos the L motor neuron axons cannot grow out the contralateral posterior nerve since it is not available. Instead they grow out a variety of ipsilateral nerves and/or connective tracts. The P mechanosensory cells, which normally grow out of the ganglion in specific ipsilateral nerves, extend their axons along their normal pathways. In these abnormal embryos the L motor neurons did not preferentially grow into the ipsilateral posterior nerve, normally the pathway taken by the bilateral homologue and the nerve most similar to the L motor neuron’s normal pathway. The failure of these L neurons to either consistently choose or avoid the ipsilateral posterior root suggests that the bilateral homologues ignore one another’s pathfinding cues or that such cues are missing or changed in these embryos. The axons of the P neurons, however, appear to require no cues or interactions with contralateral structures or cells for normal development.
Fine structure of the interdigital membranes during the morphogenesis of the digits of the webbed foot of the duck embryo
Authors: Hurle J. M. , Fernandez-Teran M. A. 
Published: April 2021

ABSTRACT
Fine structural study of interdigital membranes during formation of the digits of the duck foot reveals that the interdigital necrosis is accompanied by a high deposition of collagenous material in the epithelio-mesenchymal interface, rupture of the basal lamina and detachment of ectodermal cells into the amniotic sac. These changes are similar to those observed in the regressing interdigital membrane of the chick although their intensity and temporal extension are less pronounced in the duck. It is suggested that these changes account for the disappearance of the marginal zone of the duck interdigital membranes. The possible causal relationship between the different structural changes are discussed.
Epithelial induction of osteogenesis in embryonic chick mandibular mesenchyme studied by transfilter tissue recombinations
Authors: Exan R. J. Van , Hall B. K. 
Published: April 2021

ABSTRACT
The initiation of osteogenesis in the mandibular mesenchyme of the embryonic chick at 7 days is dependent upon an epithelial induction which occurs in the mandible up to the fourth day in ovo. In the present study, transfilter tissue recombinations were used to study this inductive mechanism. The epithelial and mesenchymal components of the mandibles were separated before the completion of the induction and recombined to form transfilter explants which were either cultured for 9 days or grafted onto the chorioallantoic membrane for host embryos for 7 days.
Control experiments demonstrated that the tissue separation and recombination techniques did not interfere with the normal epithelial induction, and confirmed that mandibular mesenchyme isolated at this stage was incapable of forming bone.
Bone was observed in 86 % of the CAM-grafted intact mandible controls and in 80 % of the cultured intact mandible controls. Bone failed to form in the mesenchyme of transfilter explants when Millipore filters with 0·45 μm pores were used. Bone was observed as frequently as in control explants when the mandibular mesenchyme was separated from its epithelium by 0·8μm or 0·4μm porosity Nuclepore filters. Only about 30% of the transfilter explants prepared with 0·1μm porosity Nuclepore filters formed bone and none of the explants prepared with 0·03μm porosity Nuclepore filters formed bone. SEM studies demonstrated a distinct correlation between the formation of bone in transfilter explants and the ability of the epithelium and mesenchyme to penetrate the pores of the filters.
Thus, the present study provides evidence that the site of the induction is restricted to the epithelial-mesenchymal interface, and that the induction is not mediated by a diffusible substance. The nature of the inductive mechanism is discussed with respect to this and other recent studies which suggest that the induction may be mediated by a non-diffusible epithelial cell product resident in the epithelial basal lamina.
Electron microscopic evidence for the presence of an asialoglycoprotein receptor on isolated foetal rat hepatocyte surface
Authors: Devirgiliis Laura Conti , Dini Luciana , Russo-Caia Salvatore 
Published: April 2021

ABSTRACT
The ontogeny of asialoglycoprotein receptor was investigated by electron microscopic cytochemistry in hepatocytes isolated from foetal and adult rat. The binding capacity for asialofetuin coupled to horseradish peroxidase was lacking before the 18th day of intrauterine life; it arises at this time and increases with developmental age.
The ligand-receptor complexes form small patches. The distribution pattern of positivity is very similar in pre and postnatal age, covering the entire cell surface.
These results indicate a rather late appearance of the galactose-binding capacity related to the asialoglycoprotein clearance function, which is typical of adult mammalian liver.
Relation between Somite Segregation Rate and ATP-ase Activity in Early Chick Embryos
Authors: Deuchar E. M. 
Published: April 2021

ABSTRACT
In the preceding paper (Deuchar, 1960) it was established that the first-formed somites of the chick embryos at 40–45 hours’ incubation (Hamburger & Hamil-ton’s stage 11, 1951) have a higher calcium-activated ATP-ase activity per unit nitrogen than the somite mesoderm which is not yet segmented at this stage. It was inferred that there is an increase of ATP-ase (possibly connected with myosin synthesis) in the somite tissue as it segments. A question that at once arises is how far the ATP-ase activity is essential to the process of somite segmentation. Besides presaging myosin, the ATP-ase could conceivably play an immediate role during the movements and changes of shape that the mesoderm cells undergo at this time. If so, one would expect some correlation between intensity of ATP-ase activity and the efficiency of segmentation, if either were modified experimentally. To test this possibility, in the work to be described here chick embryos have been grown in media to which the agents ω-bromo-allylglycine, leucine, and adenosine triphosphate had been added, ω-bromo-allylglycine (BAG) is an analogue of leucine which was found by Herrmann, Konigsberg, & Curry (1955) to block completely the segmentation of chick somites. Its effects are reversible by the simultaneous addition of leucine. In the present experiments its effects on ATP-ase activity as well as segmentation rate were measured, both alone and in the presence of leucine. Leucine was also tested by itself to see if it would increase either segmentation rate or ATP-ase activity above the normal level. Finally, ATP was added to some cultures as a possible means of raising both ATP-ase activity and segmentation rate. ATP was then used in combination with BAG to see if it would reverse the effects of this inhibitor.
Some Degenerative Phenomena in Drosophila Ovaries
Authors: Waddington C. H. , Okada Eiko 
Published: April 2021

ABSTRACT
A description is given of degenerative phenomena in the Drosophila ovary. Three types of degeneration are dealt with: (1) degeneration of the follicle cells; (2) degeneration occurring in the unfertilized egg, a major feature of which is the segregation of the different constituents of the egg into comparatively large masses; and (3) degenerative phenomena in the nurse cells and oocytes of abnormal eggs produced in ovaries homozygous for deep-orange.
In all these instances it is noteworthy that a considerable degree of structural organization (formation of double membranes, or sets of parallel or concentric membranes, &c.) occurs in cytoplasm which is clearly degenerating. It is suggested that such organization does not always represent the formation of functioning organelles, but may be a mere consequence of the inherent physicochemical properties of the materials involved.
In degenerating deep-orange ovaries masses of fragmented porous membranes are found. These seem to be derived from the nuclear membranes of the nurse cells, which appear to persist even when the rest of the cell is rather completely destroyed. Fragments of nuclear envelopes tend to lie close together and parallel to one another, and it is suggested that this indicates that there is some force of attraction between them, which may be comparable to the forces involved in the formation of stacks of annulate lamellae, or of concentric or parallel double-membrane structures in ergastoplasm, and in chromosome pairing in healthy functional cells.
La culturein vitrode l’épithélium germinatif isolé des gonades mâles et femelles de l’embryon de Canard
Authors: Haffen Katy 
Published: April 2021

ABSTRACTUndifferentiated germinal epithelium was isolated following trypsinization from embryonic duck gonads of 5 to 7 days of incubation. This epithelium was associated with ovarian and testicular medullae taken from sexually differentiated embryos. Ovarian cortex differentiates from female germinal epithelium of 5 days, whatever the source of the medullary tissue with which it is associated (Plate 1, fig. 3; Plate 2, figs. 5, 6a, b, c). In control experiments the female epithelium undergoes similar development in the presence of mesonephros (Plate 2, fig. 5). Five-to seven-day male germinal epithelium is influenced by tissues with which it is in contact. In the presence of testicular medulla it gives rise to male medullary cords (Plate 1, fig. 4). In the presence of ovarian medulla, ovarian cortex differentiates (Plate 3, figs. 7a, b, c). When in contact with mesonephros no differentiation of the male epithelium ensues. These results are particularly clear in the case of germinal epithelia explanted between 5 and 6 days of incubation.
The Influence of the Hypophysis and the Thyroid on the Ultimobranchial Body of the Anura of Israel
Authors: Boschwitz Dvorah 
Published: April 2021

ABSTRACTThe ultimobranchial body originates independently of the thyroid, as seen in congenitally athyreotic tadpoles of P. syriacus. Experiments concerning the influence of the hypophysis and thyroid on the ultimobranchial body were performed on H. arborea, R. ridibunda, and B. viridis. With the beginning of metamorphosis, the increasing thyroid secretion inhibits the original growth rate of the ultimobranchial body; experimental hyperthyroidism enhances this physiological interference, so that the follicle shrinks. Experimental hypothyroidism causes hypertrophy of the ultimobranchial body, evidenced by an increase in surface area of the follicle. This effect is negligible before metamorphosis, significant during metamorphosis, and less extreme in young adults, when thyroid activity declines. Hypophysectomy in young adults causes atrophy of the organ. It is assumed that the hypophysis maintains the ultimobranchial body and the thyroid inhibits its growth and activity. The antagonistic effects of both glands produce the normal state of the organ.
The roles of node regression and elongation of the area pellucida in the formation of somites in avian embryos
Authors: Stern Claudio D. , Bellairs Ruth 
Published: April 2021

ABSTRACT
Experiments have been carried out on explanted chick embryos to test certain widely accepted concepts about the role of Hensen’s node in somite formation. The relationship between elongation of the area pellucida and regression of Hensen’s node has also been investigated.
We conclude from these experiments that: (a) The timing of somite formation is not controlled by the regression of Hensen’s node, nor by the shearing of the mesoderm into right and left halves.(b) Somite size and shape are probably controlled by local conditions in the chick embryo.(c) Elongation and regression are two different events.(d) The position of the somites probably depends on mechanical tensions in the area pellucida.(e) The notochord is not required for the stability of somites in vivo.
Do larval epidermal cells possess the blueprint for adult pattern in Drosophila?
Authors: Madhavan Mekkara Mandaravally , Madhavan Kornath 
Published: April 2021

ABSTRACT
When the diploid histoblasts, the precursors of adult abdominal epidermal cells, of the larva of Drosophila are deleted by γ-radiation, the polytene larval epidermal cells survive metamorphosis and secrete cuticle and cuticular outgrowths. A comparison of the morphology of the cuticle secreted by the larval epidermal cells in the different regions of the abdominal segments to that secreted by the histoblasts of the unirradiated animal suggests that the former contain the blueprint for the pattern of landscape of the adult abdominal cuticle and possibly could provide this information to the dividing and spreading histoblasts during the normal ontogeny of the fly.