bluuebunny/crossref_metadata_2025_split huggingface dataset:
Responses of the early chick embryo to external cAMP sources
Authors: Gingle Alan R. , Robertson Anthony 
Published: April 2021

ABSTRACT
Early chick embryos were stimulated with local sources of cAMP. Three major effects were observed: bending of the embryonic axis, attraction of cells on the ventral surface of the embryo, and disruption of the blastodisc. Each had a characteristic concentration dependence. These results are compared with those from studies of cells disaggregated from similar embryos.
Cell differentiation in isolated inner cell masses of mouse blastocystsin vitro:onset of specific gene expression
Authors: Dziadek Marie 
Published: April 2021

ABSTRACTInner cell masses (ICMs) were isolated by immunosurgery from giant blastocysts formed by the aggregation of three morulae. A layer of endoderm cells formed on the outer surface of these primary ICMs in vitro. When this layer was removed by immunosurgery, a secondary endoderm layer formed. Alphafetoprotein (AFP) was used as a biochemical marker to characterize visceral endoderm formation in these cultured ICMs. The immunoperoxidase reaction on sections of ICMs cultured for intervals up to 120 h in vitro showed that some primary endoderm cells contained AFP, but these were always in the minority. The secondary endoderm layer, on the other hand, was composed of predominantly AFP-positive cells. It is concluded that the primary endoderm contains mainly parietal endoderm cells, while the secondary layer contains visceral endoderm cells. A model is proposed for the consecutive differentiation of parietal and visceral endoderm cell types from the ICM of mouse blasto-cysts.
Fate maps and cell differentiation in the amphibian embryo – an experimental study
Authors: Landström Ulf , Løvtrup Søren 
Published: April 2021

ABSTRACT
The aim of this paper is to test two different fate maps for the amphibian blastula with respect to their predictions concerning the process of cell differentiation. The first of these fate maps is the one proposed by Vogt, according to which all three germ layers can be projected on to the surface of the embryo. The second is a revision which claims that only endoderm and ectoderm are located in the surface, while the mesoderm is represented by free cells in the interior of the embryo.
The testing has been performed by observing the differentiation of small explants of cells taken from various regions of the embryo.
It was found that the spontaneous cell differentiation comprises three patterns: undifferentiated cells (free interior cells and circumpolar endodermal cells), fibroblast-like cells (the remaining endodermal cells) and epidermis (ectodermal cells).
Further differentiation occurs only through induction, exerted either by the fibroblast-like endodermal cells or by heparan sulphate. When induced, the equatorial ectodermal cells give rise to swollen, hyaline cells (chordocytes), while the remaining ectodermal cells form a sequence of cell differentiation patterns, mesenchyme cells, nerve cells, melanophores and xanthophores.
The free interior cells differentiate into striated muscle cells and elongated collagen-producing fibroblasts.
Our results thus confirm the revised fate map, and they also give an insight into the mechanisms of the initial cell differentiations in the amphibian embryo.
Development of the tibiotarsus in the chick embryo: biosynthetic activities of histologically distinct regions
Authors: Stocum David L. , Davis Richard M. , Leger Marilyn , Conrad H. Edward 
Published: April 2021

ABSTRACT
The dynamics of the histological changes which occur in the distal half of the tibial portion of the embryonic chick tibiotarsus from day 8 to day 18 of incubation are correlated with the capacities of histologically distinct zones to incorporate isotopic precursors into mucopolysaccharides and collagen. At the distal end of the tibia, which abuts the suture line formed by the fusion of the two tarsals with the tibia, there persists throughout embryonic development a narrow band of small, round or oval, rapidly dividing chondrocytes which synthesize chondroitin SO4 and collagen at low rates. Just proximal to this zone is a broader zone of flattened, disc-shaped chondrocytes which divide more slowly and are extremely active in chondroitin SO4 and collagen synthesis. Proximal to the zone of flattened chondrocytes is a zone of non-dividing, hypertrophied chondrocytes which are large and round and increase continually in size going from the distal to the proximal end of the zone. The biosynthetic activities of the cells in this zone fall sharply with their distance from the zone of flattened chondrocytes. Finally, there is a fourth zone, the marrow cavity, formed by a proximal to distal disintegration of the hypertrophied chondrocytes, starting at mid-diaphysis. The marrow cavity is surrounded by a shell of periosteal and intra-membranous bone which extends to the distal end of the zone of hypertrophied chondrocytes. Our data suggest that as the tibiotarsus grows in length the small, round rapidly dividing cells of the tibia differentiate first to flattened chondrocytes which synthesize matrix at a high rate and ultimately to low activity, hypertrophying chondrocytes. This sequence proceeds in a linear fashion.
Cell contact and positional communication in hydra
Authors: Wakeford R. J. 
Published: April 2021

ABSTRACT
Positional communication and the functional coupling of muscular reflexes were examined in grafted hydra. A head and distal gastric region inhibited head regeneration by a host sub-hypostome within 4 –5 h of grafting. Functionally coupled pathways which indicated the presence of gap junctions also formed between graft and host during this time. It is suggested that gap junctions provide a channel for positional communication.
Development of retinal synaptic arrays in the inner plexiform layer of dark-reared mice
Authors: Fisher Leslie J. 
Published: April 2021

ABSTRACT
In the central area of the retina of mouse the rate of synaptogenesis in the inner plexiform layer (IPL) drops precipitously at about the time the eyes open. To determine if the visual input at eye opening provides a signal for the neurons to stop adding synapses, mice were raised in darkness during the period of maximal synaptogenesis and through eye opening. Retinal synaptic arrays of dark-reared and normally reared animals were compared qualitatively. The rate of synaptogenesis after eye opening in dark-reared mice indicated that the onset of visual stimulation was not the cue to stop synaptogenesis. However, the synaptic arrays of the IPL of dark-reared mice consistently had more conventional synapses than those of normally reared mice. It is concluded that the number of conventional synapses in the central retina was increased by dark-rearing.
Elevation of lesioned palatal shelvesin vitro
Authors: Brinkley L. L. , Vickerman M. M. 
Published: April 2021

ABSTRACTFetuses were obtained from CD-1 mice at a time estimated to be 12 h prior to in vivo secondary palate closure. One of the palatal shelves of each partially dissected fetal head was lesioned in one of five ways, the other left intact to serve as a control. Single transverse cuts extending the width of the shelf were made at one of three positions along the longitudinal axis of the shelf : one-third, one-half or two-thirds the shelf length estimated from the rostral edge. Some specimens were cut in two places, dividing the shelf into three equal segments. Another group received a lesion which separated the caudal third of the shelf from its maxillary connections. All specimens were cultured for 18 h. At the end of the culture period the heads were fixed, examined and the degree of elevation of each shelf piece assessed.Intact, control shelves of all preparations were elevated in the rostral two-thirds of the shelf, while the caudal third was partially elevated. Results seen in lesioned shelves depended upon both the size of the segment and the region of the shelf contained in the segment. The rostral two-thirds of the shelf, the presumptive hard palate, whether intact or in segments elevated without physical connections to neighboring shelf tissue. Thus, it is unlikely that this elevation requires a wave of contraction be transmitted from the caudal soft palate region. In contrast, the presumptive soft palate requires continuity with the rostral portions of the shelf both to maintain structural stability and to elevate.
The effect of prolonged decompaction on the development of the preimplantation mouse embryo
Authors: Johnson M. H. , Chakraborty J. , Handyside A. H. , Willison K. , Stern P. 
Published: April 2021

ABSTRACT
A rabbit antiserum to a mouse embryonal carcinoma cell line blocks compaction of cleaving mouse embryos. Cell division is not affected up to the 32-cell stage but intracellular junctions fail to develop. Removal of the antibody at this stage permits compaction to occur and a normal blastocyst develops. Prolonged decompaction beyond the 32-cell embryo results in an increasing proportion of malformed blastocysts in which trophectodermal cells predominate and functional inner cell mass (ICM) cells are reduced or absent. The relationship of compaction to the generation of ICM and trophectoderm lineages in the intact embryo is discussed.
Quantitative staging of embryonic development of the grasshopper,Schistocerca nitens
Authors: Bentley David , Keshishian Haig , Shankland Martin , Toroian-Raymond Alma 
Published: April 2021

ABSTRACTDuring development of the grasshopper embryo, it is feasible to examine the structure, pharmacology, and physiology of uniquely identified cells. These experiments require a fast, accurate staging system suitable for live embryos. We present a system comprising (1) subdivision of embryogenesis into equal periods, (2) expression of stage in percent of complete embryogenesis time, (3) characterization of stages by light micrographs (and descriptive text), and (4) illustration of stages at the egg, embryo, and limb levels of resolution. Advantages of a percent-system include communicability, flexibility in temporal resolution, accurate assignment of elapsed time in developmental processes, and uniform coverage of the period of embryogenesis. The stages described are at 5 % intervals with an estimated error of ±1 %.
Translocation of neural crest cells within a hydrated collagen lattice
Authors: Davis Edward M. 
Published: April 2021

ABSTRACTChick neural tubes were cultured either on planar substrata of collagen-coated Falcon plastic in growth medium with serum or within a hydrated collagen lattice (HCL) in growth medium either with or without serum. Using time-lapse cinemicrography, neural crest cells were observed emigrating from neural tubes over the collagen substrata. Once separated from the neural tube, they seldom reunite with it. Though the average rate at which the neural crest cells translocate was the same in the different culture conditions, approximately 1·0 μm/min, distinct differences in morphology and mode of translocation were observed. Neural crest cells on collagen-coated culture dishes have a flattened fibroblastic morphology and mode of translocation; in an HC1 with serum, they have a bipolar shape and translocate by advancing a long, narrow leading protrusion and by periodically retracting the attenuated trailing portion of the cell; and in a serum-free HCL, they have a unipolar shape and translocate by advancing a long, narrow, branched leading protrusion and by periodically transferring the cytoplasm of the large, rounded trailing cell body forward, past a bulbous structure, and into the leading protrusion.
Drosophila nuclei replicate in Xenopus eggs
Authors: Smith Christina , Brill David , Bownes Mary , Ford Christopher 
Published: April 2021

ABSTRACT
Nuclei isolated from a permanent cell line derived from Drosophila melanogaster embryos have been injected, along with a radioactive DNA precursor [3H]TTP, into Xenopus laevis eggs. In culture, less than 7 % of the cells were in S phase. After a 90 min incubation, following injection into eggs, 99% of the nuclei were shown by autoradiography to have synthesized DNA. In a similar experiment, a density label BrdUTP was injected into eggs along with the nuclei. Subsequent analysis on caesium chloride gradients showed that this DNA synthesis was semi-conservative replication. Therefore we conclude that signals present in Xenopus egg cytoplasm can initiate and sustain true semi-conservative DNA replication in nuclei from an invertebrate organism.
The effect of 6-aminonicotinamide on limb development
Authors: Mclachlan John C. 
Published: April 2021

ABSTRACTThe morphological effect of the nicotinamide analogue 6-aminonicotinamide on the development of the embryonic chick limb was studied, with special reference to muscle, cartilage, feather germ formation, and ossification. No evidence was found to support theories of control of differentiation by nicotinamide-like substances, although the effect of nicotinamide analogues has often been quoted as evidence for such theories.However, the effect of 6-AN in shortening the limb provides an opportunity to study the interaction of various tissues in normal growth and development, and the results are used to shed further light on the processes involved in muscle splitting, and feather germ formation.
On the role of germ cells in planarian regeneration:II. Cytophotometric analysis of the nuclear Feulgen-DNA content in cells of regenerated somatic tissues
Authors: Gremigni V. , Miceli C. , Picano E. 
Published: April 2021

ABSTRACTPrevious findings by our group have shown how primordial male germ cells take part in regenerative blastema formation in planarians by migrating to the wound.The role of these cells in rebuilding transected tissues has been investigated in a population of Dugesia lugubris s.l. which is particularly suited for our purpose. In fact, these planarians provide a clear karyological marker to distinguish diploid male germ cells (2n = 8) from tryploid embryonic or somatic cells (3n = 12). In this study we employed the cytophotometric analysis of the nuclear Feulgen-DNA content in order to distinguish non-replicating male germ cells from reserve and somatic cells. The Feulgen-DNA content in cells from the gonad-free caudal area was measured after complete regeneration. Most non-replicating cells (94–95 %) were found to have a DNA amount typical of cells previously estimated as triploid. Some (5–6%) nuclei containing a DNA amount typical of cells previously estimated as diploid male gonia were also found. These findings seem to support the view that primordial male germ cells also participate in rebuilding somatic tissues according to the field influence they encounter during regeneration. The possibility that metaplasia (or cell transdifferentiation) may occur in planarians is finally discussed.
Expression of the maternally derived X chromosome in the mural trophoblast of the mouse
Authors: Frels William I. , Chapman Verne M. 
Published: April 2021

ABSTRACT
Only the maternally derived allelic form of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1) is observed in the mural trophoblast of heterozygous female progeny in F1 and backcross matings. We have demonstrated that this expression of the maternally derived PGK-1 is not a result of maternal tissue contamination nor of selection of cells expressing the maternal X chromosome (Xm). Our results suggest that the expression of Xm in mural trophoblast is a consequence of nonrandom X-chromosome inactivation in trophectoderm cells.
Intercalary regeneration in the amphibian limb and the rule of distal transformation
Authors: Maden M. 
Published: April 2021

ABSTRACT
The applicability to the amphibian limb of the rule of distal transformation, which states that tissue from any level can only become more distal, has been tested during intercalary regeneration following various types of shift-level transplantation. Following the grafting of distal blastemas to proximal levels, such that part of the presumptive pattern is missing, complete limbs nevertheless formed (Series 1). That the intercalated tissue arose entirely from the stump was shown by exchanging blastemas between black and white animals. When the proximal stump was irradiated and its contribution eliminated, intercalary deletions were produced (Series II). This was not due to the inability of irradiated and normal tissue to communicate since irradiated distal blastemas grafted onto proximal stumps still stimulated intercalary regeneration (Series III). When proximal blastemas were grafted to distal levels intercalary regenerates were obtained in about 20% of the cases (Series IV) and under these circumstances the grafted blastema was the sole source of intercalated tissue. The precise structure of these intercalated elements was impossible to ascertain, but it is suggested that they might be of reversed polarity as found in insects. These results are discussed in relation to similar experiments on the insect limb.
In vitro imaginal disc development and moulting hormone
Authors: Guillermet Christiane , Mandaron Paul 
Published: April 2021

ABSTRACT
imaginal leg and wing discs obtained from late-third-instar Drosophila larvae were cultured in vitro in various concentrations of ecdysterone ranging from 10−10 to 10−5 M in order to test the effect of hormone concentration on evagination and cell differentiation.
At the optimal concentration of 8 × 10−8 M discs evaginated normally, secreted the pupal cuticle, underwent apolysis, differentiated imaginal structures and secreted the imaginal cuticle.
At suboptimal concentrations (10−8 M and less), evagination was incomplete in a variable proportion of appendages. Morphogenetic movements were limited to the earlier ones; so that appendages did not emerge from the peripodial sac. Subsequent development, whenever it occurred, took place inside the peripodial sac. This particular type of ‘endoevagination’ was only obtained with sub-optimal hormone concentration.
At supra-optimal concentrations (10−6 M and more), evagination was always complete but further differentiation was inhibited.
These results show that endoevagination is strictly related to insufficient supply of hormone and that morphogenesis and cell differentiation in imaginal discs are two independent phenomena, which respond to different levels of hormone stimulation.
Regeneration of an abnormal ipsilateral visuotectal projection inXenopusis delayed by the presence of optic fibres from the other eye
Authors: Straznicky Charles , Tay David , Glastonbury John 
Published: April 2021

ABSTRACTOptic fibre regeneration was studied by [3H]proline autoradiography and by mapping electrophysiologically the direct visuotectal projections to the contralateral and ipsilateral tecta 12 –16 weeks after sectioning the right optic nerve in Xenopus two to four weeks after metamorphosis. The experiments were carried out in three groups : (A) optic nerve section in newly metamorphosed animals with embryonic left-eye enucleation; (B) optic nerve section with simultaneous left-eye enucleation; and (C) optic nerve section with delayed left-eye enucleation 5 –31 days prior to sacrifice.In all but three animals regenerated optic fibres were demonstrated morphologically both in the contralateral and ipsilateral tecta. The contralateral visuotectal projection was fully restored within the 12 –16 weeks in all animals. In animals with embryonic enucleation or in those where the enucleation was carried out simultaneously with optic nerve section, a direct ipsilateral visuotectal projection was established at the same time as the restoration of the contralateral projection. In contrast, no direct ipsilateral visuotectal projection was detectable in the presence of optic fibres from the other eye in the doubly innervated tecta. However, 14 –31 days after the removal of the incumbent optic fibres by left-eye enucleation a direct visuotectal projection from the right eye to the ipsilateral tectum was established, and its polarity corresponded to the normal contralateral retinotectal projection.The apparent disparity between morphological and electrophysiological findings in the doubly innervated tectum suggests that superimposed optic fibres are unable to form normal synaptic relations with tectal neurons during early regeneration, delaying the establishment of the induced direct ipsilateral visuotectal projection.
Experiments on developing limb buds of the axolotl Ambystoma mexicanum
Authors: Maden M. , Goodwin B. C. 
Published: April 2021

ABSTRACT
Various experiments were performed on the limb buds of axolotls to compare the behaviour of amphibian limbs with that previously reported for chick limbs. Following removal of the tip or whole limb bud, extensive powers of regulation were observed since complete limbs always formed. Similarly after distal to proximal grafts intercalary regulation occurred to produce perfect limbs and after proximal to distal grafts serial repetitions resulted. Transplantation and rotation of limb buds to reverse either the dorso-ventral, antero-posterior or both axes resulted in the induction of supernumerary limbs in a large proportion of cases. Such regulatory behaviour of axolotl limb buds is in contrast to the mosaic nature of chick limbs and as a result, theories such as the progress-zone theory which have been formulated on the basis of data from chick limbs are not relevant to general principles of vertebrate limb development. Possible reasons for the diverse behaviour between the two systems are discussed.
Changes in fucosyl-glycopeptides during early post-implantation embryogenesis in the mouse
Authors: Muramatsu Takashi , Condamine Hubert , Gachelin Gabriel , Jacob François 
Published: April 2021

ABSTRACTSix-day to 12-day mouse embryos were dissected and radiolabelled by culture in the presence of [3H]fucose. The radiolabelled embryos were extensively digested with Pronase. The resulting glycopeptides were analysed by Sephadex G-50 column chromatography. Glycopeptides from 6-day-old embryos were separated into two main peaks: one eluted near the excluded volume, the other in a well-retarded position. This elution profile was similar to that observed with glycopeptides prepared from embryonal carcinoma cells. The relative amount of the high-molecular-weight glycopeptides decreased during embryonic development and particularly around day 9. Glycopeptide elution profiles from 10-day embryos, or isolated organs of 12-day embryos, were indistinguishable from those obtained from differentiated teratocarcinoma-derived or adult cells. At least 30% of the large molecular weight glycopeptides appear to be located at the cell surface.