bluuebunny/crossref_metadata_2025_split huggingface dataset:
Insensitivity to cytochalasin B of surface contractions keyed to cleavage in the Xenopus egg
Authors: Christensen Kathy , Merriam R. W. 
Published: April 2021

ABSTRACT
In fertilized eggs of Xenopus laevis a marked flattening of the pigmented animal hemisphere has been observed. The flattening begins 15 –20 minutes before the appearance of the cleavage furrow. As the furrow develops, the pigmented surface relaxes and rounds up. The initial appearance of the furrow is thus shown to be a combination of furrow deepening and rounding up of adjacent pigmented surfaces.
It is demonstrated that the flattening is not caused by gravity or osmotic mechanisms and that internal pressure is increased during the flattening. The flattening is interpreted to be an isodiametric contraction of the pigmented surface. The contraction is not inhibited by injected cytochalasin B in sufficient concentrations to completely inhibit cleavage furrow formation.
These results are discussed with respect to the presence of two surface contractile systems, distinguishable on the basis of their differing sensitivity to cytochalasin B.
Experimental induction of testicular teratomas in dissociated–reaggregated chimaeric gonads
Authors: Regenass Urs , Friedrich Thomas D. , Stevens Leroy C. 
Published: April 2021

ABSTRACT
Testicular teratomas can be experimentally induced in some strains of mice by grafting 12·5-day male genital ridges to the testes of adults. The grafts develop into testes and most of them have teratomas. The cells of 12·5-day foetal gonads were dissociated and the germ cells and somatic cells were separated. When germ cells were reaggregated with somatic cells and implanted in adult testes, they formed seminiferous tubules with teratomas. The somatic cell populations were contaminated with about 1 % germ cells, and when they were implanted in adult testes, they formed testes with a comparatively low incidence of teratomas. When germ cells of a highly susceptible strain were combined with somatic cells from a resistant strain, they formed chimaeric testes with a high incidence of teratomas. When germ cells from a resistant strain were combined with somatic cells from a susceptible strain they formed chimaeric gonads and the incidence of teratomas was low. This indicates that at 12·5 days the genotype of the germ cells is responsible for susceptibility. When germ cells from older foetal gonads were combined with somatic cells of 12·5-day gonads, the incidence of tera-tomas was low. This showed that 12·5-day somatic cells cannot ‘rejuvenate’ older germ cells in a way to regain their susceptibility. When 12·5-day germ cells of highly susceptible strains were combined with older somatic cells the incidence of tumours was low indicating that the age of the somatic cells influences susceptibility to teratocarcinogenesis.
Development of the optic nerve inXenopus laevis: I. Early development and organization
Authors: Cima Charles , Grant Philip 
Published: April 2021

ABSTRACTDevelopment of the Xenopus laevis optic nerve was studied by light and electron microscopy from embryonic stage 26, before the retina has formed, to juveniles, 8 months post-metamorphic. Low-power EM photographs of sections through the retinal optic nerve (RON), middle optic nerve (MON) and chiasmatic optic nerve (CON) were prepared at different stages and the areas containing large axons (0·5 μm) were traced in optic nerve reconstructions. Ordering of fibre size along a dorsoventral axis was noted in the embryonic nerve, and this pattern persisted throughout development. Most large fibres, myelinated and unmyelinated, occupy an eccentric dorsoventral position in the MON while small axons are seen in a ventral peripheral crescent. In the CON, the dorsal one third to one half is occupied by large fibres while the ventral CON contains small fibres exclusively. If, as assumed, large axons are older than small axons (0·1 –0·3 μm), then patterns of large and small axons along the nerve might reveal a chronotopic fibre ordering. Chronotopic ordering was confirmed by autoradiographic analysis of the distribution of old, labelled fibres and young, unlabelled newly arriving fibres in optic nerves between stage 51 and 57. The young-old labelling pattern corresponds to the small and large axon patterns respectively, in all sections of the optic nerve. Chronotopic ordering of fibres in the developing optic nerve can be explained, in part, by the dorsoventral asymmetric marginal growth of the developing retina and the phenomenon of fibre following as ganglion cell axons join near neighbour fascicles in the retina, converge at the optic disc and grow through the optic nerve.
Increased adhesiveness at sites of high acetylcholine receptor density on embryonic amphibian muscle cells cultured without nerve
Authors: Moody-Corbett F. , Cohen M. W. 
Published: April 2021

ABSTRACT
In culture, myotomal muscle cells from Xenopus laevis embryos develop discrete patches of high acetylcholine receptor (AChR) density. To examine the relative adhesiveness of these sites, muscle cells having AChR patches on their lower surface (apposed to the culture dish) were identified and were then treated with dibucaine or potassium-Ringer in order to cause the cells to round up. More than 90% of these cells remained attached at an AChR patch after rounding up, and this was the case even when the cells had a single patch on their lower surface. When the cells were torn away from the culture dish by mechanical agitation, small cellular fragments still remained firmly attached to the dish and many of these fragments contained an AChR patch. It is concluded that AChR patches on the lower surface of the cell are often located at sites of increased adhesiveness to the culture dish. The findings are discussed in terms of the formation and maintenance of AChR patches.
Experimental Neoplastic Formation in Embryonic Chick Brains
Authors: Källén Bengt 
Published: April 2021

ABSTRACT
In mammalian teratology, a malformation consisting of ‘overgrowth’ of the neural tube has been described by, among others, Patten (1952,1957) and Ariens Kappers (1956, 1957). Sjodin (1957) thought it to be a post-mortem effect and not a true malformation. The present author (1955) demonstrated that a similar malformation could be produced in the rostral part of the brain of chick embryos by operations at somite stages on the rostral end of the rhombencephalon which damaged underlying notochordal structures. Bergquist (1959 a, b) has discussed this problem further. The overgrowth is made up of an excessive proliferation in the neural epithelium with a reduced cell differentiation, giving rise to only a thin layer of migrated cells but to a marked development of neural epithelium in 4-to 5-day embryos. The vesicles of the hemispheres and mesencephalon are strongly folded, and Bergquist (1959c) has produced evidence that the folding is due to the accumulation of mitoses along the ventricular lining of the vesicles. For further details of this malformation the reader is referred to Bergquist’s papers.
Incorporation de l’adénine-C14 dans l’embryon de Poulet
Authors: Barbieri par Francisco D. 
Published: April 2021

ABSTRACT
Malgré le grand nombre de données déjà publiées sur le métabolisme des acides nucléiques pendant le développement embryonnaire, quelques aspects de cette question complexe méritent d’être reconsidérés, surtout quand on dispose de méthodes de recherche précises.
Volumetric Investigations on Overgrowth (Hypermorphosis) in Chick Embryo Brains
Authors: Bergquist Harry 
Published: April 2021

ABSTRACT
The present paper is intended as a continuation of preceding publications (Bergquist, 1959 a, b) on possible causes of the phenomenon of ‘overgrowth’ (Patten, 1952) in the brain of the chick embryo. Reference should be made to these publications for the relevant literature. In these earlier investigations, it was observed that the mitotic rate in the altered portions of the neural tube seemed higher than in the normal regions, and that the hemispheres and tectum opticum showed marked folding.
Osteolathyrogenic Effects on the Developing Rat Foetus1
Authors: Ferm Vergil H. 
Published: April 2021

ABSTRACT
Skeletal and aortic changes in foetal rats treated with osteolathyrogenic agents via the maternal system throughout pregnancy or very late in pregnancy have been described by Stamler (1955). Developmental changes in Xenopus larvae (Chih, Witschi, & Ponseti, 1954) and in salamander and toad larvae (Levy, 1955) have also been described. The abnormalities produced in these forms by these agents have apparently been related to a direct effect of the agent on the mucopolysaccharide ground substance. No attempt has been made in a mammal to determine if there are specific time-susceptible periods in embryogenesis when this type of stimulus may induce true teratogenic effects. The present study was devised to determine the effect of a known osteolathyrogenic agent during specific stages of gestation and especially to observe the effect of this agent during the early critical stages of embryogenesis.
Development of the apical ectodermal ridge in the chick wing bud
Authors: Todt William L. , Fallon John F. 
Published: April 2021

ABSTRACT
Histological examination of the stage-18 to stage-23 chick wing bud apex revealed the following. Initially, the wing bud was covered by a cuboidal to columnar epithelium with an overlying periderm. Thickening of the apical ectoderm was not obvious until late stage 18 (36 pairs of somites), after the appearance of the wing bud. At late stage 18, cells of the inner layer of ectoderm had elongated slightly along an axis perpendicular to the epithelial-mesenchymal interface. Well-defined apical ectodermal ridge morphology, i.e., pseudostratified columnar epithelium with an overlying periderm, was not apparent until stage 20. Subsequently the ridge lengthened along the anteroposterior perimeter of the wing bud. We demonstrated histologically that the apical ectodermal ridge of the wing bud was asymmetric with respect to the anteroposterior axis, in that there was more ridge associated with posterior mesoderm. Other observations include the spatial and temporal location of a groove in the base of the thickest part of the ridge. The groove can be correlated with the specification of distal wing elements. The groove was first seen at stage 20 and became more prominent through stage 23. An anteroposterior progression of ectodermal cell death was also observed. This began at late stage 18 and continued through each of the stages examined.
Heterogeneous differentiation of external cells in individual isolated early mouse inner cell masses in culture
Authors: Nichols J. , Gardner R. L. 
Published: April 2021

ABSTRACT
Inner cell masses (ICMs) were isolated from early blastocysts by immunosurgery and incubated in a dense suspension of melanin granules for 3h after 21 h in culture. The majority of such labelled ICMs subsequently formed outgrowths in vitro in which either giant cells or small solitary cells contained melanin granules. However, a substantial minority produced outgrowths in which both types of cell were unequivocally labelled. Labelled cells appeared from the results of control experiments to have originated within the external layer of the ICM. The giant cells were indistinguishable morphologically from those formed by authentic trophectodermal tissue. The small cells were identified as belonging to the extraembryonic endodermal lineage on the basis of their distribution in host conceptuses following injection into blastocysts. These findings support the conclusion reached in previous studies that early ICM cells can engage in trophectodermal differentiation under certain conditions. In addition, by providing evidence that both trophectoderm and endoderm cells can differentiate from the outer layer of the same ICM, they argue that loss of cellular lability is not coordinated throughout this tissue. Heterogeneity in the differentiation of external cells may depend on differences in both the stage of the mitotic cycle and the number of such cycles that they have completed since fertilization.
Finally, cell number in isolated early ICMs was found to increase approximately two-fold during the first 24 h of culture in the present experiments. This contrasts with the results of previous experiments in which cell number either increased more modestly or failed to do so altogether.
The pigmentary system of developing axolotls
Authors: Frost S. K. , Epp L. G. , Robinson S. J. 
Published: April 2021

Abstract
A biochemical and transmission electron microscopic description of the wild-type pigment phenotype in developing Mexican axolotls (Ambystoma mexicanunm) is presented. There are three pigment cell types found in adult axolotl skin - melanophores, xanthophores and iridophores. Both pigments and pigment cells undergo specific developmental changes in axolotls. Melanophores are the predominant pigment cell type throughout development; xanthophores occur secondarily and in fewer numbers than melanophores; iridophores do not appear until well into the larval stage and remain thereafter as the least frequently encountered pigment cell type. Ultrastructural differences in xanthophore organelle (pterinosome) structure at different developmental stages correlate with changes in the pattern of pteridine biosynthesis. Sepiapterin, a yellow pteridine, is present in larval axolotl skin but not in adults. Riboflavin (also yellow) is present in minimal quantities in larval skin and large quantities in adult axolotl skin. Pterinosomes undergo a morphological “reversion” at some point prior to or shortly after axolotls attain sexual maturity. Correlated with the neotenic state of the axolotl, certain larval pigmentary features are retained throughout development. Notably, the pigment cells remain scattered in the dermis such that no two pigment cell bodies overlap, although cell processes may overlap. This study forms the basis for comparison of the wild type pigment phenotype to the three mutant phenotypes-melanoid, axanthic and albino-found in the axolotl.
The pigmentary system of developing axolotls
Authors: Frost S. K. , Epp L. G. , Robinson S. J. 
Published: April 2021

ABSTRACT
The melanoid mutant in the Mexican axolotl (Ambystoma mexicanum) is analysed with respect to the differentiation of pigment cells. Pigment cells were observed with the transmission electron microscope in order to determine any unusual structural characteristics and to determine what happens to each of the cell types as development proceeds. Chemical analysis of pteridine pigments was also carried out, and changes in pteridine biosynthesis were found to correlate well with changes in xanthophore morphology and number.
In melanoid axolotls, as development proceeds, melanophore numbers increase, xanthophores decrease, and iridophores fail to differentiate at all. This is considered to result from: (a) conversion of xanthophores (that are present in young larvae) to melanophores; (b) the gradual programming of the majority of chromatoblasts to become, exclusively, melanophores, and (c) the failure of some chromatoblasts (possibly iridoblasts) to differentiate altogether. The ultrastructural and chemical evidence presented in this study is compared to similar data for wild-type axolotls, and a mechanism regarding how the melanoid gene might act is suggested.
Apolipoprotein expression by murine visceral yolk sac endoderm
Authors: Shi Wei-Kang , Heath John K. 
Published: April 2021

ABSTRACT
Apolipoprotein expression was examined in the postimplantation mouse embryo. Antibodies directed against murine Apolipoprotein AI and human low-density lipoprotein (LDL) particles specifically immunoprecipitated metabolically labelled radioactive apolipoproteins from the culture supernatant of 10 ·5 days post coitum (days p.c.) yolk sac visceral endoderm cultured in vitro. No evidence for apolipoprotein expression by other embryonic or extraembryonic tissues at this stage was obtained. Immunohistochemical staining at sectioned 10 ·5 days p.c. embryos with anti-Apolipoprotein AI antibodies revealed specific localization of immunoreactive material in the yolk sac visceral endoderm. We conclude that the yolk sac visceral endoderm is a source of lipoproteins during postimplantation embryonic development.
Development of the iris in the chicken embryo: I. A study of growth and histodifferentiation utilizing immunocytochemistry for muscle differentiation
Authors: Ferrari Patricia A. , Koch William E. 
Published: April 2021

ABSTRACT
The development of the iris was studied in chicken embryos from 4 days of incubation through hatching and in chicks up to 17 days posthatching. Serial sections of the eye were stained routinely or by immunocytochemical methods using myosin antiserum to enhance detection of differentiating muscle by light microscopy. Eyes from embryos at each stage were also examined by scanning electron microscopy.
Outgrowth of the iris occurs in a sequential pattern around the eye, beginning at days of incubation in the region temporal to the choroid fissure and proceeding around the eye. Since differentiation of the iris follows the same pattern, similar areas of the iris were compared at each stage of development.
At days of incubation, pigment granules can be seen in the anterior epithelium at the root of the iris, but it is not until 8 days of incubation that pigment is identified in the same area of the posterior epithelium. As development proceeds, the pigmentation of both epithelial layers progresses from the root of the iris to the pupillary margin.
Early features of the development of the sphincter muscle can first be recognized in the 7day embryo, when epithelial buds form from the anterior epithelium adjacent to the pupillary margin. Cells from these buds detach from the epithelium and populate the entire irideal stroma; these cells are the precursors of the sphincter muscle. The epithelial buds increase in size and distribution, and coalesce into a continuous ridge of cells around the iris by 10 days of incubation. The first muscle cells differentiate at 11 days of incubation when striated fibres can be identified by immunocytochemistry. The first striated fibres of the dilator muscle are seen in the 13-day embryo. Differentiation of the dilator muscle begins near the root of the iris and proceeds toward the pupillary margin, ultimately arising from the entire anterior epithelium except near the pupillary margin. Further differentiation of the sphincter and dilator muscles continues throughout incubation and for several weeks beyond hatching.
Development of the iris in the chicken embryo
Authors: Ferrari Patricia A. , Koch William E. 
Published: April 2021

ABSTRACT
The developmental capabilities of the iris rudiment in the chicken embryo, as well as the role of tissue interactions in the differentiation of the iris, were investigated in vitro.
Sectors of the intact iris from through 9-day embryos (stages 32 through 35) lost their morphological organization in vitro, but were capable of normal histodifferentiation. The pigmentation of the epithelium increased, and muscle differentiation occurred. Developing muscle was identified using immunocytochemistry with antiserum against chicken muscle myosin; this procedure permitted positive identification of myoblasts, myotubes, and muscle fibres in cultures in which histological features alone were equivocal. The proportion of irideal explants which developed muscle increased with the age of the embryo, and correlated with the incidence of epithelial buds and epithelial cells in the stroma.
Irideal mesenchyme from stage-32 through stage-35 embryos was already populated with stromal epithelial cells when isolated, but growth and muscle differentiation in these cultures compared poorly with that in the intact iris in vitro. Isolated irideal epithelium (stages 32 through 37) demonstrated even more limited muscle differentiation in vitro, suggesting reciprocal interaction between irideal epithelium and mesenchyme during development. Irideal epithelium was also cultured in direct association with non-irideal mesenchyme from various embryonic organ rudiments, but muscle differentiation was not enhanced.
Intermediate filaments in the Xenopus oocyte: the appearance and distribution of cytokeratin-containing filaments
Authors: Godsave S. F. , Wylie C. C. , Lane E. B. , Anderton B. H. 
Published: April 2021

ABSTRACT
Cytokeratins have previously been shown to exist in the Xenopus oocyte cortex. Using three monoclonal antibodies against cytokeratins, we follow the appearance of cytokeratin-containing filaments, and their changes in distribution during oocyte differentiation and maturation. Cytokeratin-containing filaments are shown to change dramatically in distribution in the oocyte during its ontogeny.
Characterization of a reduced-eye mutant of the grasshopper, Melanoplus sanguinipes
Authors: Emery D. J. , Bell K. A. , Chapco W. , Steeves J. D. 
Published: April 2021

ABSTRACT
A reduced-eye (re) mutant grasshopper of Melanoplus sanguinipes has been characterized by small flat compound eyes lacking facets, no lateral ocelli and only a remnant of the median ocellus. The re grasshoppers walk, jump, fly and feed in a normal manner, but do not respond to visual and auditory stimuli, suggesting they may be blind and deaf. Extracellular recordings from the ventral nerve cord of re mutants verified the lack of neural activity in response to visual and auditory inputs, yet the mutants detected mechanical and tactile stimuli. Electroretinograms implied that a visual deficit may be within the photoreceptors of the compound eye.
Histological examination of the compound eyes and ocelli indicated that the cells of the mutant compound eye incompletely differentiate. The optic lamina underlying the retina is missing, as is the outer optic chiasma. The medulla and lobula of the mutant optic lobe are present, however, the neuropil of the medulla lacks the characteristic axonal projection patterns of wild-type grasshoppers. The re grasshopper also lacks all ocellar nerves. Ocellar nerves are normally formed from processes of second order ocellar neurons (SONs), suggesting that if the mutant SONs are present within the protocerebrum, their morphology is drastically altered. Comparison of embryos and juvenile nymphs supports the suggestion that the alterations in the re visual system are the result of abnormal differentiation during development.
Even though there is clear evidence of morphological alterations in second and third order optic lobe interneurons, one higher order visual interneuron of the midbrain, the descending contralateral movement detector (DCMD), has the same morphology as the DCMD in a wildtype brain. In this instance, the complete deprivation of the primary sensory input does not appear to alter cellular development.
DNA methylation versus gene expression
Authors: Bird Adrian P. 
Published: April 2021

ABSTRACT
Vertebrate DNA is methylated at a high proportion of cytosine residues in the sequence CpG, and it has been suggested that the distribution of methylated and non-methylated CpGs in a given cell type influences the pattern of gene expression in those cells. Since a DNA methylation pattern is normally transmitted faithfully to daughter cells via cell division, this idea suggests an origin for stable, clonally inherited patterns of gene expression. This article discusses some of the current evidence for a relationship between DNA methylation and gene expression. Although the evidence is incomplete, it appears already that the relationship is variable: transcription of some genes is repressed by the presence of 5-methylcytosine at certain CpGs, and may be controlled by methylation, while transcription of other genes is indifferent to methylation. In attempting to explain this variability it is helpful to adopt an evolutionary perspective.