bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temporal pattern of cleavage and the onset of gastrulation in amphibian embryos developed from eggs with the reduced cytoplasm
Authors: Kobayakawa Yoshitaka , Kubota Hiroshi Y. 
Published: April 2021

ABSTRACT
Fertilized eggs of the Japanese newt, Cynops pyrrhogaster, were divided into two or four equal-sized parts with fine glass rods before the first cleavage. In such cases one of the egg fragments, at least, proceeds to cleavage and gastrulates.
The temporal pattern of cell division and the onset of gastrulation in such half or quarter embryos were investigated and compared with normal development. The following results were obtained: (1) desynchronization starts two divisions earlier in quarter embryos and one division earlier in half embryos compared with whole embryos, (2) the time from the first cleavage to the onset of gastrulation does not widely vary among quarter, half and whole embryos and (3) the numbers of blastomeres which constitute embryos at the pigment stage decrease in proportion to the diminution of egg volume.
Sexual differentiation of the urogenital tract in the chicken embryo: autoradiographic localization of sex-steroid target cells during development
Authors: Gasc Jean-Marie , Stumpf Walter E. 
Published: April 2021

ABSTRACT
The determinant role ascribed to steroid hormones in sexual differentiation of the reproductive tract of the embryo implies the presence of target cells for sex steroids. An autoradiographic technique adapted for diffusible compounds was employed to characterize and localize cells which concentrate either [3H]oestradiol (E2) or [3H]dihydrotestosterone (DHT) in their nuclei. This paper describes the topographical distribution of cells containing receptor sites for oestrogen or androgen in various tissues of the reproductive tract of chicken embryos from day 6 to 15 of incubation. Receptor sites for oestradiol are present in the mesenchyme of the cloaca and in urodeum and vascular body. In the lower part of the Wolffian duct, only epithelial cells display nuclear labelling. In the Müllerian duct, nuclear receptor sites for [3H]oestradiol are observed not before day 15. Receptor sites for DHT are localized in the mesenchyme of the cloacal region from day 7 to 15. The Wolffian, but not the Müllerian duct contains receptor sites for DHT in the nuclei of epithelial and mesenchymal cells. Cross-competition experiments between [3H]E2 or [3H]DHT and unlabelled DHT or E2 respectively, show that 2 different types of receptor sites exist. The observations indicate: (a) complementary roles for oestrogenic and androgenic hormones in embryonic sexual differentiation; (b) precocity of receptors for sex hormones during embryonic development; (c) importance of mesenchyme in differentiation processes which are sex-steroid dependent.
A gradation of hyaluronate accumulation along the proximodistal axis of the embryonic chick limb bud
Authors: Kosher Robert A. , Savage Mary P. , Walker Kordasey H. 
Published: April 2021

ABSTRACTWe are currently investigating the mechanism by which the apical ectodermal ridge (AER) of the embryonic chick limb bud exerts its negative effect on the cytodifferentiation of limb mesenchymal cells directly subjacent to it, and the mechanism by which cytodifferentiation is triggered when the cells leave the influence of the AER. Since there is a gradation of differentiation along the proximodistal axis of the limb bud, we have dissected limb buds into discrete segments along the proximodistal axis, and biochemically examined the accumulation of hyaluronate (HA) and other glycosaminoglycans (GAG) in each segment. The unspeciajized subridge region of stage-25 limb buds was separated into distal (segment 1) and proximal (segment 2) regions, and the remaining proximal portion of the limb was separated into four segments (segments 3, 4, 5 and 6) along the proximodistal axis. Stage-24 limb buds were separated into corresponding regions. Since in the proximal regions of the limb (segment 3 through 6), only the cells comprising the central cores of the limb are involved in chondrogenic differentiation, the central core tissue was surgically separated from the peripheral tissue. We have found that HA is by far the predominant GAG accumulated by cells comprising the distal subridge region (representing greater than 50% of the total GAG accumulated during a 90-min labelling period with [3H]glucosamine), and that there is a progressive decline in HA accumulation along the proximodistal axis. The relative and total amount of HA accumulated is highest in the distal subridge region (segment 1), intermediate in the proximal subridge region (segment 2) and lowest in the proximal central core regions Of the limb (segments 3 through 6). The striking decrease in HA accumulation in the central core of segment 3 is accompanied by a striking increase in the accumulation of chondroitin sulphate, one of the major constituents of cartilage matrix. In contrast to the central core regions of segments 3 through 6, the relative and total amount of HA accumulated by the peripheral non-chondrogenic regions of these segments remains relatively high, being similar to the accumulation observed in the proximal subridge region. These results indicate that there is a gradation of HA accumulation along the proximodistal axis of both stages-24 and -25 limb buds which correlates with distance of cells from the AER and the state of differentiation of the cells.
A SEM study of cell shedding during the formation of the area pellucida in the chick embryo
Authors: Fabian Barry , Eyal-Giladi Hefzibah 
Published: April 2021

ABSTRACT
Intrauterine eggs at different stages of development were retrieved from hens and the blastodiscs were dissected out and prepared for scanning electron microscopy. Our observations trace the polarized shedding of cells from the central area of the lower layers of the blastodisc, which leads to the formation of the area pellucida. Prior to the shedding, single central blebs appear on the ventral side of the cells facing the sub-blastodermic cavity. We also noted the presence of lobopodia which establish contact with nearby cells. The possible function of the lobopodia is discussed. The cells of the blastodisc are at the same time (stages IV and V, E.-G.&K). also intimately interconnected via a profusion of threadlike cytoplasmic processes (filopodia). When shedding starts the blebs as well as the lobopodia disappear, and the filopodia undergo typical withdrawal steps such as showing a beaded stage and appearing drawn out or taut, before they finally disrupt to leave behind a smooth round cell which is detached from its neighbours. The beading phenomenon points to the possibility of a disassembly of the microtubular skeleton of the filopodia operated by some physical force influenced by gravity.
Secondary lens formation from the cornea following implantation of larval tissues between the inner and outer corneas of Xenopus laevis tadpoles
Authors: Reeve Julie G. , Wild Arthur E. 
Published: April 2021

ABSTRACT
Secondary lens formation from the cornea of larval Xenopus laevis has been used as a measure of the lens-inducing capacities of various larval Xenopus tissues. The experimental design employed involved implantation of selected body tissues between the inner and outer corneas of stage-50 tadpole eyes, in such a way that the integrity of the inner cornea and eye cup was not disrupted.
Implantation of retina, pituitary, limb blastema or limb bud resulted in secondary lens formation from the outer cornea. Such lenses were similar in appearance to stage-5 lens regenerates described by Freeman (1963). No secondary lenses were observed in eyes receiving either heart or hind brain implants or in eyes which underwent corneal separation but which received no implant.
It is concluded that the retina is the natural source of a stimulatory factor which initiates and maintains corneal transformation to lens during lens regeneration following lensectomy. Influences emanating from pituitary, limb blastema and limb bud, but apparently not from heart or hind brain, are able to act on cornea in a way similar to the retinal factor. Furthermore, our findings support the contention that in the normal eye, the inner cornea is a barrier to the passage of retinal factor and so maintains the single lens structure of the eye. When this barrier is by-passed by lens-inducing tissue, as in the present experimental design, lens formation from the cornea is able to take place. Electronmicroscopical studies have shown that the inner cornea, in the stage-50 tadpole eye, consists of a dense meshwork of collagen fibrils and a basal layer of cohesive elongated mesenchymal cells well suited for this barrier function.
Proliferation and migration of primordial germ cells during compensatory growth in mouse embryos
Authors: Tam P. P. L. , Snow M. H. L. 
Published: April 2021

ABSTRACT
Primitive-streak-stage mouse embryos were treated with Mitomycin C injected intraperitoneally into pregnant females at 6·75–7·0 days post coitum. The newborn mice developed poorly and mortality was high during the suckling period. Many weaned survivors showed impaired fertility and poor breeding performance. Histological examination revealed a paucity of germ cells in the adult gonads. The deficiency was mainly caused by a severe reduction of the primordial germ cell population in early embryonic life, which was not fully compensated for during the compensatory growth phase of the Mitomycin C-treated embryo. Also contributing to such impaired fertility were retarded migration of the primordial germ cells into the genital ridges, poor development of the foetal gonad and secondary loss of the germ cells during gametogenesis in males.
Cytoplasmic regulation of the duration of cleavage in amphibian eggs
Authors: Aimar Christian , Delarue Michel , Vilain Claude 
Published: April 2021

ABSTRACT
Relations between a cytoplasmic species specificity and the duration of cleavage cycles were investigated by reciprocal injections of egg cytoplasm. Xenogenic cytoplasm induces an early or delayed cleavage of the recipient egg depending on the chronological specificity of the injected cell cytoplasm. Activity of the so-called cleavage timing system (CTS) was first detected in the cytoplasm of maturing oocytes at the stage of germinal vesicle breakdown (GVBD). This specific cytoplasmic property was not dependent on the maturation promoting factor (MPF). Relations between the CTS and other cytoplasmic components which are known to induce cleavage are discussed.
On the ‘clock’ mechanism determining the time of tissue-specific enzyme development during ascidian embryogenesis II. Evidence for association of the clock with the cycle of DNA replication
Authors: Satoh Noriyuki , Ikegami Susumu 
Published: April 2021

ABSTRACTAcetylcholinesterase (AChE) is a tissue-specific enzyme of the muscle cells of ascidian embryos and its synthesis begins at the neurula stage. Embryos which had been permanently cleavage-arrested with cytochalasin B could develop AChE activity. The time of first AChE occurrence in embryos which had been arrested in the 32-cell stage with cytochalasin was about the same as in normal embryos. The nucleus in the cell of cytochalasin-arrested embryos divided in good synchrony with that of normal embryos. Embryos which had been continuously arrested with colchicine could also produce AChE activity at nearly the same time as did normal embryos. In the cell of colchicine-arrested embryos normal nuclear divisions did not occur, but the cell showed repeated cycles of nuclear envelope breakdown and nuclear envelope reformation in almost parallel with cell cycles of normal embryos. The cell of colchicine-arrested embryos incorporated [3H]thymidine. Aphidicolin, a specific inhibitor of DNA synthesis, prevented cleavages of ascidian eggs. Embryos which had been permanently arrested with aphidicolin in the cleavage stages up to the 64-cell stage did not develop AChE activity, while embryos which had been treated with it from the 76-cell stage onwards were found to be able to differentiate AChE activity. Based on these findings it was proposed that DNA replication is prerequisite for development of the histospecific protein and that the cycle of DNA replication is closely associated with the clock mechanism which is determining the time of initiation of the enzyme development.
Avian primordial germ cells are of epiblastic origin
Authors: Eyal-Giladi Hefzibah , Ginsburg Malka , Farbarov Aharon 
Published: April 2021

ABSTRACTWe have demonstrated that quail PGCs possess a characteristic heterochromatin nuclear marker demonstrable already at stage 6 H & H with Feulgen staining. Chimaeras of stage-XIII E. G & K. chick epiblast and quail hypoblast and vice versa have been made. The chimaeras were incubated up to stage 7−8 H & H and checked histologically with Feulgen staining for the presence of the heterochromatin marker in every detectable PGC. It was found that the PGCs are of epiblastic origin, contrary to previous data and speculations concerning avian PGCs.
Factors involved in the development of ipsilateral retinothalamic projections inXenopus laevis
Authors: Kennard C. 
Published: April 2021

ABSTRACTThe extent, and the development, of the ipsilateral retinothalamic projection in the frog Xenopus laevis have been studied using terminal degeneration and autoradiographic techniques. This ipsilateral projection derives only from those retinal areas receiving visual information from the binocular portion of the visual field. In Xenopus, the ipsilateral retinothalamic projection arises from a larger area of the retina than was found to be the case in earlier studies on Rana. This correlates with the fact that Xenopus has a larger binocular visual field than does Rana.The ipsilateral retinothalamic projection is just detectable at about stage 56 of larval life, considerably later than its contralateral counterpart. Experimental manipulation of the developing eye vesicle at early larval stages followed by histological studies of the ipsilateral retinothalamic projections showed, however, that the retinal areas which give rise to this projection are determined by stage 32 of larval life. Further studies, in which monocular enucleation was performed at different larval stages with subsequent examination of the retinothalamic projections from the remaining eye, indicated that the selective pattern of decussation and non-decussation of retinothalamic fibres at the optic chiasma does not require interactions, at the chiasma, between optic fibres from the two eyes.
Distribution of endogenous β-galactoside-specific lectin, fibronectin and type I and III collagens during dermal condensation in chick embryos
Authors: Kitamura Kunio 
Published: April 2021

ABSTRACT
The distribution of endogenous β-galactoside-specific lectin, fibronectin, type I and III collagens was studied by the indirect immunofluorescence method during the formation of dermal condensation in the feathered region (dorsal skin) of a chick embryo. Endogenous β-galactoside specific lectin was concentrated in the condensed dermal region, coinciding with the formation of condensation of dermal cells. It was also detected in epidermal placodes. Fibronectin was weakly stained in dermis prior to the formation of dermal condensation but not in epidermis. Condensation of dermal cells resulted in the formation of thicker fibrils of fibronectin in the condensed region. Distribution of type I collagen was found to be very different from that of endogenous β-galactoside-specific lectin and fibronectin. Type I collagen in dermis decreased along with the formation of dermal condensation. Epidermis had no type I collagen. Type Ill collagen was not found in dorsal skin. Relationship found between these distribution patterns and dermal condensation in the embryonic chick skin is discussed.
Culture of mouse embryos during neurulation
Authors: Sadler T. W. , New D. A. T. 
Published: April 2021

ABSTRACT
A comparison between static versus rotator culture systems and a variety of media (rat serum, new born calf serum, DMEM and Waymouth’s) was made in an attempt to promote in vitro growth of mouse embryos from the beginning of neurulation (headfold stage) to the closure of the neural tube and formation of the limb buds (48 h). The results demonstrate that good development can be achieved for 48 h using a rotator system and that 80 % of embryos cultured on rotators show growth and differentiation similar to that obtained for the same time period in vivo. Static cultures are less successful and embryos grown in this system show lower protein content and somite numbers than those maintained on rotators. Undiluted rat serum is superior to all other media tested and supports better growth and development as monitored by total protein and developmental abnormalities.
Accumulation, spatial distribution and partial characterization of poly(A)+RNA in the developing oocytes of Xenopus laevis
Authors: Wakahara M. 
Published: April 2021

ABSTRACT
In situ hybridization using [3H]poly(U) was applied to developing oocytes of Xenopus laevis, which had been fixed in Bouin’s solution. Tissue sections were pretreated with DNase I, annealed with [3H]poly(U) and post-treated with RNase A and TCA. After the autoradiographical processing, silver grains over the oocyte were counted. As a result of the control experiments which included RNase A, RNase T2, DNase I and Pronase E hydrolysis and Cordycepin (3’-deoxyadenosine) incubation before in situ hybridization, it was concluded that the poly(U)-binding activity detected upon the oocytes was due to the possible presence of poly(A)+RNAs. Spatial distribution of the poly(U)-binding sites changed during the development of the oocytes; in a small oocyte before the pachytene stage, silver grains developed over the nucleus, while in a larger oocyte after the diplotene the grains were concentrated over the cytoplasm. After yolk platelets were deposited in the cytoplasm, two types of poly(U)-binding activities were noted; a bound-type activity which was firmly associated with the cytoplasm, so that the positions of the silver grains were not influenced by fixation, and an unbound type which did not bind so firmly to the cytoplasm and was therefore easily influenced by inflow of fixative. The bound-type activity persisted in the cytoplasm throughout the oogenesis, but the unbound type appeared only after the vitellogenesis, especially in the yolky cytoplasm. The total poly(U)-binding activity per oocyte increased continuously with the growth of the oocyte.
Specificity in the differentiation and morphogenesis of neural crest-derived scleral ossicles and of epithelial scleral papillae in the eye of the embryonic chick
Authors: Hall Brian K. 
Published: April 2021

ABSTRACTEnzymatic digestion followed by recombination of epithelia and ectomesenchyme from embryonic sclera and mandibles has been used to demonstrate that isolated scleral ectomesenchyme is only able to form scleral ossicles if in prior contact with scleral epithelium until H.H. stage 36 (10 days of incubation); that this induction by epithelial scleral papillae is a prolonged one, commencing as early as H.H. stage 30 (6·5–7 days); that scleral ectomesenchyme can respond to mandibular epithelium by forming bony ossicles and that mandibular ectomesenchyme can respond to scleral epithelium by forming bony rods, i.e. these interactions are not site, time or tissue specific. Scleral epithelia did not form scleral papillae when maintained alone in vitro or when recombined with scleral ectomesenchyme and maintained in vitro. Nor did papillae form when mandibular epithelia were cultured with scleral ectomesenchyme. These results, coupled with data from the literature, are used to argue that papillae will only form when scleral epithelia are under the tension generated by normal intraocular pressure of the growing eye.
In vivoandin vitrodevelopment of mouse embryos homozygous for the embryonic lethal velvet coat (Ve) mutation
Authors: Rossant J. , Vijh K. M. 
Published: April 2021

ABSTRACTEmbryos homozygous for the velvet coat mutation, Ve/Ve, were recognized at 6·5 days post coitum by the reduced size of the ectodermal portions of the egg cylinder and the loose, columnar nature of the overlying endoderm. Later in development ectoderm tissues were sometimes entirely absent. Abnormalities appeared in the ectoplacental cone at 8-5 days but trophoblast giant cells and parietal endoderm appeared unaffected. Homozygotes could not be unequivocally identified at 5·5 days nor at the blastocyst stage but were recognized in blastocyst outgrowths by poor development of the inner cell mass derivatives, It has previously been suggested that Ve may exert its action at the blastocyst stage by reducing the size of the inner cell mass, but no evidence for such a reduction was found. Most of the observations on Ve/Ve homozygotes are, however, consistent with the hypothesis that Ve exerts its action primarily on later primitive ectoderm development.
Partial characterization of a morphogenetic factor in the developing chick limb
Authors: Maccabe Jeffrey A. , Richardson Kathryn E. Y. 
Published: April 2021

ABSTRACTA morphogenetic substance from the posterior region of the developing chick limb appears to be a glycoprotein with a molecular weight in the range of 370000–415000. This morphogen is capable of maintaining the apical ectodermal ridge of the limb in culture and is probably related to the previously hypothesized polarizing or maintenance factors in limb mesoderm.
Cell interactions in the developing somite: in vitro comparisons between amputated (am/am) and normal mouse embryos
Authors: Flint O. P. , Ede D. A. 
Published: April 2021

ABSTRACT
Facial, axial and limb development are all abnormal in the homozygous mutant mouse embryo (amputated). An interpretation of cell behaviour in vivo based on sectioned material which may explain these abnormalities has been previously suggested. In this study, somite cells cultured in vitro were found to behave exactly as predicted in this interpretation: they clump together, forming extensive areas of cell contact, and this has a profound effect on their mobility as measured by time-lapse cinemicrography. The similarity of cell behaviour in vitro and in vivo under two distinct sets of environmental conditions suggests that the abnormal cell behaviour is intrinsic to the cell, and directly linked to the mutation. The more extensive areas of cell contact formed between mutant cells suggests that the mutation changes the adhesive properties of the cell surface, but it cannot be excluded that the cells’ motile apparatus is also affected.
Cell shapes on the surface of the Drosophila wing imaginal disc
Authors: Brower Danny L. , Smith R. J. , Wilcox Michael 
Published: April 2021

ABSTRACT
Antibodies that bind to antigens on the surfaces of imaginal disc cells can be used to visualize the cellular morphology of the disc exterior. Using this technique, we have examined wing imaginal discs at various times during the third larval instar, paying particular attention to those areas where the anteroposterior and dorsoventral compartment borders are located. We have been unable to detect any distinguishing feature in the shapes of the cells at the anteroposterior compartment border. However, there is a line of unusually shaped cells extending across the disc, from anterior to posterior and which, in the central region of the disc, takes the form of a shallow groove in the epithelium. A number of observations suggest that this line is coincident with the dorsoventral compartment border.