bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amino Acids in Developing Tissues of Xenopus laevis
Authors: Deuchar E. M. 
Published: April 2021

ABSTRACT
Free amino acids in embryos and larvae of Xenopus laevis have been studied chromatographically. Quantitative measurements have been made on eight amino acids, and their concentrations have been compared between different regions of the embryo and between different tissues of the larva. Extracts of whole embryos showed higher concentrations of free aspartic acid and glutamic acid in the morula than in the early gastrula; significantly more leucine in the late gastrula than in the early gastrula, and less glutamine in the neurula than in the early tailbud. A number of free amino acids were more highly concentrated in the dorsal lip than in other parts of the early gastrula. Differences were also apparent between dorsal and ventral halves of the neurula, early tailbud stage, and hatched larva. In the early tailbud stage there was more glutamine in the head than in other regions and a higher percentage of glycine in the trunk. The main features of the free amino-acid concentrations in larval brain, eyes, somites, heart, liver, and skin are described and compared. In some features the free amino-acid concentrations in embryonic tissues resemble those of the larval tissues that derive from them in development. The evidence for special functions of certain amino acids in morphogenesis and in the synthesis of specific proteins is discussed.
Changes in the properties of the developing trophoblast of preimplantation mouse embryos as revealed by aggregation studies
Authors: Burgoyne Paul S. , Ducibella Thomas 
Published: April 2021

ABSTRACTMouse embryos (8-cell to early blastocyst) were denuded with pronase, and apposed in pairs which represented a wide range of stage combinations. These pairs either formed aggregates which differentiated into double-sized blastocysts, or they failed to aggregate. The 8-16-cell stages would not envelop late morulae/early blastocysts to form layered aggregates. This must mean that as the embryo differentiates into a blastocyst, the outer surface of the trophoblast loses its capacity for supporting cell spreading. The aggregation data also demonstrate that embryos almost completely lose their potential for aggregation at a very discrete stage in development -namely, between 8 and 9 h before blastocoel formation. It is argued that this is the stage at which the zonular tight junctional seal is completed, and that it is this physical barrier which prevents aggregation.It has been argued previously that the zonular tight junctional seal allows the creation of the special microenvironment which is necessary for the determination of the inner cells as inner cell mass. The completion of this seal 8-9 h before it is required for the formation of a blastocoel would provide a suitable time period for this cell determination to occur.The results obtained also relate to the technique of chimera production. Since the aim of this technique is to generate mice with mixed cell populations, it is important that the blastocyst formed following aggregation should have both cell lines present in the inner cell mass. This can best be assured by using relatively late morula stages (75 h post-HCG injection) since these will have already segregated their inner cells, but the incomplete seal will still allow aggregation to take place.
Cell growth and differentiation of murine extra-embryonic fetal and adult hematopoietic tissues in diffusion chamber cultures
Authors: Weinberg Sheila R. , Chovaniec Margaret E. , Stohlman Frederick 
Published: April 2021

ABSTRACTStudies were conducted with diffusion chambers (DC) filled with cell suspensions from different CFr murine hematopoietic tissues: adult peripheral blood; adult tibial marrow; day 17·5 of gestation fetal liver, spleen and thymus; day 14·5 of gestation fetal liver; day 10-5 of gestation yolk sac. After an initial decrease in DC cell numbers on day 2 of culture, growth of each cell group continued, but, at different rates. ATM had the highest growth ratio and FT-D17·52 had the lowest. The growth rates for APB and FL-D17·5 were similar. FS-D17·5 and FL-D14·5 cultures did not recover from the day 2 values (i.e. FL-D14-5 DC values on day 13–14 of culture were half that recorded on day 2). The YS-D10·5 DC cell numbers continued to increase throughout the 14 days of study. The profile of cellular elements from the DCs did not reflect the original cell suspensions. The predominant cell type recovered from peripheral blood cultured for 14 days was the macrophage. By day 10–14 of culture, the populations of cells harvested from the fetal tissue DC groups were similar to that of tibial marrow. Both proliferative and mature granulocytes, and macrophages were the predominant cell types. The yolk-sac pattern of cytodifferentiation recorded on day 7—14 was unlike that of the other groups. These DC cultures were comprised of mainly macrophages and plasma cells.
Nuclear transplantation from intestinal epithelial cells of early and lateXenopus laevistadpoles
Authors: Marshall J. A. , Dixon K. E. 
Published: April 2021

ABSTRACTThe aim of these experiments was to test whether the developmental potential of nuclei from intestinal epithelial cells of Xenopus laevis tadpoles declined during the life of the functional larval gut. The results of transplantation of nuclei from three different stages of development were compared: stages 46-48, when feeding begins and while yolk is still present but before the formation of the typhlosole; stage 57, just prior to the onset of metamorphic reorganization; and stage 54, an intermediate stage. The results showed that there was no change in developmental potential of these nuclei during the life of the larval gut, thereby disproving the hypothesis that nuclear transplants from intestinal epithelial cells of early tadpoles of X. laevis will support extensive development because the cells are not fully functional. However, nuclei from the intestinal epithelial cells were less able to support development than blastula nuclei. It was concluded therefore, that the developmental potential of the gut nuclei is restricted relative to that of the blastula nuclei, but that these restrictions are reversed in a small proportion of cases.
The blastomere pattern in echinoderms: cleavages one to four
Authors: Prothero John W. , Tamarin Arnold 
Published: April 2021

ABSTRACT
The results of a longitudinal study of the blastomere pattern in six embryos during the first four cleavages are reported. At each cleavage stage optical sections through an embryo, taken at vertical intervals of 5 or 10 μm, were recorded on 35 mm film: digitization of the blastomere contours and computer analysis allow calculation of the center, radius, surface area and volume of each blastomere.
The subjective impression of exquisite regularity seen in normal echinoderm blastulae acquires a quantitative dimension from the present study. For example, the individual angles formed by the various quartets of blastomeres depart from right angles by at most a few degrees. The egg volume was found to be conserved up to the fourth cleavage. At the 16-cell stage, unlike the earlier stages, the blastomere positions cannot be ascribed solely to the position and orientation of the respective cleavage planes. Finally, a few features of a formal model of these early cleavages are sketched.
Cell disposition and adhesiveness in the developing chick neural retina
Authors: Jones G. E. 
Published: April 2021

ABSTRACT
The adhesive properties of neural retinal cells located in the ventral and dorsal hemispheres of chick embryonic eyes were investigated. Cell adhesion was monitored using the collision efficiency method; this technique provides a system in which it is possible to identify any preferential adhesions that may occur between cells. In this study no adhesive specificity was detected between cells of the dorsal and ventral retina. This evidence would not support theories which invoke preferential cell adhesion as an explanation of the ordered projection of the neural retina onto the optic tectum during development.
Fusion of dissociated fish embryonic cells
Authors: Mizukami Setsuro , Satoh Noriyuki 
Published: April 2021

ABSTRACT
The induction of a frequent fusion in dissociated fish embryonic cells is reported. Fusion was induced during mechanical isolation of blastomeres in normal saline solution or Ca2+-free saline solution by quickly bringing about physical contact between cells within about 1·5 min of dissociation. Fused blastomeres were obtained in about 18% yield from early morula cells, in about 68% yield from early blastula cells and in about 5% yield from early gastrula cells.
Alkaline phosphatase activity in the preimplantation mouse embryo
Authors: Johnson Lincoln V. , Calarco Patricia G. , Siebert Margaret L. 
Published: April 2021

ABSTRACT
Alkaline phosphatase (AP) activity has been assayed in frozen sections of preimplantation mouse embryos by an azo-dye cytochemical method. The results indicate that during preimplantation mouse development AP activity is first expressed between the 8- and 16-cell stages and develops in all cells by the late morula stage. During blastocyst formation AP activity is lost or greatly reduced in trophoblast cells while activity is maintained in the inner cell mass.
The development of functional innervation in the chick wing-bud following truncations and deletions of the proximal-distal axis
Authors: Stirling R. Victoria , Summerbell Dennis 
Published: April 2021

ABSTRACTSections of the proximal-distal axis were removed so as to produce wings lacking entire skeletal levels. The innervation of the resulting limb from the appropriate spinal nerves was tested by electrophysiological recording, gross dissection and serial sections. The nerves form repeatable and ordered patterns in the modified limbs which can be readily related to the normal pattern. In general the segmental nerves only innervate their appropriate territory irrespective of its location; the route followed by the nerves is characteristic for the skeletal level they traverse. If a target is missing then so is the normal nerve branch to that region.
Aspects ultrastructuraux de 1’interaction uretère-mesenchyme, au cours de l’induction néphrogène, chez les amphibiens
Authors: Gipouloux J.-D. , Delbos M. 
Published: April 2021

ABSTRACTUltrastructural features of ureter-mesenchyme interaction, during nephrogenic induction in AmphibiaTransmission electron microscopy was used to study the interface between the ureter and the mesonephric blastema. When the blastema is induced in a functional organ, numerous pseudopodial protrusions of the ureter and of the mesonephric cells lead to a close apposition between the two structures. The presence of squamous material, perhaps of a mucopoly-saccharidic nature, with a network of collagen fibres is always found on this interface. These particular processes seem to play a role as a morphological basis for the phenomenon of induction. The importance of the extracellular matrix is discussed. Neither the occurrence of zones of close contact, reported by several authors, in other species, nor the fusion of membranes has ever been observed, in Amphibia.
Uridine and guanosine incorporation by the mouse one-cell embryo
Authors: Young R. J. , Sweeney K. , Bedford J. M. 
Published: April 2021

ABSTRACT
The activity of the embryonic genome prior to the first cleavage has been assessed by studying the uptake of [3H]uridine, its phosphorylation and incorporation into RNA by mouse one-cell embryos. One-cell embryos incorporated [3H]uridine linearly into cold trichloracetic acid (TCA) insoluble material at a low level 1-9 h post fertilization. The incorporation of [3H]guanosine was also low but followed a biphasic curve which had a steeper slope at 1-3 h than during the period 4-9 h post fertilization. Unfertilized mouse ova incorporated very little [3H]uridine or [3H]guanosine into TCA insoluble material, and much of this was RNase insensitive. Dimethyl sulfoxide (DMSO) enhanced the uptake of [3H]thymidine and its incorporation into pronuclear DNA by one-cell embryos, but had no effect on the incorporation of [3H]uridine by them, or of [3H]uridine and [3H]guanosine by unfertilized ova. The uptake and incorporation of [3H]guanosine by one-cell embryos were enhanced by DSMO, but only during the period 1-3 h post fertilization.
Sugar derivatives of UDP, and UMP, UDP, UTP, CMP, CDP and CTP have been identified in the soluble fraction obtained from mouse one-cell embryos incubated with [3H]uridine 1-3 h post fertilization. Very little of the [3H]uridine taken up by the embryos is present as [3H]UTP, or [3H]CTP; most is found as [3H]UMP or [3H]UDP or as the sugar derivatives. Alkaline or ribonuclease (A, T1 and T2)hydrolysis of the 3H-labeled ethanol insoluble material precipitated from the lysate of one-cell embryos incubated with [3H]uridine 1-3 h post fertilization liberated radioactive cytidine and uridine-3’-phosphates. This demon strates that [3H]uridine is incorporated into an internal position in RNA and suggests that RNA synthesis does occur in the one-cell embryo 1-3 h post fertilization. Since pronuclei of one-cell embryos incubated with [3H]uridine were not labeled it appears, however, that the RNA synthesized at the one-cell stage is not a product of the embryonic genome.
The diencephalic course of regenerating retinotectal fibres in Xenopus tadpoles
Authors: Gaze R. M. , Grant P. 
Published: April 2021

ABSTRACT
The normal retinotectal path in the diencephalon of Xenopus tadpoles is widely distributed in the form of a wedge of fibres extending from the central grey to the outer margin of the diencephalon. Regenerating optic nerve fibres were shown, by silver-staining and proline autoradiography, to follow an abnormal path up the extreme lateral edge of the diencephalon. Study of tadpoles at various stages of development, and of optic nerves allowed to regenerate for various periods, indicates that all new incoming optic fibres pass up the lateral edge of the diencephalon. The inner/outer order of the fibres in the normal diencephalon thus reflects the radial distribution of the retinal cells of origin.
Morphogenesis by dissociated immature rat testicular cells in primary culture
Authors: Davis John C. 
Published: April 2021

ABSTRACT
Dissociated cells from immature (15-day) rat testes maintained in primary culture were shown to undergo morphogenesis. Dissociated cells (1–4 ×106) were cultured in 2 ml medium NCTC-135 containing 10% rat serum at 32·5 °C under an air: CO2 atmosphere (95%:5%). During the initial culture period (1–3 days) the dissociated cells attached to the culture dish and formed a monolayer. After 4–5 days of culture, aggregates of cells formed at discrete foci within the monolayer; these structures averaged 50 μ m in diameter and numbered 3–4 × 103/dish. Within 5–6 days of culture some of these aggregates (2–3 × 102) released their contact with the substratum. Histological examination of released aggregates indicated a more regular, tissue-like organization with increasing time in culture. Aggregates at earlier time periods (4–5 days) exhibited concentric rings of cell while by day 6 some aggregates exhibited a vesicular appearance with a single layer of columnar epithelium surrounding a fluid-filled lumen. The type of structure formed varied with plating density; at densities less than 2 × 10G/dish the structures were spheroid while at greater densities tubes were formed. Time lapse observations indicated that spheres formed by movements of cells into an aggregating center while tubes formed by a rolling from the edge of the monolayer. The cells comprising the vesicle epithelium appeared to be predominantly one cell type as determined by light microscopy. These results therefore indicate that dissociated testicular cells have the ability to reform tissue-like associations in culture.
Cinemato graphical study of cell migration in the opened gastrula of Ambystoma mexicanum
Authors: Kubota H. Y. , Durston A. J. 
Published: April 2021

ABSTRACT
The migration of inner marginal cells was studied in the Ambystoma gastrula, using scanning electron micrography and time-lapse cinemicrography.
Scanning electron micrographs of gastrulae which were fixed while intact revealed that the migrating cells have flattened lamellipodia at their anterior end and a rounded cell body, which can sometimes be seen to be attached to a neighbouring cell by a slender posterior process. Films of opened gastrulae showed actively moving cells, with the same features described above. Details of their movements are reported and discussed in relation to the mechanism of gastrulation.
Cell culture of individual Drosophila embryos: I. Development of wild-type cultures
Authors: Cross David P. , Sang James H. 
Published: April 2021

ABSTRACT
A new procedure is described for the preparation of in vitro cell cultures from individual early gastrulae of Drosophila melanogaster. In these cultures several identifiable cell types differentiate within 24 h (nerve, muscle, fat-body, haemocyte and chitin-secreting): their initial appearance and continuing development over a period of weeks is described. It is proposed that this technique may be used to analyse abnormalities of cellular development in embryonic lethal mutants. Culture in vitro of cells from lethal embryos is seen to have two broad roles: (1) to test the developmental capacity of individual cell types in a situation where they are relatively free from possible deleterious interactions with other cell types and are liberated from the system of the dying embryo, and (2) through the preparation of mixed cultures from normal and mutant embryos, to determine the influence of the presence of wild-type cells on observed abnormalities of a particular cell type.
Catch-up growth in the rat skull after retardation during the suckling period
Authors: Williams J. P. G. , Hughes P. C. R. 
Published: April 2021

ABSTRACT
In rats whose growth was restricted by rearing in large litters the skull was less affected than the spine and the brain case less than the face. No sex difference was apparent during undernutrition but on subsequent rehabilitation females had caught up to controls in four out of five skull measurements within 4 weeks and by the end of the experiment the skulls of the neonatally undernourished females were the same size and shape as the controls. In the case of males, however, the skull of the undernourished rats never attained the same width as the controls.
Time of commitment of inside cells isolated from preimplantation mouse embryos
Authors: Handyside A. H. 
Published: April 2021

ABSTRACTGroups of inside cells (ICs) and inner cell masses (ICMs) were isolated from individual mouse embryos between the late morula and day expanded blastocyst stages using a modified immunosurgical procedure, and their purity and developmental potential were assessed in vitro.Several different techniques failed to detect the presence of viable contaminating outside cells on ICs isolated from any of the stages studied. The numbers of inside cells isolated from the earlier stages, counted in air-dried preparations, were considerably higher than previous estimates from serial sections; whereas the numbers isolated from expanded blastocysts were in reasonable agreement. Thus the proportion of inside cells recovered by immunosurgery decreases over this period of development. In view of the evidence that inside cells divide at a faster rate than outside cells at these stages, it is argued that there may be an outward movement of inside cells capable of forming trophectoderm, during expansion of the blastocyst.ICs and ICMs in vitro were observed to develop in one of two distinct ways according to the stage at which they were isolated. ICs from late morulae and some early cavitating blastocysts formed blastocyst-like vesicles over a period of 24-36 h in culture. The presence of trophectoderm cells in these vesicles was confirmed by the persistence of giant cells after ectopic transfer. In contrast ICs from a minority of early cavitating blastocysts, and all ICMs from day expanded blastocysts did not form vesicles, but proliferated endodermlike cells. Thus at least some inside cells do not appear to lose the capacity to form trophectoderm and do not become committed to an ICM fate until after the initial formation of the blastocoel cavity.
Postembryonic development of the visual system of the locust, Schistocerca gregaria:I. Patterns of growth and developmental interactions in the retina and optic lobe
Authors: Anderson Hilary 
Published: April 2021

ABSTRACT
The visual system of the locust, Schistocerca gregaria, has a highly ordered and predictable arrangement of neurons. The retina and the outermost layer, or lamina, of the optic lobe are each composed of repeating units, ommatidia and cartridges respectively. Each ommatidium has eight photoreceptor cells, which send axons directly to a group of five neurons in the lamina to form the cartridge. The importance, for the development of this precise pattern, of the mode of growth of the two arrays and of interactions between them was investigated.
The spatial and temporal sequences of cell proliferation, differentiation and death in the developing retina and optic lobe were examined quantitatively under normal and experimental conditions.
The retina grows from its anterior margin by addition of new ommatidia formed from recruited epidermal cells. The lamina also grows by addition of new neurons to its anterior margin, but these neurons are derived from a stem cell population. The parallel pattern of growth of the retina and lamina may be important for the formation of neuronal connexions between them.
The retina grows and differentiates even when deprived of the underlying lamina. In laminae deprived of the ingrowth of new axons from the retina, the production of new neurons is also autonomous, but these neurons do not differentiate, but degenerate. A limited amount of cell death occurs in the laminae of control insects. These two observations suggest that a plausible mechanism for coordinating the sizes of the two arrays during normal development might be production of lamina neurons in excess of requirements and death of those remaining non-innervated.