bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation and limb regeneration: the effect of partial irradiation
Authors: Maden M. 
Published: April 2021

ABSTRACT
The regulative ability of the regeneration blastema has been studied by the technique of partial irradiation. Longitudinal halves of fore- and hindlimbs were irradiated and the product of regeneration from the unirradiated halves characterized. Such half irradiated limbs could regulate only to a very limited extent. In the upper arms the anterior halves merely produced a few autopodial elements whereas complete limbs regenerated from the posterior halves. This striking regenerative inequality was less marked in the lower arm where the two halves each produced regenerates of two to three digits. In the hindlimb dorsal halves produced more than ventral halves and thus it was concluded that the posterior-dorsal quadrant has some special regenerative property. These results highlight the inadequacy of current models of limb regeneration and are discussed with reference to the arrangement of positional values in the limb and the question of the totipotency of blastemal cells.
The Early Development of the Interorbital Septum and the Fate of the Anterior Orbital Cartilages in Birds
Authors: D’A. Bellairs A. 
Published: April 2021

ABSTRACT
The development of the interorbital septum and anterior orbital cartilages in birds has been studied with special reference to the chick embryo. In the chick the trabeculae are at first separated by a bar of intertrabecular mesenchyme which projects downwards between them to form a prominent keel. Later this mesenchyme fuses with the trabeculae and anterior orbital cartilages (preoptic roots) to form the interorbital septum. In some other Sauropsida (i.e. certain turtles and birds) the intertrabecular bar of mesenchyme is also well developed and has a keel. Although this bar is always partly blended with the trabeculae and orbital cartilages, its appearance is sufficiently distinctive to justify the use of the term intertrabecula for it. In other Sauropsida (i.e. lizards, the sparrow) the trabeculae seem to develop closer together and the intertrabecular mesenchyme is less clearly differentiated. The ventral keel is not well developed, and the use of the term intertrabecula is not indicated. The differences between this and the previous group (chick, turtles, &c.) are, however, probably of degree rather than kind. During embryonic life the olfactory nerves in the chick are temporarily enclosed in cartilaginous tunnels formed mainly by the fusion of the anterior orbital cartilages with the roof of the nasal capsule. The subsequent regression of the orbital cartilages is responsible for the exposure of the nerves in the orbits. The different relationships of the olfactory nerves in certain other birds are shown to depend on relatively slight variations of the structure of the orbitonasal region of the chondrocranium. The formation of the interorbital septum, the growth and regression of the anterior orbital cartilages and the disposition of the olfactory nerves are virtually unaffected by the experimental ablation or partial ablation of one eye at a stage before the onset of skull development. Conditions similar to those in the operated specimens were found in three chick embryos which showed naturally occurring, unilateral microphthalmia.
The Dependence of the Embryonic Inductive Action of HeLa Cells on Their Growth Media
Authors: Saxén Lauri , Toivonen Sulo 
Published: April 2021

ABSTRACTHeLa cells which had been cultured in various growth media were used as implantation material in induction experiments, the object of which was to find out to what extent the inductive capacity of the cells is dependent on the media.HeLa cells grown in untreated (‘active’) pooled human serum proved to be strong deuterencephalic-spinocaudal inductors. The inductive capacity was the same in cells grown in different pooled sera. Heating of cells grown in active serum for 30 minutes at 56° C. did not influence their inductive capacity. By contrast, heating for 30 minutes at 65° C. completely destroyed the deuterencephalic and spinocaudal inductive effects, but subsequently the cells still induced archencephalic structures. Continuous cultivation in serum heated at 56° C. almost completely destroyed the spinocaudal inductive effect of the cells. Simultaneously, the archencephalic effect was strengthened. Cultivation under the same conditions for a short time (3 days) caused a similar, though slighter, change. When some of the cells continuously grown in heat-inactivated serum were returned for 3 days to active serum, their inductive capacity was found to be almost the same as that of cells continuously grown in active serum. Cultivation in serum heated for 30 minutes at 65°C. markedly weakened the spinocaudal inductive capacity of the cells, although the latter still grew normally. Even after cultivation for 14 days this weakening was clearly observable, and at the same time there was an increase in the number of archen-cephalic structures. After 28 days’ cultivation the cells exhibited the same inductive effect as cells continuously grown in serum inactivated at 56°C. Cultivation in serum-free Parker’s 199 solution rapidly weakened the spinocaudal inductive capacity of the cells, but the latter were not capable of growing continuously in this solution. The conclusion is drawn that, in accordance with the gradient theory previously advanced by the authors, the change in inductive capacity may be explained as a weakening of the mesodermalizing (M) principle in the cells, whilst the neuralizing (N) principle remains the same. A result of this change in the N/M balance would be that the spinocaudal action is weakened and the archencephalic effect is strengthened. At the same time the results show that the mesodermalizing action of the cells is dependent on external factors, whilst the neuralizing principle seems to be more stable. The results are compared with previous investigations on the changes in the inductive capacity of tissues caused by starvation, rapid growth, and malignancy.
Metabolism of [14C]glucose by postimplantation mouse embryos in vitro
Authors: Clough J. R. , Whittingham D. G. 
Published: April 2021

ABSTRACT
Carbon dioxide and lactate production from [14C]glucose were measured for post-implantation mouse embryos aged 6 to days post coitum in static cultures with a defined medium. The rate of metabolism increased rapidly and paralleled the increase in protein content indicating a fairly uniform rate of metabolism throughout the period. At all stages studied more than 90 % of the glucose utilized was converted to lactate. Over a quarter of carbon dioxide produced was derived from the C-l position resulting in high C-l: C-6 ratios, indicating that the Pentose Phosphate Shunt is a major oxidative pathway.
The influence of various culture condition on CO2 production showed that high concentrations of glucose did not affect glucose utilization whilst high lactate concentrations had a significant inhibitory effect. Pyruvate had no discernible effect.
Pattern regulation in isolated halves and blastomeres of early Xenopus laevis
Authors: Kageura H. , Yamana K. 
Published: April 2021

ABSTRACT
Xenopus embryos at the 2-cell stage were cut into right and left halves, those at the 4-cell stage into dorsal and ventral halves or individual blastomeres, and those at the 8-cell stage into lateral, animal and vegetal halves. Defect embryos, that is, 8-cell embryos from which a particular pair of blastomeres had been removed, were also prepared. These halves, blastomeres and defect embryos were cultured in 50 % Leibovitz (L-15) medium supplemented with 10 % foetal calf serum and then in 10 % Steinberg solution. Their development was determined from their macroscopic appearance when controls reached stage 26 (early tailbud stage) or later.
The only halves that could develop into normal larvae or frogs were lateral ones of 2- and 8-cell embryos. An interesting finding was that these halves of 2-cell embryos developed into only half-embryos when cultured in the above Leibovitz medium beyond the beginning of gastrulation. On the other hand, most or all the dorsal and ventral halves at the 4-cell stage and the animal and vegetal quartets at the 8-cell stage did not form normally proportioned embryos. Defect embryos lacking any two blastomeres of the animal half gave rise to nearly normal embryos, whereas those lacking two dorsal or two ventral blastomeres of the vegetal half did not.
From the present results and those of studies now in progress, it is concluded that development of blastomeres and halves from these early embryos, except lateral halves from 2- and 8-cell embryos, is not regulative as expected earlier, and that a certain combination of blastomeres is essential for complete pattern regulation.
Establishment of embryonic axes in larvae of the starfish, Asterina pectinifera
Authors: Kominami Tetsuya 
Published: April 2021

ABSTRACT
In order to clarify the relationships between the first cleavage plane and the embryonic axes, early cleavage pattern of the fertilized eggs of the starfish, Asterina pectinifera was reexamined. It was ascertained that the polar bodies were formed at the site to which the germinal vesicle had closely located before the initiation of the meiotic division, and that the first cleavage plane passed near this site of polar body formation. While some of the early embryos of this starfish were observed to show various cleavage patterns during early cleavage stage, more than 70 % of the embryos developed according to, so to say, the ‘typical’ cleavage pattern.
Next, horseradish peroxidase (HRP) was injected into one of the blastomeres of the 2-cell- or 8-cell-stage embryos. The embryos were allowed to develop up to either the early gastrula or the early bipinnaria stage and stained to detect the descendants of the blastomere injected with HRP. In early gastrulae still retaining radial symmetry, the activity of HRP injected at the 2-cell stage was found only in one side of the embryo partitioned by one of the symmetrical planes. When one of the four blastomeres lying nearer to the polar bodies at the 8-cell stage was marked with HRP, its descendants constituted one quarter of the anterior part of the gastrula, and descendants of a blastomere opposite the polar bodies were found in the posterior region of the embryo. It was concluded that the animal-vegetal (AV) axis was preexisting in the fertilized egg and that the first cleavage plane contained this primary axis.
In early bipinnariae with their dorsoventral (DV) axes already established, the region of activity of the HRP injected at the 2-cell stage was still demarcated by a plane which passed through the AV axis, but the plane of the boundary had no fixed relation to the DV axis. The results indicate that the first cleavage plane does not necessarily correspond to the median plane of the starfish larva, unlike the case in sea-urchin eggs (Horstadius & Wolsky, 1936). In other words, the DV axis of the starfish embryo is not predetermined in the fertilized egg, and might be established in the course of development through cell-to-cell interactions, while the AV axis is established mainly according to the pre-existing egg polarity.
Quantitative regulation of acetylcholinesterase development in the muscle lineage cells of cleavage-arrested ascidian embryos
Authors: Whittaker J. R. 
Published: April 2021

ABSTRACTSome embryos of Ciona intestinalis which were permanently cleavage-arrested with cytochalasin B at the 1-cell, 4-cell, or 8-cell stages produced, after 12 or 16 h of development time (18 °C), a level of muscle acetylcholinesterase activity equal to that found in normal early and later larval stage embryos of the same age. Enzyme activity was measured quantitatively in single whole embryos by a colorimetric procedure using microdensitometry. Quantitative regulation of a differentiation end product indicated that the usual transcriptional and translational control mechanisms for that histospecific protein continued to operate normally in the cleavage-arrested embryos. Acetylcholinesterase expression was apparently regulated independently of the usual cell cytoplasmic volume in the muscle lineage cells and possibly also independently of the normal nuclear number in the lineage. There is an egg cytoplasmic determinant that is segregated into the muscle lineage cells during cleavage and which appears to specify the pathway of larval muscle development. Quantitative control of muscle acetylcholinesterase is possibly one of the consequences of how the agent releases genetic expression in the presumptive muscle cells. Quantitative regulation was not, however, a general functional activity of cleavage-arrested embryos. Mitochondrial cytochrome oxidase, an enzyme whose development is believed to be unaffected by cytoplasmic determinants, was not regulated quantitatively in cleavage-arrested embryos. Cytochrome oxidase activity of cleavage-arrested embryos, measured in single whole embryos by a colorimetric microdensitometry assay, increased only slightly during 16 h of development time whereas the activity in normal control embryos doubled during that time.
Development of the lateral line system in Xenopus laevis : II Cell multiplication and organ formation in the supraorbital system
Authors: Winklbauer Rudolf , Hausen Peter 
Published: April 2021

ABSTRACT
Cell multiplication was studied during development of the supraorbital lateral line system in Xenopus laevis. The increase in cell number is biphasic. The first phase extends from the beginning of primordial elongation to the end of primary organ formation. Cell number increases linearly during this interval. Throughout this phase, a constant number of cells is in S phase of the cell cycle at a given time, despite a more than 10-fold increase in total cell number. After their formation, the number of the primary organs remains essentially constant. The individual primary organs are not clones of cells. Different organs grow at different rates, and become more and more heterogeneous in size. The second phase which is correlated with accessory organ formation is characterized by an elevated growth rate. This phase was not studied in detail. If developing larvae are starved, growth is normal up to completion of the first growth phase but is arrested at this point. The frequency distribution of the sizes of such growth-arrested organs approximates a binominal distribution. From its characteristics, a detailed model of cell proliferation and organ formation can be deduced: cell multiplication occurs through asymmetrically dividing stem cells, which become allocated to the forming organs at random and go through a fixed number of cell divisions.
The transition from oocyte-coded to embryo-coded glucose phosphate isomerase in the early mouse embryo
Authors: West John D. , Green J. F. 
Published: April 2021

ABSTRACT
The proportions of glucose phosphate isomerase (GPI-1) allozymes produced by early (Gpi-1sa/Gpi-1sb ♀ × Gpi-1sc/Gpi-1sc ♂)F1 mouse embryos were analysed by quantitative cellulose acetate electrophoresis. Technical controls showed that this system is extremely sensitive, quantitatively reproducible and quite accurate. Genetic controls established that the Gpi-1sa/Gpi-1sb mothers were homozygous for the Gpi-1tb temporal allele, that produces relatively high GPI-1 activity in the oocyte. The oocyte-coded enzyme lasted until about days post coitum (p.c.) or shortly thereafter. The maternally derived, embryonic Gpi-1s allele was expressed no earlier than the paternally derived allele. This was first expressed between and days p.c. In this cross, most of the transition from oocyte-coded to embryo-coded GPI-1 occurred between and days p.c.
Inhibition of proteolysis in rat yolk sac as a cause of teratogenesis. Effects of leupeptin in vitro and in vivo
Authors: Freeman Stuart J. , Lloyd John B. 
Published: April 2021

ABSTRACT
Conceptuses from 9·5-day pregnant rats were cultured for 48 h in heat-inactivated homologous serum to which leupeptin, a specific inhibitor of the lysosomal cysteifie-proteinases, was added for the final or the penultimate 6h.
The presence of leupeptin (25 μg/ml or above) increased the protein content of yolk sacs at harvesting to approximately twice the control value. The protein content of the embryo at harvesting was lower than that of controls.
When 125I-labelled polyvinylpyrrolidone was added to the culture serum for the final 6 h of culture, radioactivity was found in the yolk sac at harvesting, but not in the embryo. The presence of leupeptin did not affect the rate of uptake of the radiolabelled macromolecule by the yolk sac, nor facilitate its entry into the embryo.
When formaldehyde-denatured 125I-labelled bovine serum albumin was added to the culture medium for the final 6 h of culture, little radioactivity was found in the yolk sac at harvesting, and barely any was found in the embryo. Trichloroacetic acid-soluble radioactivity was found in the culture serum. The presence of leupeptin sharply increased the levels of radioactivity in the yolk sac (but not the embryo) and sharply decreased the acid-soluble radioactivity of the culture medium.
When rat serum whose proteins were labelled with [3H]leucine was used as culture medium, radioactivity was found in both yolk sac and embryo at harvesting. The presence of leupeptin increased the amount found in the yolk sac and decreased that found in the embryo.
These results are interpreted as follows. Leupeptin enters the lysosomes of the yolk sac, inhibiting their cysteine proteinases. The digestion of proteins pinocytosed by the yolk sac is consequently inhibited, resulting in the accumulation of protein by the yolk sac and a decreased flow of amino acids to the embryo.
Leupeptin (50 mg/kg), injected into pregnant rats at either 8·5 days or 9·5 days of gestation, induced congenital malformation in the offspring. It is proposed that leupeptin exerts its teratogenic action by inhibiting proteolysis in the lysosomes of the yolk sac, and so depriving the developing embryo of its supply of amino acids at a critical stage of development.
Effect of exogenous sex steroids upon the number of germ cells and the growth of foetal ovaries grafted under the kidney capsule of adult ovariectomized hamsters
Authors: Arrau J. , Roblero L. , Cury M. , González R. 
Published: April 2021

ABSTRACT
The effect of estradiol E, progesterone P and testosterone propionate T upon growth and germ cell population of foetal ovaries transplanted under the kidney capsule of adult ovariectomized hamsters was examined. Foetal ovaries were obtained 15 dayspostcoitum and the host received daily subcutaneous injections of E (1 μg/day), P (5 mg/day), T (500 μ g/day) or E + P in 0·1 ml oil for 25 days beginning 5 days before grafting. One day after the last injection, the size of the ovary, the germ cell population and plasma steroid levels were assessed. The results of hormone assays indicate that daily steroid administration was able to maintain continuously elevated plasma levels of the corresponding hormone. Interconversions or steroid secretion by the graft, if any, were not reflected in the peripheral circulation. The growth of the graft was stimulated by T and inhibited by P, in comparison with E and oil-treated controls. All germ cells were at the stage of primary oocyte forming part of a primordial or growing follicle. Their absolute number was significantly increased by T and E and significantly decreased by P and E + P. The number of oocytes per mm3 of ovary was increased 80 %, 48 % and 40 % with E, T and E + P, respectively.
It is concluded that, in the hamster, exogenous sex steroids given to the host can exert specific effects upon the growth and oocyte population of a grafted foetal ovary. Whether or not the action of steroids upon the graft is a direct one and whether they influenced oogonial mitosis, the evolution of the meiotic prophase or atresia of primary oocytes remains to be determined.
The distribution of muscle fibre types in chick embryo wings transplanted to the pelvic region is normal
Authors: Laing N. G. , Lamb A. H. 
Published: April 2021

ABSTRACT
Chick embryo wing buds were transplanted to the pelvic region in place of, or in addition to, the hindlimb bud prior to innervation. The wrist muscle ulnimetacarpalis dorsalis (umd) was innervated by middle-dorsal or middle-ventral motoneurons in the lumbar lateral motor column (LMC) in a rostrocaudal position which varied with the rostrocaudal position of the wing. Despite the heterotopic innervation the subsequent development of the distributions of fast and slow muscle fibres, as judged by ATPase staining, was normal in all muscles examined. The pattern of innervation in the umd, as judged by acetylcholinesterase staining also developed normally. It is probable that muscle fibre type is intrinsically, not neurogenically, determined.
Mechanical aspects of mesenchymal morphogenesis
Authors: Oster G. F. , Murray J. D. , Harris A. K. 
Published: April 2021

ABSTRACT
Many embryonic cells generate substantial contractile forces as they spread and crawl. These forces mechanically deform each cell’s local environment, and the resulting distortions can alter subsequent cell movements by convection and the mechanisms of contact guidance and haptotaxis. Here we develop a model for the cumulative effects of these cell-generated forces and show how they can lead to the formation of regular large-scale patterns in Cell populations. This model leads to several predictions concerning the effects of cellular and matrix properties on the resulting patterns. We apply the model to two widely studied morphogenetic processes: (a) patterns of skin-organ primordia, especially feather germ formation, and (b) the condensation of cartilagenous skeletal rudiments in the developing vertebrate limb.
Special Problems of Experimenting in ovo on the Early Chick Embryo, and a Solution
Authors: Silver P. H. S. 
Published: April 2021

ABSTRACT
A method has been described for experimenting on the early chick embryo. By its use it is possible to make an opening in the vitelline membrane large enough for the easy performance of any major operative procedure. The air space over the blastoderm is not topped up. The egg is incubated on a horizontal ttirntable, rotating around a vertical axis, at about 8 cycles per minute through an angle of about 90°, until the embryo has reached the end of the 3rd day of development. Successful results, using embryos of 4–12 somites, have been achieved in 74 per cent, of 120 major experimental procedures. The rationale of the method has been explained.
The histogenetic capacity of tissues in the caudal end of the embryonic axis of the mouse
Authors: Tam P. P. L. 
Published: April 2021

ABSTRACT
The caudal end of the embryonic axis consists of the primitive streak and the tail bud. Small fragments of this caudal tissue were transplanted from mouse embryos of various developmental stages to the kidney capsule in order to test their histogenetic capacity. The variety of mature tissues obtained from these small fragments was similar to that obtained by grafting a larger caudal portion of the embryo. Initially, the grafted tissue broke up into loose masses of embryonic mesenchyme and this was later re-organized into more compact tissues and into cysts that were lined with various types of epithelia. After 14 days in the ectopic site, grafted tissues coming from embryos of the primitive-streak, the early-somite and the forelimb-bud stages differentiated into structures that has presumably originated from the three embryonic germ layers. Many of these structures were related to the caudal region of the adult body, such as the mid- and hindgut segments and urogenital derivatives. The histogenetic capacity for endodermal tissues and urogenital organs was lost when the grafted tissue consisted entirely of the tail bud of the hindlimb-bud-stage embryos. The behaviour of the caudal tissues suggested that (1) the primordia for the various parts of embryonic body were derived from a small progenitor population in the primitive streak and the tail bud, and (2) the histogenetic capacity of this population changed during development.