bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of X-rays on nucleic acid metabolism during cleavage and gastrulation inPleurodeles waltliieggs
Authors: Alexandre H. 
Published: April 2021

ABSTRACTX-irradiation produces a rapid and substantial decrease in DNA synthesis in cleaving eggs of Pleurodeles, as shown by thymidine incorporation experiments; this decrease is presumably due to the arresting of the cell cycle in many blastomeres. DNA replication is partly resumed at the late blastula stage after irradiation at the 2- to 4-cell stage.The present work demonstrates a high radiosensitivity of the metabolic pathway leading to the incorporation of uridine into DNA; this could be the result of the inhibition of the activity or the synthesis of such enzymes as ribonucleotide reductase, thymidylate synthetase and CTP synthetase. The radiosensitivity of this metabolic pathway becomes lower after gastrulation.Finally, irradiation strongly inhibits the synthesis of new RNA species at gastrulation, but seems to have no effect on heterodisperse RNA (mRNA) synthesis during cleavage.The results are discussed in relation to the biochemistry of early stages of development in Amphibians.
The cellular basis of movement of the migrating grex of the slime mouldDictyostelium discoideum:chemotactic and reaggregation behaviour of grex cells
Authors: Garrod D. R. 
Published: April 2021

ABSTRACTThe chemotactic behaviour of cells of the migrating grex of D. discoideum has been studied by observing the responses of small groups of cells placed near to aggregation streams, agar blocks containing cyclic AMP or migrating grexes. Grex cells placed near aggregation streams were not attracted to the streams initially; after about I h, however, some cells were attracted to the streams. Similarly, grex cells placed near agar blocks containing cyclic AMP were not initially attracted towards the blocks, but some attraction was observed after about 1 h; the most effective cyclic AMP concentration was 10_4 M. Grex cells which were placed in heaps against the sides of aggregation streams, instead of a short distance away, were often incorporated into the streams within . Grex cells were not attracted towards migrating grexes.Because of these results it is suggested that (1) migrating grex cells are not chemotactically sensitive to cyclic AMP, but they acquire chemotactic sensitivity after separation from the grex for about 1 h ; (2) chemotaxis is probably not involved in the movement of the migrating grex; (3) grex cells retain the adhesive property found in aggregating cells, which is involved in the formation of end-to-end contacts necessary for the behaviour known as contact following.Reaggregation of dispersed grex cells was studied by time-lapse photography. Reaggregation was found to be a two-stage process: first, an adhesive phase dependent on the development of intercellular contacts at the expense of adhesions with the substratum; secondly, a chemotactic phase which begins about 1 h after dispersal of the grex cells. It is suggested that the first phase may be accounted for by assuming that the cells are more cohesive than adhesive.
Extent and properties of the regeneration field in the larval legs of cockroaches (Leucophaea maderae): III. Origin of the tissues and determination of symmetry properties in the regenerates
Authors: Bohn Horst 
Published: April 2021

ABSTRACT
Previous papers dealing with the regeneration field of cockroach (Leucophaea maderae) legs have shown that two elements of the leg surroundings are indispensable for regeneration of a leg: the basal sclerites and the ‘]eg-inducing membrane’ (LIM). The experiments of this paper partly clarify the way in which these two tissues interact; the origin of the regenerative tissues and the determination of polarity and symmetry in the regenerated legs were studied.
By combination of sclerites and LI M of different species or segments it has been shown that each of the tissues makes up half of a leg regenerate -the sclerite tissues the anterior longitudinal half, the LIM the posterior longitudinal half.
The trochantin was implanted in four different orientations (normal, turned 90° clockwise or anti-clockwise, turned 180’) into a normally orientated field of LIM. The anterior-posterior and medio-lateral axes of the regenerates had the same orientation as those of the sclerites. Therefore, the sclerites alone determine symmetry of the regenerate; the LIM has no influence in this respect. Neither of the two axes is fixed irreversibly in the cells of the LIM; the cells seem able to accept any polarity which is forced upon them by the sclerites. The symmetry properties are more strongly fixed in the cells of the sclerites, but an inversion of polarity (through 180°) is possible for both axes.
Regeneration of a leg from the level of the trochantin seems to be initiated by or dependent on a small medial region of the trochantin. A tiny fragment of the medial wedge of the trochantin, when transplanted to a field of LIM, can form a complete leg regenerate; a lateral half of the trochantin never does. As long as this small medial part of the trochantin is prevented from making contact with LIM by a praecoxa fragment, no regeneration takes place at the anterior border of the trochantin, even when the greatest part of the border has contact with LIM.
The regenerative capacities of the praecoxal sclerite are different at the anterior and posterior cut surfaces, irrespective of the level of the cut and the orientation of the sclerite. An anterior cut surface never forms a leg regenerate, but a posterior cut surface does.
Biochemical control of fresh-water sponge development : effect on DNA, RNA and protein synthesis of an inhibitor secreted by the sponge
Authors: Rozenfeld Francine 
Published: April 2021

ABSTRACT
During their growth, fresh-water sponges release into the medium a dialysable inhibitor (gemmulostasin) which reversibly blocks development of the gemmules at an early phase, prior to the first mitoses.
The incorporation of [3H]labelled precursors into DNA, RNA and proteins has been measured throughout development, in the presence or absence of inhibitor. Autoradiographic controls of the nuclear incorporation of [3H]thymidine have been made. Gemmulostasin erases the peak of [3H]thymidine incorporation that otherwise occurs just before the first mitoses. Its overall effect is to bring about, either directly or indirectly, a high peak in the incorporation of [3H]uridine and [3H]leucine at a time when the incorporation of these precursors is low in the controls.
It is suggested that a causal relation exists between these phenomena.
Dedifferentiation, redifferentiation and bundle formation of smooth muscle cells in tissue culture : the influence of cell number and nerve fibres
Authors: Chamley Julie H. , Campbell Gordon R. , Burnstock Geoffrey 
Published: April 2021

ABSTRACT
Smooth muscle from newborn guinea-pig vas deferens was enzymically dispersed into single cells or small clumps and grown in culture in the presence or absence of sympathetic ganglion explants.
Most single smooth muscle cells gradually lost their typical ultrastructural features and contractile properties during the first few days in culture. At 7 days of culture these de-differentiated smooth muscle cells underwent extensive proliferation. If sufficient cells were present in the culture inoculate, a continuous monolayer formed at about 9 days of culture and redifferentiation of smooth muscle began. At 11–12 days of culture the cells reaggregated into clumps, began to contract spontaneously, and formed into well-organized muscle bundles in two layers at right angles, resembling the muscle layer organization of the in vivo NZS deferens. In cultures where a continuous monolayer was not formed at 9 days, isolated cells did not redifferentiate. The process of dedifferentiation and proliferation was delayed in those smooth muscle cells which had sympathetic nerve fibres in close association.
Clumps of vas deferens tissue which were not fully dispersed by the enzyme treatment did not dedifferentiate with time in culture but muscle bundles were disrupted and asyn-chronous contractions resulted. After 8–12 days of culture the muscle bundles reformed and foci of synchronous contractions developed. Nerve fibres appeared to accelerate bundle and nexus formation in this situation, with synchronous contractions resuming at 3–5 days.
The relation of these findings to the process of wound healing in smooth muscle tissues in vivo is discussed.
A block to cross-fertilization located in the egg jelly of the frog Rana clamitans
Authors: Elinson Richard P. 
Published: April 2021

ABSTRACT
The egg of Rana clamitans enrobed in its native jelly was not fertilized by sperm of R.pipiens. However, when R. clamitans eggs were enrobed by R. pipiens jelly, they were fertilized by R. pipiens sperm. Male pronuclei were found in the eggs, and most of the resulting embryos were diploid. The embryos gastrulated, but most arrested at mid-to late gastrula stages. Some begun neurulation, but none survived longer than 4 days. When R. clamitans eggs in R. pipiens jelly were fertilized by R. clamitans sperm, the embryos developed normally except that they failed to hatch.
In the reciprocal experiment, R. pipiens eggs were enrobed in R. clamitans jelly. The eggs were not fertilized by R. pipiens sperm but were fertilized by R. clamitans sperm. Therefore, the R. clamitans jelly plays a major role in preventing fertilization by sperm of other species.
The R. clamitans jelly’s block to cross-fertilization was not a block to sperm migration. Further, the R. clamitans jelly contained factors which permitted R.pipiens sperm to fertilize dejellied R. pipiens eggs. Dejellied eggs are usually not fertilizable in the absence of jelly factors.
Structure and development of ommatidia in Oncopeltus fasciatus
Authors: Shelton P. M. J. , Lawrence P. A. 
Published: April 2021

ABSTRACT
The structure and development of ommatidia has been examined in Oncopeltus fasciatus (Lygaeidae). Each ommatidium is composed of 18 cells comprising four crystalline cone cells, two primary pigment cells, four secondary pigment cells and eight retinula cells. Ommatidia are of the apposition type and the retinula cells are arranged on the open rhabdomere plan.
During the five larval stages the retina grows anteriorly to provide a 12-fold increase in numbers of ommatidia. Grafts of presumptive eye epidermis show that the proliferating anterior border of the developing retina is an area of epidermal cell recruitment rather than a special budding zone.
Mosaic retinae were formed by grafting epidermis from near the eye of wild-type donors into the corresponding region of mutant hosts. Ommatidia which developed at the borders of the graft contained mixtures of wild-type and mutant cells in variable and unpredictable combinations. Similar mosaic structures were seen in retinae generated by irradiation at early stages of development. The suggestion that each ommatidium is clonally derived from a single epidermal stem cell is thus disproved.
The frequent occurrence of mosaic ommatidia containing only one cell of a different genotype from the rest suggests that the formation of ommatidial clusters follows the main proliferative phase of eye growth. We conclude that cell determination within ommatidia is not connected with lineage but is dependant upon cell position within the developing ommatidium.
A quantitative study of blastemal growth and bone regression during limb regeneration in Triturus cristatus
Authors: Smith A. R. , Lewis J. H. , Crawley A. , Wolpert L. 
Published: April 2021

ABSTRACT
Soft X-ray photographs show both the outlines of the soft parts of the regenerating limb and the bones. This enables one to make quantitative studies on bone regression and the growth of the regenerate, since good reference points are available. Bone regression of about 0·5 mm was observed to occur within about 20 days following amputation. Growth curves of regenerates cut at different levels confirm Spallanzani’s old observation that the total time for regeneration is fairly constant for different levels of amputation -regenerates from proximal levels regenerate faster. However, the intrinsic growth rate curves are remarkably similar for different levels of amputation; the difference in final length arises because the short period of high intrinsic growth rate continues for slightly longer in regenerates from proximal levels.
In terms of the progress zone theory of limb development, three phases of regeneration are recognized: the formation of the blastema and progress zone; the laying down of the skeletal rudiments by the rapidly proliferating progress zone; and the subsequent slower growth of the rudiments. A quantitative model is put forward and it is shown that it can provide a good description of the observed growth curves. An important assumption is that the various skeletal rudiments are the same size when they leave the progress zone and the final differences in size reflect differences in the final growth phase. The progress zone model provides new quantitative insights into the relationship between the growth of the limb as a whole and the behaviour of individual cells.
Participation of cartilage grafts in amphibian limb regeneration
Authors: Wallace H. , Maden M. , Wallace B. M. 
Published: April 2021

ABSTRACT
Irradiated axolotl arms bearing grafts of pure cartilage obtained from the non-irradiated humerus of other specimens show a variable response to amputation of the hand. Some arms grow spikes with little morphogenesis, others produce one or more digits, and some regenerate small and defective but recognizable hands. Identically irradiated control arms which carry no grafts or grafts of irradiated tissue show none of these features. The cartilage grafts must therefore be responsible for the limited amount of regeneration observed. The origin of the regenerated tissues could not be independently determined in this experiment, although grafts were made reciprocally between white and dark genotypes, as all the regenerates were either very pale or completely unpigmented. A previous demonstration that grafted tissue does not reactivate irradiated host cells, however, permits the conclusion that the grafted cartilage provides all the mesodermal tissues of these regenerates.
The grafts consisted exclusively of chondrocytes, while the regenerates contained cartilage, muscle, blood vessels, nerve sheaths and general connective tissue. It is concluded that chondrocytes dedifferentiate into pluripotent blastemal mesenchyme cells which can re-differentiate into all other internal tissues of the limb. The concepts of modulation and neo-blasts (undifferentiated reserve cells) thus have no basis in amphibian limb regeneration.
Regional developmental capacities of the rat embryonic endoderm at the head-fold stage
Authors: Švajger A. , Levak-švajger B. 
Published: April 2021

ABSTRACT
Three areas, composed of all three germ layers, were isolated from Fischer strain rat embryonic shields at the head-fold stage, and grafted separately under the kidney capsule of adult male rats of the same strain. The areas were from the neural plate, Hensen’s node and the primitive streak. The resulting teratomas were examined histologically for the presence of derivatives of the primitive gut.
The grafts differed strikingly in their capacity to develop into different segments of the gut. Endoderm underlying the neural plate developed into derivatives of the foregut, while endo-derm underlying the primitive streak developed mainly into derivatives of the mid-and hindgut.
It was concluded that, at the head-fold stage, the capacities to develop into different segments of the definitive gut are already roughly limited to particular areas of the endoderm.
The effect of excess vitamin A on the development of rat embryos in culture
Authors: Morriss Gillian M. , Steele C. E. 
Published: April 2021

ABSTRACT
Primitive streak stage rat embryos were cultured in serum containing added vitamin A alcohol at concentrations ranging from 0·5 to 20 μg/ml. At the higher concentrations there was an overall growth retardation, and differentiation was inhibited. This was thought to be due to inhibition of DNA synthesis. At 0· 5 μg/ml the embryos developed abnormally in a manner similar to that previously seen in vivo. This result, which was supported by an ultra-structural study, provides evidence that the teratogenic effects of vitamin A are due to a direct action on the embryos.
Comparison of embryonic development in vitro at different concentrations of vitamin A with the results obtained in vivo suggests that in the latter, only a very small proportion of the amount injected was reaching the embryos in an active form. The maternal factors involved are discussed, and excess vitamin A is defined as an excess of free and non-specifically bound retinol. The levels of vitamin A which affected differentiating embryos in vitro are lower than the minimum levels previously shown to affect differentiated tissues. This suggests that relatively minor increases in serum levels during pregnancy may cause malformations without affecting the maternal organism. Since raised serum vitamin A levels have been shown to be associated with impaired liver function in man, these factors may be significant in human teratogenesis.
Synthesis of RNA in oocytes of Xenopus laevis during culture in vitro
Authors: Colman A. 
Published: April 2021

ABSTRACT
RNA synthesis can be maintained in large oocytes of Xenopus laevis during periods of in vitro culture of at least 10 days. A simple salt medium, modified Barth’s solution, is found to be as effective a culture medium for these oocytes as several other complex media. The newly synthesized RNA is characterized electrophoretically and shown to consist predominantly of ribosomal RNA precursor, 28S and 18S ribosomal RNA, and 4S RNA. The distribution of this RNA within the oocyte is detected autoradiographically, where it is found to be greatly concentrated over the nucleoli. No qualitative alterations in either of these parameters are found during culture, within the limits of sensitivity of the assay procedures.
Studies on the locomotion of primordial germ cells from Xenopus laevis in vitro
Authors: Heasman Janet , Mohun Tim , Wylie C. C. 
Published: April 2021

ABSTRACT
The mechanism of embryonic cell movement is poorly understood. Primordial germ cells (PGCs) of the anuran amphibian Xenopus laevis migrate individually from their site of determination in the embryonic endoderm to their site of differentiation, in the developing gonad. PGCs have been isolated during their migratory phase from tadpoles, and their movement studied in vitro on a variety of natural and artificial substrates.
On all artificial substrates used, including acid-washed glass, tissue-culture plastics, poly-L-lysine-coated glass, and collagen, the PGCs move by amoeboid extrusion of hemispherical lobopodia. Several considerations make it unlikely that this is the mechanism employed in vivo.
On living cellular substrates, e.g. monolayers of Xenopus laevis embryonic cells, adult kidney cells, and adult mesentery cells, PGCs become firmly attached and undergo phases of elongation and contraction. They move by elongation, coupled with the extrusion of filopodia, followed by waves of contraction, and ultimately by retraction of the trailing end of the cell. Evidence is presented that this is the mode of locomotion normally employed by PGCs in vivo.
Tractus uro-génital des chimères chez l’amphibien modèle Triturus alpestris Laur
Authors: Houillon Charles 
Published: April 2021

ABSTRACT

Urogenital tract in chimaeras of the urodele amphibian Triturus alpestris
Embryonic grafting in Triturus alpestris allows homosexual (♀-♀ and ♂-♂) and heterosexual (♀-♂ and ♀ ♂) connexions of anterior and posterior part of two different tail-bud-stage embryos. Most of the 46 chimaeric animals obtained have been shown to possess two pairs of gonads. Among homosexual chimaeras, females (♀-♀) possess four ovaries and males (♀-♂) four testes. Among heterosexual chimaeras, some animals (♂-♂) show two sterile anterior ovaries and two normal posterior testes, other heterosexual chimaeras (♂-♀) possess normal anterior testes and sometimes well-differentiated posterior ovaries. These results confirm those obtained in Pleurodeles waltlii by the same author.
Final sex differentiation of the gonads seems likely to be an effect of their reciprocal position down the longitudinal axis of the chimaera : an anterior ovary is entirely inhibited by a posterior testis, but a posterior ovary may differentiate and reach sexual maturity notwithstanding a well-developed anterior testis. These kinds of adult heterosexual chimaeras (♂-♀) can be accounted as hermaphrodites.
Statistically, the number of homosexual chimaeras ♂-♂ is significantly greater than the other homosexual ♀-♀ or heterosexual ♀-♂ and associations. This fact may be due to the total inhibition of anterior ovaries in some heterosexual chimaeras, but also, to a phenotypic sex reversal of the female part.
Precocious evagination of the embryonic chick thyroid in ATP-containing medium
Authors: Hilfer S. Robert , Palmatier Bernice Y. , Fithian Eileen M. 
Published: April 2021

ABSTRACT
The identification of actin and myosin in many cell types other than muscle has given support to the hypothesis that contractile proteins are involved in cell shape changes. However, there is no direct evidence that a contractile process participates in morphogenetic movements during organogenesis. As a first step in testing this possibility, thyroid placodes of chick embryos were treated with an incubation medium containing Triton X-100 and ATP. Pharyngeal regions, isolated in Medium 199, were photographed at timed intervals. At a concentration of 10−3 M ATP, the thyroid region formed a deep pit within minutes after addition of this ‘contraction medium’, whereas evagination requires approximately 7 h in ovo. Treatment with Medium 199 containing either Triton X alone, ATP alone, or Triton X and pyrophosphate did not result in evagination of the thyroid. Substitution of other nucleotides for ATP suggested a specific requirement for ATP. Surgical removal of selected portions of the pharyngeal floor and examination of sectioned material by light microscopy indicated that the cells involved in the shape change were located at the periphery of the thyroid placode before treatment. The sharp bends that were formed in ‘contraction medium’ cannot be explained entirely by pinching of cell apices at the point of folding; rather the effect of several forces is indicated in the evagination.
The onset of phosphatase activity in early mammalian embryos
Authors: Ishiyama V. , Izquierdo L. 
Published: April 2021

ABSTRACT
The onset of acid and alkaline phosphatase activity is determined by means of Burstone’s azo dye coupling methods in oocytes and embryos of the mouse, rat and hamster, and in mouse embryos cultured in vitro. Acid phosphatase activity is detected in all cases while alkaline phosphatase activity begins during the 4-cell stage and is always present thereafter. The method is sensitive regarding detection of activity but does not permit the quantification nor a precise localization of the enzymes.
Vitesse de croissance et renouvellement des dents chez les Amphibiens
Authors: Chibon Pierre 
Published: April 2021

ABSTRACT

Growth rate and replacement of teeth in Amphibians
The growth rate of teeth depends on age: it varies from 5 days for the first teeth, functional at hatching time, to 2 months for 2-year-old animals. The life time of a functional tooth is 20 days in the young larva and in the young post-metamorphic individual; it is not precisely known in adults. The proteins of organic matrices are elaborated in ergastoplasm, transported through the Golgi apparatus and Golgian vesicles, and deposited outside the cells within 1 h. Destruction of old teeth begins before metamorphosis; it is performed by pulp cells necrosis, and intervention of macrophages and osteoclasts; teeth are completely destroyed in situ, allowing growth of the replacement teeth. Thyroxine hastens tooth replacement.