bluuebunny/crossref_metadata_2025_split huggingface dataset:
Abnormalities in somite segmentation following heat shock to Xenopus embryos
Authors: Elsdale Tom , Pearson Murray , Whitehead Margaret 
Published: April 2021

ABSTRACT
The typical abnormality induced by a 15 min shock at 37 °C is a single discrete length along the somite file within which segmental boundaries are absent or irregular. The two sides of the same embryo present a similar but not necessarily identical appearance. Usually all the embryos in a treated batch show abnormalities of similar severity. Survival of treated embryos, the details of the visible malformations, and temporal aspects of the phenomenon have been studied.
The results indicate a temperature sensitive period that traverses the neurula, from head to tail at about the same rate as the somites form, but some hours beforehand. The temperature sensitive process is not associated with cell determination and differentiation, and there are reasons for thinking that the specification of the normal somite number occurs independently.
The results are discussed in relation to Cooke & Zeeman’s model of a wave front interacting with an oscillator.
Stabilité de la determination et de la différenciation des caractères sexuels somatiques chez Nereis pelagica L. (Annélide Polychèté)
Authors: Boilly-Marer Yolande 
Published: April 2021

ABSTRACT
Stability of determination and differentiation of the somatic sexual characters in Nereis pelagica L. (Annelida polychaeta)
Experiments of regeneration in situ or on grafts were carried out to test the stability of determination of the somatic sexual characters in Nereis pelagica.
The sexual characters of the parapodial cirri (male and female swellings, male crenellations) are always expressed on stump or regenerate according to the genetic sex. Super-numary parapodia which developed at the site of junction of the heterologous faces of host and graft of opposite sexes, might have the characters of either sex; this result can be interpreted by supposing that a supernumary parapodium is derived from tissues of either host or graft, of the corresponding sex.
Conversely, the pygidial papillae, which normally occur only on the heteronereid male, will appear on regenerating female pygidia, triggered to transform to the heteronereid condition naturally or by decerebration, with a frequency depending on the age of the regenerate, the length of the regenerate, and the genital condition of both the stump and the regenerate. It is concluded that the presence of the papillae is not a sex-specific character, but that their development is normally inhibited in the maturing female.
Observations on the migration and proliferation of gonocytes in Xenopus laevis
Authors: Kamimura Michiko , Ikenishi Kohji , Kotani Minoru , Matsuno Toru 
Published: April 2021

ABSTRACT
The process of primordial germ cell formation in the normal course of development of Xenopus laevis was examined with a light microscope on paraffin and Epon sections of embryos or tadpoles, extending over the period from the gastrula to the feeding tadpole stage. Positional changes of gonocytes with development were nearly the same as those reported on the same species by Blackler (1958) and Whitington & Dixon (1975). The following points were newly demonstrated. Gonocytes which have been located in a deep endodermal position till mid tail-bud stage come to be located in a rather peripheral region of the endoderm cell mass at stage 31 (late tail-bud), suggesting that the initial step of migration of the gonocytes towards the future genital ridge has already begun at this stage. Gonocytes at stages 33/34 and 35/36 were observed in a more dorsal part of the endoderm than at stage 31. Gonocytes which seem to have begun their migration are roundish in external shape and have a large intercellular space around them. At stage 40 gonocytes were located in the dorsal endodermal crest, and at stage 41 gonocytes were found with cell bodies extending over both the dorsal endoderm crest and the dorsal mesentery, indicating that the separation of the gonocytes from the endoderm was in progress at this stage. The present results seem to indicate that gonocytes migrate not passively but actively from the deep endodermal position to the genital ridge, passing through the dorsal mesentery. Counting the number of gonocytes at successive stages of development revealed that gonocytes proliferated exponentially throughout the developmental stages from gastrula to tadpole.
Cytological and microspectrophotometric analysis of mesodermalized explants of Triturus gastrula ectoderm
Authors: Noda Shinichi , Kawakami Izumi 
Published: April 2021

ABSTRACT
Using isolated presumptive ectoderm of the newt (Triturus pyrrhogaster) embryos as a reactor and extract of rat bone marrow as a mesodermal inductor, changes of cell number and mitotic index of the reactor cells were studied. In early stages of cultivation the increase in cell number in the mesodermalized ectodermal piece was slower than in the non-mesodermalized epidermal piece; but after 24 h it showed abrupt increase and reached a cell population equal to that of the control at 48 h of cultivation. In the experimental series, the mitotic index was 0 at 4 h after the application of the inducing stimulus, but increased precipitously in the next 8 h and reached a level of 4·4 % at 12 h and thereafter decreased gradually. The cell cycle stopped at the S phase and stayed in it for several hours after the application of inductor. A sudden fall in cell number, observed in the mesodermalized epidermal piece between the 4th and the 8th h after the application of inducing stimulus, seems to be attributable to cell death which was brought about by the inducing stimulus. In the histogenetic process phases of repression on mitosis by an inducing stimulus, cell proliferation and nonproliferation seem to succeed each other.
Properties and development of erythropoietic stem cells in the chick embryo
Authors: Samarut Jacques , Nigon Victor 
Published: April 2021

ABSTRACT
When injected into irradiated chickens, haemopoietic stem cells give rise to well-defined erythrocytic colonies in the host marrow. Such stem cells (CFU-M — Colony Forming Unit in Marrow) have been found in different tissue of the chick embryo (yolk sac, blood, marrow). Analysis of the properties of CFU-M reveals that they represent two classes of stem cells: pluripotent stem cells mainly in adult marrow and erythrocytic-committed stem cells present in yolk sac. Yolk sac contains the main pool of CFU-M during the major part of embryonic life. In the blood of 6-day-old embryo, there are three or four times more CFU-Ms than in the yolk sac; they are no longer detected in the blood after the 16th day of incubation. During development of the marrow, stem cells are actively differentiating and their total number remains the same from 16 days to hatching.
Experiments on blocking and unblocking of first meiotic metaphase in eggs of the parthenogenetic stick insect Carausius morosus Br. (Phasmida, Insecta)
Authors: Pijnacker L. P. , Ferwerda M. A. 
Published: April 2021

ABSTRACT
The eggs of the parthenogenetic stick insect Carausius morosus, which remain arrested in first meiotic metaphase until oviposition, must be activated in order to develop. The activating agent is oxygen from the air, which enters the egg cell through the micropyle. An exposure shorter than one minute is sufficient to release the blockage.
In non-activated (micropyle-less) eggs the first metaphase chromosomes either degenerate or change into an interphase nucleus. This nucleus polyploidizes by endoreduplication, and then either degenerates or multiplies by amitosis. Similarly more generations of nuclei may arise resulting in a chaotic development. These nuclei survive better in the anterior region of the egg.
The question of whether the cytoplasmic factors which control nuclear behaviour, also operate in eggs of C. morosus is discussed.
The effects of a t-allele (t
AE5) in the mouse on the lymphoid system and reproduction
Authors: Vojtí škový M. , Viklickí V. , Vorácová B. , Lewis S. E. , Gluecksohn-Waelsch S. 
Published: April 2021

ABSTRACT
Mice homozygous for tAE5, a recessive allele at the complex T-locus, are characterized by their unique short-tailed phenotype as well as by runting and low fertility. Histological and histochemical studies of the lymphoid and reproductive systems disclosed structural changes in the mutant spleen resembling those found in autoimmune conditions. Involution of the mutant thymus was greatly accelerated compared to normal. Necrotic changes occurred during spermiogenesis whereas ovarian structure was normal in mutants. The possible mechanisms of the mutant effects are discussed in the framework of other similar syndromes and the mode of action of alleles at the complex T-locus.
The response of the brachial ventral horn of Xenopus laevis to forelimb amputation during development
Authors: Fortune Joanne E. , Blackler Antonie W. 
Published: April 2021

ABSTRACT
The normal development of the brachial ventral horn of the frog Xenopus laevis and the response of the brachial ventral horn to complete forelimb extirpation at five developmental stages were assessed histologically. Differentiation of brachial ventral horn neurons occurred in pre-metamorphic tadpoles between stages 52/53 and 57. Mean cell number in the brachial ventral horn reached a peak of 2576 (S.E.M. = ± 269, n = 2) per side of the spinal cord at stage 55 and decreased to 1070 (S.E.M. = ± 35, n = 7) by the end of metamorphosis. Cell degeneration was presumed to be the mode of cell loss since it was most prevalent during the period of rapid decrease in cell numbers. The response of the ventral horn to forelimb removal varied with the stage of the animal at amputation. Following amputation at stage 52/53 or 54 the ipsilateral ventral horn neurons appeared less differentiated than those on the control side and a rapid cell loss of about 80% occurred on the operated side. These effects occurred more rapidly after ablation at stage 54 than at stage 52/53. Amputation at stage 58, 61, or 66 caused chromatolysis in the ventral horn, a period of relative cell excess on the operated side, and a delayed neuronal loss of 32–66%. It was concluded that excess cell degeneration accounted for cell loss and that suppression of normal neuronal degeneration caused the relative cell excess on the operated side. The data indicate that the brachial ventral horn was indifferent to the periphery before stage 54, was quickly affected by limb removal between stages 54 and 58, and by stage 58 had entered a phase in which a delay preceded cell death. No forelimb regeneration occurred.
Three-dimensional anatomy of the 8-day mouse conceptus: a study by scanning electron microscopy
Authors: Tamarin A. , Boyde A. 
Published: April 2021

ABSTRACT
The three-dimensional anatomy of the 8-day mouse conceptus was studied by scanning electron microscopy aided by microdissection within the microscope specimen chamber. Attention was given to the relationship of the extra-embryonic membranes and their subtended compartments and particular emphasis was placed on the ‘inverted’ condition of the embryo at this stage of development.
The main points brought forth in this study are: the five basic brain segments are discernible on the basis of surface contours;the cervical fold, extending from the ventrum of themetencephalon to the so ma top leu re, forms a partition which separates the branchial region from the rest of the amniotic space;the procephaiic membrane bifurcates in a vertical plane to form the splanchnopleure andsomatopleure lateral to the forebrain, and it bifurcates horizontally to form the dorsal and ventral coverings of the pericardial coelom;the antrum of the pericardial-peritoneal canal opens into the lateral coelom posterior to the cervical fold;the midgut of the embryo is delineated laterally by longitudinal grooves connecting the foregut and hindgut antra;embryonic ectoderm in the neural-fold region is formed by a single layer of pseudostratified columnar cells;the allantois is hollow near its base and the inner surface is formed by a discontinuous layer of squamous cells;blood islands in the extra-embryonic mesoderm form a ring of bulges around the middle of the exocoel.
Other structures such as the ectopiacental cavity, the ectoplacental cone and the parietal capsule are also described.
Ultrastructural observations of preimplantation stages of the sheep
Authors: Calarco Patricia G. , Mclaren Anne 
Published: April 2021

ABSTRACT
Sheep embryos were examined with the electron microscope in order to characterize their organelles and the changes that occur during the preimplantation period. The first sign of differentiation of trophoblast cells was the appearance of junctions between external cells at the 16-cell stage. Nucleoli developed a granular component suggesting the synthesis of ribosomal RNA at the 16-cell stage also. Centrioles were seen as early as the 8-cell stage. Jntra-cytoplasmic vesicles were present in large numbers in all cleavage stages but disappeared at blastulation. Mitochondria progressed from a very electron-dense hook-or U-shaped form with a few cristae to a cylindrical or spherical form of light density with many transverse cristae. Microvilli were not seen until the blastocyst stage and then only on the exterior surface of the trophoblast cells. Crystalloid or virus inclusions were not observed. It was concluded that the fine structure and developmental changes in the early sheep embryo are very similar to those of other mammalian species.
Cell patterning in migrating slugs of Dictyostelium discoideum
Authors: Sampson J. 
Published: April 2021

ABSTRACT
When front quarters of migrating slugs of Dictyostelium discoideum are isolated by surgery and induced to fruit immediately they produce fruiting bodies with disproportionately large stalks (Raper, 1940). The data in this communication show that the ‘stalky’ character of fruits derived from front quarters persists even if the cells of the front quarters are disaggregated and hence have to reaggregate before fruiting. The data also demonstrate that fruits derived from rear quarters of slugs have disproportionately large spore heads, and that this effect becomes more pronounced with increasing age of the slugs. These observations support the view that the cells of the front and rear of migrating slugs are to some extent committed to different fates.
The structure of the mitochondrial cloud of Xenopus laevis oocytes
Authors: Billett F. S. , Adam Elizabeth 
Published: April 2021

ABSTRACT
The ultrastructure of the mitochondrial cloud (Balbiani body) of the pre-vitellogenic oocytes of Xenopus laevis has been examined using transmission and stereoscan electron microscopy. Examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands of mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200 μm in diameter, contain relatively more vesicles. Using a standard electron microscope at 100 kV very long and coursing arrays of mitochondrial profiles can be detected. The presence of very long mitochondrial elements has been confirmed using a high voltage microscope operating at 500–1000 kV. Stereoscan preparations, isolated from pre-vitellogenic oocytes, lend some support to the view that the mitochondrial cloud may consist of a mass of long filamentous mitochondria and the possibility that there are large continuous regions of mitochondrial material cannot be ruled out.
Binding and uptake of trypan blue by developing oocytes of Locusta migratoria migratorioides
Authors: Wajc Esther , Bakker-Grunwald Tilly , Applebaum Shalom W. 
Published: April 2021

ABSTRACT
Resorbing oocytes are heavily stained by trypan blue injected into the haemolymph; this selves as a basis for a quick and convenient method for measuring the degree of resorption. Oocytes in the beginning of their development are most susceptible towards resorptive tendencies.
The uptake of trypan blue by normally developing oocytes is proportional to the oocyte surface. From ‘double-marker’ experiments, in which trypan blue is injected into the haemolymph together with [3H]inulin (which does not bind to the oocyte membrane) it is estimated that the contribution of binding in the interiorization of trypan blue is in the order of 80 %, under the conditions given.
In vitro incubations show the interaction of trypan blue with the membrane to be electrostatic in nature.
The eversion and differentiation of Drosophila melanogaster leg and wing imaginai discs cultured in vitro with an optimal concentration of β-ecdysone
Authors: Milner Martin J. 
Published: April 2021

ABSTRACT
The stages of the eversion and differentiation of prothoracic leg and wing discs of Drosophila melanogaster, in Shields and Sang’s medium 3, are described. The range of specific imaginai structures produced, including patterns of sensilla trichodea and sensilla campaniformia, are noted, and the relationship of these structures to those differentiated in situ is discussed.
Regulation of pre-natal haemopoiesis: evidence for negative feedback control of erythropoiesis in the foetal mouse
Authors: Cole R. J. , Regan T. 
Published: April 2021

ABSTRACTThe effects of medium conditioned by erythrocytes on in vitro differentiation of mouse prenatal erythroblasts were examined. Haem synthesis was inversely proportional to the concentration of erythrocyte-conditioned medium (ECM) in either presence or absence of erythropoietin (EP), but concentrations of ECM which limited haem synthesis to 50% of normal had no effect on changes in erythroblast numbers. ECM reduced uridine incorpora-tion into RNA and limited the rise in incorporation due to stimulation by EP. ECM enhanced thymidine incorporation into DNA. This enhancement was additive with that due to EP, but appeared earlier. Thymidine labelling indices of liver cells were not changed by ECM in vitro. Serum from polycythaemic animals limited haem synthesis by EP stimulated foetal liver cells in vitro. These observations provide evidence for susceptibility of foetal liver erythroblasts to negative feedback control of differentiation, dependent on the concentration of circulating erythrocytes. Characteristic changes in kinetics of prenatal erythropoiesis in vivo can also be related to increasing erythrocyte concentration.
The effect of synchronous and asynchronous egg transfer on foetal weight in mice selected for large and small body size
Authors: Aitken R. J. , Bowman P. , Gauld I. 
Published: April 2021

ABSTRACT
The weight difference between large, small and unselected strains of mice were maintained when blastocysts of each genotype were transferred to unselected control recipients, suggesting that foetal genotype was an important factor in determining prenatal body size. The asynchronous transfer of large, small and unselected embryos resulted in a highly significant (P &lt; 0·001) elevation of foetal weight compared with synchronously transferred groups, genetically small mice attaining a foetal weight greater than the normal large strain. This result suggested that foetal genotype did not limit the capacity of each strain for prenatal growth. It is postulated that foetal genotype exercises its control over embryonic growth by affecting the state of embryonic development at implantation.
Pattern and polarity of sclerites in adult abdominal segments of Calliphora erythrocephala (Diptera): anlage rotation experiments
Authors: Pearson M. J. 
Published: April 2021

ABSTRACT
The anlagen of imaginal histoblasts in the abdominal segments of Calliphora (higher Diptera) present an interesting problem, which bears on recent concepts employed in the consideration of spatial patterning in insects. They differ from imaginal discs with respect to larval organization and activity, and in the absence of the progressive pattern of genetic determination during the larval period, characteristic of imaginal discs. How is the adult pattern in the abdominal segments determined?
The experiments presented here seek to clarify the spatial parameters involved in control of adult pattern and polarity in the adult segment. A series of 180° rotations of hypodermal grafts bearing the anlagen singly, or in combination, or of larval intersegmental hypodermis, indicate that polarity is determined within the anlagen, through interaction with local larval epidermis either before or during histoblast migration. The nature of the sclerites, too, is primarily carried by the anlagen rather than determined by intersegmental information.
The whole question of ‘determination of polarity’ is set out more carefully than hitherto in the light of (a) observations of the movement of epidermal cells in other systems in response to disturbance of pattern, and (b) the obvious vectorial nature of the phenomenon, which cannot be a genetic matter, but one of cell axes and of the relation of cells to segment/organism.
The demonstration that (i) hemitergite and hemisternite are primarily determined by the anlagen themselves, and not by larval intersegmental membranes; and (ii) evidence indicates an influence of epidermal cells of the larva on the differentiation (as well as polarity) of imaginal histoblasts, leads to the conclusion that neither of two models considered will account for the establishment of the adult abdominal pattern among the histoblasts at metamorphosis. These models are (a) of a segmental gradient, set by the intersegmental boundaries of the previous instar, to which imaginal cells respond by interpretation of positional information; and (b) of progressive compartmentalization of pattern within the anlagen, without reference to epidermal context.
An experimental investigation into the early development of the chick elbow joint
Authors: Holder N. 
Published: April 2021

ABSTRACTThe theory that differential growth of opposed chondrogenic centres is important in early joint formation has been tested experimentally by removing structures in relation to the chick elbow joint. The humerus and its cap of differentiating joint cells were found to develop independently of structures distal to them. Removal of the presumptive joint region at early stages resulted in fusion of the humerus with the radius and ulna. Results are discussed in terms of concepts concerning pattern formation of cell types in the early wing-bud.