bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell death during the formation of tubular heart of the chick embryo
Authors: Ojeda J. L. , Hurle J. M. 
Published: April 2021

ABSTRACT
Light and electron microscopical examination of the heart of the chick embryo between stages 9 and 11 (Hamburger & Hamilton) revealed degenerating and dead cells specifically localized in the midline of endocardial tubes. The morphology of cell death in this system does not differ from that described in other embryonic tissues and organs. Phagocytosing cells are rarely seen.
The results of this study show that a destruction of midline cells of both endocardial tubes takes place during the fusion of heart anlages. The possible roles of this cell death in the morphogenesis of the tubular chick heart are discussed.
An analysis of the spatial distribution of ciliary units in a ciliate, Euplotes minuta
Authors: Frankel Joseph 
Published: April 2021

ABSTRACT
Six to eleven longitudinal ciliary rows are arrayed over the dorsal surface of the ciliate Euplotes minuta. Forty-two to 129 ciliary units are distributed among these rows. The number of rows depends on genotype, clonal age, and vegetative ancestry, while the total number of units is controlled partly by the number of rows and also by the separate action of genetic and environmental factors. The pattern of distribution of units among different rows of non-dividing cells can be analysed on the basis of the percentage of the total unit complement of the cell that is found in each individual row. If the assumption is made that ciliary rows are uniformly spaced over a dorsal field whose width is independent of the number of rows, then it can be shown that units are distributed among rows according to a relatively invariant spatial pattern. The form of this pattern remains the same in the face of variation in the absolute number of rows and of units. Prior to cell division new units develop anterior and posterior to old units situated within the equatorial zone of each row. About one-half of the original units are included within this zone. The cell fission line develops within this zone such that the total number of units passed to the anterior and posterior division products are about equal. The pattern according to which units of different zones (proliferating and non-proliferating) are distributed among different rows has been mapped in cells that have completed the process of proliferation of units but have not yet completed cell division. The results of this mapping show that the pattern of distribution of units in the equatorial zone at the conclusion of proliferation is not the same as the overall pattern in non-dividing cells. Further analysis indicates that the geometry of proliferation can be most simply represented as a result of two superimposed processes, one of which is the recruitment of old units into the zone of proliferation, while the other is the intensity of proliferation, i.e. the number of new units formed adjacent to each old unit. Both recruitment and intensity have constant values in the central region of the dorsal field, while recruitment is higher and intensity lower near both margins. The recruitment and intensity distributions are mutually nearly reciprocal, with slight asymmetries that formally account for the more dramatic asymmetry of the pattern of non-dividing cells. A dualistic hypothesis is formulated for the control of the formation of new ciliary units within ciliary rows. The position of each new unit is largely controlled locally in relation to pre-existing units, while the decision of whether or not new units will develop at all, and how many will be formed, depends on superimposed positional systems operating within the context of the entire dorsal surface.
On the origin of haemopoietic stem cells in the avian embryo: an experimental approach
Authors: Dieterlen-Lievre Françoise 
Published: April 2021

ABSTRACT
It is currently accepted that stem cells of the definitive blood cell lines originate from the yolk-sac blood islands. Experiments were devised to examine the validity of this theory in the avian embryo. These involved grafting two-day-old quail embryos on to chick yolk-sacs of comparable developmental stages, i.e. before or shortly after the establishment of vascularization. The conclusions of the experiments are based on the possibility of distinguishing chick cell nuclei from those of the quail.
In the developing haemopoietic organs (spleen and thymus) of quail embryos grafted on to the chick and subsequently incubated for 6 – 11 days, all cells, whether belonging to the granulopoietic, erythropoietic or lymphopoietic series, are of quail type. Thus these organs have not been colonized by chick stem cells.
On the other hand, coelomic graft experiments show that the development of these organs is indeed dependent on an extrinsic colonization by haemopoietic cells; quail spleen or thymus rudiment, developing in the coelom of a chick, is populated by chick cells. Thus no incompatibility which would prevent heterospecific colonization exists in this system.
It is concluded that haemopoietic stem cells of the definitive blood cell series originate from some source other than the yolk-sac, and that this source must be intra-embryonic.
Development of parthenogenetic and fertilized mouse embryos in the uterus and in extra-uterine sites
Authors: Iles S. A. , Mcburney M. W. , Bramwell S. R. , Deussen Z. A. , Graham C. F. 
Published: April 2021

ABSTRACTMouse eggs were activated with hyaluronidase in vitro and subsequently transferred to the oviduct. In the female reproductive tract they formed morulae and blastocysts which died soon after implantation. Haploid blastocysts were transferred beneath the kidney capsule and here some formed disorganized egg-cylinder structures in a week. Morulae and blastocysts from haploid and diploid parthenogenones were also transferred beneath the testis capsule. Two to four months later the growths which had formed were sectioned. They contained neural tissue, pigment, keratinized epithelium, glandular epithelium, ciliated epithelium, cartilage, bone, muscle, adipose tissue, and haemopoietic tissue. The range of cell types was similar to that produced by fertilized control blastocysts except that the parthenogenones did not form identifiable yolk-sac carcinoma or embryonal carcinoma cells.The growths from haploid and diploid parthenogenones in the testis were stained with Feulgen and their DNA content measured. Growths from diploid embryos contained the normal diploid amount of DNA while growths from haploid embryos contained less than this amount. Cell cultures were prepared from the growths. The cells which were investigated contained no Y chromosome, suggesting that they were derived from the embryonic cells rather than the cells of the male host. These cells contained a near diploid chromosome number, although some of them were originally derived from haploid embryos.
Morphogenèse de l’autopode chez l’embryon de poulet
Authors: Pautou Marie-Paule 
Published: April 2021

ABSTRACTObservations were made on chick embryo feet between 6 and days of incubation in order to (a) give a precise description of programmed cell death in the interdigital membranes; (b) correlate the evolution of interdigital necrosis with the differentiation of the cartilaginous phalangeal skeleton; (c) measure the relative growth rates of digits and interdigits.The programme of interdigital cell death proceeds in three phases which comprise the appearance, the extension and the disappearance of necrotic areas. Fourteen distinct stages are described.The evolution of programmed cell death can be strictly correlated to the chondrogenesis of successive phalanges, in the sense that each stage of necrosis (except two of them) differs from the preceding one by the differentiation of an additional phalanx.Shaping of the foot results from differential growth rates and proceeds in three phases, the second of which is characterized, between days 8 and 10 of incubation, by the actual shortening (decrease of absolute length) of the interdigital membranes.These observations are compared to those that were previously made on other avian and mammalian species and the morphogenetic role of programmed cell death is discussed in the light of that comparison.
The development of the notochord in the chick embryo, studied by scanning and transmission electron microscopy
Authors: Bancroft Mary , Bellairs Ruth 
Published: April 2021

ABSTRACTThe notochord of the chick embryo between stages 5 and 23 inclusive has been studied by scanning electron microscopy, supplemented by transmission electron microscopy. Three main phases of development are described, and these have been designated: bilaminar; rod-like, unvacuolated; rod-like and vacuolated. The change in shape of the organ from bilaminar to rod-like is accompanied by changes in the shape, orientation and position of the cells, an increase in the complexity of the cell contacts, and the laying down of a basal lamina. The change from the unvacuolated to the vacuolated phase is accompanied by increasing complexity within the cytoplasm. Most of the vacuoles are intracellular and appear empty though some contain a granular material. The notochordal sheath appears to be secreted by the notochordal cells and fine fibrillar material has been seen in the intercellular spaces. By stage 23, most of the notochordal cells have become so highly vacuolated that the cytoplasm has become closely packed around the nucleus.
Foetal and placental ornithine decarboxylase activity in the rat - effect of maternal undernutrition
Authors: Williams John P. G. , Mcanulty Peter A. 
Published: April 2021

ABSTRACTThe activity of the enzyme ornithine decarboxylase and the accumulation of nucleic acids were examined in the rat foetus and placenta during normal development and during maternal undernutrition.Maternal undernutrition resulted in a reduced rate of increase in weight of both the foetus and placenta towards the end of gestation. In the placenta the failure to increase in weight was accompanied by a failure of DNA to increase. In the foetus the amount of DNA failed to increase over a short period and then made a compensatory response to return to a normal amount by the end of gestation. Undernutrition failed to affect RNA in either the foetus or placenta. These results differ from those obtained during maternal protein deficiency.The activity of foetal and placental ornithine decarboxylase was normal during much of gestation in the undernourished group. However, at the same time as the compensatory increase in foetal DNA, there was a marked increase in enzyme activity in both tissues. It is suggested that a single compensatory stimulus is responsible for the changes in both ornithine decarboxylase and DNA.
Comparison of growthin vitroandin vivoof post-implantation rat embryos
Authors: New D. A. T. , Coppola P. T. , Cockroft D. L. 
Published: April 2021

ABSTRACTRat embryos explanted at early head-fold stage and grown in vitro by improved culture methods were compared with littermates in vivo. Very similar rates of growth and differentiation were obtained over a period of 48 h, while the embryos developed to around the 25-somite stage.
Investigation of inner cell mass determination by aggregation of isolated rat inner cell masses with mouse morulae
Authors: Rossant J. 
Published: April 2021

ABSTRACTInner cell masses (ICMs) dissected from -day rat blastocysts were aggregated with -day mouse morulae. Successful aggregates formed blastocysts in vitro and morphologically normal -day conceptuses in the mouse uterus. Immunofluorescent analysis of these conceptuses revealed that rat cells were only present in the embryonic ectoderm and endoderm and never in the trophectoderm derivatives, although rat trophoblast did develop in the mouse uterus in various control experiments. The single-cell resolution of this technique extends the results obtained from aggregating mouse ICMs with mouse morulae and provides strong evidence that ICM cells, although not overtly differentiated, are determined by the blastocyst stage.
Incorporation of tritiated cytochalasin B into ectodermal explants of the amphibian gastrula
Authors: Perry M. M. , Selman G. G. , Jacob J. 
Published: April 2021

ABSTRACTEctodermal explants from gastrulae of Trituras alpestris were exposed to tritiated cytochalasin B (5 and 10 μg/ml) for . The flat explants failed to heal into compact spheres and the component cells gradually rounded up. Radioactivity in the fixed and sectioned material was analysed by light and electron microscopic autoradiography. Silver grains were found predominantly over the yolk platelets, but were also scattered over other cellular components. Areas containing pigment granules or the feltwork material, present in the apices of dissociating cells of the superficial layer, exhibited higher activity than areas containing mitochondria or cytoplasmic matrix. Lipid droplets and nuclei showed comparatively little activity. The results are discussed in relation to previous findings on the uptake of tritiated cytochalasin D by cell fractions.
Postimplantation development of blastomeres isolated from 4- and 8-cell mouse eggs
Authors: Rossant J. 
Published: April 2021

ABSTRACTBlastomeres isolated from 4- and 8-cell mouse eggs were inserted into empty zonae and transferred to the oviduct. The products of both types of blastomere were capable of inducing decidual formation. One implant produced by an isolated blastomere from a 4-cell egg contained a small, retarded embryo at days but most decidua from blastomeres of either 4- or 8-cell eggs contained only a few trophoblast giant cells. It is suggested that this lack of totipotency is due to insufficient cells being present at cavitation rather than restriction in developmental potential.
Polarity and gradients in lepidopteran wing epidermis: II. The differential adhesiveness model: gradient of a non-diffusible cell surface parameter
Authors: Nardi James B. , Kafatos Fotis C. 
Published: April 2021

ABSTRACTFor explaining the Manduca wing gradient (Nardi & Kafatos, 1976) a model which postulates a proximo-distal gradient in cellular adhesiveness is considered. The model is based on Steinberg’s (1963) differential adhesiveness hypothesis. Rosette formation in certain transposed and/or reoriented grafts can be adequately explained by this model. Several predictions, formulated by using the concept of surface free energy as a thermodynamic measure of adhesiveness, have been tested and proven correct. (1) Transposed grafts tend to assume circular forms, which are configurations of minimum free energy. (2) Because of the pressure difference expected across the interface of two cell populations with different surface free energies, cell densities increase in both distally and proximally transposed grafts. As a corollary to this rule, final size of a graft is a function of its distance from the original position. (3) Histological sections of host-graft boundaries suggest minimal cell contact at the interface. In proximal grafts placed in distal regions, cell density is far lower near the host-graft interface, as compared to the high interior density; the peripheries of distal grafts do not show this effect. (4) Juxtaposition of three different wing regions in all possible arrangements yields the expected two-dimensional configurations. (5) Differences in adhesiveness can be demonstrated by allowing two different wing grafts to interact in an essentially neutral environment (i.e. at a leg or antenna site). As the distance between two given graft regions increases, the extent of their final contact decreases.When applied to other insect systems, the model not only offers an alternative interpretation for results currently explained by diffusible substance models, but also accounts for certain features that were unexplained by other models.
Injected nuclei in frog oocytes: fate, enlargement, and chromatin dispersal
Authors: Gurdon J. B. 
Published: April 2021

ABSTRACTA method is described by which nuclei associated with some cytoplasm can be rapidly prepared from a suspension of cells. The method involves the use of lysolecithin and bovine serum albumin.Oocytes of Xenopus laevis were injected with about 200 nuclei prepared from human HeLa cells by this method. Nuclei were deposited in oocyte cytoplasm, in the oocyte nucleus, or in the dispersed contents of a ruptured oocyte nucleus.Injected HeLa nuclei enlarge up to several hundred times in volume in the course of a few days. Their enlargement is associated with chromatin dispersion, increased binding of an acidic dye, and with the reduction in size, and eventual disappearance, of nucleoli. The amount of HeLa nucleus enlargement is much greater when the oocyte nucleus is ruptured. The fate of injected nuclei was followed by the use of HeLa nuclei whose DNA had been previously labelled with [3 H]thymidine. Labelled DNA does not pass from injected HeLa nuclei into the oocyte nucleus. Injected nuclei appear not to fuse with each other or with the oocyte nucleus.Nuclei prepared by the above method look morphologically healthy in oocytes cultured in vitro for up to one month after nuclear injection. Nuclei prepared by other methods, such as those involving the use of detergents, undergo deterioration within a few days after injection into oocytes.
Patterns of lactic dehydrogenase isozymes in mouse embryos over the implantation periodin vivoandin vitro
Authors: Monk Marilyn , Ansell John 
Published: April 2021

ABSTRACTFollowing blastocyst implantation, or outgrowth in vitro, the LDH isozyme pattern changes from that of the maternally inherited B subunit isozyme form (LDH-1) to a pattern dominated by A subunits (Auerbach & Brinster, 1967, 1968). In preimplantation embryos we have also observed additional isozyme bands, as yet unidentified. An analysis of the pattern of newly synthesized LDH isozymes and specific activity of LDH in different regions of early post implantation embryos suggests that there is a sequential activation of A and B subunits, and that activity first appears in ICM-(inner cell mass) derived tissues and then in trophoblast-derived tissues. In vitro, in the absence of ICM cells, the transition of LDH-isozyme pattern does not occur in outgrowing trophoblast giant cells. This suggests a possible inductive interaction between ICM and trophoblast.
Determination of anteroposterior polarity in the axolotl forelimb by an interaction between limb and flank rudiments
Authors: Slack J. M. W. 
Published: April 2021

ABSTRACTIt is shown that the mesoderm in the prospective forelimb-bud of the axolotl embryo is thickened and divided into somatic and splanchnic layers, while that of the flank is thinner and undivided. The first sign of the limb-bud itself appears at stage 38. A whole, a half or a third of a limb rudiment can develop into a normal or reduplicated limb when transplanted to the flank. An anterior half of a limb rudiment fails to develop when transplanted to the head but will do so if accompanied by a small piece of flank tissue. Small pieces of tissue from a wide area of the flank will cause reduplication of the fore-limb if grafted to the anterior margin of the rudiment. It is shown that the whole of the reduplication is formed from host tissue and has the morphological character of the host. Reduplications have posterior structures arranged symmetrically on both sides of the midline. Both muscles and cartilages are duplicated. It is suggested that the same interaction between prospective flank and limb is responsible for the capacity for growth on the head, the induction of reduplications and the formation of the anteroposterior pattern of the limb in normal development. A simple rule is proposed which explains the occurrence of reduplications in classical work on the amphibian limb.
On the Embryology of the Isopod Irona1
Authors: Nair S. Gopalakrishnan 
Published: April 2021

ABSTRACT
The structure of the egg is described. Segmentation of the egg is followed from the eight-celled stage up to the formation of the blastoderm. A migration of blastomeres from one pole of the egg towards the opposite has been observed and in the course of this migration a circle of 10-11 cells moves in front of the others. Gastrulation takes place by immigration. A V-shaped mesodermal headband is differentiated which gives rise to the rudiments of the naupliar appendages after gastrulation is completed. The entire post-naupliar region of the body is formed by the activity of ectodermal and mesodermal teloblasts. No caudal furrow is formed. The gut is ectodermal, formed by the union of the stomodoeum and a long proctodoeum. An ectodermal dorsal organ forms in early development and persists throughout embryonic life. The pre-antennulary mesodermal strands become attached to this organ. The origin, development, and derivatives of the pre-antennulary mesodermal somites are described. The origin of the liver is traced from the naupliar mesoderm. The probability that the liver plays an important part in yolk absorption is discussed. The development of the trunk mesoderm and an early grouping of cells into segmental and intersegmental regions are described. The formation of the heart, pericardium, and dorsal aorta is described.
The Selective Transport of Antibodies from the Yolk Sac to the Circulation of the Chick
Authors: Brierley Joan , Hemmings W. A. 
Published: April 2021

ABSTRACT
The yolk titre of eggs laid by hens actively immune to Salmonella pullorum is directly related to the serum titre, the concentration quotient being approximately 1/8. Fowl sera immune to S. pullorum or Brucella abortus when injected into the yolk-sac early in incubation give rise to circulating titres in the chick at hatching. A technique of injection into the yolk-sac after hatching is described. Immune fowl serum so injected gives rise to circulating titres. Immune rabbit, cow, and horse sera so injected do not give rise to circulating titres. Immune pigeon serum gives rise to titres at lower concentration quotient than fowl. It is concluded that the yolk-sac splanchnopleur is selective. Fowl antibody fed by mouth after hatching does not give rise to circulating titres.
Closure of the Secondary Palate in Three Strains of Mice
Authors: Walker B. E. , Fraser F. C. 
Published: April 2021

ABSTRACT
AT the time when Peter reviewed the subject of secondary mammalian palate embryology (Peter, 1924), it had been established that the secondary palate is derived from two shelves of tissue, which originate in the dorsolateral wall of the oral cavity and grow downward toward the lower jaw, passing lateral to the tongue. The shelves subsequently come to lie in the transverse plane dorsal to the tongue, where they fuse with the nasal septum and with each other, thus forming the roof of the mouth. The problem in this sequence is how the shelves manage to reach a position dorsal to the tongue after having had the tongue tightly wedged between them. Various mechanisms postulated to explain this change of position were reviewed by Lazzaro in 1940. The theories fell into three categories: (1) external forces such as muscular pressure by the tongue, (2) growth changes involving regression of the ventral portion and an outgrowth in the horizontal plane; and (3) a rapid rotation of the shelves due to some intrinsic force. Lazzaro considered the evidence to be in favour of rapid movement, and cited the cases of embryos with one shelf vertical and the other shelf horizontal as examples of a rapid transitional stage in shelf rotation. He considered his own work to indicate a swelling in the shelves due to a considerable increase of intercellular substance in the embryo’s connective tissue. The result was visualized as a type of erection which would cause the shelves to rise when the obstacle of the tongue was removed. Lazzaro considered it universally recognized that the release of the tongue took place before anything else, even if the mechanism of release was ‘slightly obscure’. The mechanisms suggested were: (1) a lowering of the mandible and tongue, (2) a forward displacement of the tongue, (3) a lifting of the roof of the oral cavity, (4) changes in form of the tongue due to muscular development, and (5) muscular movements of the tongue.