bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chromosomal changes associated with changes in development
Authors: Bostock Christopher J. 
Published: April 2021

ABSTRACT
In the past there has been a tendency to dwell on aspects of chromosomes which stress constancy of structure, number and content; even to the extent of dismissing exceptions as ‘aberrations’ or ‘oddities’. It is now becoming clear that genomes can be quite plastic, and that structural changes to chromosomes are an important and often necessary part of normal differentiation and development. Elimination of whole chromosome sets or defined portions of genomes is not uncommon and selective gene amplification has been shown to be part of normal development in both protozoa and higher organisms. Chromosomal rearrangements are now a well-documented feature of normal development of, for example, B- and T-lymphocytes and trypanosomes. Transposable elements, whose mobility may not be part of normal developmental processes, can have marked effects on development if their transposition takes them to developmentally important genes. This article reviews some of the structural changes that occur during normal development, and discusses some of the consequences for development when the mechanisms which bring about these rearrangements go wrong.
A programme for the construction of a lambda phage
Authors: Brammar W. J. , Hadfield C. 
Published: April 2021

ABSTRACT
Infection of a sensitive host by the lambdoid coliphages can cause death of the bacterial cell by lysis or can lead to a lysogenic cell, with the viral DNA stably integrated into the host chromosome. These alternative responses both require the coordination of several host and phage functions, and lambda infection follows a well controlled developmental plan. The lytic and lysogenic pathways of lambdoid infection are reviewed, with emphasis on the variety of control mechanisms involved in the commitment to a particular pathway.
The cellular dynamics of pattern formation in the eye of Drosophila
Authors: Tomlinson Andrew 
Published: April 2021

ABSTRACT
The establishment and early development of the ommatidial bundles in the presumptive eye of Drosophila have been investigated using electron microscopic serial sectioning. A progression of developmental stages has been characterized. Initially simple, symmetrically constructed bundles develop into asymmetrical, more complex constructions. Computer graphic reconstruction has been used to show the three-dimensional structure of the various ommatidial bundles. Autoradiography has been used to locate the position of a region of cell division which is intimately associated with the formation of the ommatidial bundles.
Neural induction: embryonic determination elicits full expression of specific neuronal traits
Authors: Duprat A. M. , Kan P. , Gualandris L. , Foulquier F. , Marty J. , Weber M. 
Published: April 2021

ABSTRACT
In Pleurodeles waltl, the early neuronal differentiation of precursor cells from late gastrula stage has been studied by culture in vitro from either isolated neural plate (NP) or isolated neural fold (NF).
The aim of this study was to delineate the information acquired by ectodermal target cells during neural induction. By culturing these cells in vitro either with or without the underlying chordamesoderm, we showed that in the absence of chordamesodermal influence such NP or NF cells exhibited a high degree of biochemical and morphological differentiation as revealed by the synthesis and the storage of neurotransmitters, the activity of specific enzymes, as well as by the expression of neuronal markers: specific changes in cell surface carbohydrates, tetanus toxin binding sites and neuro filament polypeptides. Remarkable changes in the cell adhesive properties were the first events observed in the different central (NP) and peripheral (NF) types.
In cocultures the chordamesodermal cells exert a beneficial influence on this differentiation, specially increasing acetylcholine synthesis. There are some differences between central (NP) or peripheral (NF) neuroblast response to this further notochord or mesodermal influence.
Recent advances in our understanding of the temporal control of early embryonic development in amphibians
Authors: Satoh Noriyuki 
Published: April 2021

ABSTRACT
Recent studies on temporal control of early amphibian development are reviewed. It is becoming clear that the development of an embryo is not timed by a single clock set in motion at fertilization, instead each developmental event seems to be timed by its own clock-like mechanism. The timing of developmental events is rigidly determined within embryonic cells, and usually can not be altered experimentally. One exception, however, is the timing of midblastula transition in amphibian embryos; recent studies have shown that its timing is regulated by the nucleocytoplasmic ratio. Several developmental events, particularly those associated with transcriptional activities, require DNA replication prior to their occurrence, suggesting an intimate relationship between DNA replication cycles and their onset. On the other hand, there are many other developmental events where timing is not controlled by the number of cell divisions, DNA replication cycles, or the nucleocytoplasmic ratio. Cytoplasmic machinery with autonomous oscillatory properties is thought to be involved in the timing of these events.
Single cell analysis of commitment in early embryogenesis
Authors: Heasman Janet , Snape Alison , Smith Jim , Wylie Christopher C. 
Published: April 2021

ABSTRACTFate maps of amphibian embryos tell us the destination of certain areas at later stages of development. After studying Vogt’s fate maps, Spemann wrote (in 1938) that “the question which at once calls for an answer is whether this pattern of presumptive primordia in the beginning gastrula is the expression of a real difference of these parts, whether they are already more or less predestined or ‘determined’ for their ultimate fate, or whether they are still indifferent and will not receive their determination until a later time.” Until recently answers to this question have relied upon explant experiments, which indicate that by the late blastula stage ectoderm, mesoderm and endoderm regions are distinctly determined. By using a method involving single cell labelling and transplantation, it is now possible to pinpoint more accurately the time during early embryogenesis at which individual blastomeres become committed. In the vegetal pole, determination towards endoderm is a gradual process beginning during the middle blastula stage (stage 8) and completed by the beginning of gastulation (stage 10). This method offers the possibilities of comparing the committed and the uncommitted state and studying at a molecular level the mechanisms of cell determination.
Inductive interactions in early amphibian development and their general nature
Authors: Nieuwkoop P. D. 
Published: April 2021

ABSTRACTAfter a short discussion on cell interactions in general and inductive interactions in particular, the almost completely epigenetic nature of amphibian development is emphasized.In the symmetrized egg undergoing cleavage a large-scale inductive interaction occurs which leads to the formation of the meso-endoderm. Meso-endoderm formation gives rise to the morphogenic process of gastrulation. In the ensuing triple-layered embryo inductive interactions are strongly enhanced. The following large-scale inductive interaction leads to the formation of the neural anlage. This is again followed by the morphogenetic process of neurulation or neural tube formation. Subsequent interactions between the germ layers of the triple-layered embryo give rise to the formation of the regional pattern of organ anlagen. Finally, the most promising approaches to the nature of inductive interactions for mesoderm and endoderm formation are discussed.
Towards understanding paternal extragenic contributions to early amphibian pattern specification: the axolotl ts—1 gene as a model system
Authors: Malacinski George M. , Barone Dorothy 
Published: April 2021

ABSTRACT
As a model system for understanding the role sperm extragenic components might play in early embryogenesis the genetics and phenotype of the ts—1 axolotl (Ambystoma mexicanum) mutant gene are reviewed. That mutant gene displays parental effects. It exhibits both maternal (egg-mediated) as well as paternal (sperm-mediated) phenotypic effects. A variety of possible modes of action of the ts—1 gene are reviewed. Comparisons of various precedents to the ts—1 genetic data are made. In addition, novel models which account for the ts—1 phenotypic data are presented.
The Development of the Phagocytic Activity of the Reticulo-endothelial System in the Chick
Authors: Kent Rosalind 
Published: April 2021

ABSTRACT
The embryonic development of the ability of some cells to undertake ex-tensive phagocytosis has been studied in the chick embryo using the particulate materials ‘Thorotrast’ and colloidal silver (Ag110). Extensive phagocytosis of Thorotrast particles by the embryo chick and the young chicken takes place in the liver and spleen and to some extent in the lung, bone-marrow, and areolar connective tissue of the mesenteries and body-wall, uptake in the latter being more evident in cases of larger doses. In addition, the embryo chick takes up Thorotrast in the mesodermal part of the yolk-sac wall. In the embryo chick rapid and extensive uptake of particulate matter does not occur until the main centres of the reticulo-endothelial system have been differentiated. Particles taken up by the yolk-sac wall of the embryo chick disappear after hatching. The exact mechanism involved has not yet been established.
The Onset and Maturation of the Graft versus Host Reaction in Chickens
Authors: Solomon J. B. 
Published: April 2021

ABSTRACTThe increase in wet weight of the host spleen following implantation of competent chick, juvenile or adult chicken spleen has been shown to be paralleled by increases in dry weight and in content of RNA, DNA, and protein. No increase in the spleen-weights of the hosts was found when non-competent spleen cells from chick embryos or 1-day-old chicks were used as donor. The onset of immunological competence with respect to this transplantation reaction has been shown to occur at about 5 days post-hatching when the spleens were implanted into embryos at 8 days of incubation and the host spleens removed 10 days later. The ability of chicken spleen cells to evoke hepatomegaly and splenomegaly of the embryo hosts increased with age and was greatest after 21 weeks of age. Sometimes a reduction in whole body-weight of the embryo hosts also occurred. Although no sex differences in host spleen-weight were observed when 8– 15-day-old male chick spleens were used as grafts, a significant increase in female host liver- and spleen-weights (compared with those of the male hosts) was noted when 8–21-day-old female chick spleens were used as grafts. Spleen cells from male chickens of 6–17-weeks old did not produce much greater splenomegaly than those from young chicks and there were no sex differences between the host embryo spleen-weights. However, when female spleen tissue from 6-to 20-week-old chicks was used as graft a significant increase in the hepatomegaly and splenomegaly of the female hosts above those in the male hosts was observed. No sex differences were obtained in embryo host spleen-weights when small implants of adult male or female spleen cells were used as grafts. Thymus, liver, and bone-marrow from competent donors have been found to be nearly as effective as spleen in producing splenomegaly of the embryo hosts.
The Two-gradient Hypothesis in Primary Induction. The Combined Effect of Two Types of Inductors Mixed in Different Ratios
Authors: Saxén Lauri , Toivonen Sulo 
Published: April 2021

ABSTRACT
On the basis of certain earlier suggestions made by Lehmann (1950) and Yamada (1950), together with our own experimental data, a modification of the two-gradient hypothesis of primary induction was presented by us some years ago (Toivonen & Saxén, 1955). Subsequently, this theory has often been referred to, accepted or criticized, and even misunderstood. There may thus be reasons for discussing it in the light of some recent experimental data.
The Differential Growth-response of Embryonic Chick Limb-bone Rudiments to Triiodothyronine in vitro
Authors: Lawson Kirstie 
Published: April 2021

ABSTRACT
The growth of the tibia and radius from 6-to 10-day-old embryos was estimated from the increase in the total nitrogen content of the rudiments. A comparison of the specific growth rates of eight limb bones showed that the bones could be arranged in the following order of diminishing specific growth rate: tibia, third metatarsus, femur, ulna, humerus, third metacarpus, radius, fourth metacarpus. If the small bones were arranged in order of the percentage growth of their rudiments in vitro, the sequence found in various media was the same as that of their specific growth rates in vivo. A comparison of the growth-promoting properties of various biological media showed that the best growth and differentiation occurred on a plasma and embryo extract clot. The growth-promoting properties of the extract were greatly enhanced in a plasma clot with which the fibroblasts of the explant, through their abundant outgrowth, were in intimate contact. In the absence of extract there was no difference between the growth of rudiments in contact with the clot or supported by lens paper floating on serum. The order of a series of bones arranged according to their growth response to T3 in a medium of plasma and embryo extract was the same as their order when arranged according to their specific growth rate in vivo: the growth of potentially fast-growing bones was reduced by T3, that of slowly growing bones was increased. The growth rates in vitro of different rudiments were varied by altering either the composition of the medium or the incubation temperature, but the rudiments continued to respond differentially to T3. The characteristic differences in the relative growth of the different bones when not treated with T3 were maintained under these conditions.
Les effets de la succion de l’un des deux premiers blastomères de l’œuf de Grenouille (Rana temporariaetRana escalenta)
Authors: Milaire par J. 
Published: April 2021

ABSTRACTLa destruction d’un blastomère au début de la segmentation de l’œuf d’Amphibien est l’une des plus anciennes opérations de l’embryologie expérimentale. Après les premières tentatives de Roux, A. Brachet (1904) répéta cette expérience en détruisant au moyen d’une aiguille chauffée, l’un des deux premiers blastomères de l’œuf de grenouille rousse. Les résultats obtenus ont conduit l’auteur à démontrer le développement normogénétique du blastomère sain et à établir l’existence d’une relation constante entre le plan de symétrie bilatérale de l’œuf fécondé et celui de l’embryon quelle que soit l’orientation du premier plan de segmentation.
Transfer of Primordial Germ-cells in Xenopus laevis
Authors: Blackler A. W. , Fischberg M. 
Published: April 2021

ABSTRACT
A technique is described whereby the so-called primordial germ-cells of X. laevis, together with some accompanying non-germinal cells, may be grafted from one embryo to another at the neurula stage. A nuclear marker enabled graft cells to be identified. Some cells from the graft migrate into the host gonads and there form functional gametes. It is concluded that primordial germ-cells actually exist in neurula stages, that these cells are probably identical with the so-called primordial germ-cells described in histological studies, and that they are directly ancestral to at least some of the definitive eggs and sperm.
The Arrangement of Bristles inDrosophila1
Authors: Smith J. Maynard , Sondhi K. C. 
Published: April 2021

ABSTRACTThe bristles of Drosophila fall into two classes, the microchaetes which are small, numerous, and which vary in number from individual to individual, and the macrochaetes, which are larger, fewer in number, and constant in arrangement within a species, although many mutants which alter their number are known. Variations in the arrangement of macrochaetes in populations of D. subobscura homozygous for the mutant ocelli-less are interpreted in terms of variations in a ‘prepattern’ determining the positions of the bristles, and of the competence of cells to respond to this prepattern by forming bristles. A process whereby such a prepattern may develop is described. It is argued that the arrangement of the microchaetes is determined by a similar process, differing only in that it is less accurately regulated. Mechanisms which may increase the accuracy of prepattern formation are discussed.
The contribution of the primitive streak to the somites in the avian embryo
Authors: Ooi V. E. C. , Sanders E. J. , Bellairs R. 
Published: April 2021

ABSTRACT
Chick embryos were removed from the egg at stages 6–11 and explanted in culture. The greater part of the postnodal primitive streak of each embryo was replaced with a similar region taken from a corresponding quail embryo. The reciprocal experiment was also carried out, chick primitive streak being grafted in place of quail. After further incubation, the grafted primitive streak cells were found to contribute to lateral plate mesoderm, somites and intermediate cell mass. In an additional series of experiments, the postnodal primitive streak was extirpated and the embryo allowed to heal without a graft being inserted; after further incubation, many more somites formed in these embryos. It is concluded therefore that the contribution of cells from the primitive streak shown in the first experiment may not be essential for somite formation. It is suggested moreover that two major morphogenetic movements are taking place simultaneously in the mesoderm during this period: one is the mediolateral migration of cells after ingression through the streak, whilst the other is an anteroposterior movement associated with regression.
A study on the pattern of prospective somites in the presomitic mesoderm of mouse embryos
Authors: Tam P. P. L. 
Published: April 2021

ABSTRACT
Consistently six to seven somites were formed in explants of presomitic mesoderm of 8·5-day to 11·5-day mouse embryos and this number correlated well with the number of somitomeres previously identified in the same tissue by stereo SEM (Tam, Meier & Jacobson, 1982). During this period of development, the size of the presomitic mesoderm varied up to two-fold but the number of prospective somites remained unchanged. This pattern in the presomitic mesoderm was stable with respect to the number and the position of somites that were formed, the cranio-caudal sequence and the rate of segmentation. The prospective somite also went through an orderly sequence of expansion and cellular rearrangement prior to segmentation. During the differentiation of the presomitic mesoderm, somites were formed at the expense of somitomeres, suggesting that the somitomere was a morphological manifestation of the prospective somite.
Chimaerism of primordial germ cells in the early postimplantation mouse embryo following microsurgical grafting of posterior primitive streak cells in vitro
Authors: Copp Andrew J. , Roberts Heather M. , Polani Paul E. 
Published: April 2021

ABSTRACT
A microsurgical grafting technique has been used to introduce primordial germ cell (PGC) precursors into intact primitive-streak-stage mouse embryos in vitro. Operated embryos were cultured for 36–40 h and then analysed by a combined histochemical and autoradiographic method. PGC chimaerism occurred in embryos that received grafts of caudal primitive streak cells but not adjacent embryonic endoderm or anterolateral ectoderm/mesoderm cells. Graft-derived PGCs were found to be migrating through the gut endoderm alongside host-derived PGCs in approximately half of the chimaeric embryos whereas in the other 50 % of cases PGCs remained at the site of grafting in association with graft-derived somatic cells. A similar pattern of somatic chimaerism was produced by primitive streak and anterolateral ectoderm/mesoderm grafts: the allantois was colonized predominantly, with, in addition, formation of amnion, surface ectoderm and caudal mesoderm in a few embryos. The majority of embryonic endoderm grafts failed to incorporate into host embryos and formed yolk-sac-like vesicles.
The findings of this study indicate that (a) PGCs originate from the embryonic ectoderm via the primitive streak during development of the mouse embryo, and (b) anterolateral ectoderm and mesoderm cells are unable to form PGCs after heterotopic grafting to the posterior primitive streak site. The combined microsurgical and embryo culture methods provide an experimental system for the analysis of PGC development in intact mouse embryos.
Timekeeping by frog embryos, in normal development and after heat shock
Authors: Elsdale Tom , Davidson Duncan 
Published: April 2021

ABSTRACT
Timekeeping refers to the uniformity of development in time. The precision of timekeeping is measured by the extent to which embryos, within an initially synchronous population, come to diverge in the course of their development. Divergence is measured as the variation in the stage of development reached between embryos allowed to develop for a fixed period of time. The lower the variation the better the timekeeping. Divergence among frog embryos that started development at the same time is hardly measurable after approx. 100 h of development. This striking uniformity indicates good timekeeping. Timekeeping is not impaired among the survivors following heat shocks that retard development and disturb and curtail morphogenesis. The immediate effect of heat shock is a stoppage of development, the duration of which is the same for all embryos in the same treatment batch. The embryos react to heat shock by rescheduling their development with the interpolation of a rest, the duration of which is controlled to the same precision as normal development. The postponement of development, without impairment of timekeeping, implies dis-engagement of the processes of morphogenesis from, and their subsequent re-engagement with, an enduring ratedetermining activity unaffected by heat shock. We have searched for embryos whose rate of development was disturbed by heat shock to run slower or faster than the norm. We have found none. It seems that the (temperature-compensated) rate of development is invariant up to the moment of failure, or a change is immediately lethal.