bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Inhibitory Action of Insulin in the Early Chick Embryo
Authors: Barron Patricia , Mckenzie J. 
Published: April 2021

ABSTRACTInsulin, in varying concentrations, has been applied to the chick embryo explanted by New’s technique after 24 hours incubation at stages 3–8 and cultured for 22–24 hours in vitro. It has been demonstrated that, in whatever manner insulin is applied to the embryo, its effects are most frequently manifest in the brain and neural tube. Somites are inhibited to a much lesser extent and heart, except with the higher doses, is unaffected. Application of either sodium pyruvate or nicotinamide with the insulin has very little protective action and larger doses of both these substances potentiate the inhibitory action of insulin. Diphosphopyridine nucleotide in the oxidized form given with the insulin provides complete protection, but the reduced form of DPN has no such effect. Previous work by Spratt and others on the metabolic characteristics of the early chick embryo, by Landauer on the teratogeni caction of insulin, and recent investigations (e.g. by Randle & Smith) are considered in the light of our findings. Like Duffey & Ebert (1957) we hesitate to accept Spratt’s (1950) hypothesis for the dependence of brain on oxidative mechanisms and the heart on glycolysis. We suggest, instead, that the heart, in contrast to the brain, can if necessary survive for a period of time under anaerobic conditions but, where possible, it makes full use of aerobic metabolic pathways. The complete protection afforded by DPN but not by DPNH leads us to believe that the site of action of insulin lies in the reoxidation of the pyridine nucleotides, i.e. in a hydrogen transport system.
A Simplified Method for the Fusion of Two or More Amphibian Embryos
Authors: Hegenauer John C. , Nace George W. 
Published: April 2021

ABSTRACTThe technique of fusing amphibian embryos in parabiotic or telobiotic union has been used extensively in the past 50 years for a variety of experimental and educational purposes (see citations in Burns, 1955; Hamburger, 1942, 1960; Rugh, 1948). Failures with current techniques, however, are too frequent. These are occasioned, most commonly, by improper juxtaposition of the embryos to facilitate wound healing, by separation of the embryos as a result of ciliary action, by freeing the embryos from the operating dish prior to completion of wound healing, by damage produced in freeing the conjoined embryos, or by infection. Many of these difficulties arise because the methods of constraining the embryos in paraffin-beeswax or permoplast operating dishes obstruct the operator’s view. It is a less obvious, but important, disadvantage that this method also prevents the free flow of medium just at the time when optimal conditions are necessary for maintenance and healing. This is especially true when anesthetized embryos are conjoined.
A Cytological Analysis of the Origin of Chromaffinoblasts in Some Mammals
Authors: Smitten N. A. 
Published: April 2021

ABSTRACTTwo major facts have been established in cytological studies of cell differentia-tion in the rudiments of ganglia from the moment of their formation: In early embryogenesis there is a divergent differentiation of the originally uniform cells into neuroblastic and spongioblastic series.At later stages of embryogenesis there occurs a separation of chromaffino-blasts from the elements of the spongioblastic series.
Prolonged Life of AnucleolateXenopusTadpoles in Parabiosis
Authors: Wallace H. 
Published: April 2021

ABSTRACTAnucleolate Xenopus mutants have survived in parabiosis with normal individuals for four times their usual life-span. All tissues survive at least twice as long in parabiosis as they do in control anucleolate larvae. Lethality is thus concluded to be a secondary effect of the mutation, probably resulting from a defective blood-circulation. Several anucleolate tissues are lost despite parabiosis, but not in a manner suggesting a cell-lethal action. The mutation is better described as cell-sub vital. The anucleolate syndrome, of neural pycnosis and general retardation of differentiation and growth, is maintained in parabiosis. These symptoms may be direct results of the mutation in each cell. Some further cellular differentiation’ and growth in parabiosis show that the mutation does not completely arrest development. The anucleolate syndrome is found to be consistent with the theory that the nucleolus regulates some basic process of cellular metabolism.
Degeneration of the Remaining Pronephros ofRana temporariaafter Unilateral Pronephrectomy
Authors: fox H. 
Published: April 2021

ABSTRACTHatched larvae of R. temporaria at stages approximately equivalent to stages 25-26 for R. dalmatina (Cambar & Marrot, 1954) were unilaterally pro-nephrectomized, and the fate of the single remaining pronephros system was compared with that of paired control systems throughout the phase of pronephric degeneration, which takes place in stages 49-54. In terms of comparable larval stages the remaining pronephros of operated specimens does not differ in its degeneration from control pronephroi, either qualitatively or quantitatively (expressed in terms of pronephric (or glomus) length), except that it includes some swollen tubules—a residue of the tubule compensatory hypertrophy resulting from unilateral pronephrectomy. After unilateral pronephrectomy unharmed glomeri in situ, which belonged to extirpated pronephroi, are likewise identical with contralateral glomeri of remaining pronephroi of the other side, and with the paired glomeri of controls. Hypo- or hyperfunction do not affect normal pronephric degeneration, and it is likely that the phenomenon is bound up with metamorphic processes independent of function.
The Effect of Chloroacetophenone on Chick Embryos Culturedin vitro
Authors: Lakshmi M. S. 
Published: April 2021

ABSTRACTThe effect of chloroacetophenone (0·0005 M), which has been described as a powerful and irreversible —SH reactant, has been studied on chick embryos cultured in vitro at the primitive-streak and head-process stages. Abnormalities were produced predominantly in the brain region, and included improper differentiation, partial or complete non-closure, and defective lumen. Neural tubes were irregular and open. Shortening of the axis was also common. Embryos at the head-process stage were not affected by the substance at the concentration used. The effect of the chemical on the morphogenesis of the chick embryo is discussed.
A single cell approach to problems of cell lineage and commitment during embryogenesis ofDrosophila melanogaster
Authors: Technau Gerhard M. 
Published: April 2021

AbstractThe mechanisms leading to the commitment of a cell to a particular fate or to restrictions in its developmental potencies represent a problem of central importance in developmental biology. Both at the genetic and at the molecular level, studies addressing this topic using the fruitfly Drosophila melanogaster have advanced substantially, whereas, at the cellular level, experimental techniques have been most successfully applied to organisms composed of relatively large and accessible cells. The combined application of the different approaches to one system should improve our understanding of the process of commitment as a whole. Recently, a method has been devised to study cell lineage in Drosophila embryos at the single cell level. This method has been used to analyse the lineages, as well as the state of commitment of single cell progenitors from various ectodermal, mesodermal and endodermal anlagen and of the pole cells. The results obtained from a clonal analysis of wild-type larval structures are discussed in this review.
Thymocyte/stromal cell chimaerism in allothymus-graftedXenopus:developmental studies using theX. borealisfluorescence marker
Authors: Horton John D. , Russ Jane H. , Aitchison Pamela , Horton Trudy L. 
Published: April 2021

AbstractThese experiments employ the X. borealis (quina-crine-fluorescence) cell marker to illustrate that froglet (normal or in vivo-irradiated) thymuses, alloimplanted to 4- to 6-week-old, 7-day-thymec-tomized hosts, become filled with host lymphoid cells, while a range of thymic stromal cell types (e.g. epithelial derivatives and reticuloendothelial cells) remain donor derived. A time-course study of 4μm historesin-embedded sections reveals that for normal thymus implants, host cells begin to immigrate in good number only after metamorphosis. In contrast, 3000 rad-irradiated thymus implants begin to be repopulated with host lymphocytes within 2 weeks postimplantation, when hosts are still at a late larval stage of development. Despite rapid colonization by host lymphoid cells, irradiated thymuses remain small and often disappear in early adult life. Donor-derived lymphocytes frequent the blood and both the red pulp and perifollicular regions of the spleen following normal thymus implantation, whereas such thymic emigrants were not seen in the periphery of thymectomized hosts grafted with irradiated thymus glands.
The establishment of the embryonic-abembryonic axis in the mouse embryo
Authors: Garbutt C. Louise , Chisholm Julia C. , Johnson Martin H. 
Published: April 2021

AbstractThe influence of cell division order on the establishment of the embryonic–abembryonic axis (EA axis) of the mouse embryo was investigated. Aggregate embryos were constructed in which a labelled cell (or pair of cells) was combined with a group of unlabelled cells all of which were up to one cell cycle earlier or later in their progress through development to the blastocyst stage. The aggregates were cultured first to the nascent blastocyst stage and then to the expanded blastocyst stage. The positions of the progeny of the labelled cells in relation to the nascent blastocoel and to the orientation of the embryonic–abembryonic axis were recorded. It was concluded that cell division order does influence the establishment of the EA axis, early dividing cells tending to be associated with the nascent blastocoel and the site of the nascent blastocoel tending to mark the site of the abembryonic pole. However, the influence of division order was diminished by a requirement for intercellular cooperation during blastocoel formation and by a counteracting influence of division order arising from its effects on the allocation of cells to the inner cell mass.
The galactose-specific receptor system in rat liver during development
Authors: Dini Luciana , Conti-Devirgiliis Laura , Russo-Caia Salvatore 
Published: April 2021

Abstract
The number and distribution of galactose-specific binding sites were investigated in rat liver cells during perinatal development. Ligand binding to hepatocytes, macrophages and endothelial cells was followed with in vitro and in situ experiments by electron microscopy, using lactosylated bovine serum albumin adsorbed onto 5 nm colloidal gold particles as ligand.
Binding capacity, starting at a late stage of fetal development, is very low both on the hepatocyte and on the macrophage surface, which show single particles statistically distributed. By contrast, bound particles are absent from fetal endothelial cells, which also lack the typical coated regions. In vivo, experiments at 37 °C show that endocytosis occurs to some extent in prenatal life.
These results indicate that the expression of galactose-specific receptors’ activity on the different liver cell types follows different developmental patterns, which are independently modulated.
The assembly and positioning of cytoskeletal elements in Tetrahymena
Authors: Williams Norman E. , Honts Jerry E. 
Published: April 2021

Abstract
The oral skeleton of Tetrahymena is a precisely arranged assemblage of basal bodies, microtubule bundles and connecting filaments found associated with the feeding structure in this cell type. Tubulin and filament proteins have been isolated but no actin has been recovered. The conditional mutant NP1 of Tetrahymena thermophila forms a normal oral skeleton at the permissive temperature (28°C), but forms an abnormal one at the restrictive temperature (37°C). Antibodies against tubulin and oral filament protein OF1 were used to visualize the abnormal oral skeleton and stages in its development, and ultrastructural comparisons of abnormal and wild-type oral skeletons were made. It was found that the overall pattern of organization was altered in the mutant, whereas the substructure appeared every where to be normal. Studies of cells in which the mutant phenotype was coming to expression revealed that normal basal bodies in the oral skeleton failed to move from the disordered state characteristic of early stages of development into the correct pattern of four organized clusters characteristic of later stages. Together, these results suggest that the lesion in NP1 does not affect cytoskeleton assembly per se, but instead affects a discrete mechanism responsible for the positioning of cytoskeletal elements with respect to each other after they have been formed (metaassembly). Reasons for suspecting the involvement of the membrane skeleton are presented.
When and how does cell division order influence cell allocation to the inner cell mass of the mouse blastocyst?
Authors: Garbutt C. Louise , Johnson Martin H. , George Martin A. 
Published: April 2021

ABSTRACT
Aggregate 8-cell embryos were constructed from four 2/8 pairs of blastomeres, one of which was marked with a short-term cell lineage marker and was also either 4 h older (derived from an early-dividing 4-cell) or 4h younger (derived from a late-dividing 4-cell) than the other three pairs. The aggregate embryos were cultured to the 16-cell stage, at which time a second marker was used to label the outside cell population. The embryos were then disaggregated and each cell was examined to determine its labelling pattern. From this analysis, we calculated the relative contributions to the inside cell population of the 16-cell embryo of older and younger cells. Older cells were found to contribute preferentially. However, if the construction of the aggregate 8-cell embryo was delayed until each of the contributing 2/8 cell pairs had undergone intercellular flattening and then had been exposed to medium low in calcium to reverse this flattening immediately prior to aggregation, the advantage possessed by the older cells was lost. These results support the suggestion that older cells derived from early-dividing 4-cell blastomeres contribute preferentially to the inner cell mass as a result of being early-flattening cells.
Neural determination of muscle fibre numbers in embryonic rat lumbrical muscles
Authors: Ross J. J. , Duxson M. J. , Harris A. J. 
Published: April 2021

ABSTRACT
The generation and development of muscle cells in the IVth hindlimb lumbrical muscle of the rat was studied following total or partial denervation. Denervation was carried out by injection of β-bungarotoxin (j3-BTX), a neurotoxin which binds to and destroys peripheral nerves. Primary myotubes were generated in denervated muscles and reached their normal stable number on embryonic day 17 (E17). This number was not maintained and denervated muscles examined on E19 or E21 contained many degenerating primary myotubes. Embryos injected with β-bungarotoxin (β-BTX) on E12 or E13 suffered a partial loss of motoneurones, resulting in a reduced number of axons in the L4 ventral root (the IVth lumbrical muscle is supplied by axons in L4, L5 and L6 ventral roots) and reduced numbers of nerve terminals in the intrinsic muscles of the hindfoot. Twitch tension measurements showed that all myotubes in partly innervated muscles examined on E21 contracted in response to nerve stimulation. Primary myotubes were formed and maintained at normal numbers in muscles with innervation reduced throughout development, but a diminished number of secondary myotubes formed by E21. The latter was correlated with a reduction in number of mononucleate cells within the muscles. If β-BTX was injected on E18 to denervate muscles after primary myotube formation was complete, E21 embryo muscles contained degenerating primary myotubes. After injection to denervate muscles on E19, the day secondary myotubes begin to form, E21 muscles possessed normal numbers of primary myotubes. In both cases, secondary myotube formation had stopped about 1 day after the injection and the number of mononucleate cells was greatly reduced, indicating that cessation of secondary myotube generation was most probably due to exhaustion of the supply of competent myoblasts. We conclude that nerve terminals regulate the number of secondary myotubes by stimulating mitosis in a nerve-dependent population of myoblasts and that activation of these myoblasts requires the physical presence of nerve terminals as well as activation of contraction in primary myotubes.
Production of fertile salamanders by transfer of germ cell nuclei into eggs
Authors: Lesimple M. , Dournon C. , Labrousse M. , Houillon Ch. 
Published: April 2021

ABSTRACT
In amphibians, the ability of somatic cell nuclei to give rise to embryos in nuclear transplantation experiments has been thoroughly investigated and shown to be limited, except in Xenopus laevis. Similar experiments have been performed with primordial germ cells from genital ridges and spermatogonia. In the present paper, we have studied the capacity of germ cell nuclei to promote development of complete and fertile adults in the urodele amphibian Pleurodeles waltl. Germ cell nuclei were taken from larvae at progressive stages of larval development up to meta-morphosis and transplanted into enucleated eggs. Two nonlethal chromosomal mutations were used as nuclear markers in two control series. Nuclei from all developmental stages tested were able to initiate larval development. Furthermore, nine individuals underwent metamorphosis (representing 3 % of normal blastulae) and six of these animals are now adults. When two of these six animals, a male and a female, were mated to each other, the offspring were normal. These results show conclusively, for the first time in amphibians, that germ cell nuclei remain totipotent at least during the larval period.
Clonal analysis of the developmental potential of 6th and 7th day visceral endoderm cells in the mouse
Authors: Cockroft D. L. , Gardner R. L. 
Published: April 2021

ABSTRACT
Single visceral endoderm cells from the embryonic regions of 6th and 7th day conceptuses were cloned by blastocyst injection using the genetically determined presence or absence of cytoplasmic malic enzyme activity as an in situ cell marker. In the 6th day cell injection experiments wild-type donor cell clones were readily discernible in the extraembryonic membranes of more than half the midgestation null host conceptuses; a much lower cloning efficiency was encountered with 7th day cells. With one exception, the clones appeared to be confined to the extraembryonic endoderm, most occurring in the parietal endoderm only. By means of the in situ marker, the morphology and arrangement of donor cells in the parietal endoderm could be compared with that of host cells, thereby demonstrating that they had undergone an appropriate phenotypic change after colonizing this tissue. Control experiments indicated that the procedures used to dissociate and select donor cells for injection were likely to have ensured that a representative sample of visceral endoderm cells had been transplanted. Hence on the 6th day of development, a high proportion of cells in the visceral endoderm seem to retain primitive endodermal characteristics, but these appear to be lost by the 7th day, when markers of visceral endoderm differentiation have first been demonstrated.
An inducer protein may control the timing of fate switching in a bipotential glial progenitor cell in rat optic nerve
Authors: Hughes Simon M. , Raff Martin C. 
Published: April 2021

ABSTRACT
In rat optic nerve, oligodendrocytes and type-2 astrocytes develop from a common (O-2A) progenitor cell. The first oligodendrocytes differentiate at birth, while the first type-2 astrocytes differentiate in the second postnatal week. We previously showed that the timing of oligodendrocyte differentiation depends on an intrinsic clock in the O-2A progenitor cell. Here we provide evidence that the timing of type-2 astrocyte differentiation, by contrast, may depend on an inducing protein that appears late in the developing nerve. We show that extracts of 3- to 4-week-old, but not 1-week-old, rat optic nerve contain a protein (apparent Mr ∼ 25 000) that induces O-2A progenitor cells in culture to express glial fibrillary acidic protein (GFAP), an astrocyte-specific marker in the rat central nervous system.
Molecular and cellular aspects of patterning sensory neurone connections in the vertebrate nervous system
Authors: Davies Alun M. 
Published: April 2021

ABSTRACT
Sensory neurones display organizational features that are common to most populations of neurones in the vertebrate nervous system. First, their cell bodies are arranged in discrete groups (the sensory ganglia) each of which has characteristic receptive and projection fields (the peripheral and central target fields, respectively, to which the peripheral and central processes of the neurones grow in development). Second, nerve fibres make specific terminations within each target field; an important feature is that different kinds of sensory receptors in the periphery are connected to the appropriate kinds of second-order neurones in the central nervous system (CNS). Third, nerve fibre terminations in the peripheral and central target fields have a similar topographic order.
Primordial germ cells of the young chick blastoderm originate from the central zone of the area pellucida irrespective of the embryo-forming process
Authors: Ginsburg Malka , Eyal-Giladi Hefzibah 
Published: April 2021

ABSTRACT
Early chick blastoderms (stages X–XII) were divided by a circular cut into two fragments. In one experimental group, the area opaca was separated from the marginal zone and the central disc of the area pellucida, while in another group the area opaca plus marginal zone were separated from the central disc. Other blastoderms of equivalent stages were each cut into three strips of equal size (either perpendicular or parallel to the axis of symmetry). The fragments were isolated and incubated for 43–48 h after which they were PAS-stained, whole-mounted and checked for the presence of primordial germ cells (PGCs). The results showed that most of the PGCs originated from the central disc and not from the periphery of the area pellucida and that they segregated from this zone even if no embryonic axis developed in the explant. In such cases, the PGCs were found to be dispersed throughout the entire explant, usually in association with forming blood islands. When an axis did develop in the explant, the PGCs were found to be concentrated around its anterior end, in a pattern resembling the germinal crescent. No indication of a quantitative regulation of PGCs was found in the expiants and the sum of PGCs, calculated for the complementary fragments of a blastoderm, matched the range of numbers in control blastoderms. Our results suggest that PGCs may already be determined as early as stage X and that their further differentiation is independent of the embryo-fonning process.