bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct exposure of postimplantation mouse embryos to 5-bromodeoxyuridinein vitroand its effect on subsequent chondrogenesis in the limbs
Authors: Agnish Narsingh D. , Kochhar Devendra M. 
Published: April 2021

ABSTRACTAs maternally administered 5-bromodeoxyuridine (BudR) is very quickly degraded by the liver, a combination of whole embryo culture and organ culture techniques was adopted to expose postimplantation mouse embryos to the analog and to study the effects of long-term treatment on the subsequent differentiation of limb-buds. Early and mid-11th-day mouse embryos were exposed to increasing concentrations of BudR for 12 or 24 h. Forelimbs of the treated embryos were then organ-cultured in drug-free medium and the extent of cartilage development in the expiants examined. Exposure of embryos to 50–150 μg/ml of BudR for 24 h resulted in significant inhibition of chondrogenesis in the subsequent limb cultures and the effect was related to dose. After treatment with 150 μg/ml of the drug, the forelimbs of the early 11-day embryos (somite stage 26–29) showed an almost complete lack of cartilage, while the limbs of mid-11 th-day embryos (somite stage 32–34) were not nearly as sensitive and exhibited about 50 % reduction in the amount of cartilage development. We conclude that if embryos in which the limb development is at a very early stage of development are exposed to BudR, the future course of limb differentiation is permanently and irreversibly damaged, resulting in a partial or even complete suppression of chondrogenesis in the organ. As both the dose and perhaps also the duration of treatment were critical, we suggest that the rather low frequency of reported limb malformations after in vivo injection of teratological doses of BudR may be due to only a small amount of the chemical reaching the embryos.
Ultrastructural analysis of some functional aspects of Xenopuslaevispancreas during development and metamorphosis
Authors: Leone Fiorella , Lambert-Gardini Stefano , Sartori Claudia , Scapin Sergio 
Published: April 2021

ABSTRACTMorphological studies using both light and electron microscope were carried out with the aim of characterizing cells present in the larval and adult pancreas of Xenopus laevis. The following cell types have been seen: (1) exocrine cells, with a very well developed r.e.r. (rough endoplasmic reticulum), well defined Golgi complexes and numerous large secretory granules (A cells) ; (2) cells without either r.e.r. or secretory granules but with a large number of well developed mitochondria (B cells); (3) endocrine cells often clustered in the typical islets and with small membrane-coated granules showing a very dense central core surrounded by a light halo (C cells).During development, the aspect is seen to change from an unorganized tissue in which the acinar structures are still not clearly visible (stage 42), to a more organized form in which the exocrine cells (A cells) are seen to be arranged around the lumen of the acinus together with some B cells.At the stages 54–56, an increasing number of acini surrounded both by A and B cells was observed. At about stage 61, large quantities of necrotic cells were seen and it became more difficult to individualize the acinar organization found in the preceding stages. Finally, there are no necrotic cells in the adult but only A, B cells which are organized in well developed acinar structures and C cells.The investigation also included a study of some pancreatic enzymes (lipase and amylase) synthesized during larval life. Lipase activity shows a peak at stage 54–56 in which the most well organized tissue of the entire larval life was observed. The activity then decreases, reaching a minimum at stage 66, after which it rapidly rises. Maximum amylase activity occurs at stage 51 after which there is a decrease, to a minimum at stage 66. The activity then remains at constant level.
Active ion transport and β-ecdysone induced differentiation ofDrosophila melanogasterimaginal discs culturedin vitro
Authors: Milner Martin J. , Sang James H. 
Published: April 2021

ABSTRACTThe theory that β-ecdysone initiates developmental changes during insect metamorphosis by causing an increase in intranuclear levels of potassium, together with a concomitant decrease in sodium levels, has been investigated by two methods. First, imaginal discs from late third instar larvae have been cultured with 0·2 μg/ml of β-ecdysone together with inhibitors of active ion transport. Non-specific inhibitors, which may have general effects on sulphydryl groups, such as iodoacetic acid, N-ethylmaleimide, ethacrinic acid and furosemide, inhibit both eversion and differentiation at concentrations of from IO-3 M to 2 × 10−3 M. Ouabain, the only specific inhibitor of the active transport of Na+ and K+ across membranes, had no effect on development even at a concentration of 10−2 M. Second, a medium containing raised levels of K+, and reduced concentrations of Na+, neither initiated disc development in the absence of β-ecdysone, nor stimulated development induced by suboptimal levels (0·02 μg/ml) of β-ecdysone, either in the presence or absence of ouabain. These results suggest that β-ecdysone induced morphogenesis is not dependent upon Na+ and K+ concentrations, or on the activity of an ouabain-sensitive ion pump.
Characterization of an organ-specific differentiator substance in the planarianDugesia etrusca
Authors: Steele Vernon E. , Lange Christopher S. 
Published: April 2021

ABSTRACTA substance which inhibits brain formation in decapitated regenerating planarians {Dugesia etrusca) was characterized and partially purified. The substance’s inhibitory activity was followed during each purification procedure by adding freshly decapitated animals of a standard size to each fraction, and later measuring the resultant regenerated brain volume. The inhibitory activity remained in the supernatant after a 10000 g centrifugation of a cell-free homogenate. Most of the activity sedimented when the 10000 g supernatant was centrifuged at 32000 g. The degree of inhibitory activity increased with increased numbers of animals in the initial homogenate. The substance has an apparent molecular weight between 2x 105 and 4x 105 daltons. Digestion by pronase destroyed the activity, but treatment with RNase, DNase I, or lipase had no significant effect. The inhibiting substance has an isoelectric point (pl) of between 4·75 and 5·38 and migrates to the anode when electrophorezed in pH 6·8 buffer.
Temporary contacts formed between developing optic fibers in the chick
Authors: Arees Edward A. , Delong G. Robert 
Published: April 2021

ABSTRACT
Temporary junctions were observed between developing optic fibers of the chick embryo and were distributed along the entire length of the axons from the cell body to the tip of the growth cone. These junctions were present in all material studied between days E-3 and E-18, the latter being the start of myelin formation of the optic tract. Junctions between adjacent axons were focal in nature and showed a decrease in the size of the intercellular space caused by a close apposition of the plasma membrane. With the experimental techniques used final identification of these junctions could not be made but are thought to be of two types - the gap and occludens junctions. Temporary fasciae adherentes junctions were observed at the end of the axon, between the growth cone and adjacent neural tissue. Speculation was made on the functional role of these temporary junctions.
Development of a placental blood circulation in rat embryosin vitro
Authors: New D. A. T. , Coppola P. T. 
Published: April 2021

ABSTRACTRat embryos explanted with their membranes at head-fold stage ( days gestation) formed an allantoic placenta which enlarged in culture and developed a foetal blood circulation. Embryos explanted at early somite stages ( days) also formed a growing allantoic placenta but only after removal of most of the ectoplacental trophoblast. Assays of total protein in the embryo and placenta suggested that, in the absence of a maternal blood circulation to the placenta, embryo and placenta compete for the respiratory and nutritional resources obtained through the yolk-sac.
Induction of melanogenesis in the epidermal melanoblasts of newborn mouse skin by MSH
Authors: Hirobe Tomohisa , Takeuchi Takuji 
Published: April 2021

ABSTRACT
The number of melanocytes positive to the dopa reaction in the epidermis was shown to increase after newborn mice were injected with α-MSH or DBc-AMP. The agents seemed to induce the initiation of melanogenesis in the pre-existing melanoblasts. Electron-microscopic observation also demonstrated that a-MSH induced not only maturation of melanosomes but also the formation of melanosomes.
Etude par immunofluorescence de l’apparition d’antigènes neuro-spécifiques d’adulte chez l’embryon de Poulet
Authors: Touzet N. , Jeanmaire-Zylberberg R. , Chaminade M. 
Published: April 2021

ABSTRACT
Immunofluorescent study of the distribution of adult neuro-specific antigens in the chick embryo
The adult neuro-specific antigens have been localized by immunofluorescence techniques in diencephalon and mesencephalon of chick embryo. This study has been made using fresh or fixed tissues from embryos 72,48 or 36 h old. At 72 h of incubation the wall of diencephalon shows marked fluorescence; at 48 h of incubation the fluorescent cells are localized in an outer layer and an inner one. In the48h-old embryo the reaction is more distinct and intensive in fresh tissues than in fixed tissues. At 36 h of incubation no fluorescence has been detected either in fresh tissues or in fixed tissues.
Experimental studies on a mutant gene (p) causing premature death ofAmbystoma mexicanumembryos
Authors: Trottier Thomas M. , Armstrong John B. 
Published: April 2021

ABSTRACTThe premature death (p) mutation is a recessive lethal, which, in the homozygous condition, gives rise to a complex of abnormalities. The mutant embryos develop only to stage 37, at which time disintegration of superficial tissue begins. Many of the abnormalities observed in sections of the stage-37 mutant embryo are related to its failure to establish a functioning circulatory system, or to the resulting edema and/or ascites that distend the abdomen and flanks. There are, however, abnormalities of heart, liver, gill and muscle development which cannot be attributed to lack of circulation and edema. All of these abnormalities can be indirectly related to the endoderm, particularly the anterior and dorsal endoderm. The findings, therefore, suggest that the mutation leads to a fairly general defect of the endoderm.
Properties of extra-embryonic ectoderm isolated from postimplantation mouse embryos
Authors: Rossant J. , Ofer L. 
Published: April 2021

ABSTRACTExtra-embryonic ectoderm isolated from the mouse embryo as late as days post coitum can form cells with the morphological characteristics of trophoblast giant cells both in ectopic sites and in vitro. This similarity to the properties of ectopiacental cone tissue provides further support for the postulated common origin of both tissues from the trophectoderm of the blastocyst.
Cell lineage and cell determination in the developing compound eye of the cockroach,Periplaneta americana
Authors: Shelton P. M. J. , Anderson H. J. , Eley S. 
Published: April 2021

ABSTRACTBy grafting between eye colour mutants of the cockroach Periplaneta americana we have investigated (i) the hypothesis that cells within an ommatidium of the fused rhabdom type are clonally derived from a single mother cell and (ii) we have tested the suggestion that cells from non-prospective eye epidermis can form ommatidia when grafted next to eye tissue. Mosaic eyes containing cells of the two genotypes contain ommatidia with unpredictable combinations of the two sorts of cells at the host/graft border. This finding is inconsistent with the first hypothesis. Using grafts of prothoracic epidermis and head epidermis from non-prospective eye regions we have shown that only cells from the prospective eye region can form ommatidia. Possible ways that eye cells could be determined are discussed in the light of these findings.
Inhibition of cranial neural crest cell development by vitamin A in the cultured chick embryo
Authors: Hassell John R. , Greenberg Judith H. , Johnston Malcolm C. 
Published: April 2021

ABSTRACTChick embryos at stage 8, prior to neural crest cell migration, were explanted on whole egg medium with or without vitamin A and cultured for 3 days. Sections through the head regions showed that the cranial neural crest cells had migrated into the first visceral arch in the controls but were absent from this structure in the treated embryos. These observations suggest that vitamin A inhibits neural crest cell development or migration, an effect which may in part account for the facial malformations produced by excess vitamin A.
Trophoblastic vesicles of preimplantation blastocysts can enter into quiescence in the absence of inner cell mass
Authors: Surani M. A. H. , Barton S. C. 
Published: April 2021

ABSTRACT
Preimplantation mouse blastocysts were dissected into inner cell mass (ICM) and tropho-blast cells. These fragments were transferred to pseudo-pregnant mice which were left intact or ovariectomized. The latter group received progesterone to permit blastocysts and the dissected fragments to enter into quiescence, prior to injection of oestradiol to induce implantation. Trophoblastic vesicles, without ICM, entered into quiescence and implanted whereas the ICM did not. The entry of trophoblast into quiescence does not appear therefore to be governed by the ICM.
Ultrastructural observations on stumpy (stm) a new chondrodystrophic mutant in the mouse
Authors: Johnson D. R. 
Published: April 2021

ABSTRACT
Stumpy (stm) is a new chondrodystrophic mutant in the mouse. Light microscopy of carti-lage reveals a slightly increased mitotic rate, more chondrocytes than is usual per lacuna and a wide zone of hypertrophy. Electron microscopy shows that many chondrocytes are in close approximation with some tight junctions: in cartilage from 14-day-old mice there is much interdigitation and folding of the cell membranes of adjacent chondrocytes.
Morphologic alterations in the parietal yolk-sac of the rat from the 12th to the 19th day of gestation
Authors: Jensh R.P. , Koszalka T. R. , Jensen M. , Biddle L. , Brent R. L. 
Published: April 2021

ABSTRACT
The rat parietal yolk-sac and its adherent epithelial cells were examined at various stages of gestation using an en face technique. Specimens were observed at both the light and electron microscopic level. Diastase pretreatment and PAS-staining were used to determine the presence of glycogen. As early as the 12th day of gestation the cytoplasm of the parietal yolk-sac cells contained numerous ribosomes and mitochondria and a large amount of endoplasmic reticulum. The glycogen content of the epithelial cells increased from the 12th day of gestation and accumulated in large quantities by the 16th day. By the 17th day many cells exhibited variable degrees of degeneration. Cellular elements of degenerating cells appeared to be trapped within Reichert’s membrane. Contrary to the reports of other investigators, the present study indicates that the capsular portion of the parietal yolk-sac consisting of Reichert’s membrane and its adherent epithelial cells remained intact until at least the 18th day of gestation. Some of the unique characteristics of the parietal yolk-sac provide experimental models to study the effects of environmental factors on (1) the synthesis of basement membranes, (2) the ageing of cells and (3) the correlation of these histologic changes with the functions of the parietal yolk-sac.
A Gene for Uncomplicated Deafness in the Mouse
Authors: Deol M. S. 
Published: April 2021

ABSTRACT
Deafness associated with locomotor disturbances of labyrinthine origin (head shaking, circular movements) has been known in the mouse for many years, and there are at least ten different gene mutations which produce this syndrome (with or without additional anomalies). Grüneberg (1947) remarked that at first sight it seems remarkable that all the known types of inherited deafness in rodents should be associated with locomotor disturbances. However, shaking and circling are too obvious to be missed, and once detected such mutants will of course be tested for their sense of hearing. Deafness not so ‘labelled’ is unlikely to be discovered in a mouse or rat unless specifically looked for and no such systematic search has so far been made. It is thus quite likely that the absence of ‘uncomplicated’ deafness in rodents is spurious and simply due to the bias against their detection. The fact that there are locomotor disturbances without deafness would seem to support such a suggestion.
The Formation of Sub-blastodermic Fluid in Hens’ Eggs
Authors: New D. A. T. 
Published: April 2021

ABSTRACT
Chick blastoderms have been grown in vitro on pieces of vitelline membrane supported over albumen. The blastoderms were found to remove fluid from the albumen and to secrete it from their endodermal surfaces. It is concluded that this could be the mechanism by which the sub-blastodermic fluid is formed in ovo. The importance of the sub-blastodermic fluid to the developing embryo is discussed.
The Ectodermal Thickening and Ridge in the Limbs of Staged Human Embryos1
Authors: O’rahilly Ronan , Gardner Ernest , Gray D. J. 
Published: April 2021

ABSTRACT
Serial sections of the limbs of seventy human embryos, ranging from developmental horizons 11 to 19 inclusive, were examined. In the upper limb an ectodermal thickening was present on the ventral aspect and lateral border at horizon 12. The lateral part of this thickening formed the ectodermal ridge at horizon 14. The ridge disappeared during horizon 17. These events occurred one horizon later for the similar thickenings and ridges on the lower limb. Changes in appearance and position of the limbs as seen in plaster reconstructions between horizons 12 and 17 are described. The limits of the thickenings and ridges were mapped out on these reconstructions and are illustrated. The significance of similar ridges in avian limbs is discussed.
On the possibility of sperm aster involvement in dorso-ventral polarization and pronuclear migration in the amphibian egg
Authors: Manes Mario E. , Barbieri Francisco D. 
Published: April 2021

ABSTRACTSperm aster involvement in the determination of the plane of bilateral symmetry of the future embryo as well as pronuclear movement and orientation has been investigated in the amphibian egg. The procedure involved injecting very small amounts of disrupted sperm cells into the subcortical region of the egg of the toad Bufo arenarum. Using this procedure we have previously shown that structural integrity of the sperm cell is not required for the determination of the symmetry plane.The present report deals with the cytological effects induced by the injection of sperm homogenate into the egg. As expected, an aster was always present in these eggs. This aster closely resembled that produced in the fertilized egg as the sperm nucleus migrates through the egg mass.Sections of injected eggs have also shown the presence of two pigment trails similar in appearance to those produced by pronuclear movement after normal fertilization. The streak analogous to the sperm entrance track emerged from the point where the pipette was introduced.None of these effects were observed in Ringer’s injected eggs. At the time of the rotation of symmetrization, the female pronucleus was seen within a clear area of cytoplasm located at a short distance below the egg cortex. An aster field organized around this clear area was probably formed as a result of the egg centriole activation. In no case was the egg nucleus seen to migrate towards the copulation site as was seen to occur in sperm homogenate-treated eggs.The active agent was found to be a particulate component which sediments with the head but not the tail fraction of Bufo arenarum sperm.Injection of blood cells caused a similar response to that elicited by the sperm homogenate.
Pattern formation inDictyostelium discoideum:I. Development of prespore cells and its relationship to the pattern of the fruiting body
Authors: Forman D. , Garrod D. R. 
Published: April 2021

ABSTRACTImmunofluorescent staining of the prespore cells of the cellular slime mould Dictyostelium discoideum was carried out using a heterologous spore antibody. The highly specific staining of the prespore vesicles (PSVs) within the prespore cells enabled quantitative determinations to be made of the rate and extent of development of these cells throughout the life cycle.The results showed that PSVs first appeared in a large proportion of the cells shortly after the cells had chemotactically aggregated into multicellular masses. During the later phases of the life cycle, the proportion of cells containing PSV increased, as did the fluorescent intensity of their PSVs, until the early culmination stage of development when 85-90% of the total cell population contained PSVs. Lowering the temperature of development delayed the onset of vesicle formation and decreased the proportion of prespore cells in the total cell population. Changing the growth conditions of the cells prior to multicellular development also had a significant effect on the proportions of prespore cells, as did the use of a mutant known to give rise to fruiting bodies with a reduced number of spores.The comparability between these estimates of prespore cell proportions at culmination and previously reported spore:stalk ratios within fruiting bodies confirms the view that PSVs are reliable indicators of prespore cells. The finding that temperature and growth conditions and the use of mutants all of which are known to affect spore:stalk ratios, also all affected prespore proportions in the expected direction, adds further weight to this argument.The fact that prespore cells are beginning to differentiate early in the multicellular phase of the life cycle and the related finding that such differentiation always precedes formation of the grex tip are results of considerable importance to the development of a model for pattern formation in D. discoideum.
Mutations ofDrosophila melanogasterthat affect muscles
Authors: Deak I. I. 
Published: April 2021

ABSTRACTEight X-chromosome mutations (falling into five complementation groups) that affect the development and morphology of the indirect flight muscles of Drosophila melanogaster were investigated using histological, behavioural and genetic techniques. All of these mutations result in flightlessness, in a marked reduction in the ability of the flies to jump, and in the wings being held in abnormal positions. Mutations in each of the complementation groups have different effects on the morphology of the muscles. Two (flapwing, vertical wing) result in absence of most of the indirect flight muscle fibres, a third (upheld) is required for the gross organization of muscle structure, another (heldup) is involved in the maintenance of muscle structure once formed, and the fifth seems to be necessary for the detailed architecture of the muscle fibre (indented thorax). The analysis of flies genetically mosaic with respect to each mutation by the technique of fate-mapping suggests that three (heldup, upheld and indented thorax) of the genes concerned have their primary site of action in the musculature itself, while the other two (flapwing and vertical wing) may function primarily in the fat-body and tracheae respectively.