bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of variable lactate/malic dehydrogenase ratios to distinguish between progenitor cells of cartilage and bone in the embryonic chick
Authors: Thorogood P. V. , Hall Brian K. 
Published: April 2021

ABSTRACT
The activities of LDH and MDH have been studied, both in differentiated cartilage and bone from the embryonic chick, and in the pool of mixed osteogenic and chondrogenic stem cells found on the quadratojugal, a membrane bone. In confirmation of the model proposed by Reddi & Huggins (1971) we found that the LDH/MDH ratio was greater than 1 in cartilage and less than 1 in bone. Furthermore we established, for the first time, that ratios occurred in the chondrogenic and osteogenic stem cells, similar to the ratios in their differentiated counterparts. Alterations in LDH/MDH resulted from variations in the level of LDH/μg protein. MDH/μg protein remained constant, even when LDH/MDH was changing. We interpret these results in terms of adaptation of chondrogenic progenitor cells for anaerobic metabolism and anticipate that our model will be applicable to other skeletal systems where stem cells are being studied.
Developmental patterns of rat muscle histochemistry
Authors: Curless Richard G. , Nelson Marilyn B. 
Published: April 2021

ABSTRACT
A developmental progression of histochemical fiber typing is demonstrated in normal rat soleus muscle. By utilizing the acid lability of ATPase, the type II fibers are subdivided into type IIA, IIB and IIC. No IIB fibers are present in the newborn or adult rat soleus. In the 1-day-old animal 90 % of the fibers can be differentiated into type I and II with all of the type II’s demonstrating IIC characteristics. Only type I and IIC fibers are present until 18 days, when poorly differentiated IIA fibers first appear and gradually become the predominant type II fiber at the expense of IIC’s.
Further analysis documents the sequence of disappearance of myotubes from up to 80 % of all fibers in the 1-day-old to less than 1 % between 15 and 18 days. An analysis of the progression of fiber size according to type is presented.
Embryological study of aT/tlocus mutation (tw73) affecting trophectoderm development
Authors: Spiegelman Martha , Artzt Karen , Bennett Dorothea 
Published: April 2021

ABSTRACTMouse embryos homozygous for the recessive lethal mutation tw73 show specific defects in trophectoderm shortly after implantation. The trophectoderm and ectoplacental cone fail to form the usual close association with the uterine decidua, and proliferation is markedly reduced. The embryo proper ceases to develop beyond the two-layered stage and degenerates and dies within 5 days of implantation.
Cell junctions in the developing compound eye of the desert locust Schistocercagregaria
Authors: Eley S. , Shelton P. M. J. 
Published: April 2021

ABSTRACTIntercellular junctions in the developing retina of the locust Schistocerca gregaria have been examined by electron microscopy. Different types of junction appear in a well-defined sequence during development. Five stages of ommatidial development are described. Close junctions and punctate junctions are present throughout development. Gap junctions appear transiently amongst the undifferentiated cells, before clearly defined preommatidia can be distinguished. The subsequent disappearance of gap junctions may be correlated with cell determination. Lanthanum studies confirm these findings.The later sequential appearance of adhesive junction types is described. These include septate desmosomes and two types of desmosomes. In the fully differentiated ommatidium only two types of junction remain, these are: desmosomes and rhabdomeric junctions.
Comparative analysis of cell distribution in the pigment epithelium and the visual cell layer of chimaeric mice
Authors: Sanyal S. , Zeilmaker G. H. 
Published: April 2021

ABSTRACT
In chimaeras of both rdrdCC⟷++cc and rdrdcc⟷ + +CC combinations two types of distribution were observed. In a majority of the chimaeras both retinal layers were chimaeric; whereas in a few cases the pigment epithelium was chimaeric but the visual cell layer was made of + + cells only. No spatial relation was observed in the distribution of the cells in the two layers. The two eyes of the individuals were nearly always identical with regard to occurrence of chimaerism in the two layers. The findings are discussed in the light of the possible site and mode of expression of the rd gene.
Cell aggregation and sexual differentiation in pairs of aggregation-deficient mutants of Dictyostelium discoideum
Authors: Gerisch G. , Huesgen A. 
Published: April 2021

ABSTRACT
A diffusible aggregation-stimulating factor (ASF) is released from a series of aggregationdeficient mutants. Biochemical markers indicate that these ASF-donor mutants are blocked at a later step of cell differentiation than an ASF-requiring mutant. ASF is able to bridge the initial block of differentiation in the latter mutant, such that development proceeds up to aggregation and even further. ASF is most probably neither identical with cyclic-AMP phosphodiesterase nor with an inhibitor of this enzyme which both are released from donor strains.
In certain combinations of aggregation-deficient mutants, macrocysts, the sexual stages of Dictyostelium, are formed. Also, motile giant cells believed to be zygotes are observed in these mutant combinations. The gamone known to be released from one mating type and to induce macrocysts in the other, is probably not identical with ASF since this factor is produced by mutants derived from either one of both mating types.
Polarity and gradients in lepidopteran wing epidermis: I. Changes in graft polarity, form, and cell density accompanying transpositions and reorientations
Authors: Nardi James B. , Kafatos Fotis C. 
Published: April 2021

ABSTRACTLepidopteran wing epidermis has certain advantages for studying the spatial organization of cell populations: ease of accessibility and manipulation, large size, an essentially two dimensional structure, and direct expression by the scale cells of their polarity. Grafting experiments reveal that polarity and density of graft cells as well as overall graft form are functions of a graft’s source and its transplantation site; graft polarity is also determined by the orientation of the graft. The results are consistent with the existence of at least one morphogenetic gradient along the proximo-distal axis of the wing’s upper epidermal layer. Various gradient models that might explain the experimental observations are considered.
Injected nuclei in frog oocytes: RNA synthesis and protein exchange
Authors: Gurdon J. B. , Partington G. A. , Robertis E. M. De 
Published: April 2021

ABSTRACTNuclei from HeLa and other mammalian cells have been injected into Xenopus oocytes. The synthesis, uptake, and release of RNA and proteins by injected nuclei have been investigated by autoradiography.Injected nuclei which undergo enlargement synthesize RNA continuously for up to 28 days. When oocytes are incubated in [3H]uridine or [3H]guanosine, injected nuclei are labelled nearly as strongly as the nucleoli, but much more strongly than the nucleoplasm of the oocyte’s germinal vesicle.Injected nuclei appear to increase their rate of RNA synthesis during incubation in oocytes. This apparent increase in the rate of RNA synthesis is correlated with nuclear enlargement, as well as with the loss of protein from injected nuclei and with their uptake of histone and nonhistone proteins from oocyte cytoplasm. Injected HeLa nuclei lose most of the previously synthesized RNA from their nucleoplasm, but little if any of the RNA from their remaining nucleoli.
Ultrastructure du nœud sino-atrial de l’embryon de souris aux jeunes stades du développement
Authors: Nanot J. , Douarin G. Le 
Published: April 2021

ABSTRACT
Ultrastructure of the embryonic mouse sinus node at the early stages of development
At early stages of development in the mouse embryo (12-13 days post-coitum) the cells of the sino-atrial node are homogeneous but are different to the atrial myocardic cells at this stage of development or a younger stage (9-10 days post-coitum).
Sino-atrial node cells are small; they have many ribosomes, the myofibrillar material and the Golgi apparatus are poorly developed. Membrane contacts are represented by simple appositions and some fascia adherentes. These cells show many pinocytic invaginations and subsarcolemmic vesicles.
From the 14th day post-coitum the sino-atrial node becomes heterogeneous. ‘Clear cells’ are present in the middle part of the node; they are characterized by their irregular shape and the poor development of their myofibrillar material. ‘Dark cells’ are observed at the periphery of the node and seem related to myocardial type cells described in the sino-atrial node of the late mouse foetuses.
Our observations do not support the existence of a 3rd cellular population, called by some authors: ‘transitional cells’. The problem of the segregation between sino-atrial cells and myocardial cells is discussed.
Fertilization of immature frog eggs: cleavage and development following subsequent activation
Authors: Elinson Richard P. 
Published: April 2021

ABSTRACTFrog eggs are normally fertilized after reaching metaphase II. When eggs are inseminated prior to that, several sperm enter, but entry does not activate the egg. When such inseminated, immature eggs were maintained until they became mature and then were artificially activated, the eggs began to cleave. The cleavage furrows were irregular and often multiple, but the eggs developed to blastulae or partial blastulae. About 2 → 5% of the eggs developed to tadpoles. Typical asters were not associated with the entering sperm; rather, asters appeared only after activation. The sperm nucleus often formed chromosomes which were attached to small spindles. It is clear that sperm which remain for a time in unactivated egg cytoplasm, retain their ability to promote cleavage and development. Aster formation required not only sperm centrioles but also activated egg cytoplasm.Sperm which entered either near the equator or in the animal half of mature eggs usually produced normal cleavage furrows. Sperm which entered the animal half of immature eggs produced multiple animal half furrows when the egg was subsequently activated. In contrast, sperm which entered near the equator of immature eggs often failed to induce furrowing on subsequent activation or produced unusual equatorial furrows. The difference in the type of furrow between eggs inseminated in the animal half or at the equator is interpreted as a consequence of dissociating sperm entry from the cortical contraction which occurs on activation.
The pattern of cell division during growth of the blastema of regenerating newt forelimbs
Authors: Smith A. R. , Crawley A. M. 
Published: April 2021

ABSTRACT
Pulse and continuous labelling with tritiated thymidine are used for a quantitative study of cell division rates in regeneration blastemas. Proliferation is initially uniform; later a proximodistal gradient develops in the mesenchyme, with the highest labelling index at the tip, where practically all cells are shown to be dividing. In the ectoderm there appear to be two growth bands, one close to the stump and the other close to the tip. The results are consistent with the progress zone theory, and agree well with the numerical estimates of growth rates used in our previously reported simulation.
The effects of ascorbic acid deficiency on collagen synthesis by mouse molar tooth germs in organ culture
Authors: Schiltz John R. , Rosenbloom Joel , Levenson Gordon E. 
Published: April 2021

ABSTRACT
Second molar tooth germs from 2-day-old Swiss-Webster mice, grown in organ culture for 7 days in ascorbic-acid-deficient medium, synthesized about 65 % as much protein (measured by incorporation of [14C]proline during a 24-h pulse) as did ascorbic-acid-supplemented controls. The newly synthesized proteins from ascorbic-acid-deficient cultures contained only about 7 % of the hydroxyproline content of the controls. Collagenase digestion of the newly synthesized proteins showed that collagen comprised the same fraction of the total protein synthesized under both culture conditions. This result indicates that the ascorbate-deficient cultures made significant quantities of underhydroxylated collagen. Partial characterization of the collagen alpha chains on carboxymethyl cellulose columns showed an αl/α2 ratio of about 5, suggesting that at least two different species of collagen were synthesized. The αl/α2 ratio of the chains recovered from the ascorbate-deficient cultures was also about 5 but the chains were slightly underhydroxylated and the total amount of these chains which could be identified accounted for only a small fraction of the total collagen which was synthesized. A large fraction of the synthesized collagenous protein was found in the culture medium, mostly in the form of lower molecular weight peptides. It is concluded that most of the collagen which is synthesized by ascorbate-deficient tooth-bud cultures is not utilized by the component tissues, but is probably degraded and released into the medium.
Developmental precocity after asynchronous egg transfer in mice
Authors: Marsk Lars 
Published: April 2021

ABSTRACT
Asynchronously transferred ova were found to implant 6-8 h earlier than did non-transferred eggs, indicating that the endometrium was receptive to implantation several hours before the native blastocysts were prepared to implant. This developmental precocity was also preserved on day 14, according to the results of a morphological rating study on day 14. Synchronously transferred ova showed no such developmental precocity. No statistically significant difference in implantation time or development on day 14 was found between the two strains, CBA and A/Jax. The importance of precocious development for planning teratological studies is emphasized.
Effects of prenatal administration of hadacidin, a cancer chemotherapeutic agent, on the development of hamster fetuses
Authors: Shah Ravindra M. 
Published: April 2021

ABSTRACTA single intraperitoneal injection of 1−2·5 g/kg body weight of hadacidin was teratogenic when administered to pregnant hamsters between days 8 and 11 of gestation. Both the frequency of malformation and resorption were related to the dose and time of hadacidin administration. The drug produced both gross and microscopic malformation in the fetus and impaired its general growth. The malformation involved craniofacial structures, central nervous system, respiratory, digestive and urinary systems, limbs and tail.Morphologically different types of cleft lip and cleft palate were related to the dose and time of hadacidin treatment. An association was observed between cleft lip, cleft palate and micrognathia on one hand, and between cleft palate and micrognathia on the other. Significance of association between the lip, the palate and the mandibular malformation was discussed and the hypothesis that human cases of Pierre Robin syndrome may result from an environmental assault was supported. It was suggested that the fetal weight and the microscopic analysis should be included in the criteria for the teratological drug safety evaluation procedures.
Partial characterization of ‘primordial germ cell-forming activity’ localized in vegetal pole cytoplasm in anuran eggs
Authors: Wakahara Masami 
Published: April 2021

ABSTRACT
Larvae of Rana chensinensis developed from fertilized eggs which had been subjected to ultraviolet (u.v.) irradiation on their vegetal hemisphere at a dose of 20000 ergs/mm2 within 60 min of fertilization contained no primordial germ cells (PGCs) when examined histologically at the stage when the operculum was complete (8 days after fertilization at 18 °C, stage 25 according to Shumway, 1940). The morphogenetic ability of vegetal pole cytoplasm from non-irradiated eggs to establish the PGCs was tested by injecting some fractions of this cytoplasm into the vegetal hemisphere of u.v.-irradiated eggs. Crude homogenate of the vegetal pole cytoplasm without large yolk platelets was able to restore the PGCs when injected into u.v.-irradiated eggs, but a similar fraction from animal half cytoplasm had no ability to form PGCs. The ‘PGC-forming activity’ demonstrated in the crude homogenate of the vegetal pole cytoplasm was not abolished by dialysis, lyophilization and heating to 90 °C for 10 min. When the homogenate was fractionated by differential centrifugation in 0·25 M sucrose, the ‘PGC-forming activity’ was recovered mainly in the precipitate of 15000 g for 30 min. The precipitate of 7000 g for 10 min had also a little ‘activity’. The possibility was discussed that the ‘PGC-forming activity’ demonstrated in the vegetal pole cytoplasm was associated with the germinal granules in the germ plasm rather than the mitochondria.
Developmental effects of X-irradiation of early Drosophila embryos
Authors: Bownes M. , Sunnell L. A. 
Published: April 2021

ABSTRACT
Drosophila embryos were treated at specific stages during early embryogenesis with various doses of X-irradiation. The lethality at various times during development was established and pattern defects in the adults noted. It was observed that the most sensitive stages of embryogenesis to X-ray-induced lethality were also the stages where most morpho-logical defects were found in the adults which emerged. This suggests that presumptive larval and adult cells are sensitive to X-rays at the same stages of embryogenesis.
A technique for introducing localized long-lasting implants in the chick embryo
Authors: Heaton Marieta B. 
Published: April 2021

ABSTRACT
A technique is described for making chronic, localized implants of drug-impregnated Silastic in early chick embryos. This silicone material has been shown to gradually and uniformly release its impregnated contents under such conditions. Following implantation of pieces of Silastic treated with the metaphase-blocking drugs colchicine and vinblastine into the wing-buds of day chick embryos, 53·75% survived 4-5 days, at which time they were sacrificed. Non-impregnated (control) Silastic was also implanted in a group of embryos. In this group, 90% survived 4-5 days. The antimitotic effects of the drugs were very well localized to implanted wings, which were reduced in size by approximately 55 % at the time of sacrifice (day 8-9 of incubation). In control embryos, the implanted wings were normal in size and general morphology. It is suggested that the technique could have numerous appli-cations for the study of neuroembryology or other aspects of embryogenesis.
Magnesium deficiency in embryos of Xenopus laevis
Authors: Miller John C. , Landesman Richard 
Published: April 2021

ABSTRACT
Embryos of Xenopus laevis reared in media with various low (⩽ 10−5 M) magnesium ion concentrations will exhibit differing degrees of a potentially lethal magnesium starvation syndrome depending on the ion concentration and rearing temperature. The higher the rearing temperature or the lower the magnesium ion content of the medium the more severely the syndrome will be expressed. (Normal development can be expected at temperatures 13-30 °C and magnesium ion concentrations &gt; 10−5 M to 10−2 M.)
The magnesium deficiency syndrome in Xenopus embryos is described in detail and compared with the normal and anucleolate conditions. The deficiency condition becomes manifest after hatching as retarded growth and differentiation with progressive paralysis and edema. At the same time alterations are observed in the pattern of soluble proteins. The use of magnesium ions as a probe for investigating developing systems is discussed.
On Early Cell Migration Processes in the Embryonic Brain
Authors: Bergquist Harry 
Published: April 2021

ABSTRACT
The earliest cell migration starts in the ventral part of the neural tube, especially around the plica encephali ventralis. A survey is given of the processes of successive migrations in different parts of the embryonic brain in different species. The first appearance of the second migration layer is in different parts of the brain in Torpedo and chick, possibly correlated with the differing functional importance of the parts in the two species. Experiments show that the formation of a second migration layer in the thalamus of chick embryos is not dependent on the presence of surrounding brain parts.
Wound Contraction in Relation to Collagen Formation in Scorbutic Guinea-pigs
Authors: Abercrombie M. , Flint M. H. , James D. W. 
Published: April 2021

ABSTRACT
In order to investigate the relation of wound contraction to collagen formation, standard skin wounds were made on two groups of guinea-pigs, one group kept on an ascorbic acid deficient diet, the other on the same diet supplemented with ascorbic acid. Ten days after wounding the amount of collagen in the repair tissue, estimated by the method of Neuman & Logan (1950), was much less in the deficient than in the non-deficient animals. Nevertheless, the amount of wound contraction which had occurred, representing a loss of 30 – 40 per cent, of the original wound area, was not significantly different in the two groups. Large amounts of hydroxyproline were found in the massive scabs commonly developed over the wounds of scorbutic animals. It is suggested that the force that brings about wound contraction may be developed by the connective tissue cells of the repair tissue.
Developmental Interactions in the Development of the Imaginal Muscles of Drosophila
Authors: Shatoury H. H. El 
Published: April 2021

ABSTRACT
The thorax of Drosophila contains two main sets of muscles, the dorsal flight-muscles and a lateral set. Among the latter are the trochanteral depressors of the legs, of which those associated with the second legs are the largest. The development of all these muscles during the pupal period is described and an account is given of the effects of the contraction of the tendons of the longitudinal muscles in producing the curvature of the mesothorax and the formation of the post-notum. The dorsal flight-muscles develop from an interaction between (a) three pairs of larval muscles; (b) mesoderm cells derived from the mesothoracic imaginal buds; (c) cells which migrate from the developing trochanteral depressors of the second leg. It is the latter cells which are responsible for splitting the three larval muscles of each side into six. The fibrillar muscles of the lateral set have a similar origin. The trochanteral depressors are tubular, not fibrillar, in structure. They are formed from mesoderm cells of the leg imaginal buds. If the imaginal bud of a first or third leg is removed from the late larva, not only the leg but also the corresponding trochanteral depressor is missing from the adult. If a second leg bud is removed, the dorsal flight-muscles and the lateral fibrillar muscles on that side also fail to develop. In extreme bithorax phenotypes, in which the metathoracic bud has formed a structure externally resembling a mesothorax, this region does not contain a second set of flight-muscles, although there are sometimes small badly differentiated representations of them. The secondary scutellum is not provided with a post-notum. If the normal mesothoracic bud of one side is extirpated from a larva which is developing the bithorax phenotype, the transformed metathoracic bud may shift forward and fuse with the mesothoracic bud of the opposite side. In some such cases the metathoracic mesoderm, in association with cells from the second trochanteral depressor, has developed into flight-muscles. It is concluded that the migrating cells of the second trochanteral depressor provide a stimulus which is essential for the differentiation of the flight-muscles.