bluuebunny/crossref_metadata_2025_split huggingface dataset:
The permeability to cytochalasin B of the new unpigmented surface in the first cleavage furrow of the newt’s egg
Authors: Selman G. G. , Jacob J. , Perry M. M. 
Published: April 2021

ABSTRACT
Two to 10 μg/ml cytochalasin B (CB) caused retraction of the first cleavage furrow in Triturus eggs, a spreading of the unpigmented surface from the furrow region and a flattening of the whole egg. CB appears to act against the contractility of the microfilamentous band at mid-cleavage so as to relax the furrow and also to weaken unpigmented surface to allow the egg to flatten. Uncleaved eggs and the initial formation of the cleavage groove were unaffected by CB. A fully-retracted first cleavage furrow reformed itself on transfer of the egg to normal medium but only at the time of second cleavage. Initiation of second cleavage depended upon there being sufficient of the original pigmented surface on the animal hemisphere.
Tritium-labelled CB of high specific activity was prepared and used to study its ability to penetrate the surface of newt eggs during cleavage. Scintillation counting of whole eggs showed that CB was not taken into the newt egg until mid-cleavage (about 17 min after the double stripe stage) when new surface began to spread in the cleavage furrow. Fixation in glutaraldehyde and osmium tetroxide retained radioactivity in the egg, but more CB was retained after fixation in osmium tetroxide alone than after double fixation. Most of the retained radioactivity was in yolk platelets. Autoradiographs were prepared of sectioned eggs which had been fixed at late cleavage after [3H]CB had flattened the furrow. These showed that CB entered the egg through the unpigmented surface which formed in the furrow but it could not enter through the pigmented surface. The impermeability of the pigmented surface explains the observations that CB does not prevent initial furrowing at cleavage. Once inside the egg CB is transported slowly. CB penetrates to a limited extent beneath the pigmented surface from its border with the unpigmented surface in the first cleavage furrow and this seems insufficient in some circumstances to suppress the contractile phase of second cleavage.
On the determination of the dorso-ventral polarity in the amphibian embryo: suppression by lactate of the formation of Ruffini’s flask-cells
Authors: Landström Ulf , Løvtrup-Rein Huguette , Løvtrup Søren 
Published: April 2021

ABSTRACTCells isolated from the vegetal hemisphere of the blastula of Ambystoma mexicanum differentiate spontaneously into ffbroblast-like cells. Similar cells may be formed from animal cells, provided they are induced either by vegetal cells or by Li+.We have found that lactate and various inhibitors of RNA synthesis suppress the spontaneous cell differentiation. The effect of lactate differs from that of the other agents in so far as lactate must be present before the second day of culture to suppress the outgrowth of fibroblasts on the third day; the other inhibitors are active also when added on the second day. An explanation of this difference may possibly be found in the fact that lactate suppresses incorporation of RNA but only by 40 %. The effect on the differentiation of various substances supposed to interfere with the metabolism of lactate was established. The results obtained were suggestive, but not conclusive.It is concluded that the effect of anaerobiosis may be explained as a lactate inhibition. The amounts of lactate under aerobic conditions are so slight that it is unlikely, but not impossible, that lactate is directly involved in the control of differentiation.
The development of Drosophila embryos after partial u.v. irradiation
Authors: Bownes M. , Sander K. 
Published: April 2021

ABSTRACT
U.v. irradiation of the anterior pole of nuclear multiplication stage Drosophila eggs produces embryos with defective anterior structures. At a low frequency embryos resembling some phenotypes of the bicaudal syndrome of Drosophila were observed. These embryos had no head or thorax and the eight abdominal segments were spread to the anterior of the embryo. Sometimes spiracles, characteristic of the most posterior embryonic segment were observed at the anterior of the embryo. The development of these embryos was followed, and abnormalities occurred as early as blastoderm formation. The extent of the blastoderm defects correlated well with the final abnormality in the embryo.
Blastemal kinetics and pattern formation during amphibian limb regeneration
Authors: Maden M. 
Published: April 2021

ABSTRACTTo investigate whether the uniqueness of proximal and distal limb regenerates could be attributed simply to differing blastema) growth characteristics, their increase in volume, cell number and cell-cycle times were determined. With respect to these parameters proximal and distal blastemas were identical and, furthermore, no evidence could be found for the existence of separate growth zones such as an apical proliferation centre or a progress zone within the blastema. It was therefore concluded that level-specific properties of the blastemal cells play the major role in determining the structure of the regenerate, not their growth characteristics. The only discernible difference was in the cell number within the two types of blastema at the onset of cartilage redifferentiation - proximal regenerates had 60 % more cells. Thus it seems that the larger the pattern to be regenerated (the more proximal the amputation plane), the larger the primordium within which that pattern first appears. These two conclusions are discussed in relation to current theories of pattern formation during limb regeneration and development and a new way of envisaging the regeneration of pattern is described.
Biosynthetic events of hydrid regeneration II. Patterns and profiles of RNA synthesis during distal morphogenesis
Authors: Brooks Dennis C. , Voland Joseph R. , Lesh-Laurie Georgia E. 
Published: April 2021

ABSTRACTThe pattern of RNA synthesis during the first 48 h of distal regeneration in Hydra oligactis has been investigated. In addition the RNA synthetic profiles during selected time periods have been studied.RNA synthesis was found to increase five-fold during the first 3 h of regeneration and remained high throughout the rest of the 48 h period. An additional increase was observed 27-30 h following subhypostomal excision, immediately preceding the appearance of the first tentacle pair. The RNA synthetic level then returned to that found at 3 h of regeneration. This pattern was similar to that reported previously for DNA synthesis.Profiles of radioactively labeled RNA remained constant during most of the times studied, showing the presence of newly synthesized 28S, 18S, 5S, and4S RNA. During two time periods, 28-32 h and 36-40 h, a novel 8S RNA species was observed. The occurrence of this species coincided with times of increased overall RNA synthesis and immediately preceded tentacle elaboration.
Sex determination in germ line chimeras ofDrosophila melanogaster
Authors: Deusen E. B. Van 
Published: April 2021

ABSTRACTOf 55 flies developing from blastoderms which had received male or female pole cell transplants, 15 (7 females and 8 males) were shown by progeny testing to be germ line chimeras. Since donor and host pole cells were genetically marked with contrasting X- or Y-linked alleles, the progeny testing scheme enabled the genotypic sex of the donor component undergoing gametogenesis to be identified as either the same as (‘homosexual’ chimeras) or opposite (‘heterosexual’ chimeras) that of the host.All seven of the fematechimeras were identified as ‘homosexual’ chimeras carrying only chromosomally female donor and XX host germ cells. Similarly, all eight males were shown to be ‘homosexual’ chimeras with chromosomally male XYdonor and JfThost germ cells. The chromosomal sex of the donor component undergoing gametogenesis was in every case the same as the phenotypic sex of the host.Since there is an equal probability of constructing either a ‘homosexual’ or a ‘heterosexual’ chimera during pole cell transplantation, the ability of pole cells to differentiate functional gametes in hosts of the opposite sex was tested 50% of the time even if sex reversal of these donor pole cells could not be demonstrated. Thus the absence of ‘heterosexual’ chimerism strongly supports the interpretation that the phenotypic sex of a germ cell in Drosophila is determined entirely by its own chromosome constitution, not by that of the gonadal mesoderm.
Effects of extremely low osmolarity on fertilized mouse eggs
Authors: Opas Jolanta 
Published: April 2021

ABSTRACT
When fertilized one-cell eggs are subjected to distilled water treatment for 2-6 min, cytoplasm bulges through the sperm-slit in the zona pellucida and forms a cytoplasmic fragment (CF). CFs were observed in 86·5% of eggs; in 20·9% of cases CFs contained a pronucleus (or pronuclei). In 53·4 % of eggs permanent incorporation of the second polar body (2 P.B.) into the egg cytoplasm occurred.
These phenomena occurring in different combinations produced 6·2 % of haploid eggs, 10·3 % of diploid eggs with a pronucleus replaced by 2 P.B. nucleus, and 43·1 % of triploid eggs. 4·4 % of eggs were enucleated. The remaining group comprised diploid eggs which were either not affected by the treatment (6·4 %) or lost a certain amount of cytoplasm by formation of an anucleate CF (29·6 %). The frequencies of the types of reaction were related to the post-fertilization stage of eggs.
All eggs except the enucleated ones were able to develop to the stage of morula or blasto-cyst. Triploids developed until the 12th day of pregnancy and diploids that had lost up to 15 % of the cytoplasm developed to term. There was a twofold reduction in the percentage of preimplantation development when treated eggs originated from induced rather than spontaneous ovulation.
Control of anteroposterior pattern in the axolotl forelimb by a smoothly graded signal
Authors: Slack J. M. W. 
Published: April 2021

ABSTRACT
In the accompanying paper (Slack, 1977), it is suggested that the normal anteroposterior pattern of the amphibian limb arises as a consequence of an interaction between the prospective limb and the flank. It has been shown that that part of the limb rudiment which is adjacent to flank tissue in the embryo becomes a posterior edge. So far we have considered neither the mechanism of this ‘posterior determination’, nor the mechanism of limb individuation, that is the process whereby cells in different anteroposterior positions differentiate to form a characteristic pattern of muscles and cartilages.
Reactivity of rat placental cells with alloantisera
Authors: Ferguson Frederick G. , Palm Joy 
Published: April 2021

ABSTRACTThe nature of the protection afforded the placental structure against the immunologic consequences that could result from maternal exposure to paternal alloantigens remains obscure. One problem has been difficulty in antigenically defining the individual cellular components of the intact placenta. These studies were designed to examine serologically, with specific antisera, five cell types isolated from the rat placenta. The results indicate that non-Ag-B antigens are present on the cytotrophoblast cells, while Ag-B antigens are absent on all the cells except an undefined population of fibroblasts. Of particular significance is the obvious absence of detectable surface antigens on the cells directly in contact with the maternal tissues, the trophoblast mononuclear giant cells.
Studies on Embryonic Induction using Radioactive Tracers
Authors: Sirlin J. L. , Brahma S. K. , Waddington C. H. 
Published: April 2021

ABSTRACT
Organizer and other tissues of urodele gastrulae were labelled by cultivation in glycine-Cu, methionine-Sss, or adenine-8-Ci4. They were then either inserted into the blastocoel of unlabelled hosts or made into ‘sandwiches’ between two flaps of gastrula presumptive ectoderm. Two or three days later the location of the tracer was investigated by stripping film autoradiography. The sandwich experiments gave the clearer results. The tracer passed into the tissues surrounding the graft and was accumulated mainly in the nuclei, though some was also present in the cytoplasm. A higher concentration was reached in the induced neural tissue and outermost layer of the epidermis than in other tissues. A greater fraction of adenine was mobile than of the amino-acids. The evidence suggests that there is no massive transfer of cytoplasmic particles and that there is considerable diffusion of tracer in the form of small molecules. It does not rule out the possibility of a relatively slight transfer of cytoplasmic particles, and, indeed, suggests that there is some specific migration of tracer into induced tissues, though it remains uncertain in what form this occurs.
Reduction of the rate of outgrowth, cell density, and cell division following removal of the apical ectodermal ridge of the chick limb-bud
Authors: Summerbell Dennis 
Published: April 2021

ABSTRACTRemoval of the apical ectodermal ridge causes a reduction in the rate of outgrowth of the wing-bud and the loss of distal parts. More specifically it causes a short-term increase in cell density and cell death and a decrease in the rate of cell proliferation. The evidence supports the hypothesis of density-dependent control of cell division and suggests that there may also be a mechanism regulating skeletal length at the time of differentiation. An informal model is presented to explain the observations.
Intercellular junctions, intramembranous particles and cytoskeletal elements of deep cells of theFundulusgastrula
Authors: Hogan James C. , Trinkaus J. P. 
Published: April 2021

ABSTRACTThe fine structure of motile deep cells of the gastrula stage of Fundulus heteroclitus was studied with transmission electron microscopy, using both thin sectioning and freeze-cleave techniques. Gastrula deep cells form extensive non-junctional appositions with each other, in which the apposed plasma membranes are parallel and separated by a distance of 26 –28 nm. They also form gap junctions. Tight junctions, desmosomes, and extensive interdigitations of apposed plasma membranes were not observed. The plasma membranes of deep cells contain numerous unclustered intramembranous particles. Cytoplasmic microtubules were found, but they appear to be small in number, sparsely distributed, and mainly randomly oriented. Microfilaments are also present and are localized largely in the cortical cytoplasm and in thin cell extensions. The significance of these findings for the contact and locomotory behavior of deep cells is discussed.
Somatic nuclei in amphibian oocytes: evidence for selective gene expression
Authors: Robertis E. M. De , Partington G. A. , Longthorne R. F. , Gurdon J. B. 
Published: April 2021

ABSTRACTPrevious work has shown that multiple HeLa nuclei injected into Xenopus oocytes remain transcriptionally active for many days and that the expression of HeLa genes in oocytes can be detected by 2-D gel electrophoresis.We show here that of 25 proteins which have the electrophoretic properties of HeLa gene products, only 3 are expressed in injected oocytes. To test that these proteins are products of HeLa genes, and not products of activated oocyte genes, we have injected HeLa nuclei into enucleated oocytes. Three days later, several HeLa proteins were synthesized.The turning off of most HeLa genes in injected oocytes is apparently not at the translational level. This is indicated by the fact that adenovirus mRNA is efficiently translated when injected into Xenopus oocytes. When adenovirus-infected HeLa cell nuclei are injected into oocytes the adenovirus genes are not expressed, although some HeLa genes are expressed by the same nuclei.The same HeLa genes as are expressed or switched off in injected Xenopus oocytes are also preferentially expressed or switched off in injected oocytes of a Urodele amphibian, Pleurodeles. This suggests that conditions or molecules may exist in oocytes which selectively impose on injected nuclei a new programme of gene expression.
Pattern formation inDictyostelium discoideum:II. Differentiation and pattern formation in non-polar aggregates
Authors: Forman D. , Garrod D. R. 
Published: April 2021

ABSTRACTCells of the cellular slime mould D. discoideum were allowed to form into spherical aggregates, by shaking vegetative cells as a suspension in phosphate buffer. In such conditions, grex polarity is never established and surface sheath is not formed (Loomis, 1975 a). Despite the absence of such characteristics of normal development, differentiation of prespore cells, as tested for by immunofluorescent staining, and the organization of such cells into a patterned structure still occurred within the aggregates.Differentiation of prespore cells was found to occur within the cultures at times equivalent to those in the normal life cycle; such differentiation could be advanced by pulsation of the cultures with cyclic-AMP. When cell contact and aggregate formation was prevented, differentiation never occurred within the single cells. Our results suggest that the prespore cells develop randomly within the aggregate and that a pattern is subsequently formed as a result of sorting out of cell types within the cell mass. Aggregates shaken for extended periods of time showed development into cyst-like structures.The process of pattern formation that occurred within these aggregates which possess neither polarity nor a grex tip, would be unlikely to involve any mechanism of positional information signalling. The relevance of polar organization in the generation of pattern in the normal life cycle may therefore be questionable. We present a model of pattern formation in the slime mould in which sorting out of predetermined cell types is viewed as the major mechanism in bringing about patterned organization of the grex precursor cells.
Abnormal oogenesis and embryogenesis resulting from centrifugingDrosophila melanogasterfemales
Authors: Bownes Mary 
Published: April 2021

ABSTRACTFemales of Drosophila melanogaster were centrifuged at 2400 g and 4200 g for 3 h in a number of different orientations. The oocytes in various stages of vitellogenesis become separated into three layers; a centrifugal yolk layer, a central cytoplasmic layer, and a centripetal lipid layer. The direction of layering is related to the orientation of the female. The process of recovery of the ovaries was followed and the development of the eggs laid analysed. Many of the eggs laid over the subsequent 3 days die very early in development and fail to produce any differentiated structures. Some hatch into normal larvae and others produce defective embryos. The most common defect being a misarrangement of the segmentation. The differences in the kinds of experimentally inducible pattern aberrations in Drosophila and other diptera is discussed.
Growth of opossum embryosin vitroduring organogenesis
Authors: New D. A. T. , Mizell M. , Cockroft D. L. 
Published: April 2021

ABSTRACTOpossum embryos, explanted between primitive streak and late fetal stages, were grown in culture for periods of 20–30 h. Many of the explants had a good heartbeat and blood circulation in embryo and yolk sac after 12 h, and a few after 24 h. Growth of the embryos included formation of the neural tube and body flexures, increase in the number of somites, differentiation of the limbs and digits, and development of the amnion and allantois. Embryos explanted during the last day of gestation showed persistent and vigorous body movements in culture, particularly of the forelimbs, head and tongue.
The formation of discrete muscles from the chick wing dorsal and ventral muscle masses in the absence of nerves
Authors: Shellswell G. B. 
Published: April 2021

ABSTRACTIt is well known that the different muscles in the vertebrate limb develop by a series of splittings and subdivisions of dorsal and ventral muscle masses. The mechanism for this process is not clear, and the suggestion from previous studies that tension exerted by the growing limb stimulates these splittings is now thought unlikely. It has also been proposed that nerves play an important part in the separations by physically pushing the muscle mass apart. There is also the possibility that nerves could stimulate differential contraction of parts of the muscle mass, leading to a shearing effect and resulting in separation.In this study, peripheral nerves are removed by the administration of the nicotinamide analogue 3-acetylpyridine before the start of muscle mass division. The resulting pattern of muscle is normal although nerves are completely absent. This clearly rules out any major role of nerves in the formation of the muscle pattern, although many authors have shown that innervation is important for the maintenance and later development of the separated muscles.While the mechanism of the process of division of the muscle masses remains unknown, it is suggested that there are changes in cellular behaviour at areas corresponding to the future spaces between the muscles. These changes may be specified by some aspect of positional information within the limb. They might involve muscle cells stopping or reversing their differentiation as muscle in the areas forming the future spaces, or perhaps change the adhesion properties of the muscle cells to cause them to ‘sort out’ and separate. Alternatively, a localized invasion of non-muscle mesenchymal cells at the future spaces could lead to separation of discrete muscles. These possibilities are at present under investigation.
Effects of the teratogenic folic acid antagonist, 9-methyl pteroylglutamic acid, on hydroxyproline levels in fetal rat limbs
Authors: Schmidt R. R. , Chepenik K. P. , Paynton B. V. 
Published: April 2021

ABSTRACTPregnant rats were subjected to either a folic-acid-deficient regimen that produces multiple congenital skeletal malformations, or a control folic-acid-supplemented regimen. Fetal limbs were extirpated on days 16 and 18 of gestation, pooled from each litter, homogenized, and aliquots set aside for hydroxyproline, protein and DNA determinations. We found that (1) the amount of protein recovered per treated limb was approximately half that of controls on both days, (2) the amount of protein recovered per treated or control day-18 limb was twice that of a day-16 limb, (3) treated limbs constituted the same percentage of total body weight as in controls on day 16, but a smaller percentage than in controls on day 18, and (4) the concentration of hydroxyproline (μg/mg protein) was significantly less for treated limbs than for controls on day 18 of gestation. We noted also that: (1) lowest hydroxyproline concentrations were found in limbs from treated fetuses with gross limb malformations, (2) intermediate concentrations were found in limbs of treated fetuses not exhibiting gross limb malformations, and (3) highest concentrations were found in control limbs. We suggest that the treatment resulted in (1) a decreased rate of accumulation of protein in limbs prior to day 16, but not from day 16 to day 18, (2) a decreased rate of accumulation of some non-protein component(s) in treated limbs from day 16 to day 18, and (3) an altered collagen metabolism.