bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression of intermediate filament proteins during development of Xenopus laevis: I.cDNA clones encoding different forms of vimentin
Authors: Herrmann Harald , Fouquet Bernadette , Franke Werner W. 
Published: April 2021

ABSTRACT
To provide a basis for studies of the expression of genes encoding the diverse kinds of intermediate-filament (IF) proteins during embryogenesis of Xenopus laevis we have isolated and characterized IF protein cDNA clones. Here we report the identification of two types of Xenopus vimentin, Viml and Vim4, with their complete amino acid sequences as deduced from the cloned cDNAs, both of which are expressed during early embryogenesis. In addition, we have obtained two further vimentin cDNAs (Vim2 and 3) which are sequence variants of closely related Viml. The high evolutionary conservation of the amino acid sequences (Viml: 458 residues; Mr ∼ 52800; Vim4: 463 residues; Mr∼ 53500) to avian and mam malian vimentin and, to a lesser degree, to desmin from the same and higher vertebrate species, is emphasized, including conserved oligopeptide motifs in their head domains. Using these cDNAs in RNA blot and ribonu clease protection assays of various embryonic stages, we observed a dramatic increase of vimentin RNA at stage 14, in agreement with immunocytochemical results ob tained with antibody VIM-3B4. The significance of very weak mRNA signals detected in earlier stages is dis cussed in relation to negative immunocytochemical re sults obtained in these stages. The first appearance of vimentin has been localized to a distinct mesenchymal cell layer underlying the neural plate or tube, respect ively. The results are discussed in relation to programs of de novo synthesis of other cytoskeletal proteins in amphibian and mammalian development.
Spots and stripes: the patterning spectrum in the cellular slime mould Polysphondylium pallidum
Authors: Mcnally James G. , Cox Edward C. 
Published: April 2021

ABSTRACT
Whorls of the cellular slime mould Polysphondylium pallidum originate as spherical cell masses that during normal morphogenesis produce tips only at equidistant positions around their equator. We have observed a series of new patterns in whorls that differ from normal whorls only in that they are larger or more elongated. Among the novel patterns found were arrays of tips distributed fairly regularly over the whole whorl surface, as well as striped patterns detected at earlier stages with a tip-specific antigen. These altered patterns demonstrate that a whorl’s size and shape are by themselves important factors in pattern determination. We have compared the range of observed patterns to those predicted by a variety of different theories. We find that while no one theory can account in detail for all of our observations, predictions based on Turing’s scheme of pattern formation come the closest.
Identification of an adult-specific glial progenitor cell
Authors: Wolswijk Guus , Noble Mark 
Published: April 2021

ABSTRACT
We have found that glial progenitor cells isolated from the optic nerves of adult rats are fundamentally different from their counterparts in perinatal animals. In our studies on bipotential oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells, we have seen that O-2Aadutt progenitor cells can be distinguished from O-2Aperinatal progenitors by their morphology and antigenic pheno type, their much longer cell cycle time (65 h versus 18 h), slower rate of migration rate (4μmh-1versus 21μm h–1), and their time course of differentiation into oligodendrocytes or type-2 astrocytes in vitro (⩽3 days versus &gt;5 days). At least some of the differences between 0–2Aadult and 0–2Aperinatal progenitor cells appear to be clearly related to the differing cellular requirements of the adult and perinatal central nervous system (CNS).
The properties of the 0–2Aadult progenitor cells may make these cells ideally suited for the needs of the adult CNS, where rapid exponential increases in the number of oligodendrocytes and 0–2A progenitor cells would be inappropriate. However, the properties of the 0–2Aadult progenitor cells are such that they may not be able to replace oligodendrocytes in sufficient numbers to repair extensive or recurrent damage in the adult brain, such as in patients suffering from the human demyelinating disease multiple sclerosis. Moreover, available information about other tissues suggests that the transition from perinatal to adult progenitor cell types may rep resent a developmental mechanism of general import ance.
Ammonia depletion and DIF trigger stalk cell differentiation in intact Dictyostelium discoideum slugs
Authors: Wang Mei , Schaap Pauline 
Published: April 2021

ABSTRACT
The differentiation-inducing factor, DIF, was previously shown to induce stalk cell differentiation in Dictyostelium discoideum cells incubated as submerged monolayers. We investigated the mechanism that regulates the differentiation of stalk cells in the intact organism. It was found that in migrating or submerged slugs DIF cannot induce stalk cell differentiation, which is most likely due to the presence of a DIF antagonist. Cyclic AMP and ammonia were earlier reported to act as DIF antagonists in vitro. We show here that ammonia, but not cAMP, acts as an antagonist for DIF-induced stalk cell differentiation in vivo. DIF can induce stalk cell differentiation when ammonia levels in the slug are enzymically depleted. However, depletion of cAMP levels does not increase the efficacy of DIF. We propose that the induction of stalk cell differentiation during early culmination may be triggered by a drop in ammonia levels inside the organism.
Locomotory competence and laminin-specific cell surface binding sites are lost during myoblast differentiation
Authors: Goodman Simon L. , Deutzmann Rainer , Nurcombe Victor 
Published: April 2021

ABSTRACT
The specific interaction of embryonal cells with the extracellular matrix (ECM) is one of the principal forces influencing embryonal development (Hay, 1984; Trinkaus, 1984). We used a muscle satellite cell line (MM14dy) to determine the relationship between locomotory response to laminin and the expression of specific cell surface binding sites for it.
Time lapse videomicroscopic analysis was used to study the locomotory response and radioligand binding assays and cell attachment assays were used to follow the expression levels of binding sites for laminin and its subfragments E8 and El –4. We report here the novel finding that the ability of MM14dy to locomote over laminin diminishes and finally vanishes as the cells differentiate. The simultaneous drop in expression of binding sites for laminin is interpreted as being of potential significance during development and repair.
Consequences of somite manipulation on the pattern of dorsal root ganglion development
Authors: Kalcheim Chaya , Teillet Marie-Aimée 
Published: April 2021

Abstract
We have investigated dorsal root ganglion formation, in the avian embryo, as a function of the composition of the paraxial somitic mesoderm. Three or four contiguous young somites were unilaterally removed from chick embryos and replaced by multiple cranial or caudal halfsomites from quail embryos. Migration of neural crest cells and formation of DRG were subsequently visualized both by the HNK-1 antibody and the Feulgen nuclear stain.
At advanced migratory stages (as defined by Teillet et al. Devi Biol. 120, 329 – 347 1987), neural crest cells apposed to the dorsolateral faces of the neural tube were distributed in a continuous, nonsegmented pattern that was indistinguishable on unoperated sides and on sides into which either half of the somites had been grafted. In contrast, ventrolaterally, neural crest cells were distributed segmentally close to the neural tube and within the cranial part of each normal sclerotome, whereas they displayed a nonsegmental distribution when the graft involved multiple cranial half-somites or were virtually absent when multiple caudal half-somites had been implanted.
In spite of the identical dorsal distribution of neural crest cells in all embryos, profound differences in the size and segmentation of DRG were observed during gangliogenesis (E4 – 9) according to the type of graft that had been performed. Thus when the implant consisted of compound cranial half-somites, giant, coalesced ganglia developed, encompassing the entire length of the graft. On the other hand, very small, dorsally located ganglia with irregular segmentation were seen at the level corresponding to the graft of multiple caudal halfsomites. We conclude that normal morphogenesis of dorsal root ganglia depends upon the craniocaudal integrity of the somites.
Alternative splicing of fibronectin is temporally and spatially regulated in the chicken embryo
Authors: Ffrench-Constant Charles , Hynes Richard O. 
Published: April 2021

ABSTRACT
The primary gene transcript for the adhesive extracellular matrix glycoprotein fibronectin (FN) is alternatively spliced in three regions (EIIIA, EIIIB and V). At least one of these regions (V) has been shown to encode cell-binding sites, suggesting that splicing represents a mechanism to create functionally different forms of FN at different times and places. In order to test this hypothesis, we have examined the extent of alternative splicing of fibronectin during embryonic development. The distribution of the different spliced forms of FN mRNA in developing chicken embryos was determined using probes specific for the spliced regions in ribonuclease protection and in situ hybridization experiments. At embryonic day 2–4 (E2–4), all three spliced regions were included wherever FN mRNA was detected. At E16, however, we found spatially distinct splicing differences within the embryo, with cell-type-specific splicing excluding EIIIA and/or EIIIB in some tissues. In contrast, we did not detect exclusion of the V region. In a more detailed developmental study of the simplest of these tissues, the chorioallantoic membrane, we found that EIIIB was preferentially excluded after the completion of growth. These results suggest that FN splicing is used during development as a mechanism to create different forms of FN within the extracellular matrix by the inclusion or exclusion of specific segments. The data are consistent with an essential role for one of these segments, E111B, in the migration and/or proliferation of embryonic cells prior to their terminal differentiation and also suggest possible roles for the EIIIA segment.
Analysis of lens cell fate and eye morphogenesis in transgenic mice ablated for cells of the lens lineage
Authors: Breitman Martin L. , Bryce Dawn Marie , Giddens Elizabeth , Clapoff Susan , Goring Daphne , Tsui Lap-Chee , Klintworth Gordon K. , Bernstein Alan 
Published: April 2021

ABSTRACT
Transgenic mice carrying the diphtheria toxin A gene driven by mouse γ2-crystallin promoter sequences manifest microphthalmia due to ablation of fiber cells in the ocular lens. Here we map ablation events in the lens by crossing animals hemizygous for the ablation construct with transgenic mice homozygous for the in situ lacT reporter gene driven by identical γ2 crystallin promoter sequences. By comparing the spatial distribution of tacZ-expressing cells and the profile of γ-crystallin gene expression in the lenses of normal and microphthalmic offspring, the contributions of specific cell types to lens development were examined. The results suggest that phenotypically and developmentally distinct populations of lens fiber cells are able to contribute to the lens nucleus during organogenesis. We also show that dosage of the transgene and its site of integration influence the extent of ablation. In those mice homozygous for the transgene and completely lacking cells of the lens lineage, we show that the sclera, cornea, and ciliary epithelium are reduced in size but, otherwise, reasonably well formed. In contrast, the anterior chamber, iris, and vitreous body are not discernible while the sensory retina is highly convoluted and extensively fills the vitreous chamber.
The oral-aboral axis of a sea urchin embryo is specified by first cleavage
Authors: Cameron R. Andrew , Fraser Scott E. , Britten Roy J. , Davidson Eric H. 
Published: April 2021

ABSTRACT
Several lines of evidence suggest that the oral–aboral axis in Strongylocentrotus purpuratus embryos is specified at or before the 8-cell stage. Were the oral-aboral axis specified independently of the first cleavage plane, then a random association of this plane with the blastomeres of the four embryo quadrants in the oral-aboral plane (viz. oral, aboral, right and left) would be expected. Lineage tracer dye injection into one blastomere at the 2-cell stage and observation of the resultant labeling patterns demonstrates instead a strongly non-random association. In at least ninety percent of cases, the progeny of the aboral blastomeres are associated with those of the left lateral blastomeres and the progeny of the oral blastomeres with the right lateral ones, respectively. Thus, ninety percent of the time the oral pole of the future oral-aboral axis lies 45° clockwise from the first cleavage plane as viewed from the animal pole. The nonrandom association of blastomeres after labeling of the 2-cell stage implies that there is a mechanistic relation between axis specification and the positioning of the first cleavage plane.
Mouse neural crest cells secrete both urokinase-type and tissue-type plasminogen activators in vitro
Authors: Menoud P. A. , Debrot S. , Schowing J. 
Published: April 2021

ABSTRACT
Neural tubes of E8·5 day mouse embryos were dissected and cultured in serum substitute-supplemented medium to allow the emigration of neural crest cells. After 48 h of culture the neural tubes were removed. The neural crest cells were then cultured for 12 h in serum-free medium, and their culture supernatant was studied by electro-phoresis and zymography. The cultured cells were shown to secrete both urokinase-type and tissue-type plasminogen activators. When the truncal neural tube was divided in four equal segments, the secretion pattern of the two types of plasminogen activators was similar for the cells from the three most anterior segments; cells having migrated from the most caudal one, i.e. consisting of the neural plate, secreted a higher level of urokinase-type plasminogen activator. The secretion in vitro of plasminogen activators by neural crest cells is in accord with the postulated importance of these proteases in cellular migration.
Cellular contacts required for neural induction in Xenopus embryos: evidence for two signals
Authors: Dixon Jane E. , Kintner Chris R. 
Published: April 2021

ABSTRACT
Neurogenesis begins in amphibian embryos around the time of gastrulation when a portion of the ectoderm receives an inducing signal from dorsal mesoderm. Two different proposals have been made for how ectoderm must come into contact with dorsal mesoderm in order for the inducing signal to pass between the two tissues. Induction in one proposal would require normal gastru-lation movements to bring dorsal mesoderm under-neath, and into apposition with, the overlying ectoderm. The inducing signal in this case would pass between dorsal mesoderm and ectoderm as apposed tissue layers. The other proposal is that induction requires only a small contact between ectoderm and dorsal mesoderm at the boundary they share before gastrulation. The in-ducing signal by this proposal would pass laterally across this small area of contact between mesoderm and ectoderm, perhaps before gastrulation, and spread within the ectodermal cell layer. Since it is not known to what extent neurogenesis depends on each of these proposed contacts between ectoderm and dorsal meso-derm, we have generated explants of embryonic tissue in which one or the other type of contact between meso-derm and ectoderm is favored. The amount of neural tissue formed under these various conditions was then assessed using a quantitative RNase protection assay to measure the levels of two neural-specific RNA tran-scripts. The results show that neural tissue forms efficiently when ectoderm and dorsal mesoderm only interact laterally within a plane of tissue. In contrast, neural tissue, forms extremely poorly when ectoderm is placed experimentally in apposition with involuting, anterior-dorsal mesoderm. Finally, a synergistic effect is obtained when both types of contacts can occur between ectoderm and mesoderm indicating that two signals may be required for neural induction in Xenopus embryos.
A vital dye analysis of the timing and pathways of avian trunk neural crest cell migration
Authors: Serbedzija George N. , Bronner-Fraser Marianne , Fraser Scott E. 
Published: April 2021

ABSTRACT
To permit a more detailed analysis of neural crest cell migratory pathways in the chick embryo, neural crest cells were labelled with a nondeleterious membrane intercalating vital dye, Dil. All neural tube cells with endfeet in contact with the lumen, including premigratory neural crest cells, were labelled by pressure injecting a solution of Dil into the lumen of the neural tube. When assayed one to three days later, migrating neural crest cells, motor axons, and ventral root cells were the only cells types external to the neural tube labelled with Dil. During the neural crest cell migratory phase, distinctly labelled cells were found along: (1) a dorsolateral pathway, under the epidermis, as well adjacent to and intercalating through the dermamyotome; and (2) a ventral pathway, through the rostral portion of each sclerotome and around the dorsal aorta as described previously. In contrast to those cells migrating through the sclerotome, labelled cells on the dorsolateral pathway were not segmentally arranged along the rostrocaudal axis. Dil-labelled cells were observed in all truncal neural crest derivatives, including subepidermal presumptive pigment cells, dorsal root ganglia, and sympathetic ganglia. By varying the stage at which the injection was performed, neural crest cell emigration at the level of the wing bud was shown to occur from stage 13 through stage 22. In addition, neural crest cells were found to populate their derivatives in a ventral-to-dorsal order, with the latest emigrating cells migrating exclusively along the dorsolateral pathway.
Regeneration and pattern formation in planarians: II. Local origin and role of cell movements in blastema formation
Authors: Saló Emili , Baguñá Jaume 
Published: April 2021

ABSTRACT
In planarians, blastema cells do not divide, and growth of blastema is thought to result from the steady accumulation, beneath the wound epithelium, of undifferentiated cells produced by cell division in the stump. However, whether these cells come only from local stump sources or whether cells placed far from the wound can also participate, after long-range migrations, in the growth of blastema, is still uncertain.
To study this problem, we have analysed three basic parameters of the process of regeneration: cell kinetics of blastema growth; number of cells produced by mitosis in the stump areas near the wound (postblastema); and rates of movement (‘migration’) of undifferentiated cells using grafting procedures with nuclear and chromosomal markers.
The results show that: (1) cells near the wound area spread (move) ar higher rates than cells placed far from it (90–140 μm day− 1versus 40–50/ μm day− 1); (2) cells originally placed farther than 500 fan from the wound boundary are hardly represented within 3- and 5-day-old blastemata; and (3) the number of cells produced by mitosis within a 200-300 fun postblastema area around the wound seem sufficient to explain, provided their rates of movement are taken into account, the increasing number of blastema cells. From this, it is concluded that blastema cells in planarians originate from local stump areas, and that mitotic activity jointly with local cell movement within a 200–300 μm postblastema area around the wound match the increasing number of blastema cells during regeneration. The implications of these results for blastema growth and pattern formation mechanisms are discussed.
Modifications of oogenesis and development in marsupial frogs
Authors: del Pino Eugenia M. 
Published: April 2021

ABSTRACT
Early development in animals is guided by the RNA reserves of the egg (see Davidson, 1986 for a review), and therefore variations in eggs might correlate with changes in their patterns of early development. Frogs are organisms especially suitable for analyzing the relationship of oogenesis to development, because many frog species have evolved distinctive changes to avoid or diminish their period of aquatic dependence (Lamotte and Lescure, 1977; Duellman and Trueb, 1986). The analysis of the developmental adaptations that accompany the modes of frog reproduction, however, is hindered by the fact that the best investigated frogs, such as Xenopus laevis or Rana pipiens, have aquatic reproduction and similar modes of oogenesis and early development, although the former is in a family considered to be primitive (Pipidae), with adult specializations for an extreme aquatic life-style, whereas the latter is in an advanced family (Ranidae), with more pronounced terrestrial adaptations in the adult (Table 1). The modes of reproduction found in the 21 living families of frogs is shown in Table 1. The traditional order of anuran classification has been maintained in Table 1, but the higher taxa are not given. In an ancient and diverse group, such as the anurans, there might be many cases of similarity due to derived features, and the current knowledge of many characters and their evolutionary change does not allow the reconstruction of the anuran phylogeny (Duellman and Trueb, 1986).
Mesoderm-inducing factors and Spemann’s organiser phenomenon in amphibian development
Authors: Cooke Jonathan 
Published: April 2021

ABSTRACT
Certain proteins from ‘growth factor’ families can initiate mesodermal development in animal cap cells of the amphibian blastula. Cells that are in early stages of their response to one such factor, XTC-MIF (Smith et al. 1988), initiate the formation of a new axial body plan when grafted to the ventral marginal zone of a similarly aged host embryo (Cooke et al. 1987). This replicates the natural control of this phase of development by the dorsal blastoporal lip when similarly grafted; the classical ‘organiser’ phenomenon. I have explored systematically the effect, upon the outcome of this pattern formation using defined inducing factors, of varying graft size, XTC-MIF concentration to which graft cells were exposed, length of exposure before grafting, and host age. The ‘mesodermal organiser’ status, evoked by the factor, appears to be stable, and the variables most influencing the degree of completeness and orderliness of second patterns are graft size and factor concentration.
Inappropriately large grafts are not effective. A Xenopus basic fibroblast growth factor homologue, present in the embryo and known to be a strong inducer but of mesoderm with a different character from that induced by XTC-MIF, produced no episode of pattern formation at all when tested in the procedure described in this paper. Organiser status of grafts that have been exposed to mixtures of the two factors is set entirely by the supplied XTC-MIF concentration. Lineage labelling of these grafts, and of classical dorsal lip grafts, reveals closely similar though not identical patterns of contribution to the new structure within the host. Implications of the results for the normal mechanism of body pattern formation are discussed.