bluuebunny/crossref_metadata_2025_split huggingface dataset:
The growth and differentiation in vitro of leg and wing imaginal disc cells from Drosophila melanogaster
Authors: Currie Douglas A. , Milner Martin J. , Evans Clive W. 
Published: April 2021

Abstract
We have devised a new in vitro culture system in which cells from dissociated Drosophila leg and wing imaginal discs grow and differentiate. Primary cultures consist of epithelial and fibroblast-like cells, together with some lamellocyte-like cells. These cultures have given rise to continuously dividing leg and wing cell lines, in which epithelial, fibroblast-like, lamellocyte-like and distinct sickle-shaped cells are found. Vesicles composed of epithelial cells form in primary cultures and these differentiate imaginal cuticular structures under the influence of 20-hydroxyecdysone. Two types of cuticle-like material are formed spontaneously in established cultures. One type is present as thin, untanned sheets resembling apolysed pupal cuticle, while the other consists of thicker, tanned material similar to imaginal cuticle.
Retinoic acid alters EGF receptor expression during palatogenesis
Authors: Abbott B. D. , Adamson E. D. , Pratt R. M. 
Published: April 2021

Abstract
Various growth factors are necessary for normal embryonic development and EGF receptors are present in developing palatal shelves of embryonic/fetal mice at least from day 12 of gestation. The medial epithelium of the palatal shelf undergoes a series of developmental events which do not occur in the oral and nasal epithelia. In utero and in organ culture, the control palatal medial epithelium shows a developmental decline in EGF receptors, demonstrated both by a decrease in the binding of antibody to EGF receptors and a decrease in the binding of l25I-EGF; decreases which are not observed in cells of the adjacent oral or nasal epithelium. During this period, medial cells cease DNA synthesis and undergo programmed cell death. Medial epithelial cells exposed to all-trans-retinoic acid continue to express EGF receptors, bind EGF, proliferate, fail to undergo programmed cell death and exhibit a morphology typical of nasal cells. The data suggest that this disturbance by retinoic acid of EGF receptor localization and subsequent alterations in differentiation of the epithelial cells plays a role in the retinoic-acid-mediated induction of cleft palate.
The behaviour and function of bottle cells during gastrulation of Xenopus laevis
Authors: Hardin Jeff , Keller Ray 
Published: April 2021

Abstract
The behaviour of bottle cells in normal and microsurgically altered gastrulae and in cultured expiants of Xenopus laevis was analysed, using time-lapse micrography, scanning electron microscopy (SEM) and cell tracing with fluorescein dextran amine (FDA). The results shed new light on the function of bottle cells. Bottle cells forming in vivo show a predominantly animal-vegetal apical contraction and a concurrent apical-basal elongation, whereas those forming in cultured expiants show uniform apical contraction and remain rotund. Bottle cells forming in embryos with fewer subblastoporal cells contract more uniformly than those in normal embryos and release of normal bottle cells from supra- and subblastoporal cells results in immediate loss of the bottle shape. These results, and an analysis of the effects of bottle cell formation on the shapes and movements of surrounding tissues, show that unique shape of bottle cells and their probable function in development are not intrinsic properties but result from a modulation of the effect of a uniform and intrinsic apical contraction by the geometric and mechanical properties of the surrounding tissue. Mechanical simulations of bottle cell formation, using the finite element method, suggest how the site of bottle cell formation and the thickness and stiffness of adjacent tissues might change the effects of their formation. These results and FDA marking of prospective bottle cells and the adjacent deep mesodermal cells suggest that bottle cells function during their formation to initiate the involution of the prospective mesodermal mantle. Later they respread to deepen the archenteron and to form its peripheral wall.
Can retinal adhesion mechanisms determine cell-sorting patterns: a test of the differential adhesion hypothesis
Authors: Thomas William A. , Yancey Janet 
Published: April 2021

Abstract
Embryonic chick neural retina cells possess two classes of adhesion mechanism, one Ca2+-independent, one Ca2+-dependent, responsible for short-term cell aggregation. This study investigates the role of these mechanisms in the long-term cell sorting potentially relevant to in vivo histogenesis. Retina cells are prepared either with both (E cells) or with only one mechanism (TC cells, CD; LTE cells, CI), respectively. The two types of cell preparations are differentially labelled using fluorescein or rhodamine isothiocyanate, mixed and allowed to aggregate in the presence or absence of cycloheximide at 0·5 μg ml-1 to retard metabolic recovery of the removed adhesive mechanism. When observed by fluorescence and phase-contrast microscopy, the aggregates formed in cycloheximide show cell sorting, the cells with both mechanisms assuming a more interior position relative to those with a single adhesion mechanism. In parallel hanging-drop experiments, preformed aggregates of cells with a single adhesion mechanism are seen to spread upon aggregates of cells with both mechanisms. No sorting occurs amongst cells from a given stage prepared using any single dissociation protocol. The observed cell sorting would thus seem to derive exclusively from differential cell adhesiveness dependent upon the different dissociation conditions and maintained in the presence of cycloheximide. The experiments support the hypothesis that the dual CI and CD adhesion mechanisms in question can play a central role in governing cell-sorting behaviour during normal histogenesis.
Analysis of hsp 30, hsp 70 and ubiquitin gene expression inXenopus laevistadpoles
Authors: Krone Patrick H. , Heikkila John J. 
Published: April 2021

AbstractHeat-induced accumulation of hsp 30 mRNA (1·1 kb) during early development of Xenopus laevis was first detectable at the tailbud stage (stage 30–34). This contrasts with heat-induced accumulation of hsp 70 mRNA (2·7 kb) and ubiquitin mRNA (size range = 1·7–3·1 kb), which was first detectable at the mid- to late-blastula stage. Continuous exposure of tadpoles to a 33 °C heat shock resulted in a coordinate, transient accumulation of hsp 30, hsp 70 and ubiquitin mRNA. A coordinate, temporal pattern was also observed for the decay of hsp 30, hsp 70 and ubiquitin mRNA in tadpoles recovering at 22°C following a Ih heat shock at 33°C. Thus, while hsp 30 genes are regulated differently during development compared with hsp 70 and ubiquitin genes, these genes all exhibit a coordinate heat-inducible pattern of expression at the tadpole stage. Levels of α-cardiac actin mRNA remained unchanged during continuous heat shock and recovery experiments.
Specific guidance of motor axons to duplicated muscles in the developing amniote limb
Authors: Victoria Stirling R. , Summerbell Dennis 
Published: April 2021

AbstractThe effect of alteration of limb pattern upon motor axon guidance has been investigated in chick embryos. Following grafting of the zone of polarizing activity (ZPA) into the anterior margin of the early limb bud, limbs develop with forearms duplicated about the anteroposterior axis. The position of motoneurones innervating the duplicated posterior forearm extensor EMU was mapped by retrograde transport of horse radish peroxidase (HRP). The motor pool labelled from injection into the anteriorly duplicated EMU muscle is consistently similar to that supplying the posterior EMU muscle on the unoperated side of the embryo. In those cases where the axons are well filled,their trajectories from the injection site are observed to change position within the radial nerve to specifically innervate the duplicated muscle. The axons modify their trajectories proximal to the level of limb duplication in a region where there is no change in the pattern of overt differentiation of the limb cells. This suggests that axons may use a cell’s positional value to navigate and provides significant support for the theory of positional information.
Disruption of the cytokeratin filament network in the preimplantation mouse embryo
Authors: Emerson Julia Andrew 
Published: April 2021

ABSTRACTThe distribution of the cytokeratin network in the intact preimplantation mouse embryo and the role of cytokeratin filaments in trophectoderm differentiation were investigated by means of whole-mount indirect immunofluorescence microscopy and microinjection of anti-cytokeratin antibody. Assembled cytokeratin filaments were detected in some blastomeres as early as the compacted 8-cell stage. The incidence and organization of cytokeratin filaments increased during the morula stage, although individual blastomeres varied in their content of assembled filaments. At the blastocyst stage, each trophectoderm cell contained an intricate network of cytokeratin filaments, and examination of sectioned blastocysts confirmed that extensive arrays of cytokeratin filaments were restricted to cells of the trophectoderm. Microinjection of anticytokeratin antibody into individual mural trophectoderm cells of expanded blastocysts resulted in a dramatic rearrangement of the cytokeratin network in these cells. Moreover, antibody injection into 2-cell embryos inhibited assembly of the cytokeratin network during the next two days of development. Despite this disruption of cytokeratin assembly, the injected embryos compacted and developed into blastocysts with normal morphology and nuclear numbers. These results suggest that formation of an elaborate cytokeratin network in preimplantation mouse embryos is unnecessary for the initial stages of trophectoderm differentiation resulting in blastocyst formation.
Retinotopic refinement of the regenerating goldfish optic tract is not linked to activity-dependent refinement of the retinotectal map
Authors: Cook Jeremy E. , Becker David L. 
Published: April 2021

ABSTRACT
The cut optic nerve of a goldfish can regenerate, restoring an orderly projection from the retina to the optic tectum. At first, regenerating axons make transient connections, many of them in inappropriate tectal locations. Later, their arrangement is gradually refined into an accurate retinotectal map by a process that depends on afferent activity.
On their way to the tectum, many regenerating axons make erroneous choices between the two arms (brachia) of the optic tract. However, since they commonly possess divergent collateral branches, a secondary refinement of the brachial pattern can occur by selective collateral elimination. How or why a particular collateral is lost is not known, but we have previously suggested that sibling branches might compete to form stable tectal synapses, implying that there might be a causal link between refinement of the brachial pattern and refinement of the retinotectal map.
In this paper, we have tested directly for such a link, blocking map refinement with tetrodotoxin (TTX) or stroboscopic light, verifying the effectiveness of the block and measuring the extent of brachial refinement by standard methods in experimental and control fish. Both TTX and stroboscopic light reliably prevented map refinement, their results being indistinguishable. However, neither had even the slightest detrimental effect on brachial refinement, either 42 days or 70 days after nerve cut.
Evidently, neither activity nor a sharp retinotectal projection is necessary for brachial refinement. Theory and experiment both dictate that the basic projection pattern be controlled by a mechanism (such as chemoaffinity) that is independent of activity, and it would seem that selective collateral loss must depend on the same mechanism.
Control of cell cycle length in amphibian eggs: evidence for a temporal relationship between the nucleus and egg cytoplasm
Authors: Aimar C. 
Published: April 2021

ABSTRACT
The role of the cytoplasm and nucleus in the control of the length of the division cycle was investigated in Pleurodeles waltl eggs. Injection of spermine into enucleated eggs showed that the ability to cleave was not restricted just to the period of normal cytokinesis (T = 1·0) but was possible throughout most of the first egg cycle. The cytoplasmic components required for cytokinesis seem to increase progressively during the first division cycle.
Nuclear transfer experiments indicated that the timing of cleavage was normal only when the nucleus and egg cytoplasm were reassociated between T = 0 ·0 (activation time) and T = 0·50. Delayed associations, after T = 0·50, provoked an alteration in the chronology of first cleavage and led to abnormal embryonic development. In the absence of a nucleus, the egg cycle seemed to stop at T = 0·50. These different observations suggest that the normal timing of cleavage not only depends on a ‘cytoplasmic clock’ but is also determined by an isochronous nucleocytoplasmic relationship during the early phase of egg development.
The albino–deletion complex in the mouse defines genes necessary for development of embryonic and extraembryonic ectoderm*
Authors: Niswander Lee , Yee Della , Rinchik Eugene M. , Russell Liane B. , Magnuson Terry 
Published: April 2021

Abstract
A detailed embryological analysis has been undertaken on embryos carrying the c4FR60Hd-, c5FR60Hg- or c2YPSj- albino deletions of mouse chromosome 7. Embryos homozygous for the c4FR60Hd deletion are abnormal at day 7 · 5 of gestation. The extraembryonic ectoderm does not develop, and primitive-streak formation and mesoderm production do not occur. In contrast, extensive development of the extraembryonic ectoderm, as well as mesoderm production, are observed in the c5FR60Hg-and c2YPSj- homozygous embryos. The mesoderm does not, however, organize into somites and the neural axis does not form. The embryos are grossly abnormal by day 8-5 of development. There are two other albino deletions (c6H and c11DSD) that are known to affect the embryo around the time of gastrulation (Niswander et al. 1988), and the lethal phenotype observed for the c4FR60Hd - homozygous embryos is similar to that described for c6H- homozygous embryos, whereas the c5FR60Hg- and c2YPSj- homozygous embryos display a phenotype that is similar to c11DSD -homozygous embryos. A detailed complementation analysis using these five deletions revealed that the c5FR60Hg, c2YPSj- and C11DSD deletions could partially complement the phenotype produced by the c4FR60Hd and c6H deletions in any combination. Extensive development of the extraembryonic structures and production of mesoderm occurs in the compound heterozygotes. These results suggest that the distal breakpoints of the c5FR60Hg, c2YPSj and c11DSD deletions lie more proximal than the distal breakpoints of the c4FR60Hd and c6H deletions. This arrangement defines new functional units of chromosome 7 such that a gene(s) important for normal development of the extraembryonic ectoderm would be located in the distal region of non-overlap between the two groups of deletions, and a gene(s) important for the development of the embryonic ectoderm would be located in the region deleted by both groups of chromosomes. The c4FR60Hd and c6H deletions appear to be missing both genes and belong to one complementation group; whereas the c5FR60Hg, c2YPSj and c11DSD deletions are missing only the gene(s) affecting the development of the embryonic ectoderm and, therefore, belong to another complementation group.
A new approach to the development of the cerebellum provided by the quail–chick marker system
Authors: Hallonet Marc E. R. , Teillet Marie-Aimée , Le Douarin Nicole M. 
Published: April 2021

ABSTRACT
We have used the quail-chick chimera system to reveal the cell migrations and settling pattern involved in the construction of the cerebellum. Three types of orthotopic transplantations were carried out, between quail and chick embryos, at the 12-somite stage: exchanges of (i) the whole metencephalic vesicle, (ii) the lateral half of this vesicle and (iii) the diencephalic plus the mesencephalic vesicles.
Histological study of chimeric embryos and young chicks provided the following results: longitudinal morphogenetic movements distort the embryonic neural tube as early as the fifth embryonic day, so that the dorsal limit of the mes-, met-and myelencephalic vesicles are displaced caudad and their ventral limits rostrad. This leads to a participation of mesencephalic vesicular material in the construction of the cerebellum. Cells originating in the mesencephalic vesicle are found in a rostromedial V-shaped region, in all the cerebellar cellular layers, except the external granular layer, the presumptive territory of which is entirely located in the metencephalic vesicle.
The chimerism of the rostromedial part of the cerebellum allows the analysis of the origin of the various cerebellar cell types. We find (i) that the Purkinje cells always have the same cellular marker as the ventricular epithelium radially beneath them. This strongly suggests that these cells reach their final localization following strictly radial migrations, (ii) Most of the small cells surrounding the Purkinje neurons and most of the neurons and glial cells of the molecular layer are also of the same type as the ventricular epithelium they surmount, i.e. different from the type of the external granular layer cells. Therefore, they are not derived from the external granular layer and are not of the same origin as the granule cells as previously believed.
Unilateral substitutions of the metencephalic vesicle revealed that transverse cell migrations occur across the sagittal plane. They have been observed mainly in the inner and external granular layers, but also, though to a lesser extent, in the molecular layer and in the cell layer located at the level of the Purkinje neurons.
These observations show that the position of cerebellar cells is determined by both morphogenetic movements and cell type-specific active radial and tangential migrations. The quail-chick chimera system is thus able to provide new information both on the origin of cerebellar cells and how each cell type assumes its final position.
Retinoic acid treatment alters the distribution of retinoic acid receptor-β transcripts in the embryonic chick face
Authors: Rowe Annie , Richman Joy M. , Brickell Paul M. 
Published: April 2021

ABSTRACT
Retinoic acid is a metabolite of vitamin A that can act as a signalling molecule in a number of developmental systems. Retinoic acid is also known to be teratogenic in mammals, causing a range of defects including abnormalities in craniofacial development. Exposure of the developing chick face to retinoic acid released slowly from a bead implanted in the wing bud results in a specific facial defect, in which outgrowth of the frontonasal mass is inhibited. This results in clefting of the primary palate and absence of the upper beak. To investigate the role of nuclear retinoic acid receptors in normal and abnormal chick face morphogenesis, we isolated chick retinoic acid receptor-β (RAR-β) cDNA clones and probed northern blots of RNA isolated from chick embryos at stages 22, 24 and 25 and from adults. RAR-β transcripts of 2.8 and 3.5 kb were present in several regions of the embryo, including the facial primordia, and were also present at much lower levels in adult tissues. In situ hybridisation showed that RAR-β transcripts were present in all of the facial primordia at embryonic stages 20, 24 and 28, but that their distribution was not uniform. Transcripts were abundant in the lateral nasal processes, at the edges and corners of the frontonasal mass and in the anterior part of the maxillary primordia. Lower levels were present elsewhere. Treatment of stage 20 embryos with retinoic acid altered the distribution of RAR-β transcripts in the maxillary primordia, such that high levels of transcripts were present throughout, rather than being confined to the anterior part. This change was detectable at stage 24, before any alterations in the morphology of the facial primordia were apparent. By stage 28, when the morphology of the facial primordia was clearly abnormal, there were more widespread changes in the distribution of RAR-/1 transcripts. These results show that RAR-β transcripts are particularly concentrated in regions of the primordia that give rise to the upper beak, the development of which is specifically affected by retinoic acid. In addition, they demonstrate that retinoic acid can induce changes in the pattern of expression of RAR-β tr in vivo.
Timing of paternal Pgk-1 expression in embryos of transgenic mice
Authors: Pravtcheva Dimitrina D. , Adra Chaker N. , Ruddle Frank H. 
Published: April 2021

ABSTRACT
In mouse development, the paternal allele of the X-linked gene Pgk-1 initiates expression on day 6, two days later than the maternal allele, which is activated on day 4. The different timing of expression of the maternal and paternal alleles may be determined by (i) imprinting of the chromosome region in which the gene resides, but not aimed specifically at the Pgk-1 gene; (ii) gene specific imprinting, acting on Pgk-1 irrespective of the chromosomal localization of the gene; (iii) an interplay between embryo cell differentiation, timing of X-inactivation and Pgk-1 expression, without the involvement of imprinting at the Pgk-1 locus itself (Fundele R., Illmensee, K., Jagerbauer, E. M., Fehlau, M. and Krietsch, W. K. (1987) Differentiation 35, 31–36). Our findings in transgenic mouse lines, carrying Pgk-1 on autosomes, indicate the importance of the X chromosomal location for the delayed expression of the paternal Pgk-1 allele, and are in agreement with the first of the explanations listed above. We propose that the late activation of the paternal Pgk-1 locus is a consequence of imprinting targeted at, and centered around, the X chromosome controlling element (Xce).
Deep cytoplasmic rearrangements during early development in Xenopus laevis
Authors: Danilchik M. V. , Denegre J. M. 
Published: April 2021

ABSTRACT
The egg of the frog Xenopus is cylindrically symmetrical about its animal-vegetal axis before fertilization. Midway through the first cell cycle, the yolky subcortical cytoplasm rotates 30° relative to the cortex and plasma membrane, usually toward the side of the sperm entry point. Dorsal embryonic structures always develop on the side away from which the cytoplasm moves. Details of the deep cytoplasmic movements associated with the cortical rotation were studied in eggs vitally stained during oogenesis with a yolk platelet-specific fluorescent dye. During the first cell cycle, eggs labelled in this way develop a complicated swirl of cytoplasm in the animal hemisphere. This pattern is most prominent on the side away from which the vegetal yolk moves, and thus correlates in position with the prospective dorsal side of the embryo. Although the pattern is initially most evident near the egg’s equator or marginal zone, extensive rearrangements associated with cleavage furrowing (cytoplasmic ingression) relocate portions of the swirl to vegetal blastomeres on the prospective dorsal side.