bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell interactions in preimplantation embryos: evidence for involvement of saccharides of the poly-N-acetyllactosamine series
Authors: Rastan S. , Thorpe S.J. , Scudder P. , Brown S. , Gooi H.C. , Feizi T. 
Published: April 2021

ABSTRACT
Roles of cell surface carbohydrates containing the 3-fucosyl-N-acetyllactosamine and poly-N-acetyllactosamine sequences (SSEA-1 and I antigens, respectively) in the compaction of mouse embryos have been investigated using the endo-β-galactosidase of Bacteroides fragilis to modify the surface of cleavage-stage embryos. Treatment with this enzyme abolished SSEA-1 activity and diminished I antigen activity on the embryonic cell surface. Embryos cultured in the presence of endo-β-galactosidase from the 2-to 4-cell stage onwards, or treated with the enzyme at the compacting 8-cell stage, continued to compact and proceeded to form blastocysts at the normal rate. However, when compacted 8-to 16-cell embryos were experimentally decompacted in calcium-free medium, treated for 1 h with endo-β-galactosidase and returned to normal culture medium, the time taken for 50 % of the embryos to recompact was prolonged five-fold. There was an even greater delay if these embryos were maintained in culture medium containing the enzyme. Blastocysts were eventually formed under both conditions. Thus, endo-β-galactosidase did not affect compaction unless the embryos were first decompacted. On the assumption that recompaction and de novo compaction occur by similar mechanisms, we propose that carbohydrate-binding molecules are involved which have high affinities for poly-N-acetyllactosamine structures and protect them from digestion by endo-β-galactosidase.
The origin of pattern duplications in segment polarity mutants of Drosophila melanogaster
Authors: Martinez-Arias Alfonso , Ingham Philip W. 
Published: April 2021

ABSTRACT
Mutations of the segment polarity group in Drosophila melanogaster produce additional denticles with reversed polarity in every segment of the larval cuticle. We have investigated the effect of mutations in different elements of the bithorax complex on the segmental identity of these additional pattern elements. Our results suggest that they are derived, primarily, from the anterior compartment of each segment.
Modulation of epidermal cell shaping and extracellular matrix during caudal fin morphogenesis in the zebra fish Brachydanio rerio
Authors: Dane P. J. , Tucker J. B. 
Published: April 2021

ABSTRACT
Distinct changes in epidermal cell shaping largely define the overall pattern of growth and form during generation of the ectodermal ridge and early stages of fin fold morphogenesis. The epidermal portion of the ridge and early fin fold are formed from a strip of epidermal cells that is only six to nine cells wide. There is apparently no increase in the number of these cells during initial formation of the ridge and its subsequent conversion into a fin fold which contains extracellular matrix fibres.
Epidermal cells adopt a wedge-shaped morphology during ridge production. Distinct changes in the shaping and contact relationships between basal portions of these cells generate intercellular spaces at several discrete loci within the ridge. These spaces become continuous with each other to form a subepidermal space. Hence, the subepidermal space is not produced by straightforward folding of an epidermal sheet.
Cells flanking the sides of the ridge start to flatten as it is converted into a fin fold. A continuous row of distinctive cells is positioned along the apex of the developing fold. The term ‘cleft cells’ is suggested for these apical cells. Each cleft cell retains a wedge-shaped form during fold formation and develops a basal cleft-shaped invagination. Invaginations are aligned in neighbouring cleft cells so that these cells cap the distal boundary of the subepidermal space where collagenous extracellular fibres called actinotrichia run anteroposteriorly along the length of the fin fold. This orientation is in direct contrast to the proximodistal orientation of actinotrichia within the remainder of the subepidermal space. During early stages of fold production a temporary set of previously unreported extracellular cross fibres spans the subepidermal space at right angles to actinotrichia. These configurations of extracellular fibres could be advantageous for maintaining the structural integrity of the early fin fold.
pH affects fruiting and slug orientation in Dictyostelium discoideum
Authors: Bonner J.T. , Hay A. , John D.G. , Suthers H.B. 
Published: April 2021

ABSTRACT
We have demonstrated two interesting facts about the transition from the migration stage to the final fruiting stage of Dictyostelium discoideum. One is that fruiting is favoured on acid substrata, and secondly, migrating slugs tend to migrate towards the acid side of a pH gradient. The suggestion is offered that these results can be interpreted in terms of the effects of NH3. It appears to be an additional mechanism (besides phototaxis and thermotaxis) to assure that the final fruiting takes place in a favourable environment.
The development of fused− embryos of Drosophila melanogaster
Authors: Martinez-Arias Alfonso 
Published: April 2021

ABSTRACT
The mutant fused (1−59.5) belongs to a class of lethal mutations in Drosophila melanogaster that produce pattern duplications in every segment of the mature embryo. A study of the embryonic development of fused− embryos derived from fused− mothers shows that extensive cell death occurs early in development. This cell death accounts for the smaller size of the segments in fused− embryos. The pattern duplication observed is, probably, a secondary consequence of the pattern deletion.
The role of microfilaments in cranial neurulation in rat embryos: effects of short-term exposure to cytochalasin D
Authors: Morriss-Kay Gillian , Tuckett Fiona 
Published: April 2021

ABSTRACT
During the late stages of cranial neurulation in mammalian embryos, the neural epithelium becomes concave. A thick subapical band of microfilament bundles, attached to junctions which are both vertical and horizontal in orientation, can be seen by TEM. Prior to this the neural epithelium is first biconvex and then V-shaped in transverse section, microfilament bundles are absent, and the subapical junctions are only vertical in orientation.
In order to determine the role of microfilaments in cranial neurulation, rat embryos were exposed to cytochalasin D (0 ·15 μgml-1) for Ih at three stages of development: convex neural fold stage, early concave (prior to midline apposition at the forebrain/midbrain junction: ‘preapposition’) and later concave (‘postapposition’). They were subsequently washed and cultured in addition-free medium for 5,12, 24 or 36h, then examined alive and by LM, TEM, or SEM.
The degree of neural fold collapse varied with the stage of development: at the convex stage there was only slight opening out of the neural groove; early concave (preapposition) neural folds collapsed laterally to a horizontal position; later concave (postapposition) neural folds showed widening of the midbrain/hindbrain neuropore and slight neuroepithelial eversion at the anterior neuropore. Neural epithelium which had been concave prior to cytochalasin D treatment changed in structure so that the cells were broader and shorter; most of the subapical junctions were vertical in orientation, and microfilament bundles were represented either as a mass of amorphous material adjacent to the junctions, or as separated and broken filaments.
Re-elevation of neural folds in ‘recovery’ cultures was accompanied by regeneration of apical microfilament bundles and horizontal junctions. Embryos which had been exposed to cytochalasin D at the convex or later concave stage of cranial neural fold development were able to complete cranial neural tube closure; none of the early-concave-stage embryos achieved apposition at the forebrain/midbrain junction, and all had major cranial neural tube defects.
The results suggest that contraction .of apical microfilament bundles plays an essential role in elevation of the neural folds and in the generation of concave curvature during the later stages of cranial neurulation. During the convex neural fold stage, microfilaments are important in maintaining neuroepithelial apposition in the neural groove, but are not crucial to maintenance of the convex shape.
Successful formation and maintenance of the forebrain/midbrain apposition point at the appropriate time is considered to be essential for subsequent brain tube closure.
Gene expression in Xenopus embryogenesis
Authors: Dawid Igor B. , Haynes Susan R. , Jamrich Milan , Jonas Erzsebet , MiyatañI Seiji , Sargent Thomas D. , Winkles Jeffrey A. 
Published: April 2021

ABSTRACT
This article considers some aspects of the storage of macromolecules in the oocyte of Xenopus laevis and the activation of previously unexpressed genes during early embryogenesis. The large quantity and complex nature of poly(A)+ RNA accumulated in the egg provides the cleavage embryo with a supply of mRNA sufficient to sustain protein synthesis for several hours of development. Onset of gene activity at the midblastula transition (MBT) leads to the synthesis and accumulation of molecules of various RNA classes, including tRNAs, rRNAs, mRNAs and mitochondrial RNAs. At gastrulation the poly(A)+ RNA population is still qualitatively similar to that of the egg but some sequences not present in egg RNA have accumulated by this time. Through the use of a subtractive cDNA cloning procedure we have prepared a library of sequences that represent genes activated for the first time between MBT and gastrula. A study of several of these cDNA clones suggests that genes in this class are restricted in their activity to embryonic and tadpole stages.
Actin genes in Xenopus and their developmental control
Authors: Gurdon J. B. , Mohun T. J. , Brennan S. , Cascio S. 
Published: April 2021

ABSTRACT
The results summarized here have established the temporal and regional activation of three kinds of Xenopus actin genes. The cardiac and skeletal muscle actin genes are among the first cell-type-specific genes to be expressed in early development. The first transcripts to be synthesized by these genes appear to be correctly initiated, spliced, and at once translated into proteins. Both cardiac and skeletal actin genes are strongly transcribed in the axial skeletal muscle of embryos.
The mechanism by which the cardiac actin gene is first transcribed in only the somite region of an embryo depends, at least in part, on materials already localized in the subequatorial region of a fertilized but uncleaved egg. Cells which acquire this material seem able to activate their cardiac actin genes without requiring normal contact with other cells.
Regional specificity of glycoconjugates in Xenopus and axolotl embryos
Authors: Slack J. M. W. , Cleine J. H. , Smith J. C. 
Published: April 2021

ABSTRACT
This paper reviews work on the presence, synthesis and developmental regulation of glycoconjugates (proteoglycans, glycoproteins and glycolipids) in the early amphibian embryo.
In the axolotl there is little regional specificity of protein synthesis until the tailbud stage, but substantial regional specificity of glycoprotein synthesis from the end of gastrulation. Glycolipid synthesis is more uniform although a number of unique species are made in the epidermis.
Isolated explants from axolotl early gastrulae show three types of behaviour in terms of glycoprotein synthesis, corresponding to the classical germ layers. Xenopus embryos at this stage show a higher degree of mosaicism.
Changes of glycoprotein synthesis in response to mesodermal or neural induction follow the predicted course depending on the regional character of the induced tissue.
The regional binding patterns of a number of lectins and monoclonal antibodies specific for particular carbohydrate determinants are presented and their significance discussed.
Information transfer during embryonic induction in amphibians
Authors: Grunz Horst 
Published: April 2021

ABSTRACT
Neural induction and differentiation has been studied using Concanavalin A, cyclic AMP, tunicamycin and calcium ionophore A 23187. Competent ectoderm of Xenopus laevis treated with Concanavalin A differentiates into neural (archencephalic) structures. Binding studies with gold-labelled ConA indicate that the superficial ectodermal layer contains fewer ConA-sensitive sites (α-D-mannoside and α-D-glucoside residues of glycoproteins) than the inner ectodermal layer. The small number of ConA-sensitive sites can be correlated with the fact that the isolated superficial ectoderm layer, in contrast to the inner layer, does not differentiate into neural structures. The gold-ConA particles bound to inner ectoderm are quickly (within 30 minutes) internalized, presumably by receptor-mediated endocytosis. However, endocytosis is not a prerequisite for neural induction. On the contrary ConA apparently must be bound to the plasma membrane for a certain period to initiate neural induction. The rapid internalization of ConA could explain why neural inductions are evoked only if ectoderm is incubated in ConA-containing medium for longer than 30 minutes.
On the other hand cyclic AMP or calcium ionophore A 23187 does not elicit neural inductions. On the contrary calcium ionophore A 23187 apparently, inhibits neural and mesodermal differentiation. This effect could be correlated with an increase of intracellular calcium level of the ectodermal target cells, which could influence the permeability of gap junctions resulting in a loss of cell communication, followed by a change of differentiation and pattern formation.
Intracellular pH and ribosomal protein S6 phosphorylation: role in translational control in Xenopus oocytes
Authors: Taylor Mark A. , Robinson Kenneth R. , Smith L. Dennis 
Published: April 2021

ABSTRACT
The induction of amphibian oocyte maturation with progesterone as well as the activation of sea urchin eggs at the time of fertilization result in increased protein synthesis. The increase in both cases involves the recruitment of maternal mRNA onto polysomes. Further, it has been reported that sea urchin eggs, like full-grown Xenopus oocytes, contain no spare translational capacity based on the observation that injected heterologous mRNA is translated only at the expense of endogenous messages. The nature of the limiting component defined by such experiments is not known, but two factors which have been proposed to play a role in regulating protein synthesis are ribosomal protein S6 phosphorylation and intracellular pH. In the current paper, we review the literature and present new evidence on the roles intracellular pH and S6 phosphorylation have in regulating protein synthesis in Xenopus oocytes. We report that pHi does not increase between stage 3 and stage 6, yet the protein synthetic rate increases at least eight fold during the same period. Hence, we conclude that increasing pHi is not a prerequisite for increasing protein synthesis. Moreover, we present three arguments against increased ribosomal protein S6 phosphorylation being sufficient or necessary for increased protein synthesis in Xenopus oocytes. First, the level of S6 phosphorylation does not increase between stages 4 and 6, a period exhibiting a two to three fold increase in protein synthesis. Second, the injection of globin mRNA into stage-4 oocytes increases total protein synthesis two to three fold, but has no effect on S6 phosphorylation. Third, when the injection of globin mRNA into stage-4 oocytes is followed by an injection of MPF, a dramatic increase in S6 phosphorylation is seen, but total protein synthesis is not further stimulated.
The Transplantation of Individual Rat and Guinea-pig Whisker Papillae
Authors: Cohen J. 
Published: April 2021

ABSTRACTA method is described for the removal and transplantation of vibrissa follicle bases (end bulbs). The whole papilla may be dissected from the capsule and follicle wall, and the dermal papillae may also be dissected out. Transplants have been made to various sites. No whisker was produced from end bulbs implanted into body skin, but whiskers were produced from end bulbs in the spleen, and from both end bulbs and whole papillae under ear skin. Several generations of whisker have been produced from some of the implants, but retention of the club whisker has not been observed. It is concluded that the whisker papilla is a permanent entity in the same sense as is the feather papilla, despite follicular changes during the growth-cycle. Dermal papillae may cause local ear epidermis to invest them, and pre-sumably this produces hair of local kind, as no whisker or whisker follicle was discovered. It is suggested that the whisker papilla is a non-specific organizer, speci-ficity residing in the ectoderm concerned.
An Analysis of the Postgastrula Differentiation of the Hypomere
Authors: Finnegan Cyril V. 
Published: April 2021

ABSTRACTA small mass of T. torosa postgastrula (stages 14–21) hypomere with its associated ectoderm, when cultured in vitro, demonstrates cell displacement posteriad along the original antero-posterior axis. Histological examination of these explants indicates that the splanchnic mesoderm disperses and differentiates, as a peritoneum for the most part, with a loose group of haematoblasts residing in the cavity formed. When a small group of endoderm cells was added to the hypomere-ectoderm ball, the results were similar to the above except that splanchnic mesoderm in the vicinity of the endoderm remained as a cell mass rather than dispersing as mesothelium. Late in the second week of culture mitotic figures became more prevalent in the splanchnic mesoderm in the immediate vicinity of the endoderm than elsewhere in the splanchnic cell mass. When epimere (somite) mesoderm was included in the hypomere-ectoderm ball, a nephric duct developed anteriorly and mesoderm cells remained as a cell mass in the vicinity of this duct. The results are discussed as indicating that the endoderm retains a meso-derm mass in its vicinity and thereby assists the differentiation of this mesoderm.
A dissection of the mechanisms generating and stabilizing polarity in mouse 8- and 16-cell blastomeres: the role of cytoskeletal elements
Authors: Johnson Martin H. , Maro Bernard 
Published: April 2021

ABSTRACT
Pairs of 8-cell or 16-cell blastomeres were cultured for up to 9h after their formation from isolated 1/4 or 1/8 blastomeres respectively. Blastomeres were examined for the incidence and orientation of their surface polarity, as assessed by binding of FITC-Con A and by distribution of microvilli, and of their cytoplasmic polarity, as assessed by distribution of cytoplasmic actin, clathrin and a 100kD antigen associated with the lysosomal/acid vesicle fraction of membranous organelles. The effect on polarity of incubating the pairs of cells in taxol, nocodazole, cytochalasin D or in a combination of nocodazole plus cytochalasin D for different parts of the incubation period was examined.
Neither the development nor the stability of the surface polarity in 8-cell blastomeres was blocked by any treatment and only the use of CCD in combination with nocodazole affected the incidence of surface polarity appreciably. However, with some treatments, the form and position of the surface poles were modified. In the presence of microtubule inhibitors surface poles extended over a larger area of the cell surface, while exposure to CCD led to poles that were not opposite to the contact point between cells. In contrast to surface polarity, the development of cytoplasmic polarity was suppressed by both microtubule- and microfilament-inhibiting drugs, which also reversed it rapidly.
In polar 16-cell blastomeres surface polarity was influenced in a similar manner to that of 8cell blastomeres, only the combined use of cytochalasin D and nocodazole having any major effect. Polarization of clathrin in polar 16-cell blastomeres was inhibited almost completely by all drug treatments applied including cytochalasin D. The focal concentration of lysosomal antigen that occurs during the 16-cell stage was reduced only in the continuous presence of nocodazole plus cytochalasin D, but once established was not reversed appreciably by any drug. However, the localization of the lysosomal antigen to the basal region of polarized cells did not seem to occur in the presence of any drug. The dissociation of surface and cytoplasmic polarity revealed in these experiments leads us to conclude that either (1) surface polarity is a prerequisite for the organization of cytoplasmic polarity, and mediates the latter via the cytoskeleton, or (2) surface and cytoplasmic polarity develop by parallel but separate mechanisms.
Cartilage morphogenesis in vitro
Authors: Archer Charles W. , Rooney Paul , Cottrill Christopher P. 
Published: April 2021

ABSTRACT
The morphogenetic capacity of prechondrogenic mesenchyme from two developmentally distinct sources was investigated in high density micromass cultures. We confirmed an earlier report (Weiss & Moscona, 1958) that scleral mesenchyme formed cartilage sheets whilst limb bud mesenchyme formed distinct cartilage nodules. It was thus suggested by these authors that this morphogenesis was tissue type specific. However, by varying cell density at inoculation (which controls cell configuration) and by varying the relative amount of prechondrogenic mesenchyme present in cultures we found that dramatic changes in morphogenesis could be brought about. Viewed in these terms we suggest that cartilage morphogenesis in vitro is dependent on cell configuration and the presence of non-chondrogenic cell types and hence is not necessarily a function of an intrinsic morphogenetic potential of the constituent cells.
X-chromosome deletions in embryo-derived (EK) cell lines associated with lack of X-chromosome inactivation
Authors: Rastan Sohaila , Robertson Elizabeth J. 
Published: April 2021

ABSTRACT
The predictions of a model for the initiation of X-chromosome inactivation based on a single inactivation centre were tested in a cytogenetic study using six different embryo-derived (EK) stem cell lines, each with a different-sized deletion of the distal part of one of the X-chromosomes. Metaphase chromosomes were prepared by the Kanda method from each cell line in the undifferentiated state and after induction of differentiation, and cytogenetic evidence sought for a dark-staining inactive X-chromosome. The results confirm the predictions of the model in that when the inactivation centre is deleted from one of the X-chromosomes neither X present in a diploid cell can be inactivated, and in addition considerably further localize the position of the inactivation centre on the X-chromosome.
Maintenance of function in single epithelial cells spatially isolated from similar cells
Authors: Maddrell S. H. P. , Overton J. A. 
Published: April 2021

ABSTRACT
We have found in an insect tissue, the Malpighian tubules of Rhodnius, instances of single epithelial cells which, as the result of a possible error in development, lie within the epithelium some distance from the main population of similar cells. This spatial separation makes it possible to measure the transport abilities of these cells. Their transport abilities were found to be the same as the cells in the main population. This finding shows that the maintenance of function in individual cells of epithelial tissues may not depend on direct contact with other similar cells.