bluuebunny/crossref_metadata_2025_split huggingface dataset:
Concanavalin A binding to amphibian embryo and effect on morphogenesis
Authors: Boucaut J. C. , Bernard B. , Aubery M. , Bourrillon R. , Houillon Ch. 
Published: April 2021

ABSTRACT
The effect of Concanavalin A (Con A) on morphogenesis in Pleurodeles waltlii has been studied. Embryos were incubated with various concentrations of the lectin for a period of 6 days. Three stages of development were examined, late blastula, young gastrula and late gastrula.
In the presence of the lectin at a concentration of 200, 150 or 100 μg/ml morphogenic movements were delayed, altered and finally blocked. At lower concentrations, 50 or 25 μg/ml, there was a slight delay in gastrulation, but in some cases development was normal. These findings indicate that Con A exerted an inhibitory effect on amphibian morphogenesis and there is evidence that the lectin effect was concentration dependent.
The effects of Con A were specific since they were totally inhibited by α-methyl-D-man-nopyranoside (0 05 M). The viability of the 24 h lectin-treated embryos was demonstrated by washing experiments.
Labelled Con A binding to the embryos was investigated before and after discarding the vitelline membrane. The results suggest a direct interaction between Con A and the cell surface and this was confirmed by using fluorescein isothiocyanate Con A.
The morphology of fetal gonads of spontaneous mouse hermaphrodites
Authors: Whitten Wesley K. , Beamer Wesley G. , Byskov Anne Grete 
Published: April 2021

ABSTRACTThe gonads of .107 spontaneous, chromosomal mosaic, day-15 fetal hermaphrodites derived from BALB/cWt strain male mice are described and photographs of seven gonads representative of the major types are presented. There were 16 ovaries, 15 testes, and 183 ovotestes. The ovotestes contained on the average more testicular tissue than ovarian, and the ovarian tissue was more frequently located at the gonad poles, particularly the craniad pole. There was no difference between left and right sides with regard to gonad type, but more pure gonads were found on the left than on the right side (21/10), Meioses were observed throughout the ovarian tissue and also in some testicular cords, particularly in the caudad pole of the gonad. Some meiotic figures contained sex vesicles.The significance of these findings is discussed in relation to several aspects of sex determination.
Interactions between optic fibres controlling the locations of their terminals in the goldfish optic tectum
Authors: Cook Jeremy E. 
Published: April 2021

ABSTRACT
Removal of the caudal half of a goldfish optic tectum induces optic fibres from the entire contralateral retina to terminate retinotopically within the remaining half. This compression has been viewed by some as the result of competition between the fibres and by others as a consequence of changes, induced by the surgery, in tectal labels guiding fibres to terminal sites.
To distinguish between these possibilities, the time-course of compression has been measured by electrophysiological mapping of the visual projection. In some fish, fibres terminating in the rostral half-tectum remained intact when the caudal half was removed. In others, the optic nerve was cut at the time of tectal surgery: even after its regeneration into a half-tectum, optic terminals were first detected in the regions they normally occupy. The subsequent reorganization was gradual and retinotopic order was maintained. However, it was slower where some fibres had never been cut.
In a third series the nerve was cut 18 days before the tectal halving to reveal any dependence of compression on progressive changes in the halved tectum; but its time-course from nerve section was found to be independent of the time within the regeneration period at which the tectum was halved.
In a fourth series the nerve was cut at the time of tectal halving and then cut again after 85−97 days when compression was complete to reveal any permanent change in the halved tectum. No change was evident: the previous compression did not preclude subsequent regeneration of an uncompressed projection and its gradual recompression as before.
In a fifth series, repeated crushing of fibres normally ending in the missing caudal tectum temporarily prevented compression among the remainder, while crushing of fibres destined for rostral tectum caused transposition of the remaining projection to the rostral half.
Surgically induced changes in the labels which are thought to guide growing fibres to their normal tectal regions do not account for these results. Indeed, this guidance persists unchanged for fibres regenerating a second time after compression. Since compression is delayed while certain fibres are withheld, it appears instead to be the direct result of competition between the fibres. The maintenance of retinotopic order in compression, despite unchanged tectal guidance, may require selective interactions between fibres from different retinal regions which could contribute to the refinement of the normal visual projection.
The visuotectal projections made by Xenopus ‘pie slice’ compound eyes
Authors: Willshaw D. J. , Fawcett J. W. , Gaze R. M. 
Published: April 2021

ABSTRACT
In Xenopus embryos at stages 28–32 one quarter to one third of the left eye rudiment was replaced by a similarly sized piece from a different position in a right eye rudiment. Three groups of operations were performed: (1) temporal tissue was placed in a nasal position; (2) nasal tissue was placed temporally; (3) ventral tissue was placed dorsally. The visuotectal projections made by these ‘pie-slice’ compound eyes were assessed electrophysiologically at 1 week to 6 months after metamorphosis. Of 97 animals, 71 yielded interpretable projections. In most cases two projections could be identified in each map. One, ascribed to the host part of the retina, extended over the entire tectal surface mapped. The other, identified as that from tissue derived from the pie-slice graft, projected to the tectum in register with that part of the host retina which matched the pie-slice in origin. Both projections were well ordered, and in the orientation expected if the corresponding piece of retinal tissue had participated in a normal projection. Consistent differences in pie-slice size and tectal coverage between the three groups were found. Pie-slices of nasal origin gave maps showing that they came from a relatively large portion of the retina and projected to a relatively large amount of the tectum; those of temporal origin occupied relatively small amounts of field and tectum. It was concluded that these results are further evidence for the existence of positional markers in the retina which are used for the assembly of the retinotectal map.
Effects of delayed amputation on denervated forelimbs of adult newt
Authors: Liversage Richard A. , McLAUGHLIN Danielle S. 
Published: April 2021

ABSTRACT
Left forelimbs of adult newts were repeatedly denervated prior to and following amputation. Limb amputations were performed at 7–, 14–, 21–, 27– and 45-day intervals after the initial denervation. Regeneration was found in the sham-denervated and control animals but did not occur in any of the experimental cases; instead cicatrix formation and dermal wound healing ensued. Soft-tissue dedifferentiation was evident, however. We conclude from these results that forelimb regeneration in the adult newt is completely nerve dependent (for growth).
A contractile ring-like mechanism in wound healing and soluble factors affecting structural stability in the cortex ofXenopus eggsand oocytes
Authors: Merriam R. W. , Christensen Kathy 
Published: April 2021

ABSTRACTHoles or tears have been made in the surface of unfertilized Xenopus eggs or oocytes in various buffered media and the surface response to the wound has been observed with the light microscope.In the presence of calcium ion in the medium, a pigmented ring appears around the wound and constricts in purse-string fashion until the hole is closed. A highly pigmented scar remains. We show that the surrounding pigmented cortex is moved over the denuded cytoplasm when wound healing closes a large excision wound in the pigmented surface. This movement of surface is consistent with a model of a purse string, closing the hole by pulling existing surface over the denuded cytoplasm.The presence of cytochalasin B in the medium inhibits wound healing completely. The sensitivity to the antibiotic is similar to that of the contractile ring in cytokinesis.Wounds made in the surface of ripe ovarian oocytes do not heal in the presence of calcium ion. The healing mechanisms, or their sensitivity to calcium, thus appear during meiotic maturation or ovulation.The egg cortex and membrane around wounds dissociate in the absence of calcium or in the presence of cytochalasin B. The cell cortex of oocytes also dissolves around wounds even in the presence of calcium. This cortical dissolution will not occur in the isolated cortex and thus requires soluble cytoplasmic factors. Models are proposed to explain these observations.
Melanophore differentiation inXenopus laevis, with special reference to dorsoventral pigment pattern formation
Authors: Ohsugi Kojune , Ide Hiroyuki 
Published: April 2021

ABSTRACTDuring the development of Xenopus laevis, after stage 26, a large number of dopa-positive cells were observed in the ventral region. Electron microscopic observations revealed that these cells became localized in the epidermal layer and contained premelanosomes. In cultured ventral skin, fully matured melanophores appeared.These results strongly suggest that a large number of melanoblasts are present in the ventral epidermis and remain there without final differentiation into melanized melanophores. Thus the positional difference of melanoblasts differentiation mainly contributes to dorsoventral pigment pattern formation of Xenopus laevis.
Blastema formation and cell division during cockroach limb regeneration
Authors: Truby Paul R. 
Published: April 2021

ABSTRACT
Recent models of pattern formation in insects have been derived largely from observations on regenerated cuticular patterns. Such models make assumptions about the behaviour of the underlying epidermal cells, their movement and patterns of cell division. The present study, designed to test these assumptions, looks at the patterns of wound healing and cell division after amputation at the trochanter-femur joint of the metathoracic leg in the cockroach. It shows that the wound is closed by cell migration and that regeneration occurs by dedifferentiation of the trochanter and distal coxa to form a blastema which grows and redifferentiates to form the new limb. The extent of the spread of dedifferentiation is confirmed by a scanning electron microscope study of the coxa after the moult following amputation. The results highlight the need for a greater knowledge of cell behaviour during pattern formation before we can begin to understand the processes involved in pattern formation.
Mevalonate reverses the developmental arrest of preimplantation mouse embryos by Compactin, an inhibitor of HMG Co A reductase
Authors: Surani M. Azim H. , Kimber Susan J. , Osborn Jeremy C. 
Published: April 2021

ABSTRACTHydroxymethyl glutaryl Co A reductase (HMG Co A reductase) is the key regulatory enzyme in the conversion of acetate to mevalonate. Mevalonate is the precursor for sterol and non-sterol isoprenes involved in membrane biogenesis, DNA replication and protein glycosylation. The influence of two inhibitors of HMG Co A reductase, Compactin (or ML236B) and an oxygenated sterol, Diosgenin, were tested on preimplantation development of mouse embryos. Compactin arrested development at about the 32-cell stage, leaving the blastomeres decompacted. Ultrastructural examination of the embryos revealed reduced membrane apposition but no major effects on cell organelles. There was however a predominance of nuclei with highly condensed chromatin. Glycosylation of proteins also appeared to be inhibited as shown by reduced incorporation of sugar precursors but not that of amino acids. The influence of Compactin was judged to be highly specific since only 10μg/ml (0·08 mM) mevalonic acid abolished the effects of Compactin. Mevalonate in embryos may not be primarily utilized in the synthesis of sterols since a specific inhibitor of cholesterol synthesis, DL-4,4,10-β-trimethyl-trans-decal-3-β-ol had no detectable effect on development. The non-sterol isoprenes of mevalonate such as dolichol and isopentenyl adenine may play a more significant role during early development since the influence of Compactin resembled that previously described using tunicamycin, a specific inhibitor of dolichol mediated synthesis of N-glycosidically linked glycoproteins. Hence, lack of dolichol may partly be the cause of arrest of embryonic development by Compactin. Diosgenin caused embryonic arrest at about the 16-cell stage and the influence was not reversible by mevalonic acid. Cholesterol was able to rescue 50 % of the embryos but the effect of Diosgenin could be non-specific and probably caused by its entry into the plasma membrane.
A bootstrap model for the proximodistal pattern formation in vertebrate limbs
Authors: Meinhardt Hans 
Published: April 2021

ABSTRACTFor the sequential determination of proximodistal structures during the outgrowth of vertebrate limbs, a ‘bootstrap’-mechanism is proposed: by increasing feedback of more dis-tally determined cells onto the production of a morphogen at the apical ectodermal ridge a successive increase of the morphogen concentration is achieved during outgrowth. The model accounts for the formation of a progress-zone at the limb tip, for the correct regeneration after truncation, for the presence and absence of proximodistal intercalation after certain graft experiments in amphibian limbs, for the tendency with which distal structures form in proximal position after certain experimental manipulations and for the intimate coupling of the anteroposterior and the proximodistal axes.
Regeneration of the eye margin in Periplaneta americana (Insecta, Blattodea)
Authors: Shelton P. M. J. , Pfannenstiel H.-D. , Wachmann E. 
Published: April 2021

ABSTRACT
The regulative ability of the proliferative zone of the insect eye margin has been investigated in larval Periplaneta americana. After sections of the eye margin are removed the eye nevertheless recovers to form a normal shape. Using chimaeras of lavender and wild-type animals we were able to show that the margin can regenerate from the differentiated parts of the eye. When differentiated eye tissue is confronted with epidermis from the head capsule adjacent to the proliferative zone (the vertex), the regenerated margin always forms from the eye. There is no evidence that intervening levels can be intercalated between host and graft tissues when sections of the eye margin are moved to new circumferential levels. However, in that situation differences between tissues from non-adjacent circumferential positions lead to the rounding up of the graft and it fails to develop normally.
The retention of primary hypoblastic cells underneath the developing primitive streak allows for their prolonged inductive influence
Authors: Azar Yehudit , Eyal-Giladi Hefzibah 
Published: April 2021

ABSTRACT
An experimental study was made of the distribution of the primary hypoblastic cells in the lower layer of the avian blastoderm throughout primitive streak formation and until stage 10 (Hamburger & Hamilton, 1951). The primary hypoblast of stage XIII (Eyal-Giladi & Kochav, 1976) chick blastoderms was exchanged for either an [H3]thymidine-labelled similar chick hypoblast, or a quail primary hypoblast. During the entire period of primitive streak formation, the lower layer proved to be a mosaic of labelled hypoblastic and non-labelled entodermal cells (chick cells of epiblastic origin). The persistance of hypoblastic cells underneath the developing primitive streak is regarded by us as a possible way to prolong the inductive influence of the hypoblast upon the forming streak.
Vascular endothelial growth factor induces VE-cadherin tyrosine phosphorylation in endothelial cells
Authors: Esser Sybille , Lampugnani Maria Grazia , Corada Monica , Dejana Elisabetta , Risau Werner 
Published: April 2021

ABSTRACT
Interendothelial junctions play an important role in the regulation of endothelial functions, such as vasculogenesis, angiogenesis, and vascular permeability. In this paper we show that vascular endothelial growth factor (VEGF), a potent inducer of new blood vessels and vascular permeability in vivo, stimulated the migration of endothelial cells after artificial monolayer wounding and induced an increase in paracellular permeability of human umbilical vein endothelial cells (HUVECs). Furthermore, VEGF increased phosphotyrosine labeling at cell-cell contacts. Biochemical analyses revealed a strong induction of VEGF-receptor-2 (flk-1/KDR) tyrosine-autophosphorylation by VEGF which was maximal after 5 minutes and was followed by receptor downregulation. 15 minutes to 1 hour after VEGF stimulation the endothelial adherens junction components VE-cadherin, β-catenin, plakoglobin, and p120 were maximally phosphorylated on tyrosine, while α-catenin was not modified. PECAM-1/CD31, another cell-cell junctional adhesive molecule, was tyrosine phosphorylated with similar kinetics in response to VEGF. In contrast, activation of VEGF-receptor-1 (Flt-1) by its specific ligand placenta growth factor (PlGF) had no effect on the tyrosine phosphorylation of cadherins and catenins. Despite the rapid and transient receptor activation and the subsequent tyrosine phosphorylation of adherens junction proteins the cadherin complex remained stable and associated with junctions. Our results demonstrate that the endothelial adherens junction is a downstream target of VEGFR-2 signaling and suggest that tyrosine phosphorylation of its components may be involved in the the loosening of cell-cell contacts in established vessels to modulate transendothelial permeability and to allow sprouting and cell migration during angiogenesis.
The nuclear import factor p10 regulates the functional size of the nuclear pore complex during oogenesis
Authors: Feldherr Carl , Akin Debra , Moore Mary Shannon 
Published: April 2021

ABSTRACT
Previtellogenic, stage-1 Xenopus oocytes produce mainly 5S and tRNA, whereas vitellogenic oocytes, stages 2-6, synthesize predominantly 18S and 28S rRNA. Using nucleoplasmin-coated gold as a transport substrate, it was determined that the shift in synthesis from small to large RNAs during oogenesis is accompanied by an increase in both the rates of signal-mediated nuclear import and the functional size of nuclear pores. It was observed that, despite the reduction in transport capacity, gold still accumulated at the cytoplasmic surface of the pores in stage-1 oocytes. This suggested that transport in these cells is limited by translocation factors, rather than by cytoplasmic binding factors. Analysis of extracts prepared from stage-1 and vitellogenic oocytes revealed that the transport factor p10 is more abundant in stage-1 cells. Microinjection of purified p10 into stage-2 oocytes reduced the nuclear import of large gold particles to the level observed in stage-1 cells. It is concluded that p10 can modulate transport through the pores by regulating the functional size of the central transporter element.
Impaired mechanical stability, migration and contractile capacity in vimentin deficient fibroblasts
Authors: Eckes Beate , Dogic Dagmar , Colucci-Guyon Emma , Wang Ning , Maniotis Andrew , Ingber Donald , Merckling Alexandra , Langa Francina , Aumailley Monique , Delouvée Annie , Koteliansky Victor , Babinet Charles , Krieg Thomas 
Published: April 2021

ABSTRACT
Loss of a vimentin network due to gene disruption created viable mice that did not differ overtly from wild-type littermates. Here, primary fibroblasts derived from vimentin-deficient (-/-) and wild-type (+/+) mouse embryos were cultured, and biological functions were studied in in vitro systems resembling stress situations. Stiffness of -/fibroblasts was reduced by 40% in comparison to wild-type cells. Vimentin-deficient cells also displayed reduced mechanical stability, motility and directional migration towards different chemo-attractive stimuli. Reorganization of collagen fibrils and contraction of collagen lattices were severely impaired. The spatial organization of focal contact proteins, as well as actin microfilament organization was disturbed. Thus, absence of a vimentin filament network does not impair basic cellular functions needed for growth in culture, but cells are mechanically less stable, and we propose that therefore they are impaired in all functions depending upon mechanical stability.
Distinct subcellular localization of calcium binding S100 proteins in human smooth muscle cells and their relocation in response to rises in intracellular calcium
Authors: Mandinova Anna , Atar Dan , Schäfer Beat W. , Spiess Martin , Aebi Ueli , Heizmann Claus W. 
Published: April 2021

ABSTRACT
Changes in cytosolic Ca2+ concentration control a wide range of cellular responses, and intracellular Ca2+-binding proteins are the key molecules to transduce Ca2+ signaling via interactions with different types of target proteins. Among these, S100 Ca2+-binding proteins, characterized by a common structural motif, the EF-hand, have recently attracted major interest due to their cell- and tissue-specific expression pattern and involvement in various pathological processes. The aim of our study was to identify the subcellular localization of S100 proteins in vascular smooth muscle cell lines derived from human aorta and intestinal smooth muscles, and in primary cell cultures derived from arterial smooth muscle tissue under normal conditions and after stimulation of the intracellular Ca2+ concentration. Confocal laser scanning microscopy was used with a specially designed colocalization software. Distinct intracellular localization of S100 proteins was observed: S100A6 was present in the sarcoplasmic reticulum as well as in the cell nucleus. S100A1 and S100A4 were found predominantly in the cytosol where they were strongly associated with the sarcoplasmic reticulum and with actin stress fibers. In contrast, S100A2 was located primarily in the cell nucleus. Using a sedimentation assay and subsequent electron microscopy after negative staining, we demonstrated that S100A1 directly interacts with filamentous actin in a Ca2+-dependent manner. After thapsigargin (1 µM) induced increase of the intracellular Ca2+ concentration, specific vesicular structures in the sarcoplasmic reticulum region of the cell were formed with high S100 protein content. In conclusion, we demonstrated a distinct subcellular localization pattern of S100 proteins and their interaction with actin filaments and the sarcoplasmic reticulum in human smooth muscle cells. The specific translocation of S100 proteins after intracellular Ca2+ increase supports the hypothesis that S100 proteins exert several important functions in the regulation of Ca2+ homeostasis in smooth muscle cells.