bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell behaviour during postembryonic pattern regulation in the insect abdomen (Oncopeltus fasciatus):I. Regeneration of segment borders
Authors: Campbell Gerard L. , Shelton Peter M. J. 
Published: April 2021

ABSTRACT
The confrontation of cells from the anterior region of an abdominal segment of Oncopeltus with those from the posterior region of the same or the adjacent segment results in the generation of a segment border. The behaviour of epidermal cells during this regulation is described. It consists primarily of cell division and transverse elongation of cells at the site of confrontation. This behaviour can be separated from any associated purely with wound healing because a similar-sized wound to that used to ablate the segment border, performed within the segment, does not result in any cell division or elongation. The results are consistent with the view that there is a discontinuity in positional values at the segment border. The stability of such a discontinuity and the regeneration of segment borders are discussed in terms of there being a special population of cells at the segment border that have the property of isolating other cells with the maximum difference in positional values.
Cell behaviour during postembryonic pattern regulation in the insect abdomen (Oncopeltus fasciatus): II. Intrasegmental regulation
Authors: Campbell Gerard L. 
Published: April 2021

ABSTRACT
Cells from different levels in the anteroposterior axis of an abdominal segment of Oncopeltus were confronted by scraping away the strip of epidermis that separated these levels. The cells migrate over the wound and meet in the centre. The subsequent behaviour of the epidermal cells was followed by preparing whole mounts of integument at various times after confrontation. These operations may lead to cell division and an alteration in cell shape at the confrontation site. The intensity of the induced cell behaviour pattern depends on which levels in the segment are confronted and the evidence suggests that it is directly related to the magnitude of the difference in positional values between confronted cells. The results can be explained by a nonlinear gradient of positional values within the segment with a crowding of values in the posterior region. It is also shown that segment border formation requires the confrontation of cells with a near maximum possible difference in positional values.
The neural tube origin of ventral root sheath cells in the chick embryo
Authors: Lunn E. R. , Scourfield J. , Keynes R. J. , Stern C. D. 
Published: April 2021

ABSTRACT
The embryonic origin of peripheral nerve Schwann/ sheath cells is still uncertain. Although the neural crest is known to be an important source, it is not clear whether the ventral neural tube also contributes a progenitor population for motor axons. We have used the techniques of immunohistochemistry, electron microscopy and quail-chick grafting to examine this problem. Immunohistochemistry with monoclonal antibody HNK-1 identified a cluster of immunoreactive cells in the sclerotome, at the site of the future ventral root. With the electron microscope, nucleated cells could be seen breaching the basal lamina of the neural tube, exclusively in the region of the ventral root and preceding axon outgrowth. After grafting a length of crest-ablated quail neural tube in place of host chick neural tube, a population of quail cells was found localized to the ventral root exit zone, associated with the ventral root axons. Taken together, these observations support the possibility of a neural tube origin for ventral root sheath cells, although we found no evidence for a more extensive migration of these cells. The ventral root cells share certain phenotypic traits, such as HNK-1 immunoreactivity, with neural-crest-derived Schwann cells, but are not necessarily identical to them. We argue that while they may help motor axons to exit the neural tube at the correct position, they are unlikely to guide axons beyond the immediate vicinity of the neural tube.
Movement of the multicellular slug stage of Dictyostelium discoideum; an analytical approach
Authors: Breen Edmond J. , Vardy Phil. H. , Williams Keith L. 
Published: April 2021

ABSTRACT
Time-lapse video recordings of migrating multicellular slugs of Dictyostelium discoideum were subjected to image analysis. A transient ‘collar-like’ structure was identified at the anterior end of the slug. This collar remains stationary in the wild-type strain WS380B; it is observed shortly after the advancing tip contacts the substratum. Stationary collars formed approximately every 12 min; they were matched with patterns revealed on the underside of slime trails with FITC-coupled monoclonal antibody MUD50. It is proposed that stationary collars are involved with the forward movement of the slug. The mutant strain HU2421 lacks the MUD50-epitope and forms collars which do not remain stationary but move backwards along the slug to collect at a ‘waist’ region. The slipping-collars observed in the mutant correlated with very slow migration rates. We propose thatHU2421 moves slowly because it lacks traction.
An amphibian cytoskeletal-type actin gene is expressed exclusively in muscle tissue
Authors: Mohun T. J. , Garrett N. 
Published: April 2021

ABSTRACT
The complete nucleotide sequence of two Xenopus actin genes encoding cytoskeletal protein isoforms has been determined. Transcripts from these genes are remarkably similar in nucleotide sequence throughout their length and code for type-5 and type-8 cytoskeletal actins. Both share some sequence homology with human γ-actin mRNA within the 3′ untranslated region but none with the equivalent region of any vertebrate β-actin transcript. The promoter regions of the two Xenopus genes are virtually identical from the cap site to the CCAAT box and show extensive homology further upstream. Despite such similarity, the two genes are divergently expressed during embryonic development. The type-5 actin gene is expressed in all regions of the developing embryo whilst the type-8 gene is coregulated with the muscle-specific skeletal actin gene. In common with mammalian and avian cytoskeletal actin counterparts, the Xenopus genes possess a conserved sequence within their promoter that has previously been identified as a transcriptionfactor-binding site.
Ontogenic expression of a Cyl actin fusion gene injected into sea urchin eggs
Authors: Katula Karen S. , Hough-Evans Barbara R. , Britten Roy J. , Davidson Eric H. 
Published: April 2021

ABSTRACT
The 5′ terminus of the Cyl actin gene transcription unit of Strongylocentrotus purpuratus was located by primer extension and other procedures, and the flanking upstream region was partially sequenced and mapped. A fusion gene was constructed containing about 2·5 kb of 5′ flanking sequence, the transcribed leader sequence, and the first few codons of the Cyl gene ligated to the bacterial gene coding for chloramphenicol acetyl transferase (CAT). This was microinjected into the cytoplasm of S. purpuratus eggs, and CAT enzyme activity was measured at various stages of embryonic development. CAT synthesis was activated between 10 and 14 h postfertilization, the same time at which newly synthesized transcripts of the endogenous Cyl gene first appear. The exogenous Cyl · CAT fusion DNA replicated actively during cleavage, as observed previously for other DNAs injected into sea urchin egg cytoplasm. Thus the absence of CAT activity prior to 10 h postfertilization could not be due to insufficient Cyl · CAT genes. The amounts of CAT enzyme produced by embryos bearing Cyl · CAT deletions that lack various regions of the Cyl sequence were measured. As little as 254 nucleotides of upstream Cyl sequence suffice for correct temporal activation of the fusion construct, although the level of CAT enzyme produced in embryos bearing any deletion retaining &lt;850 nucleotides of upstream sequence was significantly lowered compared to controls bearing the complete Cyl · CAT fusion construct.
Neurotransmitter plasticity of cultured sympathetic neurones. Are the effects of muscle-conditioned medium reversible?
Authors: Vidal Simone , Raynaud Brigitte , Clarous Dominique , Weber Michel J. 
Published: April 2021

ABSTRACT
Muscle-conditioned medium (CM) induces choline acetyltransferase (CAT) activity in primary cultures of new-born rat sympathetic neurones and depresses the development of tyrosine hydroxylase (TOH). By following these two enzymes, we have determined whether (1) the effects of CM are reversible and (2) the neurones progressively lose their sensitivity to CM with time in culture.
When neurones were cultured in the presence of 50 % CM (CM+ medium), TOH activity developed slowly but CAT activity developed at a high rate. When the cultures were then switched to unconditioned medium (CM− medium), CAT activity remained elevated and continued to develop at higher rate than in cultures that were never exposed to CM. On the other hand, the switch to CM− medium was accompanied by a transition from a low to a high rate of TOH development. CAT induction by CM was thus essentially irreversible, whereas the impairment of TOH development was fully reversible.
Conversely, we studied the effects of altering CM− to CM+ medium at progressively later culture days. CAT remained fully inducible for at least 2 to 3 weeks. On the other hand, TOH activity, which initially developed rapidly in CM− medium, first decreased to low levels after a switch to CM+ medium and then increased again, but at a slower rate.
Neuronal depolarization by elevated K+ and exposure to CM have mirror-image, and antagonistic, effects on both CAT and TOH developments (Raynaud et al. 1987a). Walicke, Campenot & Patterson (1977) showed that a previous depolarization reduced the induction of cholinergic traits by a subsequent exposure to CM. We found that (1) such a depolarization only delayed the induction of CAT by several days and did not prevent the transition to a state of low TOH expression caused by CM and (2) an exposure of the cultures to elevated K+ after exposure to CM did not cause a decline in CAT activity.
These data thus suggest that a state of high TOH expression can superimpose on a previously induced state of elevated CAT expression, but that the induction of CAT caused by a delayed exposure to CM is accompanied by a transition from a high to a lower state of TOH expression. In addition, neuronal depolarization does not stabilize the noradrenergic phenotype in a permanent manner and can not reverse cholinergic expression of sympathetic neurones to a purely noradrenergic phenotype.
A study in developing visual systems with a new method of staining neurones and their processes in fixed tissue
Authors: Godement Pierre , Vanselow Jens , Thanos Solon , Bonhoeffer Friedrich 
Published: April 2021

ABSTRACT
Carbocyanine dyes, fluorescent lipophilic substances used for optical recordings of membrane voltage and for studies of membrane fluidity, have recently been shown to provide intense and long-lasting staining of neurones in vivo and in vitro (Schwartz & Agranoff, 1981; Honig & Hume, 1985,1986; Catsicas, Thanos & Clarke, 1986; Landmesser & Honig, 1986; Thanos & Bonhoeffer, 1987).
We report here that two of these dyes, dil (1,1′,dioctadecyl-3,3,3′3′-tetramethylindocarbocyanine perchlorate) and diO (3,3’-dioctadecyloxacarbocyanine perchlorate), can also label neurones in embryonic mouse and chicken brain tissue that has been previously fixed in aldehyde fixatives. Neuronal processes and perikarya can be labelled along considerable distances in both anterograde and retrograde directions. The staining of processes and cells, including their finest extensions is smooth and clear, rivalling intracellular injections of HRP or Lucifer Yellow. The appearance and time course of progression of the staining along axons suggest that the staining in fixed tissue occurs due to a process of diffusion of dyes along the plasma membranes of cells.
This technique has allowed us to study the first stages in the development of optic fibres in mouse embryos, especially at the optic chiasm. The early retinal projection (E13-E13I) is mainly crossed, but some optic fibres grow to the ipsilateral side of the brain at the outset. Retrogradely labelled ganglion cells from the dorsocentral area of the retina participate in the formation of both the ipsilateral and the contralateral projection. Thus, at early stages, crossed and uncrossed projections arise from identical subregions of the retina and the partition of the retina with respect to the laterality of its projection arises later.
Embryonic stem cell-mediated transfer and correct regulation of the chicken δ-crystallin gene in developing mouse embryos
Authors: Takahashi Yoshiko , Hanaoka Kazunori , Hayasaka Michiko , Katoh Kazuto , Kato Yoshihiro , Okada T. S. , Kondoh Hisato 
Published: April 2021

Abstract
To study regulation of δ-crystallin expression during ontogeny, we transferred the gene from chicken into developing mouse embryos by first transforming an embryonic stem (ES) cell line of mouse and then producing chimaeric embryos by combining them with normal mouse embryos. Using this technique, genes were transferred into a variety of developing mouse tissues with high efficiency. Two δ-crystallin gene constructs were used: the wild-type gene with 2200 bp of the 5’ flanking sequence, shown to be lensspecific in an assay using cultured mouse cells, and a mutant gene with 51 bp of the 5’ flanking sequence, lacking the sequence required for expression in lens cells. Five independent lines carrying the former and two lines carrying the latter were employed in producing chimaeras. In the chimaeric embryos having the wild-type gene, δ-crystallin was expressed in the lens and in specific regions of the primitive central nervous system (CNS) as is seen in embryonic expression in the chicken. In adult mouse chimaeras also, expression was restricted to the lens and the CNS, in the pyramidal neurones of the piriform cortex and the hippocampus, δ-crystallin expression in these tissues is due to proper transcriptional regulation, since no expression was observed when chimaeras were produced with the ES lines carrying the mutant gene. The experimental results reported here demonstrate the advantage of ES-cell-mediated gene transfer in the study of embryonic gene regulation, because a number of gene constructs and chromosomal sites can be analysed shortly after embryo manipulation without requiring gene transmission to the next generation.
De novo expression of a type IV collagen gene in Drosophila embryos is restricted to mesodermal derivatives and occurs at germ band shortening
Authors: Mirre Christian , Cecchini Jean-Pierre , Parco Yannick Le , Knibiehler Bernard 
Published: April 2021

Abstract
We have examined directly the expression of one collagen gene (DCgl) during Drosophila melanogaster embryogenesis by means of in situ hybridization. Transcripts of this gene, which were demonstrated to encode a basement membrane type IV collagen chain, began to accumulate specifically in mesodermal de-rivatives at stages 12-13 of embryogenesis, and not before. Cells expressing this gene overlap, or are closely intermingled with, somatic and visceral mesoderm in stages 12-14. In stages 15-17, in addition to the strongly positive fat bodies, highly labelled cell spots are found scattered around all the parts of the gut and symmetrically on each side of the ventral nerve cord. They correspond to circulating mesodermal cells which we consider to be haemocytes or mesoblasts.
A morphological and experimental study of the mesencephalic neural crest cells in the mouse embryo using wheat germ agglutinin–gold conjugate as the cell marker
Authors: Chan W. Y. , Tam P. P. L. 
Published: April 2021

Abstract
The distribution of the mesencephalic neural crest cells in the mouse embryo was studied by mapping the colonization pattern of WGA-gold labelled cells following specific labelling of the neuroectoderm and grafting of presumptive neural crest cells to orthotopic and heterotopic sites. The result showed that (1) there were concomitant changes in the morphology of the neural crest epithelium during the formation of neural crest cells in the 4- to 7-somite-stage embryos, (2) the neural crest cells were initially confined to the lateral subectodermal region of the cranial mesenchyme and there was minimal mixing with the paraxial mesoderm underneath the neural plate, (3) labelled cells from the presumptive crest region colonized the lateral craniofacial mesenchyme, the developing trigeminal ganglion and the pharyngeal arch, (4) the formation of neural crest cells was facilitated by the focal disruption of the basal lamina and the cell-cell interaction specific to the neural crest site and (5) the trigeminal ganglion was colonized not only by neural crest cells but also by cells from the ectodermal placode.
Growth factor superfamilies and mammalian embryogenesis
Authors: Mercola Mark , Stiles Charles D. 
Published: April 2021

Abstract
With the availability of amino acid and nucleotide sequence information has come the realization that growth factors can be clustered into superfamilies. Several of these superfamilies contain molecules that were not initially identified because of growth-promoting activities; rather they were discovered through their ability to regulate other processes. Certain members of these superfamilies are present during early mammalian embryogenesis. However, until recently, it has been difficult to manipulate the developing mammalian embryo to observe directly the effects of inappropriate, excessive, or reduced expression of these molecules. Despite this limitation, at least some of these molecules have been implicated in the control of differentiation and morphogenesis, two actions unpredicted from the cell biology of most of the growth factors. Moreover, these actions are reflected in nonmammalian species where homologues of the mammalian growth factors control crucial steps in the choice of developmental fate. This review describes five growth factor superfamilies and the role these molecules may have in controlling proliferation, differentiation, and morphogenesis during mammalian development.
Enhanced expression of TGF-β and c-fos mRNAs in the growth plates of developing human long bones
Authors: Sandberg M. , Vuorio T. , Hirvonen H. , Alitalo K. , Vuorio E. 
Published: April 2021

Abstract
The expression of mRNAs for type I and type II procollagens, transforming growth factor-β (TGF-β) and c-fos was studied in developing human long bones by Northern blotting and in situ hybridization. The cells producing bone and cartilage matrix were identified by hybridizations using cDNA probes for types I and II collagen, respectively. Northern blotting revealed that the highest levels of TGF-β mRNA were associated with the growth plates. By in situ hybridization, this mRNA was localized predominantly in the osteoblasts and osteoclasts of the developing bone, in periosteal fibroblasts and in individual bone marrow cells. These findings are consistent with the view that TGF-β may have a role in stimulation of type I collagen production and bone formation. Only a low level of TGF-β mRNA was detected in cartilage where type II collagen mRNA is abundant. In Northern hybridization, the highest levels of c-fos mRNA were detected in epiphyseal cartilage. In situ hybridization revealed two cell types with high levels of c-fos expression: the chondrocytes bordering the joint space . and the osteoclasts of developing bone. These differential expression patterns suggest specific roles for TGF-β and c-fos in osseochondral development.
Reinvestigation of the role of the optic vesicle in embryonic lens induction
Authors: Grainger Robert M. , Henry Jonathan J. , Henderson Robert A. 
Published: April 2021

Abstract
The induction of the lens by the optic vesicle in amphibians is often cited as support for the view that a single inductive event can lead to determination in a multipotent tissue. This conclusion is based on transplantation experiments whose results indicate that many regions of embryonic ectoderm which would normally form epidermis can form a lens if brought into contact with the optic vesicle. Although additional evidence argues that during normal development other tissues, acting before the optic vesicle, also contribute to lens induction, it is still widely held, on the basis of these transplantation experiments, that the optic vesicle alone can elicit lens formation in ectoderm. While testing this conclusion by transplanting optic vesicles beneath ventral ectoderm in Xenopus laevis embryos, it became apparent that contamination of optic vesicles by presumptive lens ectoderm cells can generate lenses in these experiments, illustrating the need for adequate host and donor marking procedures. Since previous studies rarely used host and donor marking, it was not clear whether they actually demonstrated that the optic vesicle can induce lenses. Using careful host and donor marking procedures with horseradish peroxidase as a lineage tracer, we show that the optic vesicle cannot stimulate lens formation in neurula- or gastrula-stage ectoderm of Xenopus laevis. Since the general conclusion that the optic vesicle is sufficient for lens induction rests on studies in many organisms, we felt it was important to begin to test this conclusion in other amphibians as well. Similar experiments were therefore performed with Rana palustris embryos, since it was in this organism that optic vesicle transplant studies had originally argued that this tissue alone can cause lens induction. Under conditions similar to those used in the original report, but with careful controls to assess the origin of lenses in transplants, we found that the optic vesicle alone cannot elicit lens formation. Our data lead us to propose that the optic vesicle in amphibians is not generally sufficient for lens induction. Instead, we argue that lens induction occurs by a multistep process in which an essential phase in lens determination occurs as a result of inductive interactions preceding contact of ectoderm with the optic vesicle.
Mesoderm-inducing factors: a small class of molecules
Authors: Godsave S. F. , Isaacs H. V. , Slack J. M. W. 
Published: April 2021

Abstract
Mesoderm-inducing factors (MIFs) from chick embryos, XTC cells and WEHI-3 cells were studied using various procedures. The object was to find whether they are similar to heparin-binding growth factors (HBGFs - the only known pure mesoderm-inducing substances) and, if not, whether they are similar to each other.
The major active components from all three MIF sources behave as somewhat hydrophobic, acid-stable molecules and do not bind to heparin. They all have relative molecular masses of about 13 000 measured by HPLC size exclusion chromatography. The isoelectric points measured by chromatofocusing were 6·7 (WEHI) and 7·7 (XTC). The chick MIF seemed somewhat heterogeneous by chromatofocusing and a portion of its activity bound to heparin sepharose.
All three MIFs have similar effects on explants of Xenopus blastula ectoderm to the heparin-binding growth factors, causing an elongation at the time of gastrulation followed by the development of mesenchyme, mesothelium and muscle cells, the proportion of muscle increasing with dose. Unlike the HBGFs they all also induce notochord if sufficiently high concentrations are used.
Our study shows that the MIFs examined here form a small group of potent agents distinct from the HBGFs and from other known growth and differentiation factors. Their occurrence in various tissues and cell lines suggests that they have functions in the adult organism as well as during early development.