bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gap-junctional permeability in early and cleavage-arrested ascidian embryos
Authors: Dale Brian , Santella Luigi A , Tosti Elisabetta 
Published: April 2021

ABSTRACT
Using the whole-cell voltage clamp technique, we have studied junctional conductance (Gj), and Lucifer Yellow (LY) coupling in 2-cell and 32-cell ascidian embryos. Gj ranges from 17.5 to 35.3 nS in the 2-cell embryo where there is no passage of LY, and from 3.5 to 12.2 nS in the later embryo where LY dye spread is extensive. In both cases, Gj is independent of the transjunctional potential (Vj). Manually apposed 2-cell or 32-cell embryos established a junctional conductance of up to 10 nS within 30 min of contact. Furthermore, since we did not observe any significant number of cytoplasmic bridges at the EM and Gj is sensitive to octanol, it is probable that blastomeres in the 2-cell and 32-cell embryos are in communication by gap junctions. In order to compare Gj in the two stages and to circumvent problems of cell size, movement and spatial location, we used cytochalasin B to arrest cleavage. Gj in cleavage-arrested 2-cell embryos ranged from 25.0 to 38.0 nS and remained constant over a period of 2.5 h. LY injected into a blastomere of these arrested embryos did not spread to the neighbour cell until they attained the developmental age of a 32- to 64-cell control embryo. Our experiments indicate a change in selectivity of gap junctions at the 32cell stage that is not reflected by a macroscopic change in ionic permeability.
Integrin expression during human epidermal development in vivo and in vitro
Authors: Hertle Mark D. , Adams Josephine C. , Watt Fiona M. 
Published: April 2021

ABSTRACT
In order to investigate the role of extracellular matrix receptors of the integrin family in establishing the spatial organization of epidermal keratinocytes, we used immunofluorescence microscopy to examine the expression of a range of integrin subunits during development of human palm and sole skin. All of the integrins expressed during development were also present in mature epidermis and were largely confined to the basal layer of keratinocytes in a pericellular distribution. The α3 and β1 subunits were expressed prior to initiation of stratification and did not change in abundance or distribution during subsequent development, α4 and β3 were not detected at any time in the epidermis. Every other subunit examined showed spatial or temporal changes in expression. Staining for α3 was strong before stratification and until mid-development, but was greatly decreased in neonatal epidermis. α2 was first detected in small patches of basal cells prior to stratification, and thereafter was found in the entire basal layer, with greater staining in developing sweat glands, α5 was not expressed until mid-development, and then primarily in developing sweat glands, with faint expression in neonatal epidermis, αv was detected following stratification, in developing sweat glands, and occasionally in neonatal epidermis, α6 and β4 were peribasally expressed before stratification, but there-after became concentrated at the basal cell surface in contact with the basement membrane, co-localizing with hemidesmosomes as determined by staining with bullous pemphigoid antiserum. We also examined the distri-bution of three known ligands for keratinocyte integrins: laminin and collagen type IV were present in the basement membrane zone at all stages of development, whereas fibronectin was only evident there until about 13 weeks estimated gestational age. Finally, we found that the changes in integrin expression that occur on initiation of stratification in vivo could be reproduced in organ cultures of developing skin; such cultures there-fore provide a useful experimental model for further studies of the role of integrins in epidermal stratification.
Common precursors for neural and mesectodermal derivatives in the cephalic neural crest
Authors: Baroffio Anne , Dupin Elisabeth , Douarin Nicole M. Le 
Published: April 2021

ABSTRACT
The cephalic neural crest (NC) of vertebrate embryos yields a variety of cell types belonging to the neuronal, glial, melanocytic and mesectodermal lineages. Using clonal cultures of quail migrating cephalic NC cells, we demonstrated that neurons and glial cells of the peripheral nervous system can originate from the same progenitors as cartilage, one of the mesectodermal derivatives of the NC. Moreover, we obtained evidence that the migrating cephalic NC contains a few highly multipotent precursors that are common to neurons, glia, cartilage and pigment cells and which we interpreté as representative of a stem cell population. In contrast, other NC cells, although provided with identical culture conditions, give rise to clones composed of only one or some of these cell types. These cells thus appear restricted in their developmental potentialities compared to multipotent cells. It is therefore proposed that, in vivo, the active proliferation of pluripotent NC cells during the migration process generates distinct subpopulations of cells that become progressively committed to different developmental fates.
Gene regulatory factors of the sea urchin embryo: I. Purification by affinity chromatography and cloning of P3A2, a novel DNA-binding protein
Authors: Calzone Frank J. , Höog Christer , Teplow David B. , Cutting Ann E. , Zeller Robert W. , Britten Roy J. , Davidson Eric H. 
Published: April 2021

ABSTRACT
The P3A2 regulatory protein interacts with specific sites in the control region of the Cyllla actin gene. Previous studies showed that this interaction is required to confine expression of a Cyllla. CAT fusion to the aboral ectoderm, the embryonic territory in which Cyllla is normally utilized. P3A2 also binds specifically to similar target sites located in the regulatory region of the SM50 gene, which is expressed only in skeletogenic mesenchyme lineages. The P3A2 factor was purified by affinity chromatography from nuclear extracts of 24 h sea urchin embryos, and partial peptide sequences were used to isolate a cDNA clone encoding the complete protein. There are no significant similarities between P3A2 and any other protein in existing sequence data bases. P3A2 thus includes a novel type of DNA-binding domain. To examine the differential utilization of P3A2 in Cyllla and SM50 genes, we measured the specific affinity of this protein for the various target sites in the regulatory DNAs of each gene, and identified the core target site sequences. The stability of P3A2 complexes formed with SM50 target sites is 50-100 times greater than that of the complexes formed with Cyllla target sites, though the factor binds to very similar core sequence elements. P3A2 is one of at least twelve different proteins whose interaction with CyIIIa regulatory DNA is required for correct developmental expression. The results reported demonstrate that it might be possible to purify most of these regulatory proteins, or any other specific DNA-binding proteins of the sea urchin embryo, by using the simple procedures described for P3A2.
Changes in transcellular ionic currents associated with cytokinesis and polar lobe formation in embryos of Bithynia tentaculata (Mollusca)
Authors: Zivkovic Danica , Dohmen René 
Published: April 2021

ABSTRACT
Using the vibrating probe technique, we have measured transcellular ionic currents ranging from 0.05 to 3.00 μA cm-2 around polar-lobe-forming embryos of Bithynia tentaculata.
During maturation and the first two mitotic division cycles, we have detected recurrent changes in the current pattern, which correlated temporally and spatially with cytokinesis and polar lobe formation. The maximum inward current at the animal pole coincides with the onset of cleavages at that pole, and the maximum inward current at the vegetal pole slightly precedes the formation of the two meiotic polar lobes and the first mitotic polar lobe at that pole. This correlation was less clear with regard to the second mitotic polar lobe. The resorption of the polar lobe correlates with a reversal of the current from inward to outward at the vegetal pole. After the resorption of the first mitotic polar lobe, the transmembrane ion flow in the membrane area, which formerly covered the lobe, is different from the surrounding membrane.
Rodent CNS neuroblasts exhibit both perpendicular and parallel contact guidance on the aligned parallel neurite bundle
Authors: Nagata Isao , Nakatsuji Norio 
Published: April 2021

ABSTRACT
Mouse cerebellar granule cells showed two types of migration behavior in microexplant cultures. They first migrated along their neurites, showing the typical contact guidance, and then oriented themselves at right angles to the parallel neurites, thus exhibiting the ‘perpendicular contact guidance’ (Nakatsuji, N. and Nagata, I. 1989 Development, 106, 441–447).
To study whether other neurons have the capacity to show similar ‘perpendicular contact guidance’, we cultured dissociated neuroblasts from various parts of CNS or PNS on parallel neurite bundles. The PNS neuroblasts always extended their processes parallel to the neurite bundle. In contrast, almost all kinds of CNS neuroblasts tested oriented their processes both perpendicular and parallel to the neurite bundles that were all free of glia. Time-lapse video recording revealed that neuroblasts migrated in both directions. Thus, CNS neuroblasts possess the capacity to migrate and extend their processes at right angles to the substratum of heterotypic neurite bundles, which may play an important role in histogenesis of the CNS during development.
Expressing antisense Po RNA in Schwann cells perturbs myelination
Authors: Owens Geoffrey C. , Boyd Carol J. 
Published: April 2021

ABSTRACT
Primary Schwann cells were infected in vitro with a recombinant retrovirus expressing a dominant selectable marker, neomycin phosphotransferase (conferring resistance to the drug G418), and antisense Po RNA under the control of the human β-actin promoter. A proportion of the G418-resistant cells failed to form myelin when cocultured with dorsal root ganglion neurons under conditions that promote Schwann cell differentiation. These cells expressed high levels of Po antisense RNA. Among the impaired cells, the majority had segregated and ensheathed individual axons but had not differentiated further. They did not express Po but did express myelin-associated glycoprotein and galacto cerebroside. A minority of partially inhibited Schwann cells were also observed that elaborated thin myelin sheaths containing variable numbers of compacted and noncompacted lamellae. These data indicate that restricting the level of Po expression inhibits spiralling of the Schwann cell membrane and subsequent compaction.
Retinoic acid induces NGF-dependent survival response and high-affinity NGF receptors in immature chick sympathetic neurons
Authors: Rodriguez-Tébar Alfredo , Rohrer Hermann 
Published: April 2021

ABSTRACT
An important step in the development of peripheral sensory and sympathetic neurons is the onset of the survival response and dependence on the presence of nerve growth factor (NGF) or other neurotrophic factors. We have recently observed that immature sympathetic neurons from 7-day-old chick embryos are unable to become NGF-responsive in vitro and we have now used these cells to identify molecules that induce NGF-dependent neuronal survival. We found that retinoic acid (RA) induces the ability of these cells to survive in the presence of NGF. At RA concentrations of 10−9–10−8M virtually all neurons survived in the presence of NGF. RA was found to also induce the biologically active, high-affinity NGF receptor: highaffinity receptors were undetectable on dissociated E7 sympathetic neurons and were observed in vitro only in RA-treated neurons. These findings suggest that the induction of high-affinity NGF receptors may be sufficient to activate the survival response in sympathetic neurons and imply an important role for RA during neuron differentiation in the peripheral nervous system.
Interactions of different vegetal cells with mesomeres during early stages of sea urchin development*
Authors: Khaner Oded , Wilt Fred 
Published: April 2021

ABSTRACT
It has been known from results obtained in the classical experiments on sea urchin embryos that cell isolation and transplantation showed extensive interactions between the early blastomeres and/or their descendants. In the experiments reported here a systematic reexamination of recombination of mesomeres and their progeny (which come from the animal hemisphere) with various vegetal cells derived from blastomeres of the 32- and 64-cell stage was carried out. Cells were marked with lineage tracers to follow which cell gave rise to what structures, and newly available molecular markers have been used to analyze different structures characteristic of regional differentiation. Large micromeres form spicules and induce gut and pigment cells in mesomeres, conforming to previous results. Small micromeres, a cell type not heretofore examined, gave rise to no recognizable structure and had very limited ability to evoke poorly differentiated gut tissue in mesomeres. Macromeres and their descendants, Veg 1 and Veg 2, form primarily what their normal fate dictated, though both did have some capacity to form spicules, presumably by formation from secondary mesenchyme. Macromeres and their descendants were not potent inducers of vegetal structures in animal cells, but they suppress the latent ability of mesomeres to form vegetal structures. The results lead us to propose that the significant interactions during normal development may be principally suppressive effects of mesomeres on one another and of adjacent vegetal cells on mesomeres.
Functional tagging of regulatory elements in the plant genome
Authors: Topping Jennifer F. , Wei Wenbin , Lindsey Keith 
Published: April 2021

ABSTRACT
In comparison with animals, relatively few plant genes have been identified that have been shown to be under organ-, tissue- or cell-type-specific regulation. In this paper, we describe how the β-glucuronidase (GUS) reporter gene (gusA or uidA), fused to a weak promoter (a truncated (−90 bp) CaMV35S promoter), can be used to identify tissue-specific markers in transgenic tobacco plants. The rationale was that the expression of gusA would be determined primarily by position effect. Quantitative analysis revealed that, of 184 −90−gus transgenic plants, 73 % exhibited gusA gene activation in leaf tissue, and the level of GUS enzyme activity varied over a 300-fold range within the population. In comparison, transformation with a promoterless gusA gene resulted in GUS expression in 78 % of all plants analyzed (in leaf and/or root) and expression levels were three-fold or more lower. Qualitative GUS analysis of single locus −90-gus transformants revealed differential expression in diverse tissues. The spatial pattern of GUS activity was unique to individual transformants, was a reflection of differential gusA gene transcription, and was stably transmissible to progeny. Evidence for preferential expression in roots not only of the −90-gus, but also the promoterless gusA gene is presented. The value of the −90 bp promoter-gusA sequence, which is termed an ‘interposon’, as a tool both to identify native enhancer sequences in situ and to investigate position effects in plants, is discussed.
Well-defined growth factors promote cardiac development in axolotl mesodermal explants
Authors: Muslin Anthony J. , Williams Lewis T. 
Published: April 2021

ABSTRACT
The effect of growth factors on the formation of cardiac mesoderm in the urodele, Ambystoma mexicanum (axolotl), has been examined using an in vitro explant system. It has previously been shown that cardiac mesoderm is induced by pharyngeal endoderm during neurula stages in urodeles. In this study, explants of prospective cardiac mesoderm from early neurula stage embryos rarely formed beating cardiac tissue in culture. When transforming growth factor beta-1 (TGF-β1) or platelet-derived growth factor BB (PDGF) was added to such explants, the frequency of heart tissue formation increased markedly. The addition of other growth factors to these explants did not enhance cardiac mesoderm formation. The addition of basic fibroblast growth factor (bFGF) to prospective heart mesoderm derived from later stage embryos resulted in a decreased tendency to form cardiac tissue. These results suggest that growth factors analogous to TGF-β1 PDGF, and bFGF may regulate the initial stages of vertebrate cardiac development in vivo.
Retinoic acid modifies the pattern of cell differentiation in the central nervous system of neurula stage Xenopus embryos
Authors: i Altaba A. Ruiz , Jessell T. M. 
Published: April 2021

ABSTRACT
Neural cell markers have been used to examine the effect of retinoic acid (RA) on the development of the central nervous system (CNS) of Xenopus embryos. RA treatment of neurula stage embryos resulted in a concentration-dependent perturbation of anterior CNS development leading to a reduction in the size of the forebrain, midbrain and hindbrain. In addition the overt segmental organization of the hindbrain was abolished by high concentrations of RA. The regional expression of two cell-specific markers, the homeobox protein Xhox3 and the neurotransmitter serotonin was also examined in embryos exposed to RA. Treatment with RA caused a concentration-dependent change in the pattern of expression of Xhox3 and serotonin and resulted in the ectopic appearance of immunoreactive neurons in anterior regions of the CNS, including the forebrain. Collectively, our results extend previous studies by showing that RA treatment of embryos at the neurula stage inhibits the development of anterior regions of the CNS while promoting the differentiation of more posterior cell types. The relevance of these findings to the possible role of endogenous retinoids in the determination of neural cell fate and axial patterning is discussed.
Hepatic Nuclear Factor 1 (HNF1) shows a wider distribution than products of its known target genes in developing mouse
Authors: Blumenfeld Marta , Maury Martine , Chouard Tanguy , Yaniv Moshe , Condamine Hubert 
Published: April 2021

ABSTRACT
Hepatic nuclear factor 1 (HNF1) is a highly diverged homeoprotein that is crucial for transcription of many liver-specific genes including albumin. In particular, a minimal promoter, consisting of an HNF1-binding-site and a TATA box, is highly active only in hepatoma cell lines. The expression of the HNF1 and albumin genes has been examined in mouse embryos by in situ hybridization. At 10.5 days of gestation, the HNF1 mRNA was detected in both the hepatic primordia and visceral endoderm of the yolk sac whereas the albumin transcript was present only in the nascent liver. At later stages of development, HNF1 was detected in liver, in the epithelial cells of most of the digestive tract and in the cortex of the kidney, whereas albumin was again found only in the liver. The presence of HNF1 protein in adult kidney was demonstrated by immunodetection in gelretardation assays and western blot analysis. These experiments show that, even though the HNF1 homeoprotein is essential for expression of many liver-specific genes, it cannot, by itself, force high expression levels of these genes, in non-hepatic tissues.
Role of c-kit in mouse spermatogenesis: identification of spermatogonia as a specific site of c-kit expression and function
Authors: Yoshinaga Kazuya , Nishikawa Satomi , Ogawa Minetaro , Hayashi Shin-Ichi , Kunisada Takahiro , Fujimoto Toyoaki , Nishikawa Shin-Ichi 
Published: April 2021

ABSTRACT
Recent studies have shown that the dominant white spotting (W) locus encodes the proto-oncogene c-kit, a member of the tyrosine kinase receptor family. One symptom of mice bearing mutation within this gene is sterility due to developmental failure of the primordial germ cells during early embryogenesis. To elucidate the role of the c-kit in gametogenesis, we used an anti-c-kit monoclonal antibody, ACK2, as an antagonistic blocker for c-kit function to interfere with the development of male and female germ cells during postnatal life. ACK2 enabled us to detect the expression of c-kit in the gonadal tissue and also to determine the functional status of c-kit, which is expressed on the surface of a particular cell lineage. Consistent with our immunohistochemical findings, the intravenous injection of ACK2 into adult mice caused a depletion in the differentiating type A spermatogonia from the testis during 24 – 36 h, while the undifferentiated type A spermatogonia were basically unaffected. Intraperitoneal injections of ACK2 into prepuberal mice could completely block the mitosis of mature (differentiating) type A spermatogonia, but not the mitosis of the gonocytes and primitive type A spermatogonia, or the meiosis of spermatocytes. Our results indicate that the survival and/or proliferation of the differentiating type A spermatogonia requires c-kit, but the primitive (undifferentiated) type A spermatogonia or spermatogenic stem cells are independent from c-kit. Moreover, the antibody administration had no significant effect on oocyte maturation despite its intense expression of c-kit.
A normally attractive cell interaction is repulsive in two C. elegans mesodermal cell migration mutants
Authors: Stern Michael J. , Horvitz H. Robert 
Published: April 2021

ABSTRACT
In wild-type Caenorhabditis elegans hermaphrodites, two bilaterally symmetric sex myoblasts (SMs) migrate anteriorly to Sank the precise center of the gonad, where they divide to generate the muscles required for egg laying (J. E. Sulston and H. R. Horvitz (1977) Devi Biol. 56, 110–156). Although this migration is largely independent of the gonad, a signal from the gonad attracts the SMs to their precise final positions (J. H. Thomas, M. J. Stern and H. R. Horvitz (1990) Cell 62, 1041–1052). Here we show that mutations in either of two genes, egl-15 and egl-17, cause the premature termination of the migrations of the SMs. This incomplete migration is caused by the repulsion of the SMs by the same cells in the somatic gonad that are the source of the attractive signal in wild-type animals.
Demonstration of a phagocytic cell system belonging to the hemopoietic lineage and originating from the yolk sac in the early avian embryo
Authors: Cuadros Miguel A. , Coltey Pierre , Nieto M. Carmen , Martin Claude 
Published: April 2021

Abstract
It is well established that hemopoietic cells arising from the yolk sac invade the avian embryo. To study the fate and role of these cells during the first 2.5-4.5 days of incubation, we constructed yolk sac chimeras (a chick embryo grafted on a quail yolk sac and vice versa) and immunostained them with antibodies specific to cells of quail hemangioblastic lineage (MB1 and QH1). This approach revealed that endothelial cells of the embryonic vessels are of intraembryonic origin. In contrast, numerous hemopoietic cells of yolk sac origin were seen in embryos ranging from 2.5 to 4.5 days of incubation. These cells were already present within the vessels and in the mesenchyme at the earliest developmental stages analyzed. Two hemopoietic cell types of yolk sac origin were distinguishable, undifferentiated cells and macro-phage-like cells. The number of the latter cells increased progressively as development proceeded, and they showed marked acid phosphatase activity and phagocytic capacity, as revealed by the presence of numerous phagocytic inclusions in their cytoplasm. The macro-phage-like cells were mostly distributed in the mesen-chyme and also appeared within some organ primordia such as the neural tube, the liver anlage and the nephric rudiment. Comparison of the results in the two types of chimeras and the findings obtained with acid phosphatase/MB1 double labelling showed that some hemopoietic macrophage-like cells of intraembryonic origin were also present at the stages considered. These results support the existence in the early avian embryo of a phagocytic cell system of blood cell lineage, derived chiefly from the yolk sac. Cells belonging to this system perform phagocytosis in cell death and may also be involved in other morphogenetic processes.