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M Asashima

Publications and source records attributed to M Asashima.

At least 55 records · Page 3Linked to original sources
PubMed1999

Molecular cloning of a novel Xenopus spalt gene (Xsal-3).

The sal (spalt) gene family is characterized by unique double zinc finger motifs and is conserved among various species from Drosophila to humans. Here we report a new Xenopus member of this family, Xsal-3. It is 38% homologous at the amino acid level to the previously reported Xenopus homologue of the spalt gene, Xsal-1. Alternatively spliced Xsal-3 transcripts give rise to RNAs coding either two or three double zinc fingers, and the longer form is expressed maternally. Xsal-3 is expressed in the neural tube, the mandibular, hyoid, and branchial arch, and the pronephric duct, which is different from the expression pattern of Xsal-1. These findings suggest that Xsal-3 may have distinct roles in early Xenopus development.

Alternative Splicing↗
PubMed1999

cDNA cloning and distribution of the Xenopus follistatin-related protein.

Recently, several proteins which have a follistatin module have been isolated. One of them, the follistatin-related protein (FRP), is encoded by TSC-36 (TGF-beta-stimulated clone 36) in mouse, originally isolated as a cDNA clone up-regulated by TGF-beta1 in mouse osteogenic MC3T3E1 cells. To determine the physiological role of FRP in early Xenopus embryonic development, we cloned the Xenopus FRP (xFRP) cDNA. The resulting cDNA clone was a secreted glycoprotein consisting of 299 amino acid residues with about 70% similarity to the mammalian and avian FRPs. Northern blotting analysis revealed that xFRP gene expression started at stage 10, the onset of gastrulation, gradually increased during the blastula and neurula stages and was sustained through the tail-bud stage. Whole-mount in situ hybridization analysis showed the localization of xFRP mRNAs in the Spemann organizer, notochord, neural floor plate, hypochord and somite. The similarities with the pattern of expression of Xenopus follistatin mRNA suggests that xFRP may play a role in neuralization.

Amino Acid Sequence↗
PubMed1999

Blood cell induction in Xenopus animal cap explants: effects of fibroblast growth factor, bone morphogenetic proteins, and activin.

Cultures of Xenopus blastula animal caps were used to explore the haematopoietic effects of three candidate inducers of mesoderm: basic fibroblast growth factor (bFGF), bone morphogenetic proteins (BMPs) and activin A. In response to either bFGF or activin A, explants expanded into egg-shaped structures, and beneath an outer layer of epidermis, a ventral mesodermal lining surrounded a fluid-filled cavity containing "blood-like cells". Immunocytochemistry identified some of these cells as early leukocytes, but erythrocytes were rare. BMP-2 or BMP-4 induced primitive erythrocytes as well as leukocytes, and a high concentration was required for these cells to differentiate in only a small proportion of explants. BMP-2 but not BMP-4 induced ventral mesoderm concomitantly. High concentrations of activin A dorsalized explants, which contained infrequent leukocytes, and an optimal combination of activin A and bFGF caused differentiation of muscle with few blood cells. By contrast, BMP-2 or BMP-4 plus activin A synergistically increased the numbers of both leukocytes and erythrocytes. Explants treated with BMPs plus activin contained a well organized cell mass in which yolk-rich cells mixed with blood cells and pigmented cells did not. BMP-2 plus bFGF also induced numerous leukocytes and fewer erythrocytes, but BMP-4 antagonized the leukopoietic effect of bFGF. The data suggest that the signalling pathways these three factors use to induce leukopoiesis overlap and that erythropoiesis may be activated when inducers are present in combination.

Activins↗
PubMed1999

Expression of Brachyury-like T-box transcription factor, Xbra3 in Xenopus embryo.

The Xenopus Brachyury-like Xbra3 gene is a novel T-box gene that is closely associated with Xenopus Brachyury. The expression pattern of Xbra3 during development is similar to that of Xbra. During gastrulation Xbra3 is expressed in the marginal zone, with a gradient of increasing expression from ventral to dorsal. In the early neurula stage Xbra3 is expressed in the notochord and posterior mesoderm, but by the tailbud stage its expression is restricted to the forming tailbud and the posterior portion of the notochord.

Amino Acid Sequence↗
PubMed1999

Expression of Xenopus T-box transcription factor, tbx2 in Xenopus embryo.

We report here the cloning and expression of the Xenopus orthologue of the T-box transcription factor gene Tbx2 (optomotor-blind in Drosophila). Tbx2 is first detected in the ventral mesodermal cells just above the yolk plug at late gastrula. At the neurula stage it is strongly expressed in the cement gland, dorsal root ganglia, and otic vesicle region. At the tailbud stage strong Tbx2 expression is observed in the dorsal part of the optic cup and trigeminal ganglia, and it is also expressed in the branchial arches, heart anlage, nasal pit, proctodeum, and the region around the pronephros.

Amino Acid Sequence↗
PubMed1999

Effects of hepatocyte growth factor (HGF) and activin A on the morphogenesis of rat submandibular gland-derived epithelial cells in serum-free collagen gel culture.

To study the mechanisms of morphogenesis in salivary gland regeneration, we have established the RSMG-1 cell line derived from submandibular gland (SMG) of 10-wk-old Wistar female rats in serum-free culture. Our finding that RSMG-1 cells originated from duct cells was based on morphology and immunohistochemical results. In three-dimensional serum-free collagen gel culture, HGF induced branching morphogenesis of RSMG-1 cells. Histological examination revealed that HGF-induced branching structure exhibited well-formed lumina. This morphology closely resembles that found in vivo. The cells also expressed activin A. Exogenously added activin A at a high concentration reduced HGF-induced branching morphogenesis. These findings suggest that the morphogenesis of the salivary gland is modulated by HGF and activin A. Our results show that the RSMG-1 cell line may be useful in studies of salivary gland regeneration.

Activins↗
PubMed1999

Role of activin and other peptide growth factors in body patterning in the early amphibian embryo.

The amphibian body plan is established as the result of a series of inductive interactions. During early cleavage stages cells in the vegetal hemisphere induce overlying animal hemisphere cells to form mesoderm. The interaction represents the first major body-patterning event and is mediated by peptide growth factors. Various peptide growth factors have been implicated in mesoderm development, including most notably members of the transforming growth factor-beta superfamily. Identification of the so-called "natural" inducer from among the several candidate peptide growth factors is being achieved by employing several experimental strategies, including the use of a tissue explant assay for testing potential inducers, cloning of marker genes as indices of early induction events, and microinjection of altered peptide growth factor receptors to disrupt normal embryonic inductions. Activin emerges as the most likely choice for assignment of the role of endogenous mesoderm inducer, because it currently best fulfills the rigorous set of criteria expected of such an important embryonic signaling molecule. Activin, however, may not act alone in mesoderm induction. Other peptide growth factors such as fibroblast growth factor might be involved, especially in the regional patterning of the mesoderm. In addition, several genes (e.g., Wnt and noggin), which are expressed after the mesoderm is initially induced, probably assist in further definition of the mesoderm pattern. Following mesoderm induction, the primary embryonic organizer tissue (first described in 1924 by Spemann) develops and contributes further to body patterning by its action as a neural inducer. Peptide growth factors such as activin may also be involved in the inductive event, either directly (by facilitating gene expression) or indirectly (by serving to constrain pathways).

Activins↗
PubMed1999

Evidence that far-infrared radiation promotes growth of Xenopus laevis.

In most ectotherms, environmental temperature has differential effects on growth and differentiation. For example, amphibian size at maturity decreases with increasing temperature. To address how radiant heat in the form of far-infrared radiation (FIR) may affect development of the aquatic ectotherm Xenopus laevis, we continuously irradiated swimming larvae as they developed into young adults. Here we report evidence that FIR promotes growth of these organisms in an aqueous environment.

Animal Husbandry↗
PubMed1999

Cytochalasin B inhibits morphogenetic movement and muscle differentiation of activin-treated ectoderm in Xenopus.

Xenopus ectodermal explants (animal caps) begin to elongate after treatment with the mesoderm inducing factor activin A. This phenomenon mimics the convergent extension of dorsal mesoderm during gastrulation. To analyze the relationship between elongation movement and muscle differentiation, animal caps were treated with colchicine, taxol, cytochalasin B and hydroxyurea (HUA)/aphidicolin following activin treatment. Cytochalasin B disrupted the organization of actin filaments and inhibited the elongation of the activin-treated explants. Muscle differentiation was also inhibited in these explants at the histologic and molecular levels. Colchicine and taxol, which are known to affect microtubule organization, had little effect on elongation of the activin-treated exp ants. Co-treatment with HUA and aphidicolin caused serious damage on the explants and they did not undergo elongation. These results suggest that actin filaments play an important role in the elongation movement that leads to muscle differentiation of activin-treated explants.

Actin Cytoskeleton↗
PubMed1999

Endoderm differentiation and inductive effect of activin-treated ectoderm in Xenopus.

When presumptive ectoderm is treated with high concentrations of activin A, it mainly differentiates into axial mesoderm (notochord, muscle) in Xenopus and into yolk-rich endodermal cells in newt (Cynops pyrrhogaster). Xenopus ectoderm consists of multiple layers, different from the single layer of Cynops ectoderm. This multilayer structure of Xenopus ectoderm may prevent complete treatment of activin A and subsequent whole differentiation into endoderm. In the present study, therefore, Xenopus ectoderm was separated into an outer layer and an inner layer, which were individually treated with a high concentration of activin A (100 ng/mL). Then the differentiation and inductive activity of these ectodermal cells were examined in explantation and transplantation experiments. In isolation culture, ectoderm treated with activin A formed endoderm. Ectodermal and mesodermal tissues were seldom found in these explants. The activin-treated ectoderm induced axial mesoderm and neural tissues, and differentiated into endoderm when it was sandwiched between two sheets of ectoderm or was transplanted into the ventral marginal zone of other blastulae. These findings suggest that Xenopus ectoderm treated with a high concentration of activin A forms endoderm and mimics the properties of the organizer as in Cynops.

Activins↗
PubMed1999

Changes in the adhesive properties of dissociated and reaggregated Xenopus laevis embryo cells.

Activin A is a member of the transforming growth factor beta superfamily, and the strongest candidate mesoderm-inducer. The initial adhesive property changes in amphibians are likely to be mediated by mesoderm-inducers like activin A. The manner in which these changes actually occur, however, remains poorly understood. In the present study, the adhesive property changes mediated by activin A were directly demonstrated. Activin A functioned as a morphogen at low concentrations (less than 0.5 ng/mL), with no effect on the type A adhesive property. But at high concentrations (1 ng/mL), it induced another type of adhesive property, type N, and at very high concentrations (more than 10 ng/mL), it induced yet another type of adhesive property, type Y. Cells that have types A, N, and Y adhesive properties ultimately differentiated into atypical epidermis, notochord, and yolk-rich cells, respectively. It was also shown that these changes occurred between 5 and 10 h after induction by activin A. The implications of these results for the relationship between the adhesive property acquired during early and later stages of differentiation are also discussed.

Activins↗
PubMed1999

Peptide growth factors in amphibian embryogenesis: intersection of modern molecular approaches with traditional inductive interaction paradigms.

Recent discoveries of the role peptide growth factors (PGFs) play in regulating embryonic patterning and differentiation have profoundly influenced research on the molecular biology of early amphibian embryogenesis. Several PGFs have been recognized to be present as endogenous components of amphibian eggs and early embryos, while other PGFs -- which are known from heterologous systems (e.g., Drosophila) -- exert remarkable effects when injected as either protein or mRNA into eggs/embryos or when added to cultured embryonic tissue. For a variety of reasons (reviewed herein) optimism abounds that an understanding in molecular terms of the classical Spemann and Nieuwkoop tissue interactions which are generally believed to drive embryonic patterning is within reach. A critical assessment of the interpretations of some of the contemporary data on PGFs (included herein) should, however, temper some of that optimism. Likely, multiple rather than single PGFs act in a combinatorial fashion to contribute to individual patterning events. As well, substantial redundancy in PGF regulatory circuits probably exists, so the heavy reliance on tissue culture assays and overexpression studies which characterize much recent research needs to be circumvented. Potential experimental approaches for "next generation" experiments are discussed.

Amphibians↗
PubMed1999

Activin incorporation into vitellogenic oocytes of Xenopus laevis.

Activin uptake into Xenopus oocytes was studied by several complementary methods. Immunocytochemistry of adult ovary localized activin and follistatin in the cytoplasm of vitellogenic oocytes and surrounding follicle cells. Surface plasmon resonance analysis of protein interaction kinetics indicated that while follistatin or a complex of activin-follistatin bound to yolk vitellogenin, activin alone did not. Radioactive tracer analysis measured specific incorporation of activin by viable oocytes in vitro. Together, the results suggest that vitellogenic oocytes can import activins from follicle cells and that follistatin may act as a chaperone for binding activin to vitellogenin in yolk platelets.

Activins↗
PubMed1998

Molecular cloning of XNLRR-1, a Xenopus homolog of mouse neuronal leucine-rich repeat protein expressed in the developing Xenopus nervous system.

We report the isolation and characterization of a Xenopus sequence, XNLRR-1, that is closely related to a gene for mouse neuronal leucine-rich repeat protein (NLRR-1). The cDNA clone is 4179 bp long and encodes a putative transmembrane glycoprotein of 718 amino acids, containing 12 leucine-rich repeats followed by one C2-type immunoglobulin-like domain and one fibronectin type-III repeat. XNLRR-1 is transcribed mainly in the developing eye area and the ventricular zone from diencephalon to hindbrain and slightly in spinal cord in Xenopus tadpoles. The similarity of the XNLRR-1 gene to other known cell adhesion molecules, together with the expression pattern, suggests that XNLRR-1 is involved in interactions at the neuronal cell surface.

Amino Acid Sequence↗
PubMed1998

XCIRP (Xenopus homolog of cold-inducible RNA-binding protein) is expressed transiently in developing pronephros and neural tissue.

The pronephros functions in the amphibian larval stage. It differentiates in certain presumptive regions of the amphibian embryo. The study of molecules functioning during pronephrogenesis is important for understanding the mechanism of kidney formation. Herein, we report a gene expressed during differentiation of the pronephros and neural tissues that we isolated by differential hybridization using our pronephros in-vitro induction system. The gene, XCIRP, is 887bp in length, and encodes a putative protein composed of 163 amino acid residues. The deduced protein contains two CS-RBDs (consensus sequence RNA-binding domain) and a glycine-rich domain, and is 74% identical to homologs from other species (mouse, rat and human). The expression of XCIRP increased rapidly during gastrulation, and XCIRP localization was seen in the presumptive pronephros and neural tissues. These findings suggest that XCIRP may play important roles in pronephrogenesis and neurogenesis.

Amino Acid Sequence↗
PubMed1998

Induction of blood cells in Xenopus embryo explants.

A Xenopus-specific anti-leukocyte monoclonal antibody designated XL-2 was isolated and used to identify leukocytes in tailbud embryos and activin A-treated explants of blastula animal cap. XL-2 bound to a 135-kDa polypeptide in western blots of protein extracts from adult thymocytes, tailbud embryos, tadpoles, and explants. In cell suspensions, it immunostained the cell surface of all types of adult leukocytes including lymphocytes, monocyte/macrophages, thrombocytes, and granulocytes. At embryonic stage 24, immunocytochemistry revealed XL-2-positive leukocytes, the earliest time at which such cells have been recognized. Whole-mount staining of tailbud embryos and tadpoles showed a widely dispersed population of XL-2-reactive leukocytes, many of which had elongated shapes and ameboid pseudopodia. In activin A-treated animal caps, XL-2 recognized a subpopulation of cells within the lumen of the central fluid-filled cavity as well as cells in the interstitium of mesenchymal and mesothelial components of the explant. Together, activin A and human interleukin-11 induced 100% of explants to form lumenal blood cells. Compared to activin A alone, murine stem cell factor plus activin A significantly increased the numbers of XL-2-reactive leukocytes and erythrocytes. These results support the view that activin A induces leukocyte and erythrocyte progenitors during Xenopus embryogenesis.

Activins↗