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1.
Development ; 128(19): 3655-63, 2001 Oct.
Article in English | MEDLINE | ID: mdl-11585792

ABSTRACT

Wnts are a large family of secreted molecules implicated in numerous developmental processes. Frizzled proteins are likely receptors for Wnts and are required for Wnt signaling in invertebrates. A large number of vertebrate frizzled genes have also been identified, but their roles in mediating specific responses to endogenous Wnts have not been well defined. Using a functional assay in Xenopus, we have performed a large screen to identify potential interactions between Wnts and frizzleds. We find that signaling by Xwnt1, but not other Wnts, can be specifically enhanced by frizzled 3 (Xfz3). As both Xfz3 and Xwnt1 are highly localized to dorsal neural tissues that give rise to neural crest, we examined whether Xfz3 mediates Xwnt1 signaling in the formation of neural crest. Xfz3 specifically induces neural crest in ectodermal explants and in embryos, similar to Xwnt1, and at lower levels of expression, synergizes with Xwnt1 in neural crest induction. Furthermore, loss of Xfz3 function, either by depletion with a Xfz3-directed morpholino antisense oligonucleotide or by expression of an inhibitory form of Xfz3 (Nfz3), prevents Xwnt1-dependent neural crest induction in ectodermal explants and blocks neural crest formation in whole embryos. These results show that Xfz3 is required for Xwnt1 signaling in the formation of the neural crest in the developing vertebrate embryo.


Subject(s)
Neural Crest/embryology , Proto-Oncogene Proteins/genetics , Receptors, Cell Surface/genetics , Receptors, G-Protein-Coupled , Xenopus Proteins , Xenopus/embryology , Zebrafish Proteins , Animals , Cell Differentiation/genetics , Embryo, Nonmammalian/drug effects , Embryonic Induction , Female , Frizzled Receptors , Gene Dosage , Gene Expression Regulation, Developmental , Melanocytes/physiology , Microinjections , Mutation , Oligonucleotides, Antisense/pharmacology , Proto-Oncogene Proteins/metabolism , Receptors, Cell Surface/metabolism , Snail Family Transcription Factors , Transcription Factors/genetics , Wnt Proteins , Wnt1 Protein , Xenopus/genetics
2.
Development ; 128(19): 3665-74, 2001 Oct.
Article in English | MEDLINE | ID: mdl-11585793

ABSTRACT

Wnts are a family of secreted glycoproteins that are important for multiple steps in early development. Accumulating evidence suggests that frizzled genes encode receptors for Wnts. However, the mechanism through which frizzleds transduce a signal and the immediate downstream components that convey that signal are unclear. We have identified a new protein, Kermit, that interacts specifically with the C-terminus of Xenopus frizzled-3 (Xfz3). Kermit is a 331 amino acid protein with a central PDZ domain. Kermit mRNA is expressed throughout Xenopus development and is localized to neural tissue in a pattern that overlaps Xfz3 expression temporally and spatially. Co-expression of Xfz3 and Kermit results in a dramatic translocation of Kermit to the plasma membrane. Inhibition of Kermit function with morpholino antisense oligonucleotides directed against the 5' untranslated region of Kermit mRNA blocks neural crest induction by Xfz3, and this is rescued by co-injection of mRNA encoding the Kermit open reading frame. These observations suggest that Kermit is required for Wnt/frizzled signaling in neural crest development. To the best of our knowledge, Kermit is the first protein identified that interacts directly with the cytoplasmic portion of frizzleds to modulate their signaling activity.


Subject(s)
Adaptor Proteins, Signal Transducing , Carrier Proteins/genetics , Carrier Proteins/metabolism , Gene Expression Regulation, Developmental , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Neural Crest/embryology , Receptors, Cell Surface/metabolism , Receptors, G-Protein-Coupled , Xenopus Proteins , Xenopus laevis/genetics , Zebrafish Proteins , Amino Acid Sequence , Animals , Cell Membrane/metabolism , Cloning, Molecular , Embryo, Nonmammalian/drug effects , Embryonic Induction/genetics , Female , Frizzled Receptors , Molecular Sequence Data , Oligonucleotides, Antisense/pharmacology , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Receptors, Cell Surface/genetics , Sequence Homology, Amino Acid , Signal Transduction , Wnt Proteins , Xenopus laevis/embryology
3.
Nature ; 407(6803): 530-5, 2000 Sep 28.
Article in English | MEDLINE | ID: mdl-11029007

ABSTRACT

The Wnt family of secreted signalling molecules are essential in embryo development and tumour formation. The Frizzled (Fz) family of serpentine receptors function as Wnt receptors, but how Fz proteins transduce signalling is not understood. In Drosophila, arrow phenocopies the wingless (DWnt-1) phenotype, and encodes a transmembrane protein that is homologous to two members of the mammalian low-density lipoprotein receptor (LDLR)-related protein (LRP) family, LRP5 and LRP6 (refs 12-15). Here we report that LRP6 functions as a co-receptor for Wnt signal transduction. In Xenopus embryos, LRP6 activated Wnt-Fz signalling, and induced Wnt responsive genes, dorsal axis duplication and neural crest formation. An LRP6 mutant lacking the carboxyl intracellular domain blocked signalling by Wnt or Wnt-Fz, but not by Dishevelled or beta-catenin, and inhibited neural crest development. The extracellular domain of LRP6 bound Wnt-1 and associated with Fz in a Wnt-dependent manner. Our results indicate that LRP6 may be a component of the Wnt receptor complex.


Subject(s)
Drosophila Proteins , Proto-Oncogene Proteins/metabolism , Receptors, LDL/metabolism , Signal Transduction , Zebrafish Proteins , Animals , Cloning, Molecular , Frizzled Receptors , Humans , Low Density Lipoprotein Receptor-Related Protein-6 , Membrane Proteins/metabolism , Mice , Molecular Sequence Data , Neural Crest/metabolism , Receptors, G-Protein-Coupled , Recombinant Fusion Proteins , Wnt Proteins , Wnt1 Protein , Xenopus , Xenopus Proteins
4.
Mech Dev ; 94(1-2): 205-8, 2000 Jun.
Article in English | MEDLINE | ID: mdl-10842073

ABSTRACT

FK 506-binding proteins (FKBPs) are a family of cytosolic proteins identified by virtue of their ability to bind the immunosuppressants FK 506 and rapamycin. While their function has been extensively studied in the immune system, little is known about their role during early embryonic development. Here we describe the cloning and expression of a new Xenopus FKBP (xFKBP). xFKBP encodes a 63-kDa protein that shares high sequence homology with mouse FKBP65. It is expressed maternally and becomes restricted after the gastrula stage to dorsal mesoderm and notochord. At the tailbud stage expression persists in the notochord and begins to accumulate in epidermis, branchial arches and developing somites. In adults, xFKBP mRNA is confined to the testis.


Subject(s)
Gene Expression Regulation, Developmental , Immunophilins/genetics , Immunophilins/metabolism , Peptidylprolyl Isomerase , Xenopus Proteins , Xenopus laevis/genetics , Amino Acid Sequence , Animals , Cloning, Molecular , Embryo, Nonmammalian , Gastrula , Male , Mice , Molecular Sequence Data , Notochord/embryology , Sequence Homology, Amino Acid , Tacrolimus Binding Proteins , Tail/embryology , Testis/physiology , Xenopus laevis/embryology
5.
Science ; 275(5306): 1652-4, 1997 Mar 14.
Article in English | MEDLINE | ID: mdl-9054360

ABSTRACT

In Xenopus laevis embryos, the Wingless/Wnt-1 subclass of Wnt molecules induces axis duplication, whereas the Wnt-5A subclass does not. This difference could be explained by distinct signal transduction pathways or by a lack of one or more Wnt-5A receptors during axis formation. Wnt-5A induced axis duplication and an ectopic Spemann organizer in the presence of hFz5, a member of the Frizzled family of seven-transmembrane receptors. Wnt-5A/hFz5 signaling was antagonized by glycogen synthase kinase-3 and by the amino-terminal ectodomain of hFz5. These results identify hFz5 as a receptor for Wnt-5A.


Subject(s)
Drosophila Proteins , Embryonic Development , Embryonic Induction , Homeodomain Proteins , Membrane Proteins/metabolism , Proteins/metabolism , Receptors, Cell Surface/metabolism , Repressor Proteins , Transcription Factors , Xenopus Proteins , Animals , Calcium-Calmodulin-Dependent Protein Kinases/antagonists & inhibitors , Calcium-Calmodulin-Dependent Protein Kinases/metabolism , DNA-Binding Proteins/genetics , Frizzled Receptors , Glycogen Synthase Kinase 3 , Glycogen Synthase Kinases , Goosecoid Protein , Humans , Ligands , Membrane Proteins/chemistry , Membrane Proteins/genetics , Proteins/genetics , Receptors, Cell Surface/genetics , Receptors, G-Protein-Coupled , Signal Transduction , Wnt Proteins , Wnt-5a Protein , Xenopus laevis/embryology
6.
Proc Natl Acad Sci U S A ; 94(3): 895-900, 1997 Feb 04.
Article in English | MEDLINE | ID: mdl-9023353

ABSTRACT

Anteroposterior patterning of neural tissue is thought to be directed by the axial mesoderm which is functionally divided into head and trunk organizer. The LIM class homeobox gene Xlim-1 is expressed in the entire axial mesoderm, whereas the distinct transcription factor Xbra is expressed in the notochord but not in the prechordal mesoderm. mRNA injection experiments showed that Xenopus animal explants (caps) expressing an activated form of Xlim-1 (a LIM domain mutant named 3m) induce anterior neural markers whereas caps coexpressing Xlim-1/3m and Xbra induce posterior neural markers. These data indicate that, in terms of neural inducing ability, Xlim-1/3m-expressing caps correspond to the head organizer and Xlim-1/3m plus Xbra-coexpressing caps to the trunk organizer. Thus the expression domains of Xlim-1 and Xbra correlate with, and possibly define, the functional domains of the organizer. In animal caps Xlim-1/3m initiates expression of a neuralizing factor, chordin, whereas Xbra activates embryonic fibroblast growth factor (eFGF) expression, as reported previously; these factors could mediate the neural inducing and patterning effects that were observed. A dominant-negative FGF receptor (XFD) inhibits posteriorization by Xbra in a dose-dependent manner, supporting the suggestion that eFGF or a related factor has posteriorizing influence.


Subject(s)
Body Patterning/genetics , DNA-Binding Proteins/genetics , Fetal Proteins/genetics , Genes, Homeobox/physiology , Homeodomain Proteins/genetics , Intercellular Signaling Peptides and Proteins , Nervous System/embryology , T-Box Domain Proteins , Animals , Biomarkers , Carrier Proteins , Ectoderm , Fibroblast Growth Factors/analysis , Gene Expression Regulation, Developmental , Glycoproteins/genetics , Homeodomain Proteins/analysis , LIM-Homeodomain Proteins , Mesoderm , Nerve Tissue Proteins/analysis , Neural Cell Adhesion Molecules/genetics , Proteins/genetics , RNA, Messenger , Receptors, Fibroblast Growth Factor , Transcription Factors , Tretinoin/pharmacology , Xenopus , Xenopus Proteins
7.
Mol Cell Biol ; 17(2): 644-55, 1997 Feb.
Article in English | MEDLINE | ID: mdl-9001218

ABSTRACT

Retinoic acid receptor (RAR) and retinoid X receptor (RXR) form heterodimers and regulate retinoid-mediated gene expression. We studied binding of RXR- and RAR-selective ligands to the RXR-RAR heterodimer and subsequent transcription. In limited proteolysis analyses, both RXR and RAR in the heterodimer bound their respective ligands and underwent a conformational change in the presence of a retinoic acid-responsive element. In reporter analyses, the RAR ligand (but not the RXR ligand), when added singly, activated transcription, but coaddition of the two ligands led to synergistic activation of transcription. This activation required the AF-2 domain of both RXR and RAR. Genomic footprinting analysis was performed with P19 embryonal carcinoma cells, in which transcription of the RARbeta gene is induced upon retinoid addition. Paralleling the reporter activation data, only the RAR ligand induced in vivo occupancy of the RARbeta2 promoter when added singly. However, at suboptimal concentrations of RAR ligand, coaddition of the RXR ligand increased the stability of promoter occupancy. Thus, liganded RXR and RAR both participate in transcription. Finally, when these ligands were tested for teratogenic effects on zebra fish and Xenopus embryos, we found that coadministration of the RXR and RAR ligands caused more severe abnormalities in these embryos than either ligand alone, providing biological support for the synergistic action of the two ligands.


Subject(s)
Gene Expression Regulation/drug effects , Receptors, Retinoic Acid/metabolism , Retinoids/pharmacology , Transcription Factors/metabolism , Animals , Blastocyst , DNA/metabolism , Embryo, Nonmammalian/drug effects , Embryonal Carcinoma Stem Cells , Humans , Ligands , Mice , Neoplastic Stem Cells , Peptide Fragments , Promoter Regions, Genetic/genetics , Protein Conformation/drug effects , Receptors, Retinoic Acid/chemistry , Receptors, Retinoic Acid/genetics , Recombinant Fusion Proteins , Retinoid X Receptors , Teratogens/pharmacology , Transcription Factors/chemistry , Transcriptional Activation , Xenopus/embryology , Zebrafish/embryology
8.
Proc Natl Acad Sci U S A ; 94(25): 13713-8, 1997 Dec 09.
Article in English | MEDLINE | ID: mdl-9391091

ABSTRACT

Members of the Wnt family of signaling molecules are expressed differentially along the dorsal-ventral axis of the developing neural tube. Thus we asked whether Wnt factors are involved in patterning of the nervous system along this axis. We show that Wnt-1 and Wnt-3a, both of which are expressed in the dorsal portion of the neural tube, could synergize with the neural inducers noggin and chordin in Xenopus animal explants to generate the most dorsal neural structure, the neural crest, as determined by the expression of Krox-20, AP-2, and slug. Overexpression of Wnt-1 or Wnt-3a in the neuroectoderm of whole embryos led to a dramatic increase of slug and Krox-20-expressing cells, but the hindbrain expression of Krox-20 remained unaffected. Enlargement in the neural crest population could occur even when cell proliferation was inhibited. Wnt-5A and Wnt-8, neither of which is expressed in the dorsal neuroectoderm, failed to induce neural crest markers. Overexpression of glycogen synthase kinase 3, known to antagonize Wnt signaling, blocked the neural-crest-inducing activity of Wnt-3a in animal explants and inhibited neural crest formation in whole embryos. We suggest that Wnt-1 and Wnt-3a have a role in patterning the neural tube along its dorsoventral axis and function in the differentiation of the neural crest.


Subject(s)
Nervous System/embryology , Nervous System/metabolism , Proteins/metabolism , Proto-Oncogene Proteins/metabolism , Zebrafish Proteins , Animals , Calcium-Calmodulin-Dependent Protein Kinases/antagonists & inhibitors , Calcium-Calmodulin-Dependent Protein Kinases/genetics , Calcium-Calmodulin-Dependent Protein Kinases/metabolism , Cell Division , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Early Growth Response Protein 2 , Gene Expression Regulation, Developmental , Genetic Markers , Glycogen Synthase Kinase 3 , Glycogen Synthase Kinases , Humans , In Situ Hybridization , Mice , Nervous System/cytology , Neural Crest/cytology , Neural Crest/embryology , Neural Crest/metabolism , Proteins/genetics , Proto-Oncogene Proteins/genetics , Signal Transduction , Snail Family Transcription Factors , Transcription Factors/genetics , Transcription Factors/metabolism , Wnt Proteins , Wnt1 Protein , Wnt3 Protein , Wnt3A Protein , Xenopus , Xenopus Proteins
9.
Int J Dev Biol ; 40(2): 453-61, 1996 Apr.
Article in English | MEDLINE | ID: mdl-8793615

ABSTRACT

Polyclonal antibodies to Xlim-1 homeodomain protein of Xenopus laevis were used to study the developmental expression pattern of this protein in Xenopus, rat and mouse. Western blotting of embryo extracts injected with different Xlim-1 constructs confirmed the specificity of the antibody. Beginning at the gastrula stage, Xlim-1 protein was detected in three cell lineages: (i) notochord, (ii) pronephros and (iii) certain regions of the central nervous system, in agreement with earlier studies of the expression of Xlim-1 RNA (Taira et al., Development 120: 1525-1536, 1994a). In addition, several new locations of Xlim-1 expression were found, including the olfactory organ, retina, otic vesicle, dorsal root ganglia and adrenal gland. Similar expression patterns were seen for the Lim-1 protein in frog and rodent tissues. These observations implicate the Xlim-1 gene in the specification of multiple cell lineages, particularly within the nervous system, and emphasize the conserved nature of the role of this gene in different vertebrate animals.


Subject(s)
Homeodomain Proteins/analysis , Mesoderm/metabolism , Mice/embryology , Neural Crest/metabolism , Rats/embryology , Transcription Factors/analysis , Xenopus/embryology , Animals , Antibody Specificity/immunology , Central Nervous System/embryology , Central Nervous System/metabolism , Conserved Sequence , Female , Homeodomain Proteins/biosynthesis , Homeodomain Proteins/genetics , Homeodomain Proteins/immunology , LIM-Homeodomain Proteins , Neural Crest/embryology , Pregnancy , Sense Organs/cytology , Sense Organs/embryology , Sense Organs/metabolism , Species Specificity , Transcription Factors/biosynthesis , Transcription Factors/genetics , Transcription Factors/immunology
10.
Proc Natl Acad Sci U S A ; 93(5): 1803-7, 1996 Mar 05.
Article in English | MEDLINE | ID: mdl-8700839

ABSTRACT

Retinoids exert pleiotropic effects on the development of vertebrates through the action of retinoic acid receptors (RAR) and retinoid X receptors (RXR). We have investigated the effect of synthetic retinoids selective for RXR and RAR on the development of Xenopus and zebrafish embryos. In Xenopus, both ligands selective for RAR and RXR caused striking malformations along the anterior-posterior axis, whereas in zebrafish only ligands specific for RAR caused embryonic malformations. In Xenopus, RAR- and RXR-selective ligands regulated the expression of the Xlim-1, gsc, and HoxA1 genes similarly as all-trans-retinoic acid. Nevertheless, RXR-selective ligands activated only an RXR responsive reporter but not an RAR responsive reporter introduced by microinjection into the Xenopus embryo, consistent with our failure to detect conversion of an RXR-selective ligand to different derivatives in the embryo. These results suggest that Xenopus embryos possess a unique response pathway in which liganded RXR can control gene expression. Our observations further illustrate the divergence in retinoid responsiveness between different vertebrate species.


Subject(s)
Receptors, Retinoic Acid/physiology , Transcription Factors/physiology , Xenopus laevis/embryology , Zebrafish/embryology , Animals , Congenital Abnormalities/embryology , Gene Expression/drug effects , Gene Expression Regulation, Developmental , Ligands , Retinoid X Receptors , Retinoids/pharmacology
11.
Nature ; 374(6523): 617-22, 1995 Apr 13.
Article in English | MEDLINE | ID: mdl-7715701

ABSTRACT

Glycogen synthase kinase 3 (GSK-3) is homologous to the product of the Drosophila gene shaggy (zeste-white 3), which is required for signalling by wingless during Drosophila development. To test whether GSK-3 is also involved in vertebrate pattern formation, its role was investigated during early Xenopus development. It was found that dominant-negative GSK-3 mutants induced dorsal differentiation, whereas wild-type GSK-3 induced ventralization. These results indicate that GSK-3 is required for ventral differentiation, and suggest that dorsal differentiation may involve the suppression of GSK-3 activity by a wingless/wnt-related signal.


Subject(s)
Calcium-Calmodulin-Dependent Protein Kinases/physiology , Embryonic Development , Animals , Blastocyst/cytology , Calcium-Calmodulin-Dependent Protein Kinases/genetics , Embryo, Nonmammalian/radiation effects , Embryonic Induction , Fibroblast Growth Factor 2/metabolism , Glycogen Synthase Kinase 3 , Glycogen Synthase Kinases , Humans , Molecular Sequence Data , Mutation , RNA, Messenger/metabolism , Ultraviolet Rays , Xenopus/embryology
12.
Int J Dev Biol ; 39(2): 309-15, 1995 Apr.
Article in English | MEDLINE | ID: mdl-7669543

ABSTRACT

Using antibodies against homeoprotein XIHbox 1 from Xenopus laevis, we have detected a new embryonic protein with a much larger molecular weight, 115 kDa. Antibodies fractionated according to their affinity for 3 different domains of the XIHbox 1 protein were used to show that this new protein is related to the C-terminal region of XIHbox 1 protein, downstream from the homeodomain. By immunohistochemistry, the protein was shown to be localized in nuclei of embryonic cells. On SDS-polyacrylamide gels, the 115 kDa protein appears as a set of closely spaced bands whose pattern varies with the stage of development and with the parental origin of the embryos. The protein could be extracted from embryos in a multiprotein complex of approximately 600 kDa. In contrast, the 18 and 27 kDa proteins predicted from the sequence of cloned cDNA to be transcribed and translated from the XIHbox 1 gene could not be detected, suggesting that they are rare or unstable in embryos. These data suggest that the new protein is involved in the development of Xenopus embryos, with a function possibly related to that of the homeoprotein XIHbox 1.


Subject(s)
Antibodies , Embryo, Nonmammalian/chemistry , Homeodomain Proteins/immunology , Proteins/analysis , Xenopus Proteins , Xenopus laevis/embryology , Animals , Antibody Specificity , Blotting, Western , Embryo, Nonmammalian/ultrastructure , Homeodomain Proteins/chemistry , Homeodomain Proteins/genetics , Immunohistochemistry , Molecular Weight , Proteins/chemistry
13.
Nature ; 372(6507): 677-9, 1994 Dec 15.
Article in English | MEDLINE | ID: mdl-7990959

ABSTRACT

Like all known LIM class homeobox genes, Xlim-1 encodes a protein with two tandemly repeated cysteine-rich LIM domains upstream of the homeodomain. In Xenopus laevis, Xlim-1 is specifically expressed in the Spemann organizer, whose major functions include neural induction and dorsalization of ventral mesoderm. From RNA injection experiments we conclude here that: (1) the LIM domains behave as negative regulatory domains; (2) LIM domain mutants of Xlim-1 elicited neural differentiation in animal explants; (3) mutant, and to a lesser extent wild-type, Xlim-1 enhanced muscle formation after coinjection with Xbra; (4) both of these activities are mediated by extracellular signals as seen in combined explant experiments; (5) Xlim-1 mutants activated goosecoid (gsc) expression in animal explants, but not expression of noggin or follistatin; (6) mutant Xlim-1 elicited formation of partial secondary axes, and cooperated with gsc in notochord formation. Thus Xlim-1 has latent activities, implicating it in organizer functions.


Subject(s)
DNA-Binding Proteins/physiology , Embryonic Induction , Homeodomain Proteins , Muscles/embryology , Nervous System/embryology , Proteins , Repressor Proteins , T-Box Domain Proteins , Transcription Factors , Animals , Base Sequence , Carrier Proteins , Cell Differentiation/genetics , Cell Differentiation/physiology , Culture Techniques , DNA Primers , DNA-Binding Proteins/biosynthesis , DNA-Binding Proteins/genetics , Fetal Proteins/genetics , Fetal Proteins/physiology , Follistatin , Glycoproteins/biosynthesis , Goosecoid Protein , LIM-Homeodomain Proteins , Molecular Sequence Data , Mutation , Notochord/embryology , Protein Biosynthesis , RNA, Messenger/genetics , Signal Transduction , Xenopus Proteins , Xenopus laevis
14.
Dev Biol ; 166(2): 755-62, 1994 Dec.
Article in English | MEDLINE | ID: mdl-7813792

ABSTRACT

A fate map of the progeny derived from all blastomeres of the 32-cell stage embryo of the leopard frog Rana pipiens has been generated. Embryos presenting regular cleavages were injected into two pairs of blastomeres with fluorescein- and Texas red-lysine dextran. By stage 21, embryos were sectioned and the tissue distribution of labeled clones was determined. The results of 93 clones were pooled to give a fate map which represents the derivation of each tissue from the different blastomeres of the 32-cell embryo. The results show that all blastomeres give rise to multiple tissues and all tissues are derived from at least two, and usually more, pairs of blastomeres. Although there is a general tendency for ectoderm to derive from the animal hemisphere, endoderm from the vegetal hemisphere, and mesoderm from the equatorial region, the boundaries between germ layers are not sharply defined at the 32-cell stage but rather appear as a series of overlapping zones. The fate map of R. pipiens is quite similar to that of Xenopus laevis but differs in some details that are discussed. As in all vertebrates, the R. pipiens fate map is not fully deterministic but nevertheless has predictive value in that tissues are populated by the progeny of the same blastomeres in different embryos.


Subject(s)
Blastocyst/cytology , Rana pipiens/embryology , Animals , Blastomeres/cytology , Cell Differentiation , Ectoderm/cytology , Endoderm/cytology , Fluorescent Dyes , Microinjections , Morphogenesis , Nervous System/embryology
15.
Int J Dev Biol ; 38(4): 605-11, 1994 Dec.
Article in English | MEDLINE | ID: mdl-7779682

ABSTRACT

In an attempt to document at the molecular level the behavior of mesodermal cells in Keller explant preparation, we have analyzed the time course of expression of four molecular markers of mesoderm gsc, Xbra, Xnot and XLIM-1. Our findings demonstrate that, (i) all mesodermal markers tested were expressed in the explants, but patterning of the mesoderm appeared incomplete; (ii) during convergence and extension of the explants, mesodermal cells did not invade the ectodermal tissue at any time tested, supporting the view that mesoderm establishes exclusively planar contacts with the ectoderm in this preparation; (iii) planar contacts were not sufficient to promote the neural expression of XLIM-1 protein in these explants.


Subject(s)
Biomarkers/analysis , Gene Expression , Mesoderm/metabolism , Oocytes/metabolism , Xenopus laevis , Animals , Culture Techniques , Ectoderm/metabolism , Female , Gastrula/metabolism , Immunohistochemistry , Kinetics , Mesoderm/chemistry , Time Factors
16.
J Cell Biol ; 127(2): 521-35, 1994 Oct.
Article in English | MEDLINE | ID: mdl-7929592

ABSTRACT

Cadherins, a family of Ca-dependent adhesion molecules, have been proposed to act as regulators of morphogenetic processes and to be major effectors in the maintenance of tissue integrity. In this study, we have compared the effects of the expression of two truncated cadherins during early neurogenesis in Xenopus laevis. mRNA encoding deleted forms of XB- and N-cadherin lacking most of the extracellular domain were injected into the four animal dorsal blastomeres of 32-cell stage Xenopus embryos. These truncated cadherins altered the cohesion of cells derived from the injected blastomeres and induced morphogenetic defects in the anterior neural tissue to which they chiefly contributed. Truncated XB-cadherin was more efficient than N-cadherin in inducing these perturbations. Moreover, the coexpression of both truncated cadherins had additive perturbation effects on neural development. The two truncated cadherins can interact with the three known catenins, but with distinct affinities. These results suggest that the adhesive signal mediated by cadherins can be perturbed by overexpressing their cytoplasmic domains by competing with different affinity with catenins and/or a common anchor structure. Therefore, the correct regulation of cadherin function through the cytoplasmic domain appears to be a crucial step in the formation of the neural tissue.


Subject(s)
Blastomeres/cytology , Cadherins/physiology , Nervous System/embryology , Trans-Activators , Amino Acid Sequence , Animals , Base Sequence , Blastomeres/metabolism , Cadherins/genetics , Cell Adhesion , Cytoskeletal Proteins/metabolism , Gene Expression , Molecular Sequence Data , Morphogenesis , Protein Biosynthesis , RNA, Messenger/genetics , Sequence Deletion , Xenopus Proteins , Xenopus laevis , beta Catenin
17.
Dev Biol ; 164(2): 374-82, 1994 Aug.
Article in English | MEDLINE | ID: mdl-8045340

ABSTRACT

Epithelial-mesenchymal interactions are of major importance during development to direct correct differentiation and morphogenesis of embryonic tissues. One subset of lateral mesoderm-derived mesenchymal cells will form the smooth muscle (SM) layer of the primary epithelial lining of hollow internal organs. It has been previously reported that the differentiation of SM cells in Xenopus laevis can be followed by the expression of alpha-SM actin. It was also shown that basic fibroblast growth factor (bFGF) had the ability to induce this actin isoform in isolated blastula animal caps. In this paper, by injection at the two-cell stage of mRNA encoding a truncated form of the FGF receptor which can act as a dominant negative inhibitor, we have analyzed the role of the FGF signaling pathway in the formation of the SM lineage. We have observed that mutated embryos presented significant delay in the differentiation of the SM cells compared to control embryos, demonstrating the importance of this signaling pathway for the formation of the lateral mesoderm-derived SM cells. Moreover, a correlation could be established between this delay and the dramatic defects observed in the morphogenesis of the intestine with which mesenchyme-derived SM cells are normally associated. This phenotype was efficiently rescued by coinjection of the wild-type FGF receptor. Our data suggest that the differentiation of SM cells at the correct time could be an essential event for the proper morphogenesis of the endoderm-derived digestive tract.


Subject(s)
Mesoderm/cytology , Muscle, Smooth/embryology , Receptors, Fibroblast Growth Factor/metabolism , Signal Transduction , Actins/biosynthesis , Animals , Cell Differentiation , Cells, Cultured , Intestines/cytology , Intestines/embryology , Morphogenesis , Muscle, Smooth/cytology , Muscle, Smooth/metabolism , Mutation , Phenotype , Receptors, Fibroblast Growth Factor/genetics , Xenopus laevis
18.
Proc Natl Acad Sci U S A ; 91(8): 3049-53, 1994 Apr 12.
Article in English | MEDLINE | ID: mdl-8159704

ABSTRACT

The neural plate in the amphibian embryo is induced in the ectoderm by signals from the dorsal mesoderm. In the extensively studied species Xenopus laevis, such signals are believed to proceed along two alternate pathways, defined as vertical and planar induction. We have studied the relative importance of these pathways in Rana pipiens. In the embryo of this frog, dorsal mesoderm involution can be diverted from its normal course by injection of peptides that inhibit interaction of fibronectin with its receptor. In such embryos, dorsal mesoderm failed to migrate across the blastocoel roof but moved bilaterally along the equator, leading to the formation of two notochords. Neural tissue differentiation occurred in close association with each notochord, but no neural tissue formed along the dorsal midline as might have been predicted by a predominantly planar induction model. While in X. laevis planar induction has been reported to be a major pathway in neuralizing the ecoderm, the results presented here indicate that vertical induction predominates in initiating neural development in R. pipiens embryos.


Subject(s)
Nervous System/embryology , Rana pipiens/embryology , Amino Acid Sequence , Animals , Cell Adhesion Molecules , Cell Differentiation/drug effects , Embryonic Induction , Gastrula/cytology , Molecular Sequence Data , Oligopeptides/pharmacology
19.
C R Acad Sci III ; 316(9): 822-37, 1993 Sep.
Article in English, French | MEDLINE | ID: mdl-8076213

ABSTRACT

In this paper we examine the expression of several cell adhesion molecules and muscle differentiation markers during larval development and growth of the axial musculature of Xenopus laevis. We have identified a small group of cells, located on the dorsal extremity of the myotome, which express very high levels of N-CAM and early muscle markers such as desmin and muscle myosin, but do not express later-stage markers of muscle development such as sarcomeric actinin. These cells are most probably muscle precursor cells; they may participate in the generation of new fibres in the myotomal muscles of Xenopus. On the basis of these observations we propose a model of myotomal development in Xenopus characterized by a spatial segregation between regions of the myotome where new fibres are generated and regions where myotubes mature. As during muscle differentiation in vivo we observe a sharp change in the profile of expression of cell adhesion molecules, we suggest that different adhesion receptors are involved in the generation of new muscle fibres and in the growth and differentiation of already existing ones.


Subject(s)
Cadherins/metabolism , Cell Adhesion Molecules, Neuronal/metabolism , Muscles/metabolism , Animals , Cell Adhesion , Cell Differentiation , Immunohistochemistry , In Situ Hybridization , Xenopus laevis
20.
Exp Cell Res ; 207(2): 383-7, 1993 Aug.
Article in English | MEDLINE | ID: mdl-8344387

ABSTRACT

In the amphibian embryo, the ectoderm becomes a neural structure during gastrulation as a result of an interaction with the dorsal mesoderm. From that time onward, neurectodermal cells have the ability to express in vitro a large variety of mature phenotypes without further interaction with the inducing tissue. The neuralization of the ectoderm can be reproduced in a variety of experimental situations that do not involve the dorsal mesoderm. In this study we have analyzed biochemically the extent to which artificial inductions mimic the natural inducing process. Making use of antibodies specific to different neurotransmitter pathways, we have shown that the repertoire of the phenotypes expressed by experimentally induced neurons is always restricted compared to those obtained after induction in vivo. Only a limited number of generic neuronal characteristics are expressed. These results suggest that the expression of a complete neuronal phenotype normally involves a sequence of inductive events that can be experimentally uncoupled.


Subject(s)
Embryonic Induction/physiology , Nervous System/embryology , Pleurodeles/embryology , Animals , Concanavalin A/pharmacology , Ectoderm/cytology , Fluorescent Antibody Technique , Mesoderm/cytology , Phenotype
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