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T-type Cav3.2 Ca2+ channel is predominantly expressed in Xenopus laevis testis and involved in the fertilization process. Genes Genomics 2013. [DOI: 10.1007/s13258-013-0072-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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2
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Kurth T, Weiche S, Vorkel D, Kretschmar S, Menge A. Histology of plastic embedded amphibian embryos and larvae. Genesis 2011; 50:235-50. [DOI: 10.1002/dvg.20821] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 10/27/2011] [Accepted: 10/28/2011] [Indexed: 12/27/2022]
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3
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Fujimi TJ, Mikoshiba K, Aruga J. Xenopus Zic4: Conservation and diversification of expression profiles and protein function among theXenopus Zicfamily. Dev Dyn 2006; 235:3379-86. [PMID: 16871625 DOI: 10.1002/dvdy.20906] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
We compared the expression and function of Xenopus Zic4 with those of the other four Xenopus laevis Zic family members (Zic1, Zic2, Zic3, and Zic5). Zic4 expression was detected mainly in the neural plate border, dorsal neural tube, and somites, and was similar to that of Zic1, which is adjacent to Zic4 on the same chromosome. Injection of wild-type or mutant Zic4 RNA caused the induction of neural crest marker gene expression, hyperplastic neural tissue, and ectopic pigment cell formation, indicating that Zic4 can induce neural and neural crest tissue, as can other Xenopus Zic genes. Deletion analysis showed that the zinc-finger domain is critical for many Zic4 functions, but the C-terminal region is differently involved in induction of two neural crest markers, Slug and Sox10. The protein function as determined by the animal cap explant assay was similar to that of Zic5, but different from those of Zic1, Zic2, and Zic3, suggesting that Xenopus Zic genes can be divided into two groups based on function. These results indicate that the five Xenopus Zic genes cooperatively regulate both neural and neural crest development, despite significantly diverged expression profiles and functions.
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Affiliation(s)
- Takahiko J Fujimi
- Laboratory for Comparative Neurogenesis, RIKEN Brain Science Institute, Wako-shi, Saitama, Japan
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4
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Abstract
Siamois is the transcriptional mediator of the dorsal Wnt signaling pathway and is necessary for formation of the Spemann organizer and dorsoanterior development in Xenopus. We have determined that XIC, a Xenopus I-mfa domain protein that regulates Tcf3 binding, is required for dorsoaxial development and specifically for Siamois activity in establishing the dorsal organizer. In loss-of-function studies, we found that embryos injected with a morpholino to XIC mRNA (XIC morphpolino) are missing head structures, neural tube, notochord, and paraxial mesoderm as well as NCAM and XMyoD expression. Although Siamois, Twin, and Xnr3 expression is normal in morpholino-injected embryos, levels of downstream organizer factors, including goosecoid, Xnot, Cerberus, and chordin, are severely reduced. Ectopic axis formation induced by Siamois is repressed by injection of the XIC morpholino and further repressed by coinjection of beta-catenin or a constitutively active Tcf3/HMG/G4A fusion. Activation of reporters driven by the Siamois-responsive proximal element of the goosecoid promoter is inhibited in the presence of the morpholino and can be rescued by murine I-mfa and by a dominant-negative Tcf3. The data indicate a role for XIC in limiting Tcf3-dependent repression of Siamois activities that are required for goosecoid transcription and for dorsal organizer formation.
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Affiliation(s)
- Lauren Snider
- Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024, USA
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5
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Toro E, Michael SF. In vitro fertilization and artificial activation of eggs of the direct-developing anuran Eleutherodactylus coqui. Reprod Biol Endocrinol 2004; 2:60. [PMID: 15296510 PMCID: PMC514616 DOI: 10.1186/1477-7827-2-60] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2004] [Accepted: 08/05/2004] [Indexed: 11/21/2022] Open
Abstract
Although much is known about the reproductive biology of pond-breeding frogs, there is comparatively little information about terrestrial-breeding anurans, a highly successful and diverse group. This study investigates the activation and in vitro fertilization of eggs of the Puerto Rican coqui frog obtained by hormonally induced ovulation. We report that spontaneous activation occurs in 34% of eggs, probably in response to mechanical stress during oviposition. Artificial activation, as evidenced by the slow block to polyspermy and the onset of zygote division, was elicited both by mechanical stimulation and calcium ionophore exposure in 64% and 83% of the cases, respectively. Finally, one in vitro fertilization protocol showed a 27% success rate, despite the fact that about one third of all unfertilized eggs obtained by hormone injection auto-activate. We expect these findings to aid in the conservation effort of Eleutherodactylus frogs, the largest vertebrate genus.
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Affiliation(s)
- Esteban Toro
- Department of Tropical Medicine, Box SL-17, Tulane University, New Orleans, LA 70112, USA
- Department of Developmental Biology, Stanford University, Stanford, CA 94045, USA
| | - Scott F Michael
- Department of Tropical Medicine, Box SL-17, Tulane University, New Orleans, LA 70112, USA
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6
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Gard DL. Confocal fluorescence microscopy of the cytoskeleton of amphibian oocytes and embryos. Methods Cell Biol 2003; 70:379-416. [PMID: 12512330 DOI: 10.1016/s0091-679x(02)70011-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2023]
Affiliation(s)
- David L Gard
- Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA
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7
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Wu CF, Chan APY, Etkin LD. Difference in the maternal and zygotic contributions of tumorhead on embryogenesis. Dev Biol 2003; 255:290-302. [PMID: 12648491 DOI: 10.1016/s0012-1606(02)00074-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tumorhead (TH) is a maternally expressed gene in Xenopus laevis, that when overexpressed, increased proliferation of ectodermal derivatives and inhibited neural and epidermal differentiation. However, injection of anti-TH antibodies inhibited cleavage of all blastomeres, not only those contributing to the ectoderm. The injection of TH morpholino antisense oligonucleotide (TH-MO), which inhibits translation of TH mRNA, did not affect early cleavage but inhibited cell division in both the neural field and epidermis. This was accompanied by the inhibition of neural and epidermal markers. TH-MO did not affect the formation and differentiation of mesoderm and endoderm derivatives. Our overexpression and loss-of-function studies demonstrated that TH plays an important role in differentiation of the ectoderm by regulating cell proliferation. They also supported the conclusion that the maternal component of TH may affect the cell cycle in all cells, while the zygotic component has a germ layer-specific effect on the ectoderm.
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Affiliation(s)
- Chuan Fen Wu
- Department of Molecular Genetics, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
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8
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Wu CF, Nakamura H, Chan AP, Zhou YH, Cao T, Kuang J, Gong SG, He G, Etkin LD. Tumorhead, a Xenopus gene product that inhibits neural differentiation through regulation of proliferation. Development 2001; 128:3381-93. [PMID: 11546754 DOI: 10.1242/dev.128.17.3381] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Tumorhead (TH) is a novel maternal gene product from Xenopus laevis containing several basic domains and a weak coiled-coil. Overexpression of wild-type TH resulted in increased proliferation of neural plate cells, causing expansion of the neural field followed by neural tube and craniofacial abnormalities. Overexpressed TH protein repressed neural differentiation and neural crest markers, but did not inhibit the neural inducers, pan-neural markers or mesodermal markers. Loss of function by injection of anti-TH antibody inhibited cell proliferation. Our data are consistent with a model in which tumorhead functions in regulating differentiation of the neural tissues but not neural induction or determination through its effect on cell proliferation.
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Affiliation(s)
- C F Wu
- Department of Molecular Genetics, University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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9
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Yoon JK, Moon RT, Wold B. The bHLH class protein pMesogenin1 can specify paraxial mesoderm phenotypes. Dev Biol 2000; 222:376-91. [PMID: 10837126 DOI: 10.1006/dbio.2000.9717] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A new bHLH gene from mouse that we call pMesogenin1 (referring to paraxial mesoderm-specific expression and regulatory capacities) and its candidate ortholog from Xenopus were isolated and studied comparatively. In both organisms the gene is specifically expressed in unsegmented paraxial mesoderm and its immediate progenitors. A striking feature of pMesogenin1 expression is that it terminates abruptly in presumptive somites (somitomeres). Somitomeres rostral to the pMesogenin1 domain strongly upregulate expression of pMesogenin's closest known paralogs, MesP1 and MesP2 (Thylacine1/2 in Xenopus). Subsequently, the most rostral somitomere becomes a new somite and expression of MesP1/2 is sharply downregulated before this transition. Thus, expression patterns of these bHLH genes, together with that of an additional bHLH gene in the mouse, Paraxis, collectively define discrete but highly dynamic prepatterned subdomains of the paraxial mesoderm. In functional assays, we show that pMesogenin1 from either mouse or frog can efficiently drive nonmesodermal cells to assume a phenotype with molecular and cellular characteristics of early paraxial mesoderm. Among genes induced by added pMesogenin1 is Xwnt-8, a signaling factor that induces a similar repertoire of marker genes and a similar cellular phenotype. Additional target genes induced by pMesogenin1 are ESR4/5, regulators known to play a significant role in segmentation of paraxial mesoderm (W. C. Jen et al., 1999, Genes Dev. 13, 1486-1499). pMesogenin1 differs from other known mesoderm-inducing transcription factors because it does not also activate a dorsal (future axial) mesoderm phenotype, suggesting that pMesogenin1 is involved in specifying paraxial mesoderm. In the context of the intact frog embryo, ectopic pMesogenin1 also actively suppressed axial mesoderm markers and disrupted normal formation of notochord. In addition, we found evidence for cross-regulatory interactions between pMesogenin1 and T-box transcription factors, a family of genes normally expressed in a broader pattern and known to induce multiple types of mesoderm. Based on our results and results from prior studies of related bHLH genes, we propose that pMesogenin1 and its closest known relatives, MesP1/2 (in mouse) and Thylacine1/2 (in Xenopus), comprise a bHLH subfamily devoted to formation and segmentation of paraxial mesoderm.
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Affiliation(s)
- J K Yoon
- Division of Biology, 156-29, California Institute of Technology, Pasadena, California, 91125, USA
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Sumanas S, Strege P, Heasman J, Ekker SC. The putative wnt receptor Xenopus frizzled-7 functions upstream of beta-catenin in vertebrate dorsoventral mesoderm patterning. Development 2000; 127:1981-90. [PMID: 10751186 DOI: 10.1242/dev.127.9.1981] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have isolated one member of the frizzled family of wnt receptors from Xenopus (Xfz7) to study the role of cell-cell communication in the establishment of the vertebrate axis. We demonstrate that this maternally encoded protein specifically synergizes with wnt proteins in ectopic axis induction. Embryos derived from oocytes depleted of maternal Xfz7 RNA by antisense oligonucleotide injection are deficient in dorsoanterior structures. Xfz7-depleted embryos are deficient in dorsal but not ventral mesoderm due to the reduced expression of the wnt target genes siamois, Xnr3 and goosecoid. These signaling defects can be restored by the addition of beta-catenin but not Xwnt8b. Xfz7 thus functions upstream of the known GSK-3/axin/beta-catenin intracellular signaling complex in vertebrate dorsoventral mesoderm specification.
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Affiliation(s)
- S Sumanas
- University of Minnesota Medical School, Department of Genetics, Cell Biology, Institute of Human Genetics, Room 6-160 Jackson Hall, Minneapolis, MN 55455, USA
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11
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Huynh MH, Sage EH, Ringuette M. A calcium-binding motif in SPARC/osteonectin inhibits chordomesoderm cell migration during Xenopus laevis gastrulation: evidence of counter-adhesive activity in vivo. Dev Growth Differ 1999; 41:407-18. [PMID: 10466928 DOI: 10.1046/j.1440-169x.1999.00443.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Secreted protein, acidic, rich in cysteine (SPARC) is a Ca2+-binding, counter-adhesive, extracellular glycoprotein associated with major morphogenic events and tissue remodeling in vertebrates. In Xenopus laevis embryos, SPARC is expressed first by dorsal mesoderm cells at the end of gastrulation and undergoes complex, rapid changes in its pattern of expression during early organogenesis. Another study has reported that precocious expression of SPARC by injection of native protein into the blastocoele cavity of pregastrula embryos leads to a concentration-dependent reduction in anterior development. Thus, normal development requires that the timing, spatial distribution, and/or levels of SPARC be regulated precisely. In a previous study, we demonstrated that injection of a synthetic peptide corresponding to the C-terminal, Ca2+-binding, EF-hand domain of SPARC (peptide 4.2) mimicked the effects of native SPARC. In the present investigation, peptide 4.2 was used to examine the cellular and molecular bases of the phenotypes generated by the aberrant presence of SPARC. Exposure of late blastula embryos to LiCl also generated a concentration-dependent reduction in anterior development; therefore, injections of LiCl were carried out in parallel to highlight the unique effects of peptide 4.2 on early development. At concentrations that caused a similar loss in anterior development (60-100 ng peptide 4.2 or 0.25-0.4 microg LiCl), LiCl had a greater inhibitory effect on the initial rate of chordomesoderm cell involution, in comparison with peptide 4.2. However, as gastrulation progressed, peptide 4.2 had a greater inhibitory effect on prospective head mesoderm migration than that seen in the presence of LiCl. Moreover, peptide 4.2 and LiCl had distinct influences on the expression pattern of dorso-anterior markers at the neural and tail-bud stages of development. Scanning electron microscopy showed that peptide 4.2 inhibited spreading of migrating cells at the leading edge of the involuting chordomesoderm. While still in close proximity to the blastocoele roof, many of the cells appeared rounded and lacked lamellipodia and filopodia extended in the direction of migration. In contrast, LiCl had no effect on the spreading or shape of involuting cells. These data are the first evidence of a counter-adhesive activity for peptide 4.2 in vivo, an activity demonstrated for both native SPARC and peptide 4.2 in vitro.
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Affiliation(s)
- M H Huynh
- Department of Zoology, University of Toronto, Ontario, Canada
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Brannon M, Brown JD, Bates R, Kimelman D, Moon RT. XCtBP is a XTcf-3 co-repressor with roles throughout Xenopus development. Development 1999; 126:3159-70. [PMID: 10375506 DOI: 10.1242/dev.126.14.3159] [Citation(s) in RCA: 191] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
XTcf-3 is an HMG box transcription factor that mediates Xenopus dorsal-ventral axis formation. As a Wnt pathway effector, XTcf-3 interacts with beta-catenin and activates the expression of the dorsal organizing gene siamois, while in the absence of beta-catenin, XTcf-3 functions as a transcriptional repressor. We show that XTcf-3 contains amino- and carboxy-terminal repressor domains and have identified a Xenopus member of the C-terminal Binding Protein family of transcriptional co-repressors (XCtBP) as the C-terminal co-repressor. We show that two XCtBP binding sites near the XTcf-3 carboxy-terminus are required for the interaction of XTcf-3 and XCtBP and for the transcriptional repression mediated by the XTcf-3 carboxy-terminal domain. By fusing the GAL4 activation domain to XCtBP we have generated an antimorphic protein, XCtBP/G4A, that activates siamois transcription through an interaction with endogenous XTcf-3. Ectopic expression of XCtBP/G4A demonstrates that XCtBP functions in the regulation of head and notochord development. Our data support a role for XCtBP as a co-repressor throughout Xenopus development and indicate that XCtBP/G4A will be a useful tool in determining how XCtBP functions in various developmental processes.
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Affiliation(s)
- M Brannon
- Department of Biochemistry, Howard Hughes Medical Institute, Center for Developmental Biology, University of Washington School of Medicine, Seattle, Washington 98195-7350, USA.
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Berry DL, Schwartzman RA, Brown DD. The expression pattern of thyroid hormone response genes in the tadpole tail identifies multiple resorption programs. Dev Biol 1998; 203:12-23. [PMID: 9806769 DOI: 10.1006/dbio.1998.8974] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Expression of genes up-regulated by thyroid hormone (TH) during amphibian tail resorption was localized by in situ hybridization. The constitutive thyroid hormone receptor (TRalpha) and its heterodimeric partners (RXRalpha and RXRbeta) are expressed ubiquitously in the resorbing tail. A group of early response genes, including those encoding transcription factors, are expressed at greatest levels within tissues whose cells attempt to grow and differentiate in the tail, but eventually succumb to the resorption program. The TH-inducible TR isoform, TRbeta, is expressed ubiquitously in the tail, but especially high in fibroblasts. Similarly, a group of delayed response genes including two proteolytic enzymes that appear to execute the tail resorption program, is expressed specifically in fibroblasts that line and surround the notochord and lie beneath the epidermal lamella (subepidermal fibroblasts). During active tail resorption these fibroblasts invade their neighboring epidermal and notochord lamellae as part of the resorption process. Expression analysis implicates the single layer of invasive subepidermal fibroblasts as crucial in tail resorption. Stromelysin-3 is up-regulated by TH with early kinetics, and is expressed most actively in fibroblasts within the tail fins. None of the proteases are expressed in the tadpole epidermis, which will be replaced entirely during metamorphosis. While very few TH response genes are expressed in tadpole muscle, many are activated in fibroblasts that surround muscle and could induce muscle cell death by proteolysis of the extracellular matrix. These distinct localization patterns suggest that the common fate of all cell types within the tail is the result of multiple genetic programs.
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Affiliation(s)
- D L Berry
- Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland, 21210, USA
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Aberger F, Weidinger G, Grunz H, Richter K. Anterior specification of embryonic ectoderm: the role of the Xenopus cement gland-specific gene XAG-2. Mech Dev 1998; 72:115-30. [PMID: 9533957 DOI: 10.1016/s0925-4773(98)00021-5] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In a search for novel developmental genes expressed in a spatially restricted pattern in dorsal ectoderm of Xenopus we have identified XAG-2, a cement gland-specific gene with a putative role in ectodermal patterning. XAG-2 encodes a secreted protein, which is expressed in the anterior region of dorsal ectoderm from late gastrula stages onwards. Activation of XAG-2 transcription is observed in response to organizer-secreted molecules including the noggin, chordin, follistatin and cerberus gene products. Overexpression of XAG-2 but not of the related cement gland marker XAG-1 induces both cement gland differentiation and expression of anterior neural marker genes in the absence of mesoderm formation. Further, we show that XAG-2 signaling depends on an intact fibroblast growth factor (FGF) signal transduction pathway and that XAG-2-induced anterior neural fate of ectodermal cells can be transformed to a more posterior character by retinoic acid. Based on these findings we propose a role for XAG-2 in the specification of dorsoanterior ectodermal fate, i.e. in the formation of cement gland and induction of forebrain fate of Xenopus.
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Affiliation(s)
- F Aberger
- Institute of Genetics, University of Salzburg, Hellbrunnerstrasse 34, A-5020, Salzburg, Austria.
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15
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Abstract
Recent work identified an apoptotic program in gastrulation stage Xenopus embryos (Anderson, J.A., Lewellyn, A.L., Maller, J.L., 1997. Mol. Biol. Cell 8, 1195-1206; Stack, J.H., Newport, J.W., 1997. Development 124, 3185-3195). Here, we characterize in detail this maternal cell death program, which is set up at fertilization and abruptly activated at the onset of gastrulation, following DNA damage or treatment of embryos with inhibitors of transcription, translation, or replication, between the time of fertilization and the midblastula transition (MBT). This apoptotic pathway is activated under tightly regulated developmental control(s): if the same treatments are applied after the MBT the apoptotic response is abrogated. Embryos displayed many characteristic apoptotic features, including DNA fragmentation, caspase activation, and embryonic death was blocked in vivo by the ectopic expression of Bcl-2, or injection of the caspase-3 inhibitor z-DEVD-fmk. The precise timing and the execution of this maternal cell death program is set at fertilization and does not depend on the type of stress applied, on cell cycle progression, or on de novo protein synthesis. This maternal developmental program might palliate the lack of cell cycle checkpoints in the pre-MBT embryo.
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Affiliation(s)
- C Hensey
- Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA
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Wu L, Good PJ, Richter JD. The 36-kilodalton embryonic-type cytoplasmic polyadenylation element-binding protein in Xenopus laevis is ElrA, a member of the ELAV family of RNA-binding proteins. Mol Cell Biol 1997; 17:6402-9. [PMID: 9343402 PMCID: PMC232492 DOI: 10.1128/mcb.17.11.6402] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The translational activation of several maternal mRNAs in Xenopus laevis is dependent on cytoplasmic poly(A) elongation. Messages harboring the UUUUUAU-type cytoplasmic polyadenylation element (CPE) in their 3' untranslated regions (UTRs) undergo polyadenylation and translation during oocyte maturation. This CPE is bound by the protein CPEB, which is essential for polyadenylation. mRNAs that have the poly(U)12-27 embryonic-type CPE (eCPE) in their 3' UTRs undergo polyadenylation and translation during the early cleavage and blastula stages. A 36-kDa eCPE-binding protein in oocytes and embryos has been identified by UV cross-linking. We now report that this 36-kDa protein is ElrA, a member of the ELAV family of RNA-binding proteins. The proteins are identical in size, antibody directed against ElrA immunoprecipitates the 36-kDa protein, and the two proteins have the same RNA binding specificity in vitro. C12 and activin receptor mRNAs, both of which contain eCPEs, are detected in immunoprecipitated ElrA-mRNP complexes from eggs and embryos. In addition, this in vivo interaction requires the eCPE. Although a number of experiments failed to define a role for ElrA in cytoplasmic polyadenylation, the expression of a dominant negative ElrA protein in embryos results in an exogastrulation phenotype. The possible functions of ElrA in gastrulation are discussed.
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Affiliation(s)
- L Wu
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical Center, Worcester 01655, USA
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Nakata K, Nagai T, Aruga J, Mikoshiba K. Xenopus Zic3, a primary regulator both in neural and neural crest development. Proc Natl Acad Sci U S A 1997; 94:11980-5. [PMID: 9342348 PMCID: PMC23676 DOI: 10.1073/pnas.94.22.11980] [Citation(s) in RCA: 205] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Xenopus Zic3 is a Xenopus homologue of mouse Zic and Drosophila pair-rule gene, odd-paired. We show here that Zic3 has significant roles both in neural and neural crest development in Xenopus embryo. Expression of Zic3 is first detected in prospective neural plate region at gastrulation. Onset of the expression was earlier than most proneural genes and followed chordin expression. The expression was induced by blockade of BMP4 signal. Overexpression of Zic3 resulted in hyperplastic neural and neural crest derived tissue. In animal cap explant, the overexpression of Zic3 induced expression of all the proneural genes and neural crest marker genes. These findings suggest that Zic3 can determine the ectodermal cell fate and promote the earliest step of neural and neural crest development.
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Affiliation(s)
- K Nakata
- Molecular Neurobiology Laboratory, Tsukuba Life Science Center, Institute of Physical and Chemical Research (RIKEN), Tsukuba, Ibaraki 305, Japan
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18
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Meng F, Whittaker CA, Ransom DG, DeSimone DW. Cloning and characterization of cDNAs encoding the integrin alpha2 and alpha3 subunits from Xenopus laevis. Mech Dev 1997; 67:141-55. [PMID: 9392512 DOI: 10.1016/s0925-4773(97)00108-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Integrins containing the alpha2 and alpha3 subunits associate with the beta1 subunit to form distinct receptors with partially overlapping adhesive specificities. We report the cloning and sequence of cDNAs that encode the Xenopus orthologues of integrins alpha2 and alpha3 and the expression of these subunits during embryogenesis. Integrin alpha2 and alpha3 mRNAs are first expressed in the dorsal mesoderm and developing notochord at gastrulation. We also show that alpha3 mRNAs are expressed in the entire marginal zone of gastrulae dorsalized with LiCl but that this localization is lost in embryos ventralized by ultraviolet light. Immunoblots reveal that the alpha3 protein is expressed throughout early development, however, the alpha2 protein is not detected until late tailbud stages. Injection of full-length alpha3 transcripts into the animal poles of fertilized eggs results in embryonic defects in paraxial mesoderm attributed to the failure of somites to form segments. Injection of the alpha3 transcripts into the vegetal pole and overexpression of a 5'-truncated alpha3 control construct have no apparent affect on development or somite formation. These data suggest that normal position-specific expression of integrins is important in maintaining the proper organization of tissues during early amphibian morphogenesis.
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Affiliation(s)
- F Meng
- Department of Cell Biology, School of Medicine, University of Virginia, Charlottesville 22908, USA
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19
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Damjanovski S, Karp X, Funk S, Sage EH, Ringuette MJ. Ectopic expression of SPARC in Xenopus embryos interferes with tissue morphogenesis: identification of a bioactive sequence in the C-terminal EF hand. J Histochem Cytochem 1997; 45:643-55. [PMID: 9154151 DOI: 10.1177/002215549704500502] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
SPARC is a matricellular Ca(2+)-binding glycoprotein that exhibits both counteradhesive and antiproliferative effects on cultured cells. It is secreted by cells of various tissues as a consequence of morphogenesis, response to injury, and cyclic renewal and/or repair. In an earlier study with Xenopus embryos we had shown a highly specific and regulated pattern of SPARC expression. We now show that ectopic expression of SPARC before its normal embryonic activation produces severe anomalies, some of which are consistent with the functions of SPARC proposed from studies in vitro. Microinjection of SPARC RNA, protein, and peptides into Xenopus embryos before endogenous embryonic expression generated different but overlapping phenotypes. (a) Injection of SPARC RNA into one cell of a two-cell embryo resulted in a range of unilateral defects. (b) Precocious exposure of embryos to SPARC by microinjection of protein into the blastocoel cavity was associated with certain axial defects comparable to those obtained with SPARC RNA. (c) SPARC peptides containing follistatin-like and copper-binding sequences were without obvious effect, whereas SPARC peptide 4.2, corresponding to a disulfide-bonded, Ca(2+)-binding domain, was associated with a reduction in axial structures that led eventually to complete ventralization of the embryos. Histological analysis of ventralized embryos indicated that the morphogenetic events associated with gastrulation might have been inhibited. Microinjection of other Ca(2+)-binding glycoproteins, such as osteopontin and bone sialoprotein, resulted in phenotypes that were unique. We probed further the structural correlates of this region of SPARC in the context of tissue development. Co-injection of peptide 4.2 with Ca2+ or EGTA, and injection of peptide 4.2K (containing a mutated consensus Ca(2+)-binding sequence), demonstrated that the developmental defects associated with peptide 4.2 were independent of Ca2+. However, the disulfide bridge in this region of SPARC was found to be critical, as injection of peptide 4.2AA, a mutant lacking the cystine, generated no axial defects. We have therefore shown for the first time in vivo that the temporally inappropriate presence of SPARC is associated with perturbations in tissue morphogenesis. Moreover, we have identified at least one bioactive region of SPARC as the C-terminal disulfide-bonded, Ca(2+)-binding loop that was previously shown to be both counteradhesive and growth-inhibitory.
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Affiliation(s)
- S Damjanovski
- Department of Zoology, University of Toronto, Ontario, Canada
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20
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Aberger F, Schmidt G, Richter K. The Xenopus homologue of hepatocyte growth factor-like protein is specifically expressed in the presumptive neural plate during gastrulation. Mech Dev 1996; 54:23-37. [PMID: 8808403 DOI: 10.1016/0925-4773(95)00458-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Using a RT-PCR approach, we were able to isolate a cDNA encoding the Xenopus homologue of hepatocyte growth factor-like protein, which we have termed accordingly Xhl. The deduced Xhl protein consists of 717 amino acids, contains four putative kringle domains and a serine protease-like domain characteristic for mammalian HGF and HGF-like protein. The mRNA of Xhl is exclusively expressed in the midline of the prospective neural plate during the period of neural induction, only. Ectopic expression of Xhl causes a 'spina bifida'-like phenotype with enlargement of neural tissue. Activation of Xhl mRNA transcription can be induced by delayed reaggregation of animal caps and appears to require vertical rather than planar signals from the organizer. These data suggest that Xhl is involved in the formation of the embryonic nervous system of Xenopus.
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Affiliation(s)
- F Aberger
- Institute of Genetics and Developmental Biology, University of Salzburg, Austria
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21
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Isom LL, Ragsdale DS, De Jongh KS, Westenbroek RE, Reber BF, Scheuer T, Catterall WA. Structure and function of the beta 2 subunit of brain sodium channels, a transmembrane glycoprotein with a CAM motif. Cell 1995; 83:433-42. [PMID: 8521473 DOI: 10.1016/0092-8674(95)90121-3] [Citation(s) in RCA: 362] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Voltage-gated sodium channels in brain neurons are complexes of a pore-forming alpha subunit with smaller beta 1 and beta 2 subunits. cDNA cloning and sequencing showed that the beta 2 subunit is a 186 residue glycoprotein with an extracellular NH2-terminal domain containing an immunoglobulin-like fold with similarity to the neural cell adhesion molecule (CAM) contactin, a single transmembrane segment, and a small intracellular domain. Coexpression of beta 2 with alpha subunits in Xenopus oocytes increases functional expression, modulates gating, and causes up to a 4-fold increase in the capacitance of the oocyte, which results from an increase in the surface area of the plasma membrane microvilli. beta 2 subunits are unique among the auxiliary subunits of ion channels in combining channel modulation with a CAM motif and the ability to expand the cell membrane surface area. They may be important regulators of sodium channel expression and localization in neurons.
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Affiliation(s)
- L L Isom
- Department of Pharmacology, University of Washington Seattle 98195-7280, USA
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22
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Fu Y, Izumo S. Cardiac myogenesis: overexpression of XCsx2 or XMEF2A in whole Xenopus embryos induces the precocious expression of XMHCα gene. ACTA ACUST UNITED AC 1995; 205:198-202. [PMID: 28306081 DOI: 10.1007/bf00357766] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/1995] [Accepted: 08/09/1995] [Indexed: 11/28/2022]
Abstract
XCsx2, a homeobox-containing gene, is expressed in cardiac muscle during Xenopus development, while the XMEF2A gene is expressed in both cardiac and skeletal muscle. Microinjection of either XCsx2 or XMEF2A mRNA into single blastomeres of two-cell stage Xenopus embryos induced precocious expression of the myosin heavy-chain alpha (XMHCα) gene at the neural plate stage (stage 14). Co-injection of both XCsx2 and XMEF2A mRNAs induced still earlier expression at the late gastrula stage (stage 12). These changes were evident in whole embryos but not in animal pole explants from injected embryos. Overexpression of XCsx2 or XMEF2A also caused an enlarged heart and abnormalities of notochord and tail in Xenopus embryos. These findings suggest that both XCsx2 and XMEF2A transcription factors have an important role in regulating the expression of the XMHCα gene and the morphogenesis of heart tissue in Xenopus development.
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Affiliation(s)
- Yuchang Fu
- Molecular Medicine Unit, Beth Israel Hospital, and Department of Medicine and Program in Cell and Developmental Biology, Harvard Medical School, 02215, Boston, MA, USA
| | - Seigo Izumo
- Cardiovascular Research Center, Department of Internal Medicine, University of Michigan, 48109, Ann Arbor, MI, USA
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23
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Ekker SC, McGrew LL, Lai CJ, Lee JJ, von Kessler DP, Moon RT, Beachy PA. Distinct expression and shared activities of members of the hedgehog gene family of Xenopus laevis. Development 1995; 121:2337-47. [PMID: 7671800 DOI: 10.1242/dev.121.8.2337] [Citation(s) in RCA: 150] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The hedgehog family of signaling proteins is associated with a variety of spatial patterning activities in insects and vertebrates. Here we show that new members of this family isolated from Xenopus laevis are expressed embryonically in patterns suggestive of roles in patterning in the ectoderm, nervous system and somites. Banded hedgehog is expressed throughout the neural plate and subsequently in both the nervous system and in the dermatome of somites. Cephalic hedgehog is expressed in anterior ectoderm and endodermal structures, and sonic hedgehog is expressed in patterns which parallel those in other species. Injection of RNAs encoding Xenopus hedgehogs induces ectopic cement gland formation in embryos. Similar to reported activities of noggin and follistatin, Xenopus hedgehogs share a common ability to induce cement glands in animal cap explants. However, hedgehog activities in naive ectoderm appear capable of acting independently of noggin and follistatin since, although all three are induced by activin in animal cap explants, X-hh expression does not induce noggin or follistatin.
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Affiliation(s)
- S C Ekker
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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24
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Abstract
The Wnts are a family of secreted glycoproteins involved in cell-cell signalling and pattern formation during development, although the extent to which various Wnts are functionally equivalent remains unclear. We have cloned zebrafish (Danio rerio) wnt4, characterized its expression, and compared its activity relative to other Wnts. The wnt4 transcript is first detected early in somitogenesis, in the dorsocaudal region of the forebrain, and then appears in the dorsal and lateral regions of the caudal hindbrain and neural keel. During somitogenesis, wnt4 appears in the floor plate, and this expression is absent in cyclops mutants, which lack floor plate. wnt4 is also expressed in the developing pronephros and gill slit. To characterize the biological activity of wnt4, synthetic zebrafish wnt4 mRNA was injected into embryos of zebrafish and Xenopus laevis. The phenotypic effects of misexpression in the zebrafish include cyclopia, misfolding in the brain, and an anteriorly forking notochord. Comparison of the phenotypes arising from misexpression of wnt4 and Xwnt-5A in both organisms suggests close parallels in the response to these Wnts. Our data suggest that wnt4, like Xwnt-5A, inhibits cell movements, and that these Wnts define a functional class distinct from the class which includes Wnt-1, Xwnt-3A and Xwnt-8.
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Affiliation(s)
- A R Ungar
- Department of Pharmacology, University of Washington School of Medicine, Seattle 98195, USA
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25
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Cui Y, Brown JD, Moon RT, Christian JL. Xwnt-8b: a maternally expressed Xenopus Wnt gene with a potential role in establishing the dorsoventral axis. Development 1995; 121:2177-86. [PMID: 7635061 DOI: 10.1242/dev.121.7.2177] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In amphibian embryos, establishment of dorsal-ventral asymmetry is believed to involve dorsal-ventral differences in vegetally derived mesoderm-inducing signals and/or differences in the competence of animal hemisphere (ectodermal) cells to respond to these signals. Previous studies have shown that certain Wnt proteins can generate an ectopic dorsal axis when misexpressed, and that they do so by modifying the response of ectodermal cells to inducers. None of these Wnt proteins are expressed at an appropriate time to do so in vivo. In this study, we describe the isolation and characterization of a full length cDNA for the Xenopus Wnt gene, Xwnt-8b, whose biological activity and expression pattern suggest that it may be involved in establishment of the dorsoventral axis. Both maternal and zygotic Xwnt-8b transcripts undergo alternative splicing to generate mRNAs which encode two different forms of Xwnt-8b protein. During early cleavage stages Xwnt-8b transcripts are confined primarily to animal hemisphere blastomeres, while zygotically derived Xwnt-8b transcripts are restricted almost exclusively to a band of cells in the prospective forebrain of neurula and tailbud stage embryos. Ectopically expressed Xwnt-8b can completely rescue dorsal development of embryos ventralized by exposure to ultraviolet light, and can induce a complete secondary axis in wild-type embryos. Axis induction is observed only if Xwnt-8b is supplied prior to the onset of zygotic gene transcription. This biological activity, together with the presence of maternal Xwnt-8b transcripts in cells that will be induced to form the dorsal mesoderm, is consistent with the possibility that Xwnt-8b may be the endogenous agent that establishes asymmetry in the response of ectodermal cells to mesoderm-inducing signals, thereby initiating dorsal development.
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Affiliation(s)
- Y Cui
- Department of Cell Biology and Anatomy, Oregon Health Sciences University, School of Medicine, Portland 97201, USA
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26
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Du SJ, Purcell SM, Christian JL, McGrew LL, Moon RT. Identification of distinct classes and functional domains of Wnts through expression of wild-type and chimeric proteins in Xenopus embryos. Mol Cell Biol 1995; 15:2625-34. [PMID: 7739543 PMCID: PMC230492 DOI: 10.1128/mcb.15.5.2625] [Citation(s) in RCA: 257] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Wnts are secreted signaling factors which influence cell fate and cell behavior in developing embryos. Overexpression in Xenopus laevis embryos of a Xenopus Wnt, Xwnt-8, leads to a duplication of the embryonic axis. In embryos ventralized by UV irradiation, Xwnt-8 restores expression of the putative transcription factor goosecoid, and rescues normal axis formation. In contrast, overexpression of Xwnt-5A in normal embryos generates defects in dorsoanterior structures, without inducing goosecoid or a secondary axis. To determine whether Xwnt-4 and Xwnt-11 fall into one of these two previously described classes of activity, synthetic mRNAs were introduced into animal caps, normal embryos, and UV-treated embryos. The results indicate that Xwnt-4, Xwnt-5A, and Xwnt-11 are members of a single functional class with activities that are indistinguishable in these assays. To investigate whether distinct regions of Xwnt-8 and Xwnt-5A were sufficient for eliciting the observed effects of overexpression, we generated a series of chimeric Xwnts. RNAs encoding the chimeras were injected into normal and UV-irradiated Xenopus embryos. Analysis of the embryonic phenotypes and goosecoid levels reveals that chimeras composed of carboxy-terminal regions of Xwnt-8 and amino-terminal regions of Xwnt-5A are indistinguishable from the activities of native Xwnt-8 and that are the reciprocal chimeras elicit effects indistinguishable from overexpression of native Xwnt-5A. We conclude that the carboxy-terminal halves of these Xwnts are candidate domains for specifying responses to Xwnt signals.
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Affiliation(s)
- S J Du
- Department of Pharmacology, University of Washington School of Medicine, Seattle, USA
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27
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Moon RT, Campbell RM, Christian JL, McGrew LL, Shih J, Fraser S. Xwnt-5A: a maternal Wnt that affects morphogenetic movements after overexpression in embryos of Xenopus laevis. Development 1993; 119:97-111. [PMID: 8275867 DOI: 10.1242/dev.119.1.97] [Citation(s) in RCA: 225] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To contribute to an understanding of the roles and mechanisms of action of Wnts in early vertebrate development, we have characterized the normal expression of Xenopus laevis Wnt-5A, and investigated the consequences of misexpression of this putative signalling factor. Xwnt-5A transcripts are expressed throughout development, and are enriched in both the anterior and posterior regions of embryos at late stages of development, where they are found primarily in ectoderm, with lower levels of expression in mesoderm. Overexpression of Xwnt-5A in Xenopus embryos leads to complex malformations distinct from those achieved by ectopic expression of Xwnts −1, −3A, or −8. This phenotype is unlikely to result from Xwnt-5A acting as an inducing agent, as overexpression of Xwnt-5A does not rescue dorsal structures in UV-irradiated embryos, does not induce mesoderm in blastula caps, and Xwnt-5A does not alter the endogenous patterns of expression of goosecoid, Xbra, or Xwnt-8. To pursue whether Xwnt-5A has the capacity to affect morphogenetic movements, we investigated whether overexpression of Xwnt-5A alters the normal elongation of blastula cap explants induced by activin. Intriguingly, Xwnt-5A blocks the elongation of blastula caps in response to activin, without blocking the differentiation of either dorsal or ventral mesoderm within these explants. The data are consistent with Xwnt-5A having the potential activity of modifying the morphogenetic movements of tissues.
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Affiliation(s)
- R T Moon
- Department of Pharmacology, University of Washington School of Medicine, Seattle 98195
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28
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von Dassow G, Schmidt JE, Kimelman D. Induction of the Xenopus organizer: expression and regulation of Xnot, a novel FGF and activin-regulated homeo box gene. Genes Dev 1993; 7:355-66. [PMID: 8095482 DOI: 10.1101/gad.7.3.355] [Citation(s) in RCA: 202] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We have searched for homeo box-containing genes expressed during gastrulation in Xenopus embryos with the expectation that analysis of the spatial and temporal expression of these genes will lead to greater understanding of the regionalization of the mesoderm. We describe the cloning and expression of Xnot, a novel homeo box-containing gene expressed primarily in the gastrula organizing region. We have studied the regulation of Xnot by signaling molecules involved in mesoderm induction and regionalization. Surprisingly, we found that FGF signaling is required for expression of Xnot in the gastrula organizing region, clearly implicating FGF in the induction of dorsal mesoderm. Furthermore, we found that Xnot is initially expressed throughout the embryo and that progressive translation of an unknown protein restricts expression of Xnot to the organizing region. Our results provide experimental evidence supporting the proposed division of Spemann's organizer into independently regulated organizing centers.
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Affiliation(s)
- G von Dassow
- Department of Biochemistry, University of Washington, Seattle 98195
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29
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Gard DL. Confocal immunofluorescence microscopy of microtubules in amphibian oocytes and eggs. Methods Cell Biol 1993; 38:241-64. [PMID: 8246784 DOI: 10.1016/s0091-679x(08)61006-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- D L Gard
- Department of Biology, University of Utah, Salt Lake City 84112
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30
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Gard DL, Kropf DL. Confocal immunofluorescence microscopy of microtubules in oocytes, eggs, and embryos of algae and amphibians. Methods Cell Biol 1993; 37:147-69. [PMID: 8255242 DOI: 10.1016/s0091-679x(08)60249-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- D L Gard
- Department of Biology, University of Utah, Salt Lake City 84112
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31
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Christian JL, Moon RT. Interactions between Xwnt-8 and Spemann organizer signaling pathways generate dorsoventral pattern in the embryonic mesoderm of Xenopus. Genes Dev 1993; 7:13-28. [PMID: 8422982 DOI: 10.1101/gad.7.1.13] [Citation(s) in RCA: 359] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
This study analyzes the hierarchy of signals that spatially restrict expression of Xenopus Xwnt-8 to mesodermal cells outside of the Spemann organizer field and examines the potential role that endogenous Xwnt-8 may play in dorsoventral patterning of the embryonic mesoderm. The effects of ectopic introduction of a Nieuwkoop center-like activity or of ectopic expression of goosecoid, on the distribution of endogenous Xwnt-8 transcripts were analyzed. The results of these studies are consistent with the hypothesis that maternally derived signals from the Nieuwkoop center function to positively regulate expression of the homeo box gene goosecoid in Spemann organizer cells, leading to a subsequent repression of Xwnt-8 expression in these cells. This exclusion of Xwnt-8 from cells of the organizer field may be important for normal dorsal development, in that ectopic expression of Xwnt-8 in organizer cells after the midblastula stage, by injection of plasmid DNA, ventralizes the fate of these cells. This is distinct from the previously observed dorsalizing effect of Xwnt-8 when expressed prior to the midblastula stage by injection of RNA. The effects of plasmid-derived Xwnt-8 on isolated blastula animal cap ectoderm were also analyzed. Expression of Xwnt-8 in animal pole ectoderm after the midblastula stage ventralizes the response of dorsal animal pole cells to activin and allows naive ectodermal cells to differentiate as ventral mesoderm in the absence of added growth factors. Collectively, these data are consistent with the hypothesis that Xwnt-8 plays a role in the mesodermal differentiation of ventral marginal zone cells during normal development. Furthermore, endogenous Xwnt-8 may ventralize the response of lateral mesodermal cells to dorsalizing signals from the organizer, thus contributing to the graded nature of the final body pattern.
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Affiliation(s)
- J L Christian
- Department of Pharmacology, University of Washington School of Medicine, Seattle 98195
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