Germ Layer Induction in ESC—Following the Vertebrate Roadmap

Jim Smith1, Fiona Wardle1, Matt Loose2, Ed Stanley3, Roger Patient4

1 Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Cambridge, 2 Institute of Genetics, University of Nottingham, Nottingham, 3 Monash Immunology and Stem Cell Laboratories, Monash University, Clayton, Victoria, 4 Weatherall Institute of Molecular Medicine, University of Oxford, Oxford
Publication Name:  Current Protocols in Stem Cell Biology
Unit Number:  Unit 1D.1
DOI:  10.1002/9780470151808.sc01d01s1
Online Posting Date:  June, 2007
GO TO THE FULL TEXT: PDF or HTML at Wiley Online Library

Abstract

Controlled differentiation of pluripotential cells takes place routinely and with great success in developing vertebrate embryos. It therefore makes sense to take note of how this is achieved and use this knowledge to control the differentiation of embryonic stem cells (ESCs). An added advantage is that the differentiated cells resulting from this process in embryos have proven functionality and longevity. This unit reviews what is known about the embryonic signals that drive differentiation in one of the most informative of the vertebrate animal models of development, the amphibian Xenopus laevis. It summarizes their identities and the extent to which their activities are dose‐dependent. The unit details what is known about the transcription factor responses to these signals, describing the networks of interactions that they generate. It then discusses the target genes of these transcription factors, the effectors of the differentiated state. Finally, how these same developmental programs operate during germ layer formation in the context of ESC differentiation is summarized. Curr. Protoc. Stem Cell Biol. 1:1D.1.1‐1D.1.22. © 2007 by John Wiley & Sons, Inc.

Keywords: embryonic signals; transcription factors; differentiation; Xenopus; zebrafish; mouse; mesendoderm; mesoderm; endoderm; ectoderm; neural; Wnt; TGF‐β; nodal; activin; BMP; FGF; antagonists; T‐box; VegT; brachyury; Mix; Sox; GATA; ES cells

     
 
GO TO THE FULL PROTOCOL:
PDF or HTML at Wiley Online Library

Table of Contents

  • Lessons from Frogs (and Fish)
  • Germ Layer Induction During Embryonic Stem Cell Differentiation
  • Conclusions
  • Literature Cited
  • Figures
     
 
GO TO THE FULL PROTOCOL:
PDF or HTML at Wiley Online Library

Materials

GO TO THE FULL PROTOCOL:
PDF or HTML at Wiley Online Library

Figures

Videos

Literature Cited

Literature Cited
   Afouda, B.A., Ciau‐Uitz, A., and Patient, R. 2005. GATA4, 5 and 6 mediate TGFβ maintenance of endodermal gene expression in Xenopus embryos. Development 132:763‐774.
   Agius, E., Oelgeschlager, M., Wessely, O., Kemp, C., and De Robertis, E.M. 2000. Endodermal Nodal‐related signals and mesoderm induction in Xenopus. Development 127:1173‐1183.
   Ahmed, N., Howard, L., and Woodland, HR. 2004. Early endodermal expression of the Xenopus Endodermin gene is driven by regulatory sequences containing essential Sox protein‐binding elements. Differentiation 72:171‐184.
   Albano, R.M., Godsave, S.F., Huylebroeck, D., Van Nimmen, K., Isaacs, H.V., Slack, J.M., and Smith, J.C. 1990. A mesoderm‐inducing factor produced by WEHI‐3 murine myelomonocytic leukemia cells is activin A. Development 110:435‐443.
   Amacher, S.L., Draper, B.W., Summers, B.R., and Kimmel, C.B. 2002. The zebrafish T‐box genes no tail and spadetail are required for development of trunk and tail mesoderm and medial floor plate. Development 129:3311‐3323.
   Amack, J.D. and Yost, H.J. 2004. The T box transcription factor no tail in ciliated cells controls zebrafish left‐right asymmetry. Curr. Biol. 14:685‐690.
   Amaya, E., Stein, P.A., Musci, T.J., and Kirschner, M.W. 1993. FGF signalling in the early specification of mesoderm in Xenopus. Development 118:477‐487.
   Asashima, M., Nakano, H., Shimada, K., Kinoshita, K., Ishii, K., Shibai, H., and Ueno, N. 1990. Mesodermal induction in early amphibian embryos by activin A (erythroid differentiation factor). Roux's Arch. Dev. Biol. 198:330‐335.
   Aubert, J., Dunstan, H., Chambers, I., and Smith, A. 2002. Functional gene screening in embryonic stem cells implicates Wnt antagonism in neural differentiation. Nat. Biotechnol. 20:1240‐1245.
   Babu, M.M., Luscombe, N.M., Aravind, L., Gerstein, M., and Teichmann, S.A. 2004. Structure and evolution of transcriptional regulatory networks. Curr. Opin. Struct. Biol. 14:283‐291.
   Ben‐Haim, N., Lu, C., Guzman‐Ayala, M., Pescatore, L., Mesnard, D., Bischofberger, M., Naef, F., Robertson, E.J., and Constam, D.B. 2006. The nodal precursor acting via activin receptors induces mesoderm by maintaining a source of its convertases and BMP4. Dev. Cell 11:313‐323.
   Birsoy, B., Kofron, M., Schaible, K., Wylie, C., and Heasman, J. 2006. Vg 1 is an essential signaling molecule in Xenopus development. Development 133:15‐20.
   Bjornson, C.R., Griffin, K.J., Farr, G.H., 3rd, Terashima, A., Himeda, C., Kikuchi, Y., and Kimelman, D. 2005. Eomesodermin is a localized maternal determinant required for endoderm induction in zebrafish. Dev. Cell 9:523‐533.
   Bouwmeester, T., Kim, S., Sasai, Y., Lu, B., and De Robertis, E.M. 1996. Cerberus is a head‐inducing secreted factor expressed in the anterior endoderm of Spemann's organizer. Nature 382:595‐601.
   Boyer, L.A., Lee, T.I., Cole, M.F., Johnstone, S.E., Levine, S.S., Zucker, J.P., Guenther, M.G., Kumar, R.M., Murray, H.L., Jenner, R.G., Gifford, D.K., Melton, D.A., Jaenisch, R., and Young, R.A. 2005. Core transcriptional regulatory circuitry in human embryonic stem cells. Cell 122:947‐956.
   Casey, E.S., O'Reilly, M.A., Conlon, F.L., and Smith, J.C. 1998. The T‐box transcription factor Brachyury regulates expression of eFGF through binding to a non‐palindromic response element. Development 125:3887‐3894.
   Cha, Y.R., Takahashi, S., and Wright, C.V. 2006. Cooperative non‐cell and cell autonomous regulation of Nodal gene expression and signaling by Lefty/Antivin and Brachyury in Xenopus. Dev. Biol. 290:246‐264.
   Chiba, S., Kurokawa, M.S., Yoshikawa, H., Ikeda, R., Takeno, M., Tadokoro, M., Sekino, H., Hashimoto, T., and Suzuki, N. 2005. Noggin and basic FGF were implicated in forebrain fate and caudal fate, respectively, of the neural tube‐like structures emerging in mouse ES cell culture. Exp. Brain Res. 163:86‐99.
   Clements, D. and Woodland, H.R. 2000. Changes in embryonic cell fate produced by expression of an endodermal transcription factor, Xsox17. Mech. Dev. 99:65‐70.
   Clements, D. and Woodland, H.R. 2003. VegT induces endoderm by a self‐limiting mechanism and by changing the competence of cells to respond to TGF‐beta signals. Dev. Biol. 258:454‐463.
   Conlon, F.L., Lyons, K.M., Takaesu, N., Barth, K.S., Kispert, A., Herrmann, B., and Robertson, E.J. 1994. A primary requirement for nodal in the formation and maintenance of the primitive streak in the mouse. Development 120:1919‐1928.
   Cooke, J. and Smith, J.C. 1987. The midblastula cell cycle transition and the character of mesoderm in u.v.‐induced nonaxial Xenopus development. Development 99:197‐210.
   Cunliffe, V. and Smith, J.C. 1992. Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature 358:427‐430.
   D'Amour, K.A., Agulnick, A.D., Eliazer, S., Kelly, O.G., Kroon, E., and Baetge, E.E. 2005. Efficient differentiation of human embryonic stem cells to definitive endoderm. Nat. Biotechnol. 23:1534‐1541.
   Dale, L., Howes, G., Price, B.M., and Smith, J.C. 1992. Bone morphogenetic protein 4: A ventralizing factor in early Xenopus development. Development 115:573‐585.
   Dale, L., Matthews, G., and Colman, A. 1993. Secretion and mesoderm‐inducing activity of the TGF‐beta related domain of Xenopus Vg1. EMBO J. 12:4471‐4480.
   Dale, L. and Slack, J.M. 1987. Fate map for the 32‐cell stage of Xenopus laevis. Development 99:527‐551.
   Dale, L., Smith, J.C., and Slack, J.M. 1985. Mesoderm induction in Xenopus laevis: A quantitative study using a cell lineage label and tissue‐specific antibodies. J. Embryol. Exp. Morphol. 89:289‐312.
   Dell'Era, P., Ronca, R., Coco, L., Nicoli, S., Metra, M., and Presta, M. 2003. Fibroblast growth factor receptor‐1 is essential for in vitro cardiomyocyte development. Circ. Res. 93:414‐420.
   Deng, C.X., Wynshaw‐Boris, A., Shen, M.M., Daugherty, C., Ornitz, D.M., and Leder, P. 1994. Murine FGFR‐1 is required for early postimplantation growth and axial organization. Genes Dev. 8:3045‐3057.
   Dickinson, K., Leonard, J., and Baker, J.C. 2006. Genomic profiling of mixer and Sox17beta targets during Xenopus endoderm development. Dev. Dyn. 235:368‐381.
   Dominguez, I. and Green, J.B. 2000. Dorsal downregulation of GSK3beta by a non‐Wnt‐like mechanism is an early molecular consequence of cortical rotation in early Xenopus embryos. Development 127:861‐868.
   Dosch, R., Gawantka, V., Delius, H., Blumenstock, C., and Niehrs, C. 1997. Bmp‐4 acts as a morphogen in dorsoventral mesoderm patterning in Xenopus. Development 124:2325‐2334.
   Draper, B.W., Stock, D.W., and Kimmel, C.B. 2003. Zebrafish fgf24 functions with fgf8 to promote posterior mesodermal development. Development 130:4639‐4654.
   Dyson, S. and Gurdon, J.B. 1998. The interpretation of position in a morphogen gradient as revealed by occupancy of activin receptors. Cell 93:557‐568.
   Engleka, M.J. and Kessler, D.S. 2001. Siamois cooperates with TGFbeta signals to induce the complete function of the Spemann‐Mangold organizer. Int. J. Dev. Biol. 45:241‐250.
   Evans, M.J. and Kaufman, M.H. 1981. Establishment in culture of pluripotential cells from mouse embryos. Nature 292:154‐156.
   Fan, M.J. and Sokol, S.Y. 1997. A role for Siamois in Spemann organizer formation. Development 124:2581‐2589.
   Fehling, H.J., Lacaud, G., Kubo, A., Kennedy, M., Robertson, S., Keller, G., and Kouskoff, V. 2003. Tracking mesoderm induction and its specification to the hemangioblast during embryonic stem cell differentiation. Development 130:4217‐4227.
   Finley, M.F., Devata, S., and Huettner, J.E. 1999. BMP‐4 inhibits neural differentiation of murine embryonic stem cells. J. Neurobiol. 40:271‐287.
   Fisher, M.E., Isaacs, H.V., and Pownall, M.E. 2002. eFGF is required for activation of XmyoD expression in the myogenic cell lineage of Xenopus laevis. Development 129:1307‐1315.
   Fletcher, G., Jones, G., Patient, R., and Snape, A. 2006a. A role for GATA factors in Xenopus gastrulation movements. Mech. Dev. 123:730‐745.
   Fletcher, R.B., Baker, J.C., and Harland, R.M. 2006b. FGF8 spliceforms mediate early mesoderm and posterior neural tissue formation in Xenopus. Development 133:1703‐1714.
   Fujiwara, T., Dunn, N.R., and Hogan, B.L. 2001. Bone morphogenetic protein 4 in the extraembryonic mesoderm is required for allantois development and the localization and survival of primordial germ cells in the mouse. Proc. Natl. Acad. Sci. U.S.A. 98:13739‐13744.
   Furthauer, M., Thisse, C., and Thisse, B. 1997. A role for FGF‐8 in the dorsoventral patterning of the zebrafish gastrula. Development 124:4253‐4264.
   Gadue, P., Huber, T.L., Paddison, P.J., and Keller, G.M. 2006. Wnt and TGF‐beta signaling are required for the induction of an in vitro model of primitive streak formation using embryonic stem cells. Proc. Natl. Acad. Sci. U.S.A. 103:16806‐16811.
   Galloway, J.L., Wingert, R.A., Thisse, C., Thisse, B., and Zon, L.I. 2005. Loss of gata1 but not gata2 converts erythropoiesis to myelopoiesis in zebrafish embryos. Dev. Cell 8:109‐116.
   Germain, S., Howell, M., Esslemont, G.M., and Hill, C.S. 2000. Homeodomain and winged‐helix transcription factors recruit activated Smads to distinct promoter elements via a common Smad interaction motif. Genes Dev. 14:435‐451.
   Glinka, A., Wu, W., Delius, H., Monaghan, A.P., Blumenstock, C., and Niehrs, C. 1998. Dickkopf‐1 is a member of a new family of secreted proteins and functions in head induction. Nature 391:357‐362.
   Glinka, A., Wu, W., Onichtchouk, D., Blumenstock, C., and Niehrs, C. 1997. Head induction by simultaneous repression of Bmp and Wnt signalling in Xenopus. Nature 389:517‐519.
   Gotoh, Y., Masuyama, N., Suzuki, A., Ueno, N., and Nishida, E. 1995. Involvement of the MAP kinase cascade in Xenopus mesoderm induction. EMBO J. 14:2491‐2498.
   Gratsch, T.E. and O'Shea, K.S. 2002. Noggin and chordin have distinct activities in promoting lineage commitment of mouse embryonic stem (ES) cells. Dev. Biol. 245:83‐94.
   Green, J.B. 1994. Borrowing thy neighbour's genetics: Neural induction and a Brachyury mutant in Xenopus. Bioessays 16:539‐540.
   Green, J.B.A. and Smith, J.C. 1990. Graded changes in dose of a Xenopus activin A homologue elicit stepwise transitions in embryonic cell fate. Nature 347:391‐394.
   Green, J.B., New, H.V., and Smith, J.C. 1992. Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell 71:731‐739.
   Green, J.B.A., Howes, G., Symes, K., Cooke, J., and Smith, J.C. 1990. The biological effects of XTC‐MIF: Quantitative comparison with Xenopus bFGF. Development 108:229‐238.
   Greil, F., Moorman, C., and Steensel, B.V. 2006. DamID: Mapping of in vivo protein‐genome interactions using tethered DNA adenine methyltransferase. Methods Enzymol. 410:342‐359.
   Griffin, K., Patient, R., and Holder, N. 1995. Analysis of FGF function in normal and no tail zebrafish embryos reveals separate mechanisms for formation of the trunk and the tail. Development 121:2983‐2994.
   Grunz, H. 1996. Factors responsible for the establishment of the body plan in the amphibian embryo. Int. J. Dev. Biol. 40:279‐289.
   Grunz, H. and Tacke, L. 1989. Neural differentiation of Xenopus laevis ectoderm takes place after disaggregation and delayed reaggregation without inducer. Cell Differ. Dev. 28:211‐217.
   Gurdon, J.B., Harger, P., Mitchell, A., and Lemaire, P. 1994. Activin signalling and response to a morphogen gradient. Nature 371:487‐492.
   Gurdon, J.B., Mitchell, A., and Mahony, D. 1995. Direct and continuous assessment by cells of their position in a morphogen gradient. Nature 376:520‐521.
   Gurdon, J.B., Mitchell, A., and Ryan, K. 1996. An experimental system for analyzing response to a morphogen gradient. Proc. Natl. Acad. Sci. U.S.A. 93:9334‐9338.
   Hansen, C.S., Marion, C.D., Steele, K., George, S., and Smith, W.C. 1997. Direct neural induction and selective inhibition of mesoderm and epidermis inducers by Xnr3. Development 124:483‐492.
   Harland, R.M. 1994. Neural induction in Xenopus. Curr. Opin. Genet. Dev. 4:543‐549.
   Hawley, S.H., Wunnenberg‐Stapleton, K., Hashimoto, C., Laurent, M.N., Watabe, T., Blumberg, B.W., and Cho, K.W. 1995. Disruption of BMP signals in embryonic Xenopus ectoderm leads to direct neural induction. Genes Dev. 9:2923‐2935.
   Heasman, J. 2006. Maternal determinants of embryonic cell fate. Semin. Cell Dev. Biol. 17:93‐98.
   Heasman, J., Crawford, A., Goldstone, K., Garnerhamrick, P., Gumbiner, B., McCrea, P., Kintner, C., Noro, C.Y., and Wylie, C. 1994. Overexpression of cadherins and under‐expression of β‐catenin inhibit dorsal mesoderm induction in early Xenopus embryos. Cell 79:791‐803.
   Heisenberg, C.P., Tada, M., Rauch, G.J., Saude, L., Concha, M.L., Geisler, R., Stemple, D.L., Smith, J.C., and Wilson, S.W. 2000. Silberblick/Wnt11 mediates convergent extension movements during zebrafish gastrulation. Nature 405:76‐81.
   Hemmati‐Brivanlou, A., Kelly, O.G., and Melton, D.A. 1994. Follistatin, an antagonist of activin, is expressed in the Spemann organizer and displays direct neuralizing activity. Cell 77:283‐295.
   Hemmati‐Brivanlou, A. and Thomsen, G.H. 1995. Ventral mesodermal patterning in Xenopus embryos: Expression patterns and activities of BMP‐2 and BMP‐4. Dev. Genet. 17:78‐89.
   Hiiragi, T., Alarcon, V.B., Fujimori, T., Louvet‐Vallee, S., Maleszewski, M., Marikawa, Y., Maro, B., and Solter, D. 2006. Where do we stand now? Mouse early embryo patterning meeting in Freiburg, Germany (2005). Int. J. Dev. Biol. 50:581‐586; discussion 586‐587.
   Hill, C.S. 2001. TGF‐β signaling pathways in early Xenopus development. Curr. Opin. Genet. Dev. 11:533‐540.
   Hirst, C.E., Ng, E.S., Azzola, L., Voss, A. K., Thomas, T., Stanley, E.G., and Elefanty, A.G. 2006. Transcriptional profiling of mouse and human ES cells identifies SLAIN1, a novel stem cell gene. Dev. Biol. 293:90‐103.
   Holwill, S., Heasman, J., Crawley, C.R., and Wylie, C.C. 1987. Axis and germ line deficiencies caused by UV irradiation of Xenopus oocytes cultured in vitro. Development 100:735‐743.
   Honda, M., Kurisaki, A., Ohnuma, K., Okochi, H., Hamazaki, T.S., and Asashima, M. 2006. N‐cadherin is a useful marker for the progenitor of cardiomyocytes differentiated from mouse ES cells in serum‐free condition. Biochem. Biophys. Res. Commun. 351:877‐882.
   Horb, M.E. and Thomsen, G.H. 1997. A vegetally‐localized T‐box transcription factor in Xenopus eggs specifies mesoderm and endoderm and is essential for embryonic mesoderm formation. Development 124:1689‐1698.
   Hosseinkhani, M., Hosseinkhani, H., Khademhosseini, A., Bolland, F., Kobayashi, H., and Prat Gonzalez, S. 2007. Bone morphogenetic protein‐4 enhances cardiomyocyte differentiation of cynomolgus monkey ES cells in Knockout Serum Replacement medium. Stem Cells 25:571‐580.
   Howell, M. and Hill, C.S. 1997. XSmad2 directly activates the activin‐inducible, dorsal mesoderm gene XFKH1 in Xenopus embryos. EMBO J. 16:7411‐7421.
   Howell, M., Itoh, F., Pierreux, C.E., Valgeirsdottir, S., Itoh, S., ten Dijke, P., and Hill, C.S. 1999. Xenopus Smad4beta is the co‐Smad component of developmentally regulated transcription factor complexes responsible for induction of early mesodermal genes. Dev. Biol. 214:354‐369.
   Ikeda, H., Osakada, F., Watanabe, K., Mizuseki, K., Haraguchi, T., Miyoshi, H., Kamiya, D., Honda, Y., Sasai, N., Yoshimura, N., Takahashi, M., and Sasai, Y. 2005. Generation of Rx+/Pax6+ neural retinal precursors from embryonic stem cells. Proc. Natl. Acad. Sci. U.S.A. 102:11331‐11336.
   Irioka, T., Watanabe, K., Mizusawa, H., Mizuseki, K., and Sasai, Y. 2005. Distinct effects of caudalizing factors on regional specification of embryonic stem cell‐derived neural precursors. Brain Res. Dev. Brain Res. 154:63‐70.
   Isaacs, H.V., Pownall, M.E., and Slack, J.M. 1994. eFGF regulates Xbra expression during Xenopus gastrulation. EMBO J. 13:4469‐4481.
   Johansson, B.M. and Wiles, M.V. 1995. Evidence for involvement of activin A and bone morphogenetic protein 4 in mammalian mesoderm and hematopoietic development. Mol. Cell Biol. 15:141‐151.
   Jones, C.M. and Smith, J.C. 1998. Establishment of a BMP‐4 morphogen gradient by long‐range inhibition. Dev. Biol. 194:12‐17.
   Jones, C.M., Kuehn, M.R., Hogan, B.L.M., Smith, J.C., and Wright, C.V.E. 1995. Nodal‐related signals induce axial mesoderm and dorsalize mesoderm during gastrulation. Development 121:3651‐3662.
   Jones, C.M., Lyons, K.M., Lapan, P.M., Wright, C.V., and Hogan, B.L. 1992. DVR‐4 (bone morphogenetic protein‐4) as a posterior‐ventralizing factor in Xenopus mesoderm induction. Development 115:639‐647.
   Joseph, E.M. and Melton, D.A. 1997. Xnr4: A Xenopus nodal‐related gene expressed in the Spemann Organizer. Dev. Biol. 184:367‐372.
   Kanai‐Azuma, M., Kanai, Y., Gad, J. M., Tajima, Y., Taya, C., Kurohmaru, M., Sanai, Y., Yonekawa, H., Yazaki, K., Tam, P.P., and Hayashi, Y. 2002. Depletion of definitive gut endoderm in Sox17‐null mutant mice. Development 129:2367‐2379.
   Kawaguchi, J., Mee, P.J., and Smith, A.G. 2005. Osteogenic and chondrogenic differentiation of embryonic stem cells in response to specific growth factors. Bone 36:758‐769.
   Kimelman, D. and Griffin, K.J. 2000. Vertebrate mesendoderm induction and patterning. Curr. Opin. Genet. Dev. 10:350‐356.
   Kimelman, D., Abraham, J.A., Haaparanta, T., Palisi, T.M., and Kirschner, M.W. 1988. The presence of fibroblast growth factor in the frog egg: its role as a natural mesoderm inducer. Science 242:1053‐1056.
   Kofron, M., Klein, P., Zhang, F., Houston, D.W., Schaible, K., Wylie, C., and Heasman, J. 2001. The role of maternal axin in patterning the Xenopus embryo. Dev. Biol. 237:183‐201.
   Koide, T., Hayata, T., and Cho, K.W. 2005. Xenopus as a model system to study transcriptional regulatory networks. Proc. Natl. Acad. Sci. U.S.A. 102:4943‐4948.
   Kroll, K.L. and Amaya, E. 1996. Transgenic Xenopus embryos from sperm nuclear transplantations reveal FGF signaling requirements during gastrulation. Development 122:3173‐3183.
   Kubo, A., Shinozaki, K., Shannon, J.M., Kouskoff, V., Kennedy, M., Woo, S., Fehling, H.J., and Keller, G. 2004. Development of definitive endoderm from embryonic stem cells in culture. Development 131:1651‐1662.
   LaBonne, C., Burke, B., and Whitman, M. 1995. Role of MAP kinase in mesoderm induction and axial patterning during Xenopus development. Development 121:1475‐1486.
   Ladher, R., Mohun, T.J., Smith, J.C., and Snape, A.M. 1996. Xom: A Xenopus homeobox gene that mediates the early effects of BMP‐4. Development 122:2385‐2394.
   Latinkic, B.V. and Smith, J.C. 1999. Goosecoid and mix.1 repress Brachyury expression and are required for head formation in Xenopus. Development 126:1769‐1779.
   Latinkic, B.V., Umbhauer, M., Neal, K., Lerchner, W., Smith, J.C., and Cunliffe, V. 1997. The Xenopus Brachyury promoter is activated by FGF and low concentrations of activin and suppressed by high concentrations of activin and by paired‐type homeodomain proteins. Genes Dev. 11:3265‐3276.
   Launay, C., Fromentoux, V., Shi, D.L., and Boucaut, J.C. 1996. A truncated FGF receptor blocks neural induction by endogenous Xenopus inducers. Development 122:869‐880.
   Lawson, A. and Schoenwolf, G.C. 2003. Epiblast and primitive‐streak origins of the endoderm in the gastrulating chick embryo. Development 130:3491‐3501.
   Lee, T.I., Rinaldi, N.J., Robert, F., Odom, D.T., Bar‐Joseph, Z., Gerber, G.K., Hannett, N.M., Harbison, C.T., Thompson, C.M., Simon, I., Zeitlinger, J., Jennings, E.G., Murry, H.L., Gordon, D.B., Ren, B., Wyrick, J.J., Tagne, J.B., Volkert, T.L., Fraenkel, E., Gifford, D.K., and Young, R.A. 2002. Transcriptional regulatory networks in Saccharomyces cerevisiae. Science 298:799‐804.
   Lemaire, P., Darras, S., Caillol, D., and Kodjabachian, L. 1998. A role for the vegetally expressed Xenopus gene Mix.1 in endoderm formation and in the restriction of mesoderm to the marginal zone. Development 125:2371‐2380.
   Lemaire, P., Garrett, N., and Gurdon, J.B. 1995. Expression cloning of Siamois, a Xenopus homeobox gene expressed in dorsal vegetal cells of blastulae and able to induce a complete secondary axis. Cell 81:85‐94.
   Lerchner, W., Latinkic, B.V., Remacle, J.E., Huylebroeck, D., and Smith, J.C. 2000. Region‐specific activation of the Xenopus Brachyury promoter involves active repression in ectoderm and endoderm: A study using transgenic frog embryos. Development 127:2729‐2739.
   Leyns, L., Bouwmeester, T., Kim, S.H., Piccolo, S., and De Robertis, E.M. 1997. Frzb‐1 is a secreted antagonist of Wnt signaling expressed in the Spemann organizer. Cell 88:747‐756.
   Li, F., Lu, S., Vida, L., Thomson, J.A., and Honig, G.R. 2001. Bone morphogenetic protein 4 induces efficient hematopoietic differentiation of rhesus monkey embryonic stem cells in vitro. Blood 98:335‐342.
   Lindsley, R.C., Gill, J.G., Kyba, M., Murphy, T.L., and Murphy, K.M. 2006. Canonical Wnt signaling is required for development of embryonic stem cell‐derived mesoderm. Development 133:3787‐3796.
   Linker, C. and Stern, C.D. 2004. Neural induction requires BMP inhibition only as a late step, and involves signals other than FGF and Wnt antagonists. Development 131:5671‐5681.
   Liu, P., Wakamiya, M., Shea, M.J., Albrecht, U., Behringer, R.R., and Bradley, A. 1999. Requirement for Wnt3 in vertebrate axis formation. Nat. Genet. 22:361‐365.
   Loose, M. and Patient, R. 2004. A genetic regulatory network for Xenopus mesendoderm formation. Dev. Biol. 271:467‐478.
   Lowe, L.A., Yamada, S., and Kuehn, M.R. 2001. Genetic dissection of nodal function in patterning the mouse embryo. Development 128:1831‐1843.
   Lustig, K.D., Kroll, K.L., Sun, E.E., and Kirschner, M.W. 1996. Expression cloning of a Xenopus T‐related gene (Xombi) involved in mesodermal patterning and blastopore lip formation. Development 122:4001‐4012.
   Mangan, S., Zaslaver, A., and Alon, U. 2003. The coherent feedforward loop serves as a sign‐sensitive delay element in transcription networks. J. Mol. Biol. 334:197‐204.
   Martin, G.R. 1981. Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells. Proc. Natl. Acad. Sci. U.S.A. 78:7634‐7638.
   McMahon, A.P. and Moon, R.T. 1989. Ectopic expression of the proto‐oncogene int‐1 in Xenopus embryos leads to duplication of the embryonic axis. Cell 58:1075‐1084.
   Melby, A.E., Beach, C., Mullins, M., and Kimelman, D. 2000. Patterning the early zebrafish by the opposing actions of bozozok and vox/vent. Dev. Biol. 224:275‐285.
   Messenger, N.J., Kabitschke, C., Andrews, R., Grimmer, D., Miguel, R.N., Blundell, T.L., Smith, J.C., and Wardle, F.C. 2005. Functional specificity of the Xenopus T‐domain protein brachyury is conferred by its ability to interact with smad1. Dev. Cell 8:599‐610.
   Meyer, J.S., Katz, M.L., Maruniak, J.A., and Kirk, M.D. 2004. Neural differentiation of mouse embryonic stem cells in vitro and after transplantation into eyes of mutant mice with rapid retinal degeneration. Brain Res. 1014:131‐144.
   Milo, R., Shen‐Orr, S., Itzkovitz, S., Kashtan, N., Chklovskii, D., and Alon, U. 2002. Network motifs: Simple building blocks of complex networks. Science 298:824‐827.
   Mishina, Y., Suzuki, A., Ueno, N., and Behringer, R.R. 1995. Bmpr encodes a type I bone morphogenetic protein receptor that is essential for gastrulation during mouse embryogenesis. Genes Dev. 9:3027‐3037.
   Nagy, A., Rossant, J., Nagy, R., Abramow‐Newerly, W., and Roder, J.C. 1993. Derivation of completely cell culture‐derived mice from early‐passage embryonic stem cells. Proc. Natl. Acad. Sci. U.S.A. 90:8424‐8428.
   Neave, B., Holder, N., and Patient, R. 1997. A graded response to BMP‐4 spatially coordinates patterning of the mesoderm and ectoderm in the zebrafish. Mech. Dev. 62:183‐195.
   Nerlov, C., Querfurth, E., Kulessa, H., and Graf, T. 2000. GATA‐1 interacts with the myeloid PU.1 transcription factor and represses PU.1‐dependent transcription. Blood 95:2543‐2551.
   Ng, E.S., Azzola, L., Sourris, K., Robb, L., Stanley, E.G., and Elefanty, A.G. 2005. The primitive streak gene Mixl1 is required for efficient haematopoiesis and BMP4‐induced ventral mesoderm patterning in differentiating ES cells. Development 132:873‐884.
   Nieuwkoop, P.D. 1969. The formation of mesoderm in Urodelean amphibians. I. Induction by the endoderm. Wilhelm Roux's Arch. EntwMech. Org. 162:341‐373.
   Norton, W.H., Mangoli, M., Lele, Z., Pogoda, H.M., Diamond, B., Mercurio, S., Russell, C., Teraoka, H., Stickney, H.L., Rauch, G.J., Heisenberg, C.P., Houart, C., Schilling, T.F., Frohnhoefer, H.G., Rastegar, S., Neumann, C.J., Gardiner, R.M., Strahle, U., Geisler, R., Rees, M., Talbot, W.S., and Wilson, S.W. 2005. Monorail/Foxa2 regulates floorplate differentiation and specification of oligodendrocytes, serotonergic raphe neurones and cranial motoneurones. Development 132:645‐658.
   Oh, S.W., Mukhopadhyay, A., Dixit, B.L., Raha, T., Green, M.R., and Tissenbaum, H.A. 2006. Identification of direct DAF‐16 targets controlling longevity, metabolism and diapause by chromatin immunoprecipitation. Nat. Genet. 38:251‐257.
   Okada, Y., Shimazaki, T., Sobue, G., and Okano, H. 2004. Retinoic‐acid‐concentration‐dependent acquisition of neural cell identity during in vitro differentiation of mouse embryonic stem cells. Dev. Biol. 275:124‐142.
   Onichtchouk, D., Gawantka, V., Dosch, R., Delius, H., Hirschfeld, K., Blumenstock, C., and Niehrs, C. 1996. The Xvent‐2 homeobox gene is part of the BMP‐4 signalling pathway controlling [correction of controling] dorsoventral patterning of Xenopus mesoderm. Development 122:3045‐3053.
   Osada, S.I., Saijoh, Y., Frisch, A., Yeo, C.Y., Adachi, H., Watanabe, M., Whitman, M., Hamada, H., and Wright, C.V. 2000. Activin/nodal responsiveness and asymmetric expression of a Xenopus nodal‐related gene converge on a FAST‐regulated module in intron 1. Development 127:2503‐2514.
   Papin, C. and Smith, J.C. 2000. Gradual refinement of activin‐induced thresholds requires protein synthesis. Dev. Biol. 217:166‐172.
   Park, C., Afrikanova, I., Chung, Y.S., Zhang, W.J., Arentson, E., Fong Gh, G., Rosendahl, A., and Choi, K. 2004. A hierarchical order of factors in the generation of FLK1‐ and SCL‐expressing hematopoietic and endothelial progenitors from embryonic stem cells. Development 131:2749‐2762.
   Pera, M.F., Andrade, J., Houssami, S., Reubinoff, B., Trounson, A., Stanley, E.G., Ward‐van Oostwaard, D., and Mummery, C. 2004. Regulation of human embryonic stem cell differentiation by BMP‐2 and its antagonist noggin. J. Cell Sci. 117:1269‐1280.
   Piccolo, S., Agius, E., Leyns, L., Bhattacharyya, S., Grunz, H., Bouwmeester, T., and De Robertis, E.M. 1999. The head inducer Cerberus is a multifunctional antagonist of Nodal, BMP and Wnt signals. Nature 397:707‐710.
   Piepenburg, O., Grimmer, D., Williams, P.H., and Smith, J.C. 2004. Activin redux: Specification of mesodermal pattern in Xenopus by graded concentrations of endogenous activin B. Development 131:4977‐4986.
   Rao, Y. 1994. Conversion of a mesodermalizing molecule, the Xenopus Brachyury gene, into a neuralizing factor. Genes Dev. 8:939‐947.
   Reiter, J.F., Alexander, J., Rodaway, A., Yelon, D., Patient, R., Holder, N., and Stainier, D.Y. 1999. Gata5 is required for the development of the heart and endoderm in zebrafish. Genes Dev. 13:2983‐2995.
   Reiter, J.F., Kikuchi, Y., and Stainier, D.Y. 2001. Multiple roles for Gata5 in zebrafish endoderm formation. Development 128:125‐135.
   Rhodes, J., Hagen, A., Hsu, K., Deng, M., Liu, T.X., Look, A.T., and Kanki, J.P. 2005. Interplay of pu.1 and gata1 determines myelo‐erythroid progenitor cell fate in zebrafish. Dev. Cell 8:97‐108.
   Rodaway, A., and Patient, R. 2001. Mesendoderm: An ancient germ layer? Cell 105:169‐172.
   Rodaway, A., Takeda, H., Koshida, S., Broadbent, J., Price, B., Smith, J.C., Patient, R., and Holder, N. 1999. Induction of the mesendoderm in the zebrafish germ ring by yolk cell‐derived TGF‐β family signals and discrimination of mesoderm and endoderm by FGF. Development 126:3067‐3078.
   Saka, Y., Tada, M., and Smith, J.C. 2000. A screen for targets of the Xenopus T‐box gene Xbra. Mech. Dev. 93:27‐39.
   Sasai, Y., Lu, B., Piccolo, S., and De Robertis, E.M. 1996. Endoderm induction by the organizer‐secreted factors chordin and noggin in Xenopus animal caps. EMBO J. 15:4547‐4555.
   Sasai, Y., Lu, B., Steinbeisser, H., Geissert, D., Gont, L.K., and De Robertis, E.M. 1994. Xenopus chordin: A novel dorsalizing factor activated by organizer‐specific homeobox genes. Cell 79:779‐790.
   Scharf, S.R. and Gerhart, J.C. 1980. Determination of the dorsal‐ventral axis in eggs of Xenopus laevis: Complete rescue of uv‐impaired eggs by oblique orientation before first cleavage. Dev. Biol. 79:181‐198.
   Schier, A.F. 2003. Nodal signaling in vertebrate development. Annu. Rev. Cell Dev. Biol. 19:589‐621.
   Schier, A.F., Neuhauss, S.C., Helde, K.A., Talbot, W.S., and Driever, W. 1997. The one‐eyed pinhead gene functions in mesoderm and endoderm formation in zebrafish and interacts with no tail. Development 124:327‐342.
   Schmidt, J.E., von Dassow, G., and Kimelman, D. 1996. Regulation of dorsal‐ventral patterning: the ventralizing effects of the novel Xenopus homeobox gene Vox. Development 122:1711‐1721.
   Sinner, D., Kirilenko, P., Rankin, S., Wei, E., Howard, L., Kofron, M., Heasman, J., Woodland, H.R., and Zorn, A.M. 2006. Global analysis of the transcriptional network controlling Xenopus endoderm formation. Development 133:1955‐1966.
   Sinner, D., Rankin, S., Lee, M., and Zorn, A.M. 2004. Sox17 and beta‐catenin cooperate to regulate the transcription of endodermal genes. Development 131:3069‐3080.
   Slack, J.M., Darlington, B.G., Heath, J.K., and Godsave, S.F. 1987. Mesoderm induction in early Xenopus embryos by heparin‐binding growth factors. Nature 326:197‐200.
   Smith, J.C. 2001. Making mesoderm?upstream and downstream of Xbra. Int. J. Dev. Biol. 45:219‐224.
   Smith, J.C., Price, B.M., Van Nimmen, K., and Huylebroeck, D. 1990. Identification of a potent Xenopus mesoderm‐inducing factor as a homologue of activin A. Nature 345:729‐731.
   Smith, J.C. and Slack, J.M. 1983. Dorsalization and neural induction: Properties of the organizer in Xenopus laevis. J. Embryol. Exp. Morphol. 78:299‐317.
   Smith, W.C. and Harland, R.M. 1991. Injected Xwnt‐8 RNA acts early in Xenopus embryos to promote formation of a vegetal dorsalizing center. Cell 67:753‐765.
   Smith, W.C. and Harland, R.M. 1992. Expression cloning of noggin, a new dorsalizing factor localized to the Spemann organizer in Xenopus embryos. Cell 70:829‐840.
   Smukler, S.R., Runciman, S.B., Xu, S., and van der Kooy, D. 2006. Embryonic stem cells assume a primitive neural stem cell fate in the absence of extrinsic influences. J. Cell Biol. 172:79‐90.
   Sokol, S., Christian, J.L., Moon, R.T., and Melton, D.A. 1991. Injected wnt RNA induces a complete body axis in Xenopus embryos. Cell 67:741‐752.
   Song, J., Oh, S.P., Schrewe, H., Nomura, M., Lei, H., Okano, M., Gridley, T., and Li, E. 1999. The type II activin receptors are essential for egg cylinder growth, gastrulation, and rostral head development in mice. Dev. Biol. 213:157‐169.
   Spemann, H. 1938. Embryonic Development and Induction, 1988 (reprinted) ed: Garland Publishing, Inc. New York and London.
   Stennard, F., Carnac, G., and Gurdon, J.B. 1996. The Xenopus T‐box gene, Antipodean, encodes a vegetally localised maternal mRNA and can trigger mesoderm formation. Development 122:4179‐4188.
   Su, H.L., Muguruma, K., Matsuo‐Takasaki, M., Kengaku, M., Watanabe, K., and Sasai, Y. 2006. Generation of cerebellar neuron precursors from embryonic stem cells. Dev. Biol. 290:287‐296.
   Sudarwati, S. and Nieuwkoop, P.D. 1971. Mesoderm formation in the Anuran Xenopus laevis (Daudin). Roux Arch. Dev. Biol. 166:189‐204.
   Sun, B.I., Bush, S.M., Collins‐Racie, L.A., LaVallie, E.R., DiBlasio‐Smith, E.A., Wolfman, N.M., McCoy, J.M., and Sive, H.L. 1999a. derrière: a TGF‐beta family member required for posterior development in Xenopus. Development 126:1467‐1482.
   Sun, X., Meyers, E.N., Lewandoski, M., and Martin, G.R. 1999b. Targeted disruption of Fgf8 causes failure of cell migration in the gastrulating mouse embryo. Genes Dev. 13:1834‐1846.
   Suri, C., Haremaki, T., and Weinstein, D.C. 2004. Inhibition of mesodermal fate by Xenopus HNF3beta/FoxA2. Dev. Biol. 265:90‐104.
   Swiers, G., Patient, R., and Loose, M. 2006. Genetic regulatory networks programming hematopoietic stem cells and erythroid lineage specification. Dev. Biol. 294:525‐540.
   Tada, M., Casey, E.S., Fairclough, L., and Smith, J.C. 1998. Bix1, a direct target of Xenopus T‐box genes, causes formation of ventral mesoderm and endoderm. Development 125:3997‐4006.
   Tada, M. and Smith, J.C. 2000. Xwnt11 is a target of Xenopus Brachyury: Regulation of gastrulation movements via Dishevelled, but not through the canonical Wnt pathway. Development 127:2227‐2238.
   Tada, S., Era, T., Furusawa, C., Sakurai, H., Nishikawa, S., Kinoshita, M., Nakao, K., and Chiba, T. 2005. Characterization of mesendoderm: A diverging point of the definitive endoderm and mesoderm in embryonic stem cell differentiation culture. Development 132:4363‐4374.
   Takahashi, S., Yokota, C., Takano, K., Tanegashima, K., Onuma, Y., Goto, J., and Asashima, M. 2000. Two novel nodal‐related genes initiate early inductive events in Xenopus Nieuwkoop center. Development 127:5319‐5329.
   Tam, P. P., Kanai‐Azuma, M., and Kanai, Y. 2003. Early endoderm development in vertebrates: Lineage differentiation and morphogenetic function. Curr. Opin. Genet. Dev. 13:393‐400.
   Tam, P.P., Loebel, D.A., and Tanaka, S.S. 2006. Building the mouse gastrula: Signals, asymmetry and lineages. Curr. Opin. Genet. Dev. 16:419‐425.
   Tao, Q., Yokota, C., Puck, H., Kofron, M., Birsoy, B., Yan, D., Asashima, M., Wylie, C.C., Lin, X., and Heasman, J. 2005. Maternal wnt11 activates the canonical wnt signaling pathway required for axis formation in Xenopus embryos. Cell 120:857‐871.
   Taverner, N.V., Kofron, M., Shin, Y., Kabitschke, C., Gilchrist, M.J., Wylie, C., Cho, K.W., Heasman, J., and Smith, J.C. 2005. Microarray‐based identification of VegT targets in Xenopus. Mech. Dev. 122:333‐354.
   Taverner, N.V., Smith, J.C., and Wardle, F.C. 2004. Identifying transcriptional targets. Genome Biol. 5:210.
   Thomsen, G., Woolf, T., Whitman, M., Sokol, S., Vaughan, J., Vale, W., and Melton, D.A. 1990. Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell 63:485‐493.
   Thomsen, G.H. and Melton, D.A. 1993. Processed Vg1 protein is an axial mesoderm inducer in Xenopus. Cell 74:433‐441.
   Toyoizumi, R., Ogasawara, T., Takeuchi, S., and Mogi, K. 2005. Xenopus nodal related‐1 is indispensable only for left‐right axis determination. Int. J. Dev. Biol. 49:923‐938.
   Trindade, M., Tada, M., and Smith, J.C. 1999. DNA‐binding specificity and embryological function of Xom (Xvent‐2). Dev. Biol. 216:442‐456.
   Tropepe, V., Hitoshi, S., Sirard, C., Mak, T.W., Rossant, J., and van der Kooy, D. 2001. Direct neural fate specification from embryonic stem cells: A primitive mammalian neural stem cell stage acquired through a default mechanism. Neuron 30:65‐78.
   Umbhauer, M., Marshall, C.J., Mason, C.S., Old, R.W., and Smith, J.C. 1995. Mesoderm induction in Xenopus caused by activation of MAP kinase. Nature 376:58‐62.
   van Steensel, B., Delrow, J., and Henikoff, S. 2001. Chromatin profiling using targeted DNA adenine methyltransferase. Nat. Genet. 27:304‐308.
   Varlet, I., Collignon, J., and Robertson, E.J. 1997. Nodal expression in the primitive endoderm is required for specification of the anterior axis during mouse gastrulation. Development 124:1033‐1044.
   Verani, R., Cappuccio, I., Spinsanti, P., Gradini, R., Caruso, A., Magnotti, M.C., Motolese, M., Nicoletti, F., and Melchiorri, D. 2006. Expression of the Wnt inhibitor Dickkopf‐1 is required for the induction of neural markers in mouse embryonic stem cells differentiating in response to retinoic acid. J. Neurochem. 100:242‐250.
   Vignali, R., Poggi, L., Madeddu, F., and Barsacchi, G. 2000. HNF1(beta) is required for mesoderm induction in the Xenopus embryo. Development 127:1455‐1465.
   Vincent, J.P. and Gerhart, J.C. 1987. Subcortical rotation in Xenopus eggs: An early step in embryonic axis specification. Dev. Biol. 123:526‐539.
   Wardle, F.C. and Smith, J.C. 2004. Refinement of gene expression patterns in the early Xenopus embryo. Development 131:4687‐4696.
   Wardle, F.C., Odom, D.T., Bell, G.W., Yuan, B., Danford, T.W., Wiellette, E.L., Herbolsheimer, E., Sive, H.L., Young, R.A., and Smith, J.C. 2006. Zebrafish promoter microarrays identify actively transcribed embryonic genes. Genome Biol. 7:R71.
   Watabe, T., Kim, S., Candia, A., Rothbacher, U., Hashimoto, C., Inoue, K., and Cho, K.W. 1995. Molecular mechanisms of Spemann's organizer formation: conserved growth factor synergy between Xenopus and mouse. Genes Dev. 9:3038‐3050.
   Watanabe, K., Kamiya, D., Nishiyama, A., Katayama, T., Nozaki, S., Kawasaki, H., Watanabe, Y., Mizuseki, K., and Sasai, Y. 2005. Directed differentiation of telencephalic precursors from embryonic stem cells. Nat. Neurosci. 8:288‐296.
   Weber, H., Symes, C.E., Walmsley, M.E., Rodaway, A.R., and Patient, R.K. 2000. A role for GATA5 in Xenopus endoderm specification. Development 127:4345‐4360.
   Weeks, D.L. and Melton, D.A. 1987. A maternal mRNA localized to the vegetal hemisphere in Xenopus eggs codes for a growth factor related to TGF‐beta. Cell 51:861‐867.
   Wei, C.L., Wu, Q., Vega, V.B., Chiu, K.P., Ng, P., Zhang, T., Shahab, A., Yong, H.C., Fu, Y., Weng, Z., Liu, Z., Zhao, X.D., Chew, J.L., Lee, Y.L., Kuznetsov, V.A., Sung, W.K., Miller, L.D., Lim B, Liu, E.T., Yu, Q., Ng, H.H., and Ruan, Y. 2006. A global map of p53 transcription‐factor binding sites in the human genome. Cell 124:207‐219.
   Weinmann, A. S., Bartley, S. M., Zhang, T., Zhang, M. Q., and Farnham, P. J. 2001. Use of chromatin immunoprecipitation to clone novel E2F target promoters. Mol. Cell Biol. 21:6820‐6832.
   Wild, W., Pogge von Strandmann, E., Nastos, A., Senkel, S., Lingott‐Frieg, A., Bulman, M., Bingham, C., Ellard, S., Hattersley, A.T., and Ryffel, G.U. 2000. The mutated human gene encoding hepatocyte nuclear factor 1β inhibits kidney formation in developing Xenopus embryos. Proc. Natl. Acad. Sci. U.S.A. 97:4695‐4700.
   Wiles, M.V. and Johansson, B.M. 1997. Analysis of factors controlling primary germ layer formation and early hematopoiesis using embryonic stem cell in vitro differentiation. Leukemia 11:454‐456.
   Wiles, M.V. and Johansson, B. M. 1999. Embryonic stem cell development in a chemically defined medium. Exp. Cell Res. 247:241‐248.
   Williams, P.H., Hagemann, A., Gonzalez‐Gaitan, M., and Smith, J.C. 2004. Visualizing long‐range movement of the morphogen Xnr2 in the Xenopus embryo. Curr. Biol. 14:1916‐1923.
   Winnier, G., Blessing, M., Labosky, P.A., and Hogan, B.L. 1995. Bone morphogenetic protein‐4 is required for mesoderm formation and patterning in the mouse. Genes Dev. 9:2105‐2116.
   Xanthos, J.B., Kofron, M., Wylie, C., and Heasman, J. 2001. Maternal VegT is the initiator of a molecular network specifying endoderm in Xenopus laevis. Development 128:167‐180.
   Yamaguchi, T.P., Harpal, K., Henkemeyer, M., and Rossant, J. 1994. fgfr‐1 is required for embryonic growth and mesodermal patterning during mouse gastrulation. Genes Dev. 8:3032‐3044.
   Yang, J., Tan, C., Darken, R.S., Wilson, P.A., and Klein, P.S. 2002. Beta‐catenin/Tcf‐regulated transcription prior to the midblastula transition. Development 129:5743‐5752.
   Yasunaga, M., Tada, S., Torikai‐Nishikawa, S., Nakano, Y., Okada, M., Jakt, L.M., Nishikawa, S., Chiba, T., and Era, T. 2005. Induction and monitoring of definitive and visceral endoderm differentiation of mouse ES cells. Nat. Biotechnol. 23:1542‐1550.
   Ying, Q.L., Stavridis, M., Griffiths, D., Li, M., and Smith, A. 2003. Conversion of embryonic stem cells into neuroectodermal precursors in adherent monoculture. Nat. Biotechnol. 21:183‐186.
   Zernicka‐Goetz, M. 2006. The first cell‐fate decisions in the mouse embryo: Destiny is a matter of both chance and choice. Curr. Opin. Genet. Dev. 16:406‐412.
   Zhang, J., Houston, D.W., King, M.L., Payne, C., Wylie, C., and Heasman, J. 1998. The role of maternal VegT in establishing the primary germ layers in Xenopus embryos. Cell 94:515‐524.
   Zhang, J. and King, M.L. 1996. Xenopus VegT RNA is localized to the vegetal cortex during oogenesis and encodes a novel T‐box transcription factor involved in mesodermal patterning. Development 122:4119‐4129.
   Zhang, P., Zhang, X., Iwama, A., Yu, C., Smith, K.A., Mueller, B.U., Narravula, S., Torbett, B.E., Orkin, S.H., and Tenen, D.G. 2000. PU.1 inhibits GATA‐1 function and erythroid differentiation by blocking GATA‐1 DNA binding. Blood 96:2641‐2648.
GO TO THE FULL PROTOCOL:
PDF or HTML at Wiley Online Library