the neural axis. Development. 116,81-93.
Ryan, PJ. and G illespie, L.L. (1994) Phosphorylation of phospholipase C gamma 1 and its association w ith the FGF receptor is developm entally regulated and occurs during mesoderm induction in Xenopus laevis, Dev. Biol. 1 6 6 ,101-11.
Salic, A. N ., Kroll, K. L., Evans, L. M. and Kirschner, M. W. (1997) Sizzled: a secreted Xwnt8 antagonist expressed in the ventral m arginal zone of Xenopus embryos. Development 124,4739-48.
Sam brook, J., Fritsch, E.F. and M aniatis, T. (1989) M olecular cloning-A Laboratory manual. Second Edition, Cold Spring Harbor Laboratory Press.
Sasai, Y., Lu, B., Piccolo, S. and D e Robertis, E. M. (1996) Endoderm induction by the organizer-secreted factors chordin and noggin in Xenopus animal caps.
EM BO J 15, 4547-55.
Sasai, Y., Lu, B., Steinbeisser, H. and D e Robertis, E. M. (1995) Regulation of neural induction by the Chd and Bmp-4 antagonistic patterning signals in Xenopus. Nature 377, 757.
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, 779-90.
Saw in, K. E., LeG uellec, K., Philippe, M. and M itchison, T. J. (1992) Mitotic spindle organization by a plus-end-directed microtubule motor. N ature 359, 540- 3.
Schneider, V. A. and M ercola, M. (1999) Spatially distinct head and h eart inducers within the Xenopus organizer region. Curr Biol 9, 800-9.
Schultz, J., Copley, R. R., Doerks, T., Pouting, C. P. and Bork, P. (2000) SMART: a w eb-based tool for the study of genetically mobile domains. Nucleic Acids Res
28, 231-4.
Scott, I. C., Blitz, I. L., Pappano, W. N., Maas, S. A., Cho, K. W. and G reenspan, D. S. (2001) Homologues of Twisted gastrulation are extracellular cofactors in antagonism of BMP signalling. Nature 410,475-8.
Settlem an, J. (2000) Getting in shape with Rho. N at Cell Biol 2, E7-9.
S hih , J. and Fraser, S.E. (1996) C haracterizing the zebrafish organizer: microsurgical analysis at the early-shield stage. Development 122,1313-1322.
Shih, J. and Keller, R. (1992) Cell motility driving mediolateral intercalation in explants of Xenopus laevis. Development 116,901-14.
Slusarski, D. C., Corces, V. G. and Moon, R. T. (1997a) Interaction of Wnt and a Frizzled hom ologue triggers G-protein-linked phosphatidylinositol signalling.
N ature 390, 410-3.
S lu sarsk i, D. C., Y ang-Snyder, J., Busa, W. B. and M oon, R. T. (1997b) M odulation of embryonic intracellular Ca2+ signaling by Wnt-5A. Dev Biol 182, 114-20.
Sm ith, J. C., Price, B. M., Green, J. B., Weigel, D. and H errm ann, B. G. (1991) Expression of a Xenopus hom olog of Brachyury (T) is an im m ediate-early response to mesoderm induction. Cell 67, 79-87.
Sm ith, W. C. and H arland, R. M. (1991) Injected Xwnt-8 RNA acts early in Xenopus embryos to promote formation of a vegetal dorsalizing center. Cell 67, 753-65.
Sm ith, W. C. and H arland, R. M. (1992) Expression cloning of noggin, a new dorsalizing factor localized to the Spemann organizer in Xenopus embryos. Cell
Sm ith, W. C., M cKendry, R., Ribisi, S., Jr. and H arland, R. M. (1995) A nodal- related gene defines a physical and functional dom ain w ithin the Spem ann organizer. Cell 82, 37-46.
Spem ann, H. (1918) Ueber die D eterm ination der Ersten O rgananlagen des Amphibienembryo. i-iV. W. R oux' Arch. Entwicklungsmech. Organ. 43,448-555. S pem ann, H. (1931) Ueber den Abteil von Im plantat und W irtskeime an der O rientierung und Beschaffenheit der induzierten Em bryonanlagen. W. R o u x ' Arch. Entwicklungsmech. Organ. 123, 389-517
Spem ann, H. (1938) "Embryonic Development and Induction". Yale University Press, New Haven. 1938,401pp.
Spem ann, H. and M angold, H. (1924) Ueber Induktion von Embryonalanlagen durch Im plantation artfrem der Organisatoren. Wilhelm Roux Arch. Entw. Mech. Org. 100, 599-638.
Steinbeisser, H., Fainsod, A., N iehrs, C , Sasai, Y. and De Robertis, E. M. (1995) The role of gsc and BMP-4 in dorsal-ventral patterning of the marginal zone in Xenopus: a loss-of-function study using antisense RNA. Emho J 14, 5230-43.
S tennard, P., Carnac, G. and G urdon, J. B. (1996) The Xenopus T-box gene. A ntipodean, encodes a vegetally localised m aternal mRNA and can trigger mesoderm formation. Development 122,4179-88.
Sun, B. I., Bush, S. M., Collins-Racie, L. A., LaVallie, E. R., DiBlasio-Smith, E. A., W olfm an, N. M., McCoy, J. M. & Sive, H. L. (1999a) derriere: a TGF-beta family member required for posterior developm ent in Xenopus. Development 126, 1467-82.
Sun, X., M eyers, E. N., Lew andoski, M. and M artin, G. R. (1999b) T arg eted disruption of Fgf8 causes failure of cell m igration in the gastrulating mouse embryo. Genes Dev 13,1834-46.
Tada, M. and Sm ith, J. C. (2000) X w n tll is a target of Xenopus Brachyury: regulation of gastrulation m ovem ents via Dishevelled, b u t not through the canonical Wnt pathway. Development 127, 2227-38.
Tada, M., Casey, E.S., Fairclough, L and Smith, J.C. (1998) B ix l, a direct target of
X en o p u s T-box genes, causes form ation of ventral m esoderm and endoderm .
Development 125,3997-4006.
Taira, M., Jamrich, M., Good, P J. and D aw id, I. B. (1992). The LIM dom ain- containing homeo box gene X lim -1 is expressed specifically in the organizer region of Xenopus gastrula embryos. Genes Dev. 6, 356-366.
Tamai, K., Semenov, M., Kato, Y., Spokony, R., Liu, C., Katsuyama, Y., Hess, F., Saint-Jeannet, J.P., He, X. (2000) LDL-receptor-related proteins in W nt signal transduction Nature, 407,530-5.
T annahill, D. and M elton, D. A. (1989) Localized synthesis of the Vgl protein during early Xenopus development. Development 106, 775-85.
Thom as, P. and B eddington, R. (1996) A nterior prim itive endoderm m ay be responsible for patterning the anterior neural plate in the mouse embryo. C urr Biol 6,1487-96.
Ungar, A. R., Kelly, G. M. and Moon, R. T. (1995) Wnt4 affects morphogenesis w hen misexpressed in the zebrafish embryo. Mech Dev 52,153-64.
V arlet, I., C ollignon, J. and R obertson, E. J. (1997) nodal expression in the prim itive endoderm is required for specification of the anterior axis during mouse gastrulation. Development 124,1033-44.
V ignali, R., Poggi, L., M adeddu, F. and Barsacchi, G. (2000) H N Fl(beta) is required for mesoderm induction in the Xenopus embryo. Development, 127, 1455- 1465.
Vincent, J. P., Oster, G. F. and G erhart, J. C. (1986) Kinematics of gray crescent formation in Xenopus eggs: the displacement of subcortical cytoplasm relative to the egg surface. Dev Biol 113,484-500.
W addington, C. H. (1933) Induction by the prim itive streak and its derivatives in the chick. /. Exp. Biol 10, 38-46.
W allingford, J. B., R owning, B. A., V ogeli, K. M., Rothbacher, U., Fraser, S. E. and Harland, R. M. (2000) Dishevelled controls cell polarity during Xenopus gastrulation. Nature 405, 81-5.
W allingford, J. B., V o g eli, K. M. and Harland, R. M. (2001) R egulation of convergent extension in Xenopus by Wnt5a and Frizzled-8 is independent of the canonical Wnt pathway. In t J Dev Biol 45, 225-7.
Wang, S., Krinks, M., Lin, K,, Luyten, F. P. and M oos, M., Jr. (1997) Frzb, a secreted protein expressed in the Spemann organizer, binds and inhibits Wnt-8.
Cell 88, 757-66.
W eeks, D. L. and M elton, D. A. (1987) A m aternal mRNA localized to the vegetal hem isphere in Xenopus eggs codes for a grow th factor related to TGF- beta. Cell 51, 861-7.
W ehrli, M., D ougan, S T., C aldw ell, K., O'Keefe, L., Schwartz, S., V aizel- O hayon, D ., Schejter, E., Tom linson, A., DiN ardo, S. (2000) arrow encodes an LDL-receptor-related proteinessential for Wingless signalling. Nature 407,527-30. W ilson , P. and K eller, R. (1991) Cell rearrangem ent during gastrulation of Xenopus: direct observation of cultured explants. Development 112, 289-300.
W ilson, V., M anson, L., Skarnes, W. C. and Beddington, R. S. (1995) The T gene is necessary for norm al m esoderm al m orphogenetic cell m ovem ents during gastrulation. Development 121, 877-86.
W inklbauer, R. and Schurfeld, M. (1999) Vegetal rotation, a new gastrulation m ovem ent involved in the internalization of the m esoderm and endoderm in Xenopus. Development 126,3703-13.
W oodland, H. R. and Jones, E. A. (1987) The developm ent of an assay to detect mRNAs that affect early development. Development 101, 925-30.
W unnenberg-Stapleton, K., Blitz, I. L., H ashim oto, C. and Cho, K. W. (1999) Involvement of the small GTPases XRhoA and XRndl in cell adhesion and head formation in early Xenopus development. Development 126,5339-51.
W ylie, C., Kofron, M., Payne, C., Anderson, R., H osobuchi, M., Joseph, E. and Heasm an, J. (1996) M aternal beta-catenin establishes a dorsal signal' in early Xenopus embryos. Development 122, 2987-96.
Xanthos, J. B., Kofron, M., W ylie, C. and Heasman, J. (2001) M aternal VegT is the initiator of a molecular netw ork specifying endoderm in Xenopus laevis.
Development 128,167-80.
Yamaguchi, T. P., Harpal, K., H enkem eyer, M. and Rossant, J. (1994) fgfr-1 is required for embryonic grow th and m esoderm al patterning du rin g m ouse gastrulation. Genes Dev 8, 3032-44.
Yamamoto, A., Amacher, S. L., Kim, S. H., Geissert, D., Kimmel, C. B. and De Robertis, E. M. (1998) Zebrafish paraxial protocadherin is a dow nstream target of spadetail involved in m orphogenesis of gastrula mesoderm. Developm ent 125, 3389-97.
Yasuo, H. and Lemaire, P. (2001) Generation of the germ layers along the animal- vegetal axis in Xenopus laevis. Int J Dev Biol 45, 229-35.
Zhang, J., H ouston, D. W., King, M. L., Payne, C., W ylie, C. and Heasman, J, (1998) The role of m aternal VegT in establishing the prim ary germ layers in Xenopus embryos. Cell 94, 515-24.
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 122,4119-29.
Zimmerman, L. B., De Jesus-Escobar, J. M. and Harland, R. M. (1996) T h e Spem ann organizer signal noggin binds and inactivates bone m orphogenetic protein 4. Cell 86, 599-606.
Zorn, A. M., Butler, K. and G urdon, J. B. (1999) A n terio r e n d o m eso d erm specification in X enopus by W n t/b e ta -c a te n in an d TGF-beta signalling pathways. Dev Biol 209, 282-97.