Xenopus crescent encoding a Frizzled-like domain is expressed in the Spemann organizer and pronephros

The Spemann organizer can be subdivided into head- and trunk-inducing tissu es along the anteroposterior axis (Mangold, 1933. Naturwiisenschaften 33, 7 61-766; Spemann, 1931. Wilheim Roux Arch. Entwicklungsmech. Org. 133, 389-5 17). Recent studies have suggested that head formation is brought about by repression of both Wnt and BMP signalling (Glinka et al., 1998. Nature 391, 357-362; Glinka et al., 1997 Nature 389, 517-519). Several Wnt inhibitors secreted from the head organizer region have been identified in Xenopus, su ch as Cerberus (Bouwmeester et al., 1996. Nature 382, 595-601), Frzb-1 (Ley ns et al., 1997. Cell 88, 747-756; Lin et al., 1997. Proc. Natl. Acad. Sci. USA 94, 11196-11200), and Dkk-1 (Glinka ct al., 1998. Nature 391, 357-362) , supporting this two-inhibitor model. To isolate genes expressed in the he ad organizer, we screened a prechordal plate cDNA library by sequencing and expression pattern, and isolated the Xenopus ortholog of chick crescent en coding a Frizzled-like domain that is related to Wnt-binding regions of the Frizzled-family proteins. Expression of Xenopus crescent was first detecte d in the Spemann organizer region at the early gastrula stage and water in prechordal plate cells lining the boundary of mesoderm and ectoderm layers and in the anterior endoderm. At tailbud stages, the expression in the endo mesoderm region was diminished, while expression in the pronephros became d etectable. In animal cap assays, crescent gene was synergistically upregula ted by coexpression of Xlim 1, Ldb 1, and Siamois, but not by Activin treat ment. (C) 2000 Elsevier Science Inland Ltd. All rights reserved.