Activated Mutants of SHP-2 Preferentially Induce Elongation of Xenopus Animal Caps

Abstract

In Xenopus ectodermal explants (animal caps), fibroblast growth factor (FGF) evokes two major events: induction of ventrolateral mesodermal tissues and elongation. TheXenopus FGF receptor (XFGFR) and certain downstream components of the XFGFR signal transduction pathway (e.g., members of the Ras/Raf/MEK/mitogen-activated protein kinase [MAPK] cascade) are required for both of these processes. Likewise, activated versions of these signaling components induce mesoderm and promote animal cap elongation. Previously, using a dominant negative mutant approach, we showed that the protein-tyrosine phosphatase SHP-2 is necessary for FGF-induced MAPK activation, mesoderm induction, and elongation of animal caps. Taking advantage of recent structural information, we now have generated novel, activated mutants of SHP-2. Here, we show that expression of these mutants induces animal cap elongation to an extent comparable to that evoked by FGF. Surprisingly, however, activated mutant-induced elongation can occur without mesodermal cytodifferentiation and is accompanied by minimal activation of the MAPK pathway and mesodermal marker expression. Our results implicate SHP-2 in a pathway(s) directing cell movements in vivo and identify potential downstream components of this pathway. Our activated mutants also may be useful for determining the specific functions of SHP-2 in other signaling systems.

ACKNOWLEDGMENTS

We thank W. Xu (Harvard Medical School), M. Whitman (Harvard Medical School), G. L. Henry (Harvard University) B. Gumbiner (Memorial Sloan-Kettering Cancer Center), C. Der (University of North Carolina, Chapel Hill), H. Isaacs (University of Bath), J. Smith (National Institute for Medical Research), and J. Timms (Beth Israel Deaconess Medical Center) for generous gifts of reagents, K. Itoh and S. Sokol (Beth Israel Deaconess Medical Center and Harvard Medical School) for FGF and frogs, D. Goodenough (Harvard Medical School), J. Green (Dana-Farber Cancer Institute), and K. Symes (Boston University School of Medicine) for help with histological analyses, M. Mercola and M. Kirschner (Harvard Medical School), S. Sokol (Beth Israel Deaconess Medical Center), C. Carpenter (Beth Israel Deaconess Medical Center), J. Green (Dana-Farber Cancer Institute), K. Symes (Boston University School of Medicine), and S. Thomas (Beth Israel Deaconess Medical Center) for helpful discussions and critical reading of the manuscript, and S. Cohen for help with manuscript preparation.

This work was supported by grants from the NIH (RO1 CA49152 to B.G.N. and RO1 DK45943, RO1 DK51729 to S.E.S.) and the Burroughs Wellcome Fund Scholar Award in Experimental Therapeutics (to S.E.S.).