MAP KINASE IS ACTIVATED DURING MESODERM INDUCTION IN XENOPUS-LAEVIS

MAP kinase (MAPK) is activated in animal cap explants from Xenopus emb ryos in response to mesoderm induction by FGF. This activation is rapi d, appearing within 1 min of treatment with FGF, and prolonged, lastin g for at least 2 hr. By immunoblot analysis, this activation of MAPK i s coupled with an electrophoretic shift to the slowly migrating, phosp horylated form of MAPK. Activin-stimulated mesoderm induction also res ults in the activation of MAPK, but only upon prolonged exposure. Howe ver, activin can potentiate the activation of MAPK by FGF as early as 1 min after administration. These findings suggest that MAPK is involv ed in the early signaling events of FGF-mediated mesoderm induction, a nd this involvement is modulated by other mesoderm inducers such as ac tivin. (C) 1994 Academic Press, Inc.