A POU PROTEIN REGULATES MESODERMAL COMPETENCE TO FGF IN XENOPUS

XLPOU91, a POU-homeobox gene is expressed in a narrow window during ea rly Xenopus development. We show that ectopic expression of XLPOU91 RN A causes severe posterior truncations in embryos without inhibiting th e formation of Spemann's organizer. Ectopic XLPOU91 expression also in hibits mesoderm induction by fibroblast growth factor (FGF) and activi n in animal cap explants. Using antisense RNA, we depleted endogenous XLPOU91 protein in animal caps. Gastrula-stage animal caps expressing XLPOU91 antisense RNA do not lose competence to FGF, unlike controls, these animal caps express XBra after FGF treatment. Endogenous XLPOU91 levels are peaking when FGF mesoderm-inducing competence is lost in a nimal caps. Thus XLPOU91 protein may act as a competence switch during early development, as XLPOU91 levels increase in the embryo, the meso derm response to FGF is lost. (C) 1998 Elsevier Science Ireland Ltd.