title: Negative regulation of Activin/Nodal signaling by SRF during Xenopus gastrulation.
abstract: Activin/Nodal signaling is essential for germ-layer formation and axial patterning during embryogenesis. Recent evidence has demonstrated that the intra- or extracellular inhibition of this signaling is crucial for ectoderm specification and correct positioning of mesoderm and endoderm. Here, we analyzed the function of Xenopus serum response factor (XSRF) in establishing germ layers during early development. XSRF transcripts are restricted to the animal pole ectoderm in Xenopus early embryos. Ectopic expression of XSRF RNA suppresses mesoderm induction, both in the marginal zone in vivo and caused by Activin/Nodal signals in animal caps. Dominant-negative mutant or antisense morpholino oligonucleotide-mediated inhibition of XSRF function expands the expression of mesendodermal genes toward the ectodermal territory and enhances the inducing activity of the Activin signal. SRF interacts with Smad2 and FAST-1, and inhibits the formation of the Smad2-FAST-1 complex induced by Activin. These results suggest that XSRF might act to ensure proper mesoderm induction in the appropriate region by inhibiting the mesoderm-inducing signals during early embryogenesis.
authors.affiliation: Natural Medicines Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 305-333, Korea.
authors.forename: Chang-Hyun
authors.initials: CH
authors.lastname: Yun
authors.forename: Sun-Cheol
authors.initials: SC
authors.lastname: Choi
authors.forename: Eunjoo
authors.initials: E
authors.lastname: Park
authors.forename: Seong-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: An-Sik
authors.initials: AS
authors.lastname: Chung
authors.forename: Hyeong-Kyu
authors.initials: HK
authors.lastname: Lee
authors.forename: Ho-Jae
authors.initials: HJ
authors.lastname: Lee
authors.forename: Jin-Kwan
authors.initials: JK
authors.lastname: Han
mesh_terms: D028341:Activins / Q000378:metabolism*; D000818:Animals; D004475:Ectoderm / Q000737:chemistry; D004625:Embryo, Nonmammalian; D004627:Embryonic Induction; D051858:Forkhead Transcription Factors / Q000378:metabolism; D005775:Gastrula / Q000378:metabolism*; D008648:Mesoderm / Q000166:cytology; D046912:Multiprotein Complexes; D012333:RNA, Messenger / Q000032:analysis; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism
chemical_list: C102067:FOXH1 protein, Xenopus; D051858:Forkhead Transcription Factors; D046912:Multiprotein Complexes; D012333:RNA, Messenger; D026362:Serum Response Factor; D051899:Smad2 Protein; D029867:Xenopus Proteins; D028341:Activins