title: Cell fate polarization in ascidian mesenchyme/muscle precursors by directed FGF signaling and role for an additional ectodermal FGF antagonizing signal in notochord/nerve cord precursors.
abstract: Asymmetric cell division plays a fundamental role in generating various types of embryonic cell. In ascidian embryos, asymmetric cell divisions occur in the vegetal hemisphere in a manner similar to those found in Caenorhabditis elegans. Early divisions in embryos of both species involve inductive events on a single mother cell that result in production of daughters with different cell fates. Here we show in the ascidian Halocynthia roretzi that polarity of muscle/mesenchyme mother precursors is determined solely by the direction from which the FGF9/16/20 signal is presented, a role similar to that of Wnt signaling in the EMS and T cell divisions in C. elegans. However, polarity of nerve cord/notochord mother precursors is determined by possible antagonistic action between the FGF signal and a signal from anterior ectoderm, providing a new mechanism underlying asymmetric cell division. The ectoderm signal suppresses MAPK activation and expression of Hr-FoxA, which encodes an intrinsic competence factor for notochord induction, in the nerve cord lineage.
authors.affiliation: Faculty of Marine Bioscience and Technology, Kangnung National University, Gangneung Daehangno, Gangneung 210-702, Republic of Korea. gjkim@kangnung.ac.kr
authors.forename: Gil Jung
authors.initials: GJ
authors.lastname: Kim
authors.forename: Gaku
authors.initials: G
authors.lastname: Kumano
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nishida
mesh_terms: D000818:Animals; D019521:Body Patterning; D002454:Cell Differentiation; D002455:Cell Division; D019070:Cell Lineage; D004475:Ectoderm / Q000166:cytology / Q000502:physiology; D004789:Enzyme Activation; D005346:Fibroblast Growth Factors / Q000502:physiology*; D020935:MAP Kinase Signaling System / Q000502:physiology; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000502:physiology; D032446:Myoblasts / Q000502:physiology*; D009672:Notochord / Q000166:cytology / Q000502:physiology*; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism; D014561:Urochordata / Q000166:cytology* / Q000196:embryology
chemical_list: D015534:Trans-Activators; D005346:Fibroblast Growth Factors