FGF8/17/18 functions together with FGF9/16/20 during formation of the notochord in Ciona embryos.
Fibroblast growth factor (FGF) signalling has been implicated in the generation of mesoderm and neural fates in chordate embryos including ascidians and vertebrates. In Ciona, FGF9/16/20 has been implicated in both of these processes. However, in FGF9/16/20 knockdown embryos, notochord fate recovers during later development. It is thus not clear if FGF signalling is an essential requirement for notochord specification in Ciona embryos. We show that FGF-MEK-ERK signals act during two distinct phases to establish notochord fate. During the first phase, FGF signalling is required during an asymmetric cell division to promote notochord at the expense of neural identity. Consistently, ERK1/2 is specifically activated in the notochord precursors following this cell division. Sustained activation of ERK1/2 is then required to maintain notochord fate. We demonstrate that FGF9/16/20 acts solely during the initial induction step and that, subsequently, FGF8/17/18 together with FGF9/16/20 is involved in the following maintenance step. These results together with others' show that the formation of a large part of the mesoderm cell types in ascidian larvae is dependent on signalling events involving FGF ligands.
Yasuo
Hitoyoshi
H
Biologie du Développement, UMR7009 CNRS/Université Pierre et Marie Curie Observatoire Océanologique, F-06230 Villefranche-sur-mer, France. yasuo@obs-vlfr.fr
Hudson
Clare
C
D000818:Animals; D002938:Ciona intestinalis / Q000196:embryology* / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D047108:Embryonic Development; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051524:Fibroblast Growth Factor 8 / Q000378:metabolism*; D051525:Fibroblast Growth Factor 9 / Q000378:metabolism*; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008648:Mesoderm / Q000378:metabolism; D009672:Notochord / Q000196:embryology*; D016376:Oligonucleotides, Antisense / Q000378:metabolism; D015398:Signal Transduction
D051525:Fibroblast Growth Factor 9; D016376:Oligonucleotides, Antisense; C113569:fibroblast growth factor 18; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases