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1: Dev Biol. 2007 Feb 1;302(1):92-103. Epub 2006 Sep 9.

FGF8/17/18 functions together with FGF9/16/20 during formation of the notochord
in Ciona embryos.

Yasuo H, Hudson C.

Biologie du Développement, UMR7009 CNRS/Université Pierre et Marie Curie
Observatoire Océanologique, F-06230 Villefranche-sur-mer, France.
[e-mail]

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.

PMID: 17022960 [PubMed - indexed for MEDLINE]

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