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Dev Biol 2009 Dec 15;3362:313-26. doi: 10.1016/j.ydbio.2009.09.039.
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Downstream of FGF during mesoderm formation in Xenopus: the roles of Elk-1 and Egr-1.

Nentwich O , Dingwell KS , Nordheim A , Smith JC .

Signalling by members of the FGF family is required for induction and maintenance of the mesoderm during amphibian development. One of the downstream effectors of FGF is the SRF-interacting Ets family member Elk-1, which, after phosphorylation by MAP kinase, activates the expression of immediate-early genes. Here, we show that Xenopus Elk-1 is phosphorylated in response to FGF signalling in a dynamic pattern throughout the embryo. Loss of XElk-1 function causes reduced expression of Xbra at neurula stages, followed by a failure to form notochord and muscle and then the partial loss of trunk structures. One of the genes regulated by XElk-1 is XEgr-1, which encodes a zinc finger transcription factor: we show that phosphorylated XElk-1 forms a complex with XSRF that binds to the XEgr-1 promoter. Superficially, Xenopus tropicalis embryos with reduced levels of XEgr-1 resemble those lacking XElk-1, but to our surprise, levels of Xbra are elevated at late gastrula stages in such embryos, and over-expression of XEgr-1 causes the down-regulation of Xbra both in whole embryos and in animal pole regions treated with activin or FGF. In contrast, the myogenic regulatory factor XMyoD is activated by XEgr-1 in a direct manner. We discuss these counterintuitive results in terms of the genetic regulatory network to which XEgr-1 contributes.

PubMed ID: 19799892
Article link: Dev Biol
Grant support: [+]

Species referenced: Xenopus tropicalis Xenopus laevis
Genes referenced: egr1 elk1 fgf2 kcnt1 myc myod1 srf tbxt
Antibodies: Notochord Ab2
Morpholinos: egr1 MO1 egr1 MO2 elk1 MO1

Article Images: [+] show captions