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Nodal signaling
Nodal signaling is a signal transduction pathway that is important in pattern formation and differentiation during embryo development.
The nodal family of proteins, a subset of the transforming growth factor beta (TGFβ) superfamily, is responsible for mesoendoderm induction, patterning of the nervous system, and determination of dorsal- ventral axis in vertebrate embryos. Activation of the Nodal pathway involves nodal binding to activin and activin-like receptors which leads to phosphorylation of the Smad2. The P-Smad2/Smad4 complex translocates into the nucleus to interact with transcription factors such as FoxH1, p53 and Mixer (''Xenopus'' mix-like endodermal regulator). This will, in turn, lead to induction of target genes such as Nodal, Lefty, the antagonist of nodal Cerberus, and others.
The activation of Nodal pathway induces the transcription of many target genes including of its own, but at the same time, micro-RNAs and other proteins interfere with this positive feedback loop in a negative manner at different points of the pathway.〔 This balance of activation and inhibition of the signal is necessary to achieve the precise location, concentration and duration of downstream target genes that have an important role early in development. This article will summarize the role of some of the components that participate positively and negatively in regulation the signaling pathway. Although all the major components of Nodal signaling are evolutionary conserved in almost all vertebrates, the regulation of each component of the pathway sometimes varies according to the species.
==History==
The ''nodal'' gene was originally discovered by Conlon et al. by retroviral mutation in mice which led to the isolation of a gene that interfered with normal mouse gastrulation and embryo development. Further study of this gene by Zhou et al. showed that the nodal genes encode a secreted signaling peptide that was sufficient to induce mesoderm cells in the mouse embryo. This was an important finding as many other factors had been implicated in the formation of mesoderm in ''Xenopus'' whereas the difficulty of removal of these factors due to embryonic lethality and maternal contribution of genes had kept the ability to assay the knock out phenotypes elusive. Further studies of nodal signaling in other vertebrates such as Cyclops and Squint in zebrafish proved that nodal signaling is adequate to induce mesoderm in all vertebrates.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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