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Inhibition of Nodal signalling by Lefty mediated through interaction with common receptors and efficient diffusion
Rui Sakuma1, Yu-ichiro Ohnishi Yi, Chikara Meno
1Division of Molecular Biology, Institute for Molecular and Cellular Biology, Osaka University, 1-3 Yamada-oka, Suita, Osaka 565, Japan.
Background:
Two TGFbeta-related proteins, Nodal and Lefty, are implicated in early embryonic patterning of vertebrates. Genetic data suggest that Nodal is a signalling molecule, while Lefty is an antagonist of Nodal, but their precise function remains unknown.
Results:
The signalling pathway of Nodal was investigated with the use of a Nodal-responsive assay system based on frog animal caps. Expression of dominant negative mutants of various receptors indicated that ALK4, and either ActRIIA or ActRIIB, function as type I and type II receptors for Nodal, respectively. A soluble form of Cripto lacking the COOH-terminal region interacted with Nodal but failed to mediate Nodal signalling, indicating that the native Cripto protein functions as a membrane-bound co-receptor for Nodal. Processed forms of Lefty proteins, both smaller and larger forms, inhibited Nodal signalling. Such Lefty-induced inhibition was rescued by excess ActRIIA or ActRIIB, suggesting that Lefty antagonizes Nodal signalling through competitive binding to the common receptor ActRIIA or ActRIIB. This idea was supported by the demonstration of a genetic interaction between lefty2 and ActRIIB in mouse. Behaviours of GFP-Nodal and GFP-Lefty2 proteins were also investigated in chick embryos. Both proteins could diffuse over a long distance, but the latter diffused faster than the former.
Conclusions:
Efficient inhibition of Nodal signals by Lefty may involve competitive binding of Lefty to the common receptors and faster diffusion of Lefty.
Insights
Lefty proteins antagonize Nodal signaling by competitively binding to common receptors and diffusing faster, revealing key mechanisms in early vertebrate development.
Area of Science:
- Developmental Biology
- Molecular Signaling
Background:
- Nodal and Lefty are TGF-beta proteins crucial for vertebrate embryonic patterning.
- While Nodal is a signaling molecule and Lefty its antagonist, their exact roles are unclear.
Purpose of the Study:
- To elucidate the precise functions and mechanisms of Nodal and Lefty in embryonic development.
- To identify the receptors and co-receptors involved in Nodal signaling and Lefty's antagonism.
Main Methods:
- Utilized a Nodal-responsive assay system in frog animal caps.
- Employed dominant-negative receptor mutants and analyzed protein diffusion in chick embryos.
- Investigated genetic interactions between Lefty2 and ActRIIB in mice.
Main Results:
- Identified ALK4 and ActRIIA/ActRIIB as Nodal receptors.
- Cripto acts as a membrane-bound co-receptor for Nodal.
- Lefty proteins inhibit Nodal signaling via competitive binding to ActRIIA/ActRIIB and faster diffusion.
Conclusions:
- Lefty antagonizes Nodal signaling through competitive binding to shared receptors.
- Faster diffusion of Lefty compared to Nodal contributes to efficient signal inhibition.