The Axin-like protein PRY-1 is a negative regulator of a canonical Wnt pathway in C. elegans

Area of Science:

• Developmental Biology
• Molecular Genetics
• Wnt Signaling Pathways

Background:

• The Wnt pathway, crucial for development, is regulated by a destruction complex involving Axin, APC, and GSK3 beta, which controls beta-catenin stability.
• In C. elegans, Wnt signaling is involved in development, but a canonical Axin ortholog was missing, and SGG-1/GSK3 beta and APR-1 acted as positive regulators.
• Previous work established that EGL-20/Wnt signaling controls mab-5 expression in neuroblasts via BAR-1/beta-catenin and POP-1/Tcf.

Purpose of the Study:

• To investigate the regulation of BAR-1/beta-catenin by the EGL-20/Wnt pathway in C. elegans.
• To identify and characterize novel components of the Wnt destruction complex in C. elegans.
• To determine the functional role of PRY-1 in Wnt signaling and its relationship to Axin.

Main Methods:

• Genetic analysis in C. elegans to identify and characterize the pry-1 gene.
• Protein interaction studies (co-immunoprecipitation) to assess interactions between PRY-1, BAR-1, SGG-1, and APR-1.
• Functional assays including gene overexpression and rescue experiments in C. elegans and zebrafish.
• Analysis of Wnt pathway target gene expression (e.g., mab-5).

Main Results:

• PRY-1 was identified as a negative regulator of the EGL-20 pathway and encodes an RGS and DIX domain-containing protein distantly related to Axin.
• PRY-1 functions as a C. elegans Axin homolog, interacting with BAR-1/beta-catenin, SGG-1/GSK3 beta, and APR-1.
• Overexpression of PRY-1 inhibited mab-5 expression, and pry-1 rescued the zebrafish axin1 mutation (masterblind).
• SGG-1 may act as a negative regulator in the EGL-20 pathway, contrasting its positive role in early embryonic Wnt signaling.

Conclusions:

• A highly divergent destruction complex, comprising PRY-1 (Axin homolog), SGG-1, and APR-1, regulates BAR-1/beta-catenin signaling in C. elegans.
• PRY-1 is a functional Axin homolog capable of interacting with both nematode and vertebrate Wnt pathway components.
• The findings elucidate a unique mechanism of Wnt pathway regulation in C. elegans, highlighting evolutionary divergence of the destruction complex.