A lipid transfer protein ensures nematode cuticular impermeability

The cuticle of C. elegans is impermeable to chemicals, toxins and pathogens. However, increased permeability is a desirable phenotype because it facilitates chemical uptake. Surface lipids contribute to the permeability barrier. Here, we identify the lipid transfer protein GMAP-1 as a critical element setting the permeability of C. elegans cuticle. A gmap-1 deletion mutant increases cuticular permeability to sodium azide, levamisole, Hoechst and DiI. Expressing GMAP-1 in the hypodermis or transiently in the adults is sufficient to rescue this gmap-1 permeability phenotype. GMAP-1 protein is secreted from the hypodermis to the aqueous fluid filling the space between collagen fibres of the cuticle. In vitro, GMAP-1 protein binds Phosphatidyl-Serine and Phosphatidyl-Choline while in vivo, GMAP-1 sets the surface lipid composition and organisation. Altogether, our results suggest GMAP-1 secreted by hypodermis shuttles lipids to the surface to form the permeability barrier of C. elegans.