A lipid transfer protein ensures nematode cuticular impermeability

Abstract

The cuticle of <i>C. elegans</i> 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 the <i>C. elegans</i> cuticle. A <i>gmap-1</i> 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 <i>gmap-1</i> permeability phenotype. GMAP-1 protein is secreted from the hypodermis to the aqueous fluid filling the space between collagen fibers of the cuticle. <i>In vitro</i>, GMAP-1 protein binds phosphatidylserine and phosphatidylcholine while <i>in vivo</i>, GMAP-1 sets the surface lipid composition and organization<i>.</i> Altogether, our results suggest GMAP-1 secreted by hypodermis shuttles lipids to the surface to form the permeability barrier of <i>C. elegans</i>.