Xavier Michelet, Laura Benkemoun, Nathalie Roudier, Christophe Lefebvre and Renaud Legouis. Class E VPS (Vacuolar Protein Sorting) proteins are involved in the formation of MultiVesicular Body in yeast. They are components of the Endosomal Sorting Complexes Required for Transport (ESCRTI, II and III). We have previously shown that the inactivation of the C. elegans class E vps genes resulted in various phenotypes ranging from lethality to an absence of obvious phenotype (1). In particular VPS-27 is involved in endosomal and autophagic pathways and its inactivation affects cholesterol traffic and larval molting (1). We present here the characterization of VPS-32, a component of ESCRT III. Phylogenetic and functional analyses of the two
vps-32 homologues present in the C. elegans genome indicated that only one encodes a functional protein, meanwhile the other is a pseudogene. Using antibodies and VPS-32::GFP fusion proteins, we observed that VPS-32 is expressed in vesicular structures and enriched in epithelial cells during the morphogenesis of the embryo..
vps-32(RNAi) and
vps-32 null mutant animals arrest their development at mid-embryogenesis and early L1 stage respectively, with a disorganisation and degradation of the epidermis. Moreover,
vps-32 RNAi feeding of larvae result in L4 arrest with the same epidermal defect associated with abnormal molting. Optical and electron microscopy analyses of
vps-32 animals, revealed the presence of enlarged VPS-27-positive endosomes and an excess of autophagy. Theses results indicate that, similarly to several VPSE, VPS-32 protein is required for endosomal and autophagic pathways. However despite these similarities, inactivation of vpsE genes results in different developmental phenotypes. A model to explain the heterogeneity between vpsE phenotypes will be presented.