The NED-8 conjugating system in Caenorhabditis elegans is required for embryogenesis and terminal differentiation of the hypodermis.

This work has identified the enzymes involved in the activation and conjugation of the ubiquitin-like protein NED-8 in Caenorhabditis elegans. A C. elegans conjugating enzyme, UBC-12, is highly specific in its ability to utilize NED-8 as a substrate. Immunostaining shows that NED-8 is conjugated in vivo to a major target protein with a conjugate size of 90 kDa. While the amount of this conjugate is developmentally regulated with reduced levels in the larval stages, the mRNA encoding C. elegans UBC-12 is constitutively produced throughout development, as is NED-8 itself. The importance of the NED-8 conjugating system in C. elegans was determined by RNA interference (RNAi) assays using double-stranded RNA encoding NED-8, UBC-12, or the NED-8 activating enzyme component ULA-1. The progeny of both ned-8 and ubc-12 RNAi-treated hermaphrodites either arrested during embryonic development or underwent abnormal postembryonic development. The effect on postembryonic development was pleiotropic, the most frequent gross abnormality being vulval eversion during the L4 stage. Individuals with an everted vulva either burst at the L4 to adult molt or gave rise to adults incapable of egg laying. Additionally, both ned-8 and ubc-12 RNAi induced a striking abnormality in the alae, structures produced by the lateral hypodermal seam cells in the adult nematode. Affected alae were patchy and frequently diverged around a central space. Vulval defects were also produced by RNAi directed at C. elegans ula-1. This is the first demonstration of a requirement for NED-8 conjugation in metazoan development.