Glucosylceramide (GlcCer) and galactosylceramide (GalCer) are the base cerebrosides essential for synthesizing glycosphingolipids (GSLs). GSLs are enriched in membrane rafts, where they are playing essential roles in signal transduction with GPI anchored proteins, cholesterol and sphingomyelin. In C. elegans , GalC er is not present, and GSLs are presumably synthesized from GlcCer. Thus, knocking out of the genes for GlcCer synthesis could reveal the essential functions of GSLs in vivo. Ceramide glucosyltransferase (Ugcg) synthesizes GlcCer from ceramide and UDP-glucose. In the worm genome, we found three Ugcg genes (
cgt-1 ,
cgt-2 ,
cgt-3 ), with each gene coding for an active enzyme synthesizing GlcCer in vitro (Ichikawa 1998). Leipelt et al. (2000, 2001) reported similar findings, and Marza et al. (2009) showed that the enzymes are indispensable only in a few intestinal cells and dispensable in all other embryonic tissue cells. In this study, by using RNAi and knockout (KO) worms, we demonstrated that the genes are essential for oocyte formation and early embryogenesis. When each gene function was disrupted, the brood size of the animal markedly decreased, and abnormal oocytes and multinucleated embryos were formed. The CGT-3 protein had the highest Ugcg activity, and KO of its g ene resulted in the severest phenotype. When
cgt-3 RNAi was performed on
rrf-1 worms lacking somatic RNAi machinery, a number of abnormal oocytes and multinucleated eggs were observed, although the somatic phenotype, i.e., L1 lethal effects of
cgt-1 /
cgt-3 RNAi, was completely suppressed. Studies with OD70 worms revealed that germline membrane formation was severely affected in the cgt deficient worms, demonstrating that the Ugcg genes are indispensable in the germline membrane formation. The results strongly indicate the importance of GlcCer for meiosis and mitosis.