Lamin is essential for nuclear localization of the GPI synthesis enzyme PIG-B and GPI-AP production in Drosophila

Membrane lipid biosynthesis is a complex process that occurs in various intracellular compartments. In Drosophila, phosphatidylinositol glycan (PIG)-B (DPIG-B), which catalyzes addition of the third mannose in glycosylphosphatidylinositol (GPI), localizes to the nuclear envelope (NE). Although this NE localization is essential for Drosophila development, the underlying molecular mechanism remains unknown. To elucidate this mechanism, we identified DPIG-B-interacting proteins by performing immunoprecipitation followed by proteomic analysis. We then examined which of these proteins are required for the NE localization of DPIG-B. Knockdown of Lamin Dm0, a B-type lamin, led to mislocalization of DPIG-B from the NE to the endoplasmic reticulum. Lamin Dm0 associated with DPIG-B at the inner nuclear membrane, a process that required the tail domain of Lamin Dm0. Furthermore, GPI moieties were distributed abnormally in the Lamin Dm0 mutant. These data indicate that Lamin Dm0 is involved in the NE localization of DPIG-B and is required for proper GPI-anchor modification of proteins.