Regulated lipid synthesis and LEM2/CHMP7 jointly control nuclear envelope closure

The nuclear permeability barrier depends on closure of nuclear envelope (NE) holes. Here, we investigate closure of the NE opening surrounding the meiotic spindle in C. elegans oocytes. ESCRT-III components accumulate at the opening but are not required for nuclear closure on their own. 3D analysis revealed cytoplasmic membranes directly adjacent to NE holes containing meiotic spindle microtubules. We demonstrate that the NE protein phosphatase, CNEP-1/CTDNEP1, controls de novo glycerolipid synthesis through lipin to prevent invasion of excess ER membranes into NE holes and a defective NE permeability barrier. Loss of NE adaptors for ESCRT-III exacerbates ER invasion and nuclear permeability defects in cnep-1 mutants, suggesting that ESCRTs restrict excess ER membranes during NE closure. Restoring glycerolipid synthesis in embryos deleted for CNEP-1 and ESCRT components rescued NE permeability defects. Thus, regulating the production and feeding of ER membranes into NE holes together with ESCRT-mediated remodeling is required for nuclear closure.