FIGURE 1:

Features of the nuclear envelope and ER and regulation of and functions for lipid asymmetry at the inner nuclear membrane (INM). (A) Schematic of the continuous NE and ER membranes. The inner nuclear membrane (INM) facing the nucleoplasm and outer nuclear membrane (ONM) physically linked to the ER at NE-ER junctions are separated by a lumen designated perinuclear space (PNS). A nuclear pore complex (NPC) is located at a fusion point between the INM/ONM to generate the pore membrane. Highlighted in different shades of red are proteins that may regulate lipid trafficking between the NE and ER as well as enzymes and proteins that are regulated by or sense bilayer lipid composition (PKC and Nup133), or that regulate de novo lipid synthesis (CTDNEP1/lipin and CCTα). The curvature of the membrane bilayers may also play a role in restricting diffusion of lipid species past NE-ER junctions (negative curvature) or the pore membrane (positive curvature). Schematic of a membrane fusion reaction (middle) highlights membrane bending at each intermediate step. (B) The de novo glycerolipid synthesis pathway. Mol% for lipid species specific to ER/NE membranes is shown (van Meer et al., 2008).