Models of seipin function from lipid and protein perspectives. (A) Model of seipin as a LD-nucleating agent that promotes nascent TG lens to form in the ER membrane. (B) Model of seipin as a protein gatekeeper that regulates the movement of proteins and potentially some lipids between the ER and LDs. (C) Corral complex model of seipin as an oligomer that complexes with various adaptor proteins like LDAF1 to modulate its structure and interactions with lipids. (D) Model of seipin as a regulator of PA biosynthesis. Seipin loss is associated with PA accumulation in the ER network.