Lipins constitute a novel family of Mg 2+ -dependent phosphatidate phos-phatases that catalyze the dephosphorylation of phosphatidic acid to yield diacylglycerol, an important intermediate in lipid metabolism and cell signaling. Whereas a single lipin is detected in less complex organisms, in mammals there are distinct lipin isoforms and paralogs that are differen-tially expressed among tissues.