New kid on the block: lipid droplets in the nucleus.

The regulation of lipid homeostasis is essential for normal cell physiology and its disruption can lead to disease. Lipid droplets are ubiquitous organelles dedicated to storing non-polar lipids which are used for metabolic energy production or membrane biogenesis. Lipid droplets normally emerge from, and associate with, the endoplasmic reticulum and interact with other cytoplasmic organelles to deliver the stored lipids. Recently, lipid droplets were found to reside also at the inner side of the nuclear envelope and inside the nucleus in yeast and mammalian cells. This unexpected finding raises fundamental questions about the nature of the inner nuclear membrane, its connection with the endoplasmic reticulum and the pathways of lipid droplet formation. In this viewpoint we will highlight recent developments relating to these questions and discuss possible roles of lipid droplets in nuclear physiolog