Figure 1.

The biogenesis of LDs. The process of de novo LD biogenesis can be divided in three main discrete steps: (A) Nucleation, (B) growth and (C) budding. The nucleation step is characterized by the formation of an oil lens structure in between the two lipid bilayers of the ER limiting membrane, which is catalyzed by ER resident proteins such as FITM1/FITM2 and BSCL2/seipin. The growth of the nascent LDs starts with an accumulation of TAGs and SE, and involves a ripening phenomenon that regulates their size. The partial (in yeast) or complete (in mammalian cells) detachment of the LDs from the ER membrane defines the LDs budding. LDs can also expand (D) by increasing their size through the coalescence of LDs and/or the local synthesis of TAGs. Several enzymes involved in the biogenesis and function of LDs, which are discussed in the review, are indicated.