In this research project we determined if biogenesis of lipid droplets (LDs) is a random process that occurs stochastically in the endoplasmic reticulum (ER), or does it occur at some discrete ER subdomains. We used yeast as model eukaryote for our study. Here we show that induction of triacylglycerol (TAG)-synthesis in yeast by either of the two TAG-synthases, Lro1, or Dga1 results in formation of droplets at discrete ER sites. We have found that these discrete ER subdomains are marked by two ER proteins, Fld1, a homolog of mammalian seipin, and a regulator of diaclyglycerol (DAG) production, Nem1. Remarkably, Both Fld1 and Nem1 localize to ER sites, independent of each other, and of the presence of LDs, but both are required together to create functional sites of LD biogenesis. Fld1-Nem1 marked ER subdomains recruit TAG-synathses and other LD biogenesis factors: Pex30, an ER shaping protein; Yft2, a homolog of mammalian FIT2; Pet10, yeast perilipin homolog; Erg6, an LD marker protein of yeast. In addition these Fld1-Nem1 defined ER sites become enriched in diaclyglycerol (DAG), a neutral lipid precursor. We conclude that both Fld1 and Nem1 perform a crucial role in the first steps of LD biogenesis. Cells lacking either Fld1 or Nem1 show ectopic TAG synthesis and aberrant LD biogenesis.
Findings from this study has recently been accepted for publication in the Journal of Cell Biology with me as first and lead corresponding author (Choudhary et al., 2020, forthcoming, doi: 10.1083/jcb.201910177.).
During the tenure of this fellowship, the recruited researcher presented findings from this study as an oral presentation in a scientific conference and as a poster in a scientific workshop. The researcher also participated in an outreach activity within the scope of this fellowship.
