The lipodystrophy protein seipin is found at endoplasmic reticulum lipid droplet junctions and is important for droplet morphology.
Lipodystrophy is a disorder characterized by a loss of adipose tissue often accompanied by severe hypertriglyceridemia, insulin resistance, diabetes, and fatty liver. It can be inherited or acquired. The most severe inherited form is Berardinelli-Seip Congenital Lipodystrophy Type 2, associated with mutations in the BSCL2 gene. BSCL2 encodes seipin, the function of which has been entirely unknown. We now report the identification of yeast BSCL2/seipin through a screen to detect genes important for lipid droplet morphology. The absence of yeast seipin results in irregular lipid droplets often clustered alongside proliferated endoplasmic reticulum (ER); giant lipid droplets are also seen. Many small irregular lipid droplets are also apparent in fibroblasts from a BSCL2 patient. Human seipin can functionally replace yeast seipin, but a missense mutation in human seipin that causes lipodystrophy, or corresponding mutations in the yeast gene, render them unable to complement. Yeast seipin is localized in the ER, where it forms puncta. Almost all lipid droplets appear to be on the ER, and seipin is found at these junctions. Therefore, we hypothesize that seipin is important for droplet maintenance and perhaps assembly. In addition to detecting seipin, the screen identified 58 other genes whose deletions cause aberrant lipid droplets, including 2 genes encoding proteins known to activate lipin, a lipodystrophy locus in mice, and 16 other genes that are involved in endosomal-lysosomal trafficking. The genes identified in our screen should be of value in understanding the pathway of lipid droplet biogenesis and maintenance and the cause of some lipodystrophies.
Szymanski
Kimberly M
KM
Department of Pharmacology, University of Texas Southwestern Medical School, Dallas, TX 75390, USA.
Binns
Derk
D
Bartz
René
R
Grishin
Nick V
NV
Li
Wei-Ping
WP
Agarwal
Anil K
AK
Garg
Abhimanyu
A
Anderson
Richard G W
RG
Goodman
Joel M
JM
D000595:Amino Acid Sequence; D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D044388:GTP-Binding Protein gamma Subunits / Q000096:biosynthesis*; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D020962:Heterotrimeric GTP-Binding Proteins / Q000096:biosynthesis*; D006801:Humans; D008055:Lipids / Q000737:chemistry*; D008060:Lipodystrophy / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid
C432679:BSCL2 protein, human; C115783:Bscl2 protein, mouse; D044388:GTP-Binding Protein gamma Subunits; D008055:Lipids; D020962:Heterotrimeric GTP-Binding Proteins