Seipin performs dissectible functions in promoting lipid droplet biogenesis and regulating droplet morphology.
Bottom Line: Furthermore, we find that the normal rate of droplet initiation depends on 14 amino acids at the amino terminus of seipin, deletion of which results in fewer, larger droplets that are consistent with a delay in initiation but are otherwise normal in morphology.Importantly, other functions of seipin, namely vectorial budding and resistance to inositol, are retained in this mutant.We conclude that seipin has dissectible roles in both promoting early LD initiation and in regulating LD morphology, supporting its importance in LD biogenesis.
Affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75235-9041.Show MeSH
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Mentions: After characterizing the effects of fld1∆Nterm on LD morphology and determining that the supersized phenotype was independent of inositol and its effect on PL synthesis, we then asked whether it could be explained by a defect in the rate of droplet initiation. We integrated fld1∆Nterm into the genomic seipin locus of the 3KO(GALDGA1) strain and observed LD formation after galactose induction as in Figure 1, with additional early time points at 1 and 2 h (Figure 6A). After 9 h, the “supersized” morphology of fld1∆Nterm was generally recapitulated, with the fld1∆Nterm droplet population displaying significantly larger sizes than FLD1 or fld1∆ (average area on projection image: FLD1, 55.02 pixels2; fld1∆, 80.43 pixels2; fld1∆Nterm, 116.6 pixels2), obviously more spherical shape, and a size distribution that exhibited less skewness than fld1∆ (average skewness of area distributions: FLD1, 1.094; fld1∆, 2.189; fld1∆Nterm, 1.406), indicating a more normally distributed droplet population than the knockout (Figure 6B).
Affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75235-9041.