Adipogenin promotes the development of lipid droplets by binding a dodecameric seipin complex.
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Adipogenin is a single-pass endoplasmic reticulum membrane protein with a cytosolic C-terminus, determined by ER-marker colocalization, APEX2 electron microscopy at near-endogenous levels, and protease protection.
"Thus, Adig is a single-pass ER protein with a cytosolic C-terminal tail"
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The study explicitly set out to adjudicate the conflicting plasma membrane, nuclear and lipid droplet localizations reported previously.
"We next assessed the subcellular location of Adig because previous reports suggest different locations, including the plasma membrane (2), nuclei (3), and the surface of LDs (4)."
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Seipin is the principal adipogenin interactor, identified as the top hit in unbiased pulldown mass spectrometry.
"The most enriched protein with substantial sequence coverage was seipin"
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Adipogenin selectively binds the dodecameric seipin oligomer and promotes its assembly by bridging and stabilizing adjacent subunits.
"Adig selectively bound to the dodecameric form and enhanced seipin assembly by bridging and stabilizing adjacent subunits."
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Adipogenin prevents seipin from aggregating, favouring functional complexes instead.
"Thus, when expressed with Adig, seipin appeared to form functional seipin-Adig complexes rather than seipin aggregates."
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Adig-bound seipin complexes are mobile and do not form stable contacts with nascent lipid droplets, unlike Adig-free seipin complexes.
"they formed stable contacts with seipin complexes without Adig, while seipin-Adig complexes moved rapidly through their vicinity"
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The seipin-adipogenin complex promotes lipid droplet development at early and late stages.
"Functionally, this complex promoted lipid droplet development at both early and late stages."
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Adipocyte-specific Adig overexpression increases fat mass and enlarges droplets; Adig deletion disrupts triglyceride accumulation in brown adipose tissue.
"In transgenic mice, adipocyte-specific overexpression of Adig increased fat mass and enlarged lipid droplets, whereas Adig deletion disrupted triglyceride accumulation in brown adipose tissues."