scholarly journals Seipin and Nem1 establish discrete ER subdomains to initiate yeast lipid droplet biogenesis

2020 ◽  
Author(s):  
Vineet Choudhary ◽  
Ola El Atab ◽  
Giulia Mizzon ◽  
William A. Prinz ◽  
Roger Schneiter
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Fat Storage ◽  
Contact Sites ◽  
Yeast Lipid

ABSTRACTLipid droplets (LDs) are fat storage organelles that originate from the endoplasmic reticulum (ER). Relatively little is known about how sites of LD formation are selected, and which proteins/lipids are necessary for the process. Here, we show that LDs induced by the yeast triacylglycerol (TAG)-synthases Lro1 and Dga1 are formed at discrete ER subdomains defined by seipin (Fld1), and a regulator of diacylglycerol (DAG) production, Nem1. Fld1 and Nem1 colocalize to ER-LD contact sites. We find that Fld1 and Nem1 localize to ER subdomains independently of each other and of LDs, but both are required for the subdomains to recruit the TAG synthases and additional LD biogeneiss factors: Yft2, Pex30, Pet10, and Erg6. These subdomains become enriched in DAG. We conclude that Fld1 and Nem1 are both necessary to recruit proteins to ER subdomains where LD biogenesis occurs.

scholarly journals Seipin and Nem1 establish discrete ER subdomains to initiate yeast lipid droplet biogenesis

2020 ◽  
Vol 219 (7) ◽  
Author(s):  
Vineet Choudhary ◽  
Ola El Atab ◽  
Giulia Mizzon ◽  
William A. Prinz ◽  
Roger Schneiter
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Fat Storage ◽  
Contact Sites ◽  
Yeast Lipid

Lipid droplets (LDs) are fat storage organelles that originate from the endoplasmic reticulum (ER). Relatively little is known about how sites of LD formation are selected and which proteins/lipids are necessary for the process. Here, we show that LDs induced by the yeast triacylglycerol (TAG)-synthases Lro1 and Dga1 are formed at discrete ER subdomains defined by seipin (Fld1), and a regulator of diacylglycerol (DAG) production, Nem1. Fld1 and Nem1 colocalize to ER–LD contact sites. We find that Fld1 and Nem1 localize to ER subdomains independently of each other and of LDs, but both are required for the subdomains to recruit the TAG-synthases and additional LD biogenesis factors: Yft2, Pex30, Pet10, and Erg6. These subdomains become enriched in DAG. We conclude that Fld1 and Nem1 are both necessary to recruit proteins to ER subdomains where LD biogenesis occurs.

scholarly journals A conserved family of proteins facilitates nascent lipid droplet budding from the ER

2015 ◽  
Vol 211 (2) ◽  
pp. 261-271 ◽  
Author(s):  
Vineet Choudhary ◽  
Namrata Ojha ◽  
Andy Golden ◽  
William A. Prinz
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Caenorhabditis Elegans ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
De Novo ◽  
Fat Storage ◽  
Higher Eukaryotes ◽  
Er Membrane

Lipid droplets (LDs) are found in all cells and play critical roles in lipid metabolism. De novo LD biogenesis occurs in the endoplasmic reticulum (ER) but is not well understood. We imaged early stages of LD biogenesis using electron microscopy and found that nascent LDs form lens-like structures that are in the ER membrane, raising the question of how these nascent LDs bud from the ER as they grow. We found that a conserved family of proteins, fat storage-inducing transmembrane (FIT) proteins, is required for proper budding of LDs from the ER. Elimination or reduction of FIT proteins in yeast and higher eukaryotes causes LDs to remain in the ER membrane. Deletion of the single FIT protein in Caenorhabditis elegans is lethal, suggesting that LD budding is an essential process in this organism. Our findings indicated that FIT proteins are necessary to promote budding of nascent LDs from the ER.

scholarly journals Human VPS13A is associated with multiple organelles and influences mitochondrial morphology and lipid droplet motility

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Wondwossen M Yeshaw ◽  
Marianne van der Zwaag ◽  
Francesco Pinto ◽  
Liza L Lahaye ◽  
Anita IE Faber ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Mammalian Cells ◽  
Lipid Droplets ◽  
Neurodegenerative Disorder ◽  
Close Contact ◽  
Mitochondrial Morphology ◽  
Published Data ◽  
Membrane Contact Sites ◽  
Contact Sites

The VPS13A gene is associated with the neurodegenerative disorder Chorea Acanthocytosis. It is unknown what the consequences are of impaired function of VPS13A at the subcellular level. We demonstrate that VPS13A is a peripheral membrane protein, associated with mitochondria, the endoplasmic reticulum and lipid droplets. VPS13A is localized at sites where the endoplasmic reticulum and mitochondria are in close contact. VPS13A interacts with the ER residing protein VAP-A via its FFAT domain. Interaction with mitochondria is mediated via its C-terminal domain. In VPS13A-depleted cells, ER-mitochondria contact sites are decreased, mitochondria are fragmented and mitophagy is decreased. VPS13A also localizes to lipid droplets and affects lipid droplet motility. In VPS13A-depleted mammalian cells lipid droplet numbers are increased. Our data, together with recently published data from others, indicate that VPS13A is required for establishing membrane contact sites between various organelles to enable lipid transfer required for mitochondria and lipid droplet related processes.

scholarly journals Getting a handle on lipid droplets: Insights into ER–lipid droplet tethering

2019 ◽  
Vol 218 (4) ◽  
pp. 1089-1091 ◽  
Author(s):  
Truc B. Nguyen ◽  
James A. Olzmann
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Human Cells ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Cell Biol ◽  
Membrane Contact

Lipid droplets (LDs) are hubs for lipid metabolism that form membrane contact sites with multiple organelles. In this issue, Hariri et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808119) reveal the functions of Mdm1-mediated endoplasmic reticulum (ER)–LD tethering in yeast and Datta et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808133) identify a role for the Mdm1 orthologue, Snx14, as an ER–LD tether that regulates lipid metabolism in human cells.

scholarly journals Mdm1 maintains endoplasmic reticulum homeostasis by spatially regulating lipid droplet biogenesis

2019 ◽  
Vol 218 (4) ◽  
pp. 1319-1334 ◽  
Author(s):  
Hanaa Hariri ◽  
Natalie Speer ◽  
Jade Bowerman ◽  
Sean Rogers ◽  
Gang Fu ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Fatty Acyl ◽  
Nutrient Depletion ◽  
Coenzyme A Ligase ◽  
Response To Stress ◽  
Acyl Coenzyme A ◽  
Er Homeostasis

Lipid droplets (LDs) serve as cytoplasmic reservoirs for energy-rich fatty acids (FAs) stored in the form of triacylglycerides (TAGs). During nutrient stress, yeast LDs cluster adjacent to the vacuole/lysosome, but how this LD accumulation is coordinated remains poorly understood. The ER protein Mdm1 is a molecular tether that plays a role in clustering LDs during nutrient depletion, but its mechanism of function remains unknown. Here, we show that Mdm1 associates with LDs through its hydrophobic N-terminal region, which is sufficient to demarcate sites for LD budding. Mdm1 binds FAs via its Phox-associated domain and coenriches with fatty acyl–coenzyme A ligase Faa1 at LD bud sites. Consistent with this, loss of MDM1 perturbs free FA activation and Dga1-dependent synthesis of TAGs, elevating the cellular FA level, which perturbs ER morphology and sensitizes yeast to FA-induced lipotoxicity. We propose that Mdm1 coordinates FA activation adjacent to the vacuole to promote LD production in response to stress, thus maintaining ER homeostasis.

scholarly journals The seipin complex Fld1/Ldb16 stabilizes ER–lipid droplet contact sites

2015 ◽  
Vol 211 (4) ◽  
pp. 829-844 ◽  
Author(s):  
Alexandra Grippa ◽  
Laura Buxó ◽  
Gabriel Mora ◽  
Charlotta Funaya ◽  
Fatima-Zahra Idrissi ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Neutral Lipid ◽  
Diffusion Barrier ◽  
Lipid Droplets ◽  
Lipid Binding ◽  
Contact Sites ◽  
Packing Defects ◽  
Specific Proteins ◽  
Lipid Binding Proteins

Lipid droplets (LDs) are storage organelles consisting of a neutral lipid core surrounded by a phospholipid monolayer and a set of LD-specific proteins. Most LD components are synthesized in the endoplasmic reticulum (ER), an organelle that is often physically connected with LDs. How LD identity is established while maintaining biochemical and physical connections with the ER is not known. Here, we show that the yeast seipin Fld1, in complex with the ER membrane protein Ldb16, prevents equilibration of ER and LD surface components by stabilizing the contact sites between the two organelles. In the absence of the Fld1/Ldb16 complex, assembly of LDs results in phospholipid packing defects leading to aberrant distribution of lipid-binding proteins and abnormal LDs. We propose that the Fld1/Ldb16 complex facilitates the establishment of LD identity by acting as a diffusion barrier at the ER–LD contact sites.

scholarly journals A Unique Junctional Interface at Contact Sites Between the Endoplasmic Reticulum and Lipid Droplets

2021 ◽  
Vol 9 ◽  
Author(s):  
Vineet Choudhary ◽  
Roger Schneiter
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Droplets ◽  
Neutral Lipids ◽  
Close Contact ◽  
Lipid Storage ◽  
Metabolic Energy ◽  
Lipid Monolayer ◽  
Storage Diseases ◽  
Contact Sites ◽  
Ordered Assembly

Lipid droplets (LDs) constitute compartments dedicated to the storage of metabolic energy in the form of neutral lipids. LDs originate from the endoplasmic reticulum (ER) with which they maintain close contact throughout their life cycle. These ER–LD junctions facilitate the exchange of both proteins and lipids between these two compartments. In recent years, proteins that are important for the proper formation of LDs and localize to ER–LD junctions have been identified. This junction is unique as it is generally believed to invoke a transition from the ER bilayer membrane to a lipid monolayer that delineates LDs. Proper formation of this junction requires the ordered assembly of proteins and lipids at specialized ER subdomains. Without such a well-ordered assembly of LD biogenesis factors, neutral lipids are synthesized throughout the ER membrane, resulting in the formation of aberrant LDs. Such ectopically formed LDs impact ER and lipid homeostasis, resulting in different types of lipid storage diseases. In response to starvation, the ER–LD junction recruits factors that tether the vacuole to these junctions to facilitate LD degradation. In addition, LDs maintain close contacts with peroxisomes and mitochondria for metabolic channeling of the released fatty acids toward beta-oxidation. In this review, we discuss the function of different components that ensure proper functioning of LD contact sites, their role in lipogenesis and lipolysis, and their relation to lipid storage diseases.

scholarly journals Multiple C2 domain-containing transmembrane proteins promote lipid droplet biogenesis and growth at specialized ER subdomains

2021 ◽  
pp. mbc.E20-09-0590
Author(s):  
Amit S. Joshi ◽  
Joey V. Ragusa ◽  
William A. Prinz ◽  
Sarah Cohen
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Droplets ◽  
Transmembrane Domain ◽  
Neutral Lipids ◽  
Transmembrane Proteins ◽  
C2 Domain ◽  
General Role ◽  
C2 Domains ◽  
Contact Sites ◽  
Er Membrane

Lipid droplets (LDs) are neutral lipid-containing organelles enclosed in a single monolayer of phospholipids. LD formation begins with the accumulation of neutral lipids within the bilayer of the endoplasmic reticulum (ER) membrane. It is not known how the sites of formation of nascent LDs in the ER membrane are determined. Here we show that multiple C2 domain-containing transmembrane proteins, MCTP1 and MCTP2, are at sites of LD formation in specialized ER subdomains. We show that the transmembrane domain (TMD) of these proteins is similar to a reticulon homology domain. Like reticulons, these proteins tubulate the ER membrane and favor highly curved regions of the ER. Our data indicate that the MCTP TMDs promote LD biogenesis, increasing LD number. MCTPs co-localize with seipin, a protein involved in LD biogenesis, but form more stable microdomains in the ER. The MCTP C2 domains bind charged lipids and regulate LD size, likely by mediating ER-LD contact sites. Together, our data indicate that MCTPs form microdomains within ER tubules that regulate LD biogenesis, size, and ER-LD contacts. Interestingly, MCTP punctae colocalized with other organelles as well, suggesting that these proteins may play a more general role in linking tubular ER to organelle contact sites. [Media: see text] [Media: see text]

scholarly journals Endoplasmic Reticulum-Vacuole Contact Sites “Bloom” With Stress-Induced Lipid Droplets

Contact ◽  
2018 ◽  
Vol 1 ◽  
pp. 251525641875611 ◽  
Author(s):  
W. Mike Henne ◽  
Hanaa Hariri
Keyword(s):  
Endoplasmic Reticulum ◽  
Recent Work ◽  
Nutrient Availability ◽  
Lipid Droplets ◽  
Nutrient Sources ◽  
Contact Sites ◽  
Long Term Storage ◽  
Specific Proteins ◽  
Term Storage

Lipid droplets (LDs) serve as specialized cytoplasmic organelles that harbor energy-rich lipids for long-term storage and may be mobilized as nutrient sources during extended starvation. How cells coordinate LD biogenesis and utilization in response to fluctuations in nutrient availability remains poorly understood. Here, we discuss our recent work revealing how yeast spatially organize LD budding at organelle contacts formed between the endoplasmic reticulum and yeast vacuole/lysosome (sites known as nucleus-vacuole junctions [NVJs]). During times of imminent nutrient exhaustion, we observe blooms of stress-induced LDs surrounding the NVJ and find that this LD clustering is regulated by NVJ-resident protein Mdm1. We also discuss several emerging studies revealing specific proteins that demarcate a subpopulation of NVJ-associated LDs. Collectively, these studies reveal a previously unappreciated role for the spatial compartmentalization of LDs at organelle contacts and highlight an important role for interorganellar cross talk in LD dynamics under times of nutritional stress.

scholarly journals Seipin-Mediated Contacts as Gatekeepers of Lipid Flux at the Endoplasmic Reticulum–Lipid Droplet Nexus 

Contact ◽  
2020 ◽  
Vol 3 ◽  
pp. 251525642094582
Author(s):  
Veijo T. Salo ◽  
Maarit Hölttä-Vuori ◽  
Elina Ikonen
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Recent Work ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Intimate Relationship

Lipid droplets (LDs) are dynamic cellular hubs of lipid metabolism. While LDs contact a plethora of organelles, they have the most intimate relationship with the endoplasmic reticulum (ER). Indeed, LDs are initially assembled at specialized ER subdomains, and recent work has unraveled an increasing array of proteins regulating ER-LD contacts. Among these, seipin, a highly conserved lipodystrophy protein critical for LD growth and adipogenesis, deserves special attention. Here, we review recent insights into the role of seipin in LD biogenesis and as a regulator of ER-LD contacts. These studies have also highlighted the evolving concept of ER and LDs as a functional continuum for lipid partitioning and pinpointed a role for seipin at the ER-LD nexus in controlling lipid flux between these compartments.

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