Lipid droplets (LDs) are essential organelles for cellular energy homeostasis, but how metabolic cues are integrated in their life cycle is unclear. Teixeira et al. find that two protein isoforms, Ldo16 and Ldo45, differentially regulate LD dynamics under nutrient-rich and -deprived conditions, linking energy metabolism and storage.
bProper functioning of intracellular membranes is critical for many cellular processes. A key feature of membranes is their ability to adapt to changes in environmental conditions by adjusting their composition so as to maintain constant biophysical properties, including fluidity and flexibility. Similar changes in the biophysical properties of membranes likely occur when intracellular processes, such as vesicle formation and fusion, require dramatic changes in membrane curvature. Similar modifications must also be made when nuclear pore complexes (NPCs) are constructed within the existing nuclear membrane, as occurs during interphase in all eukaryotes. Here we report on the role of the essential nuclear envelope/endoplasmic reticulum (NE/ER) protein Brl1 in regulating the membrane composition of the NE/ER. We show that Brl1 and two other proteins characterized previously-Brr6, which is closely related to Brl1, and Apq12-function together and are required for lipid homeostasis. All three transmembrane proteins are localized to the NE and can be coprecipitated. As has been shown for mutations affecting Brr6 and Apq12, mutations in Brl1 lead to defects in lipid metabolism, increased sensitivity to drugs that inhibit enzymes involved in lipid synthesis, and strong genetic interactions with mutations affecting lipid metabolism. Mutations affecting Brl1 or Brr6 or the absence of Apq12 leads to hyperfluid membranes, because mutant cells are hypersensitive to agents that increase membrane fluidity. We suggest that the defects in nuclear pore complex biogenesis and mRNA export seen in these mutants are consequences of defects in maintaining the biophysical properties of the NE. T he nuclear envelope (NE) of eukaryotic cells compartmentalizes the nuclear material and separates it from the cytoplasm. The double membrane of the NE consists of an outer and an inner nuclear membrane (ONM and INM) that differ in protein and lipid composition. The NE is structurally and functionally related to the endoplasmic reticulum (ER), and the ONM is contiguous with the ER (1, 2). Embedded in the NE are the nuclear pore complexes (NPCs) and, in budding yeast, the spindle pole body (SPB). NPCs are extremely large and are constructed from multiple copies of about 30 different nucleoporins (nups) (3, 4). NPCs mediate selective trafficking of proteins and other macromolecules between the nucleus and the cytoplasm but also serve other important functions, including gene activation and mRNA surveillance (5, 6). The biogenesis of NPCs and their distribution over the NE are highly regulated processes and are coordinated with the cell cycle (7). During interphase, the number of NPCs doubles. In budding yeast, the NE remains intact throughout the cell cycle, and all the formation of NPCs occurs through de novo construction within the NE.In addition to the ONM and the INM, the NE contains a pore membrane domain (POM), formed by the fusion of the INM and ONM at sites where NPCs are assembled (8). The POM is a highly curved region of the NE that is i...
Osmostress triggers profound adaptive changes in the physiology of the cell with a great impact on gene expression. Saccharomyces cerevisiae has served as an instructive model system to unravel the complexity of the stress response at the transcriptional level. The main signal transduction pathways like the HOG (high osmolarity glycerol) MAP kinase cascade or the protein kinase A pathway regulate multiple specific transcription factors to accomplish large changes in the expression pattern of the genome. Transcription profiling and proteomic studies give us an idea about the impact of osmostress on gene expression and the overall protein composition. Recent genome wide location studies for several transcription factors and signaling kinases involved in the transcriptional stress response shed light on the genomic organization of the osmostress response at the level of the dynamic association of regulators with chromatin. Finally, global surveys of mRNA stability complete our picture of the mechanisms underlying the massive reprogramming of global gene expression, which leads to efficient adaptation to osmotic stress.
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