Yeast nuclear envelope subdomains with distinct abilities to resist membrane expansion

The Laboratory of Molecular and Cellular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 05/2006; 17(4):1768-78. DOI: 10.1091/mbc.E05-09-0839
Source: PubMed


Little is known about what dictates the round shape of the yeast Saccharomyces cerevisiae nucleus. In spo7Delta mutants, the nucleus is misshapen, exhibiting a single protrusion. The Spo7 protein is part of a phosphatase complex that represses phospholipid biosynthesis. Here, we report that the nuclear protrusion of spo7Delta mutants colocalizes with the nucleolus, whereas the nuclear compartment containing the bulk of the DNA is unaffected. Using strains in which the nucleolus is not intimately associated with the nuclear envelope, we show that the single nuclear protrusion of spo7Delta mutants is not a result of nucleolar expansion, but rather a property of the nuclear membrane. We found that in spo7Delta mutants the peripheral endoplasmic reticulum (ER) membrane was also expanded. Because the nuclear membrane and the ER are contiguous, this finding indicates that in spo7Delta mutants all ER membranes, with the exception of the membrane surrounding the bulk of the DNA, undergo expansion. Our results suggest that the nuclear envelope has distinct domains that differ in their ability to resist membrane expansion in response to increased phospholipid biosynthesis. We further propose that in budding yeast there is a mechanism, or structure, that restricts nuclear membrane expansion around the bulk of the DNA.

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Available from: Alexander Lorenz, Oct 16, 2014
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    • "Due to its conical shape, negative charge and membrane bending functions PA may have additional structural effects on nER membranes [40]. Cells lacking Spo7, the regulatory subunit of the Nem1/Spo7 protein phosphatase complex, produce single nuclear protrusions, which emerge from the nuclear envelope adjacent to the nucleolus [41]. It is conceivable that this site is the origin of the postulated LDAD and may also represent the previously described 'flare' region at the nuclear periphery [11]. "
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    ABSTRACT: Yeast Fld1 and Ldb16 resemble mammalian seipin, implicated in neutral lipid storage. Both proteins form a complex at the endoplasmic reticulum-lipid droplet (LD) interface. Malfunction of this complex either leads to LD clustering or to the generation of supersized LD (SLD) in close vicinity to the nuclear envelope, in response to altered phospholipid (PL) composition. We show that similar to mutants lacking Fld1, deletion of LDB16 leads to abnormal proliferation of a subdomain of the nuclear envelope, which is tightly associated with clustered LD. The human lipin-1 ortholog, the PAH1 encoded phosphatidic acid (PA) phosphatase, and its activator Nem1 are highly enriched at this site. The specific accumulation of PA-binding marker proteins indicates a local enrichment of PA in the fld1 and ldb16 mutants. Furthermore, we demonstrate that clustered LD in fld1 or ldb16 mutants are transformed to SLD if phosphatidylcholine synthesis is compromised by additional deletion of the phosphatidylethanolamine methyltransferase, Cho2. Notably, treatment of wild-type cells with oleate induced a similar LD clustering and nuclear membrane proliferation phenotype as observed in fld1 and ldb16 mutants. These data suggest that the Fld1-Ldb16 complex affects PA homeostasis at an LD-forming subdomain of the nuclear envelope. Lack of Fld1-Ldb16 leads to locally elevated PA levels that induce an abnormal proliferation of nER membrane structures and the clustering of associated LD. We suggest that the formation of SLD is a consequence of locally altered PL metabolism at this site. Copyright © 2015. Published by Elsevier B.V.
    Full-text · Article · Aug 2015 · Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids
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    • "Analysis of a dominant allele of MPS3 in budding yeast and two-hybrid analysis of Sad1 binding proteins in fission yeast suggest that SUN proteins may tether proteins involved in membrane organization at specific sites in the NE, such as at the site of SPB insertion (Friederichs et al. 2011; Miki et al. 2004). At least four possible candidates where identified in our screen: Nem1, a regulator of nuclear morphology and phospholipid biosynthesis (Campbell et al. 2006; Santos-Rosa et al. 2005; Siniossoglou et al. 1998), Apq12, a NE protein required for NPC assembly at low temperatures and for SPB insertion in S. pombe (Baker et al. 2004; Scarcelli et al. 2007; Tamm et al. 2011), Per33, a transmembrane ER and NPC-associated protein (Chadrin et al. 2010), and the nucleoporin Nup170, which forms part of the core scaffold essential for anchoring the NPC in the NE (Alber et al. 2007; Makio et al. 2009; Onischenko et al. 2009). When taken together, our genetic data point to a possible new function of SUN domain containing proteins in membrane dynamics that may account for their role at both SPBs/centrosomes and at NPCs (Liu et al. 2007; Talamas and Hetzer 2011). "
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    ABSTRACT: In virtually all eukaryotic cells, protein bridges formed by the conserved inner nuclear membrane SUN (for Sad1-UNC-84) domain-containing proteins and their outer nuclear membrane binding partners span the nuclear envelope (NE) to connect the nucleoplasm and cytoplasm. These linkages are important for chromosome movements within the nucleus during meiotic prophase and are essential for nuclear migration and centrosome attachment to the NE. In Saccharomyces cerevisiae, MPS3 encodes the sole SUN protein. Deletion of MPS3 or the conserved SUN domain is lethal in three different genetic backgrounds. Mutations in the SUN domain result in defects in duplication of the spindle pole body, the yeast centrosome-equivalent organelle. A genome-wide screen for mutants that exhibited synthetic fitness defects in combination with mps3 SUN domain mutants yielded a large number of hits in components of the spindle apparatus and the spindle checkpoint. Mutants in lipid metabolic processes and membrane organization also exacerbated the growth defects of mps3 SUN domain mutants, pointing to a role for Mps3 in nuclear membrane organization. Deletion of SLP1 or YER140W/EMP65 (for ER membrane protein of 65 kDa) aggravated growth of mps3 SUN domain mutants. Slp1 and Emp65 form an ER-membrane associated protein complex that is not required directly for spindle pole body duplication or spindle assembly. Rather, Slp1 is involved in Mps3 localization to the NE.
    Full-text · Article · Dec 2012 · G3-Genes Genomes Genetics
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    • "Since an increase in nuclear volume requires additional nuclear membrane, it is likely that lipid biosynthesis rates affect nuclear growth [Siniossoglou, 2009]. As mentioned earlier, spo7Δ mutants, in which lipid biosynthesis is altered, exhibit a single nuclear " flare " [Siniossoglou et al., 1998; Campbell et al., 2006], and when vesicle trafficking genes are mutated in cells depleted of Spo7 activity, multiple flares form around the entire nucleus [Webster et al., 2010]. Strikingly, in both single and multi-flared nuclei, the surface area of the NE increased but the nuclear/cell volume was unchanged compared to wild type cells [Webster et al., 2010]. "
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    ABSTRACT: Take a look at a textbook illustration of a cell and you will immediately be able to locate the nucleus, which is often drawn as a spherical or ovoid shaped structure. But not all cells have such nuclei. In fact, some disease states are diagnosed by the presence of nuclei that have an abnormal shape or size. What defines nuclear shape and nuclear size, and how does nuclear geometry affect nuclear function? While the answer to the latter question remains largely unknown, significant progress has been made towards understanding the former. In this review, we provide an overview of the factors and forces that affect nuclear shape and size, discuss the relationship between ER structure and nuclear morphology, and speculate on the possible connection between nuclear size and its shape. We also note the many interesting questions that remain to be explored.
    Full-text · Article · Sep 2012 · Journal of Cellular Biochemistry
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