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: 4.55). 05/2006; 17(4):1768-78. DOI: 10.1091/mbc.E05-09-0839
Source: PubMed

ABSTRACT 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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    • "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.
    Journal of Cellular Biochemistry 09/2012; 113(9):2813-21. DOI:10.1002/jcb.24178 · 3.37 Impact Factor
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    • ") that is hypomorphic at 30°C and nonfunctional at 37°C (Campbell et al., 2006). These strains also expressed the nucleoplasmic protein Pus1p fused to GFP (pGFP-PUS1; Hellmuth et al., 1998). "
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    ABSTRACT: The parameters that control nuclear size and shape are poorly understood. In yeast, unregulated membrane proliferation, caused by deletion of the phospholipid biosynthesis inhibitor SPO7, leads to a single nuclear envelope "flare" that protrudes into the cytoplasm. This flare is always associated with the asymmetrically localized nucleolus, which suggests that the site of membrane expansion is spatially confined by an unknown mechanism. Here we show that in spo7Δ cells, mutations in vesicle-trafficking genes lead to multiple flares around the entire nucleus. These mutations also alter the distribution of small nucleolar RNA-associated nucleolar proteins independently of their effect on nuclear shape. Both single- and multi-flared nuclei have increased nuclear envelope surface area, yet they maintain the same nuclear/cell volume ratio as wild-type cells. These data suggest that, upon membrane expansion, the spatial confinement of the single nuclear flare is dependent on vesicle trafficking. Moreover, flares may facilitate maintenance of a constant nuclear/cell volume ratio in the face of altered membrane proliferation.
    The Journal of Cell Biology 12/2010; 191(6):1079-88. DOI:10.1083/jcb.201006083 · 9.69 Impact Factor
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    • "Short spindles were defined as those that traversed a spherical nucleus, while long spindles traversed an hourglass nucleus with two separated DNA masses. To determine nuclear morphology, cells containing a pPUS1-GFP-URA plasmid (CAMPBELL et al. 2006) were grown to mid-log phase, fixed in 4% paraformaldehyde for one hour at 23˚C, and then observed using a Nikon Eclipse E800 fluorescent microscope. "
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    ABSTRACT: The Saccharomyces cerevisiae nuclear membrane is part of a complex nuclear envelope environment also containing chromatin, integral and peripheral membrane proteins, and large structures such as nuclear pore complexes (NPCs) and the spindle pole body. To study how properties of the nuclear membrane affect nuclear envelope processes, we altered the nuclear membrane by deleting the SPO7 gene. We found that spo7Δ cells were sickened by the mutation of genes coding for spindle pole body components and that spo7Δ was synthetically lethal with mutations in the SUN domain gene MPS3. Mps3p is required for spindle pole body duplication and for a variety of other nuclear envelope processes. In spo7Δ cells, the spindle pole body defect of mps3 mutants was exacerbated, suggesting that nuclear membrane composition affects spindle pole body function. The synthetic lethality between spo7Δ and mps3 mutants was suppressed by deletion of specific nucleoporin genes. In fact, these gene deletions bypassed the requirement for Mps3p entirely, suggesting that under certain conditions spindle pole body duplication can occur via an Mps3p-independent pathway. These data point to an antagonistic relationship between nuclear pore complexes and the spindle pole body. We propose a model whereby nuclear pore complexes either compete with the spindle pole body for insertion into the nuclear membrane or affect spindle pole body duplication by altering the nuclear envelope environment.
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