Inactivation of the C-elegans lipin homolog leads to ER disorganization and to defects in the breakdown and reassembly of the nuclear envelope

The Laboratory of Biochemistry and Genetics and National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 8 Center Drive, Bethesda, MD 20892, USA.
Journal of Cell Science (Impact Factor: 5.43). 07/2009; 122(Pt 12):1970-8. DOI: 10.1242/jcs.044743
Source: PubMed


The nuclear envelope (NE) is a dynamic structure, undergoing periods of growth, breakdown and reassembly during the cell cycle. In yeast, altering lipid synthesis by inactivating the yeast homolog of lipin, a phosphatidic acid phosphohydrolase, leads to disorganization of the peripheral ER and abnormal nuclear shape. These results suggest that lipid metabolism contributes to NE dynamics; however, since yeast undergo closed mitosis, the relevance of these observations to higher eukaryotes is unclear. In mammals, lipin has been implicated in adipose tissue differentiation, insulin resistance, lipid storage and obesity, but the underlying cellular defects caused by altering lipin levels are not known. Here, we identify the Caenorhabditis elegans lipin homolog (LPIN-1) and examine its affect on NE dynamics. We find that downregulating LPIN-1 by RNAi results in the appearance of membrane sheets and other abnormal structures in the peripheral ER. Moreover, lpin-1 RNAi causes defects in NE breakdown, abnormal chromosome segregation and irregular nuclear morphology. These results uncover cellular processes affected by lipin in metazoa, and suggest that lipid synthesis has a role in NE dynamics.

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    • "RIBO-1, for example, has been shown to play a role in chromosome segregation [52]. The polarized ER aggregations observed in OSTD-1 depletions are also distinct from the distribution of ER aggregates reported in ribo-1, car-1 and lpin-1 RNAi-treated embryos or the more disperse distribution of ER in rab-5 and yop-1/ret-1 depletions [59,61,81], suggesting that OSTD-1 may be involved in maintaining ER morphology specifically in the anterior. It is not clear how the polarization of ER functions during mitosis, but transitional ER (tER) sites have been shown to be polarized in the hyphal tips of fungi where growth and morphogenesis occur [82]. "
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    ABSTRACT: Cell division is important for many cellular processes including cell growth, reproduction, wound healing and stem cell renewal. Failures in cell division can often lead to tumors and birth defects. To identify factors necessary for this process, we implemented a comparative profiling strategy of the published mitotic spindle proteome from our laboratory. Of the candidate mammalian proteins, we determined that 77% had orthologs in Caenorhabditis elegans and 18% were associated with human disease. Of the C. elegans candidates (n=146), we determined that 34 genes functioned in embryonic development and 56% of these were predicted to be membrane trafficking proteins. A secondary, visual screen to detect distinct defects in cell division revealed 21 genes that were necessary for cytokinesis. One of these candidates, OSTD-1, an ER resident protein, was further characterized due to the aberrant cleavage furrow placement and failures in division. We determined that OSTD-1 plays a role in maintaining the dynamic morphology of the ER during the cell cycle. In addition, 65% of all ostd-1 RNAi-treated embryos failed to correctly position cleavage furrows, suggesting that proper ER morphology plays a necessary function during animal cell division.
    Full-text · Article · Oct 2013 · PLoS ONE
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    • "In humans and mice, Lpin-1 is associated with metabolic syndrome and type 2 diabetes [77-80] and mutations in human LPIN2 cause Majeed syndrome [81]. C. elegans lpin-1 has been implicated in affecting fat storage and the breakdown and assembly of the nuclear envelope [54,55]. Consistent with the mammalian Lpin1 mutation, inactivation of C. elegans lpin-1 by RNAi displayed resulted in low fat with small size of lipid droplets, as indicted by Nile Red staining (Figure 4). "
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    ABSTRACT: Background Animal models are indispensable to understand the lipid metabolism and lipid metabolic diseases. Over the last decade, the nematode Caenorhabditis elegans has become a popular animal model for exploring the regulation of lipid metabolism, obesity, and obese-related diseases. However, the genomic and functional conservation of lipid metabolism from C. elegans to humans remains unknown. In the present study, we systematically analyzed genes involved in lipid metabolism in the C. elegans genome using comparative genomics. Results We built a database containing 471 lipid genes from the C. elegans genome, and then assigned most of lipid genes into 16 different lipid metabolic pathways that were integrated into a network. Over 70% of C. elegans lipid genes have human orthologs, with 237 of 471 C. elegans lipid genes being conserved in humans, mice, rats, and Drosophila, of which 71 genes are specifically related to human metabolic diseases. Moreover, RNA-mediated interference (RNAi) was used to disrupt the expression of 356 of 471 lipid genes with available RNAi clones. We found that 21 genes strongly affect fat storage, development, reproduction, and other visible phenotypes, 6 of which have not previously been implicated in the regulation of fat metabolism and other phenotypes. Conclusions This study provides the first systematic genomic insight into lipid metabolism in C. elegans, supporting the use of C. elegans as an increasingly prominent model in the study of metabolic diseases.
    Full-text · Article · Mar 2013 · BMC Genomics
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    • "Mammalian lipin-1 and -2 were shown to complement phenotypes exhibited by yeast pah1Δ mutant cells [65], indicating the functions of PAP enzymes are evolutionarily conserved. Indeed, the discovery of yeast Pah1p led to the identification of genes encoding PAP enzymes in humans [21] [63], mice [59] [62], flies [66] [67], worms [68], and plants [69] [70]. All PAP enzymes have the HAD-like domain that contains a DXDX(T/V) catalytic motif and the NLIP domain of unknown function [21] [23] [59] [71]. "
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    ABSTRACT: Yeast Pah1p phosphatidate phosphatase (PAP) catalyzes the penultimate step in the synthesis of triacylglycerol. PAP plays a crucial role in lipid homeostasis by controlling the relative proportions of its substrate phosphatidate and its product diacylglycerol. The cellular amounts of these lipid intermediates influence the synthesis of triacylglycerol and the pathways by which membrane phospholipids are synthesized. Physiological functions affected by PAP activity include phospholipid synthesis gene expression, nuclear/endoplasmic reticulum membrane growth, lipid droplet formation, and vacuole homeostasis and fusion. Yeast lacking Pah1p PAP activity are acutely sensitive to fatty acid-induced toxicity and exhibit respiratory deficiency. PAP is distinguished in its cellular location, catalytic mechanism, and physiological functions from Dpp1p and Lpp1p lipid phosphate phosphatases that utilize a variety of substrates that include phosphatidate. Phosphorylation/dephosphorylation is a major mechanism by which Pah1p PAP activity is regulated. Pah1p is phosphorylated by cytosolic-associated Pho85p-Pho80p, Cdc28p-cyclin B, and protein kinase A and is dephosphorylated by the endoplasmic reticulum-associated Nem1p-Spo7p phosphatase. The dephosphorylation of Pah1p stimulates PAP activity and facilitates the association with the membrane/phosphatidate allowing for its reaction and triacylglycerol synthesis. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
    Full-text · Article · Aug 2012 · Biochimica et Biophysica Acta
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