Articles written in Journal of Biosciences
Volume 43 Issue 4 September 2018 pp 693-706 Article
Nuclear envelope morphology protein 1 (NEM1) along with a phosphatidate phosphatase (PAH1) regulates lipid homeostasisand membrane biogenesis in yeast and mammals. We investigated four putative NEM1 homologues (TtNEM1A,TtNEM1B, TtNEM1C and TtNEM1D) in the Tetrahymena thermophila genome. Disruption of TtNEM1B, TtNEM1C orTtNEM1D did not compromise normal cell growth. In contrast, we were unable to generate knockout strain of TtNEM1Aunder the same conditions, indicating that TtNEM1A is essential for Tetrahymena growth. Interestingly, loss of TtNEM1Bbut not TtNEM1C or TtNEM1D caused a reduction in lipid droplet number. Similar to yeast and mammals, TtNem1B ofTetrahymena exerts its function via Pah1, since we found that PAH1 overexpression rescued loss of Nem1 function.However, unlike NEM1 in other organisms, TtNEM1B does not regulate ER/nuclear morphology. Similarly, neitherTtNEM1C nor TtNEM1D is required to maintain normal ER morphology. While Tetrahymena PAH1 was shown tofunctionally replace yeast PAH1 earlier, we observed that Tetrahymena NEM1 homologues did not functionally replaceyeast NEM1. Overall, our results suggest the presence of a conserved cascade for regulation of lipid homeostasis andmembrane biogenesis in Tetrahymena. Our results also suggest a Nem1-independent function of Pah1 in the regulation ofER morphology in Tetrahymena.
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