Translational control of fatty acid synthesis controls nuclear division during the cell cycle Nairita Maitra, Heidi Blank, Clara Kjerfve, Vytas Bankaitis, Michael Polymenis Texas A&M University, Department of Biochemistry and Biophysics, College Station, TX 77843 • Lipid synthesis during mitosis is essential for both human cells and yeasts. From our recent mass spec study on budding yeast, we found that among all other metabolites, the abundance of lipids is the highest late in the cell cycle. However, how the lipid homeostasis is maintained during the cell cycle is not understood. • Given the involvement of lipids in cancers and other diseases such as cardiovascular disease, obesity, diabetes, etc., it is important to study the regulation of lipids during the cell cycle. Moreover, higher levels of lipogenic enzymes are indicative of poor prognosis of different cancers. • Fatty acids are the building blocks of lipids. A genome-wide study performed in budding yeast in our lab showed that the translational efficiency of mRNAs encoding two major fatty acid synthesis enzymes, acetyl CoA carboxylase (ACC1) and fatty acid synthase (FAS1) peaks late in the cell cycle. Here, we show that the higher translational efficiency of ACC1 and FAS1 not only alters the abundance of different lipid species but also significantly promotes nuclear division during mitosis. • Taken together, our data link core metabolic functions of lipogenic enzymes (Acc1p and Fas1p) to the morphological changes of the nucleus during cell division. Background Major lipids peak late in the cell cycle G1 S G2/M |----------------|---------|--------| Log2(expressed ratios) A Figure 1: Abundance of lipids is highest late in the cell cycle (Blank et al MboC, 2020) A. Heatmap of major lipid species during the cell cycle in a synchronous cell culture of wild‐type, diploid cells (BY4743 background). The data were hierarchically clustered and displayed with the pheatmap R package. B. Fatty acids are the building blocks of most lipids. Acc1p catalyzes the first committed step of the fatty acid biosynthesis pathway. Further reactions in the pathway to produce fatty acids are catalyzed by the Fas1,2p complex. Lipogenic enzymes are under translational control in the cell cycle Figure 2: ACC1 and FAS1 are under periodic translational control during the cell cycle A. Major lipogenic enzymes (ACC1 and FAS1) are under periodic translational control in synchronous elutriated cultures of wild‐type, diploid cells (BY4743 background). The x-axis shows the cell sizes (fl) at different time point in the cell cycle. The data were hierarchically clustered and displayed with the pheatmap R package. B. Abundance of FAS1p during cell cycle is queried by immunoblotting, starting at the indicated cell sizes (fl) and budding index (% B). The graphs at the bottom quantify the band intensities for each independent experiment (indicated with different open symbols plotted on the y‐axis as the log2 values of their expressed ratios against the corresponding cell size (x‐axis). Experiment‐matched loading controls (filled symbols) were also quantified. Pgk1p levels Fas1p levels A B ChrXI 100119 100388 100530 100671 FAS1 ChrXIV 662454 661715 661374 ACC1 … B A C De-repressing translation of ACC1 and FAS1 alters the abundance of lipids Figure 3: uORFs mediate translational control of ACC1 and FAS1 A. Representation of the uORFs present in the 5’ leader of ACC1 and FAS1. B. Strip plot of the protein levels of FAS1-TAP in asynchronous culture of wild-type cells and cells lacking uORFs, quantified from four independent experiments. The protein levels were normalized for loading against the Pgk1p levels and the log-2 transformed values were plotted on the y-axis for the mentioned strains. C. Metabolites that changed in abundance in wild type vs. uORFm- ACC1,FAS1 cells were identified based on the magnitude of the difference (x-axis; Log2-fold change) and statistical significance (y-axis), indicated by the red