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Transcriptional regulation of changes in growth, cell cycle, and gene expression of Saccharomyces cerevisiae due to changes in buoyancy.  CB Coleman^1,2, PL Allen¹, JM Valles³, and TG Hammond^1,2,4. ¹Department of Medicine/Nephrology, Tulane University School of Medicine, Astrobiology Center; Center for Bioenvironmental Research; ²Tulane University Graduate Program in Biomedical Sciences, ³Department of Physics, Brown University, Providence RI, and ⁴Southeast Louisiana Veterans Healthcare System, New Orleans, LA.

   To understand the cellular effects of magnetic traps requires independent analysis of the effects of magnetic field (B), gravity, and buoyancy. In the current study, buoyancy is manipulated by addition of Ficoll, a viscous substance that can create gradients of buoyancy without affecting osmolality. Specifically, we investigated whether Ficoll induces dose dependent changes in cell growth, cell cycle, and gene expression in Saccharomyces cerevisiae, with special attention paid to the neutrally buoyancy concentration of 35% Ficoll. Cell growth and cell cycle analysis were examined in wild type (WT) yeast and strains with deletions in transcription factors Msn4 or Sfp1. Gene expression of YIL052C increased at 25% Ficoll and was not dependent on Sfp1, but was dependent on Msn4. SSA4 decreased in expression at 25% and 35% Ficoll and was dependent on both Msn4 at all doses of Ficoll and Sfp1 at 10% and 25% Ficoll. YST2 gene expression was not dependent on Ficoll. Growth of WT and Msn4∆ but not Sfp1∆ strains showed a Ficoll dose dependent decrease. Changes in the cell cycle of WT, Msn4∆, and Sfp1∆ strains were dose dependent. The increase in % cells in S phase of WT and Msn4∆ strains at all doses of Ficoll, along with the increase in G2/M at 10% Ficoll and G1 at 25% Ficoll in the Sfp1∆ strain supports the changes observed in growth. This study shows that buoyancy has selective and dose dependent effects on growth, cell cycle and gene expression, some of which are Msn4 and Sfp1 dependent.