Determining the Role of the Clr6 Histone Deacetylase Subunit Prw1 and Regulation of the Flocculin Gene gsf2+ in the Flocculation of Schizosaccharomyces pombe
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Abstract
Flocculation is the nonsexual aggregation of yeast cells in liquid medium under stressed environmental conditions. This process is used as a coping mechanism to survive in undesirable conditions such as lack of nutrients or drastic changes within the environment. Flocculation in Schizosaccharomyces pombe is primarily governed by the flocculin gene, gsf2+. Gsf2 is the primary flocculin as only the absence of this flocculin causes failure to flocculate. Several transcription factors have been identified that directly regulate gsf2+. However, there has not been studies showing the intracellular localization and temporal expression of Gsf2 under various growth conditions, stressed conditions or under control of known and potential transcription factors implicated in flocculation in live cells. In this study, the intracellular localization of Gsf2 was shown using a green fluorescent protein (GFP) tag. First, we found through fluorescence microscopy that Gsf2-GFP was expressed in cells during stationary phase in minimal medium (EMM), and throughout exponential and stationary phases in flocculation-inducing medium (FIM). Next, we looked at the ectopic expression of Gsf2-GFP in the presence and absence of transcriptional activators and repressors, respectively. Second, we explored alternate inducing conditions and found that high concentrations of ferrous chloride (FeCl2) induces flocculation. Further, we tested our gsf2-GFP strain in EMM + FeCl2 medium and detected Gsf2-GFP expression in cells during exponential and stationary phases. Finally, we explored the Clr6 histone deacetylase (HDAC) complex subunit Prw1 for its ability to repress flocculation. We confirmed by plasmid complementation that the constitutive flocculation phenotype was caused by loss of prw1+. Next, we determined that overexpression of prw1+ or clr6+ was not enough to repress flocculation completely in FIM. Further, we found through qPCR analysis that the prw1? strain shows upregulation of several flocculin genes including gsf2+, as well as cell wall remodeling genes, and the former is likely responsible for the constitutive flocculation phenotype. Collectively, these results substantially contribute to a better understanding of flocculation in S. pombe.