GSE75257
Meiosis timecourse expression profile
To investigate transcriptome dynamics during the transition from vegetative growth to meiosis, we measured RNA abundance in vegetative cells (YPD), respiratory cells (pre-meiotic/YPA 8 hours), and in cells undergoing synchronous meiosis/sporulation in the budding yeast Saccharomyces cerevisiae. There is growing recognition that the binding of a transcription factor near a gene does not always indicate regulatory function, and further that a single factor may function to either activate or repress its targets depending on the cellular context. We examined these issues through a series of experiments involving the S. cerevisiae transcription factor Rap1, and its function throughout critical metabolic and developmental transitions between vegetative growth, respiratory growth, meiosis and sporulation. We simultaneously monitored the expression of all genes and the genomic binding locations of Rap1 throughout the timecourse. Genes downstream of Rap1 binding were activated and repressed dynamically, but a change - or lack of change - in Rap1 binding status was not predictive of activation, repression, or no change in regulation. Despite this, we show that Rap1 is required, at a given point in time, for both activation and repression of different gene targets, within the same cell. Specification of the transcriptional consequences of Rap1 binding is thus highly promoter-specific. The presence of other transcription factor binding motifs, the subtype of Rap1 motif, and the underlying chromatin structure of the promoter cannot fully account for the observed transcriptional outcomes. There is a better accounting for the dynamic binding behavior of Rap1 including specification of an expanded meiotic target set through a Tup1- dependent nucleosome-loss mechanism. The variable and dynamic association between binding and transcription in this simple unicellular system portends a similarly volatile relationship in more complex eukaryotes. Biological interpretations of transcription factor occupancy should be made cautiously and in conjunction with supporting data obtained under the precise condition of interest. Overall design: SK1 yeast strain SHy002 (MATa/MATa ho::LYS2/ho::LYS2 leu2::hisG/leu2::hisG lys2/lys2 ura3/ura3).  Meiosis timecourse with samples collected during vegetative growth (YPD), respiratory growth (pre-meiotic/YPA 8 hours) and 0 hr, 1.5hr, 3hr, 4.5hr, 6hr, 9hr and 12hr after transfer to sporulation media (SM).  7 separate biological replicates were used for each condition/time-point.  Labeled total RNA from each sample and a labeled genomic DNA common reference were competitively hybridized to yeast whole genome PCR based spotted arrays (resolution ~1kb).  The Rap1 ChIP, RNA abundance/expression analysis, and FAIRE analysis were all carried out on the same biological samples.