Project description:In the budding yeast Saccharomyces cerevisiae, transcription factors (TFs) regulate the periodic expression of many genes during the cell cycle, including gene products required for progression through cell-cycle events. Experimental evidence coupled with quantitative models suggest that a network of interconnected TFs is capable of regulating periodic genes over the cell cycle. Importantly, these dynamical models were built on transcriptomics data and assumed that TF protein levels and activity are directly correlated with mRNA abundance. To ask whether TF transcripts match protein expression levels as cells progress through the cell cycle, we applied a multiplexed targeted mass spectrometry approach (parallel reaction monitoring) on synchronized populations of cells. We found that protein expression of many TFs and cell-cycle regulators closely followed their respective mRNA transcript dynamics in cycling wild-type cells. Discordant mRNA/protein expression dynamics were also observed for a subset of cell-cycle TFs and for proteins targeted for degradation by E3 ubiquitin ligase complexes such as SCF (Skp1/Cul1/F-box) and APC/C (anaphase-promoting complex/cyclosome). We further profiled mutant cells lacking B-type cyclin/CDK activity (clb1-6), where oscillations in ubiquitin ligase activity, cyclin/CDKs, and cell-cycle progression are halted. We found that a number of proteins were no longer periodically degraded in clb1-6 mutants compared to wild type, highlighting the importance of post-transcriptional regulation. Finally, the TF complexes responsible for activating G1/S transcription (SBF and MBF) were more constitutively expressed at the protein level than their periodic mRNA expression levels in both wild-type and mutant cells. This comprehensive investigation of cell-cycle regulators reveals that multiple layers of regulation (transcription, protein stability, and proteasome targeting) affect protein expression dynamics during the cell cycle.
Project description:Cell division is a highly regulated process that secures the generation of healthy progeny in all organisms, from yeast to human. Dysregulation of this process can lead to uncontrolled cell proliferation and genomic instability, both which are hallmarks of cancer. Cell cycle progression is dictated by a complex network of kinases and phosphatases. These enzymes act on their substrates in a highly specific temporal manner ensuring that the process of cell division is unidirectional and irreversible. Key events of the cell cycle, such as duplication of genetic material and its redistribution to daughter cells, occur in S-phase and mitosis, respectively. Deciphering the dynamics of phosphorylation/dephosphorylation events during these cell cycle phases is important. Here we showcase a quantitative proteomic and phosphoproteomic mass spectrometry dataset that profiles both early and late phosphorylation events and associated proteome alterations that occur during S-phase and mitotic arrest in the model organism S. cerevisiae. This dataset is of broad interest as the molecular mechanisms governing cell cycle progression are conserved throughout evolution.
Project description:Cell division is a highly regulated process that secures the generation of healthy progeny in all organisms, from yeast to human. Dysregulation of this process can lead to uncontrolled cell proliferation and genomic instability, both which are hallmarks of cancer. Cell cycle progression is dictated by a complex network of kinases and phosphatases. These enzymes act on their substrates in a highly specific temporal manner ensuring that the process of cell division is unidirectional and irreversible. Key events of the cell cycle, such as duplication of genetic material and its redistribution to daughter cells, occur in S-phase and mitosis, respectively. Deciphering the dynamics of phosphorylation/dephosphorylation events during these cell cycle phases is important. Here we showcase a quantitative proteomic and phosphoproteomic mass spectrometry dataset that profiles both early and late phosphorylation events and associated proteome alterations that occur during S-phase and mitotic arrest in the model organism S. cerevisiae. This dataset is of broad interest as the molecular mechanisms governing cell cycle progression are conserved throughout evolution.
Project description:Yeast cell cycle transcription dynamics in two S. cerevisae strains: BF264-15DU (MATa ade1 his2 leu2-3, 112 trp1-1 ura3Dns, bar1) [referred to as wild type] and a mutant of the wild type strain, clb1,2,3,4,5,6 GAL1-CLB1, [referred to as cyclin mutant] that does not express S-phase and mitotic cyclins. Both strains were synchronized by elutriation and released into YEP 2% dextrose/1M sorbitol at 30c. 15 samples were taken at 16 min intervals covering ~2 cycles in wild-type and ~1.5 cycles for the mutants. A significant fraction of the Saccharomyces cerevisiae genome is transcribed periodically during the cell division cycle, suggesting that properly timed gene expression is important for regulating cell cycle events. Genomic analyses of transcription factor localization and expression dynamics suggest that a network of sequentially expressed transcription factors could control the temporal program of transcription during the cell cycle. However, directed studies interrogating small numbers of genes indicate that their periodic transcription is governed by the activity of cyclin-dependent kinases (CDKs). To determine the extent to which the global cell cycle transcription program is controlled by cyclin/CDK complexes, we compared genome-wide transcription dynamics in wild type budding yeast to mutants that do not express S-phase and mitotic cyclins. Experiment Overall Design: Cell cycle synchrony/time series experiments. G1 cells collected by elutriation was examined over time for 2 cell cycles. Strains compared: wild type vs cyclin mutants. 15 samples per time course at 16 min resolution. 2 biological replicates per strain.