Project description:To survive in nutrient-poor conditions, cells must exit the cell cycle and enter a reversible non-replicative state known as quiescence. Yeast cells reprogram their gene expression during quiescence entry to silence transcription, but how the nascent transcriptome changes in quiescence has not been determined. By investigating the nascent transcriptome in quiescent yeast cells, we found noncoding transcription represented a larger portion of the quiescent transcriptome than in G1. To enable our nascent transcriptome analyses, we annotated over a thousand noncoding RNAs (ncRNAs) in quiescence and G1. Our work revealed that both mRNA and ncRNA are subject to increased post-transcriptional regulation in quiescence compared to G1. We found that the nuclear exosome-NNS pathway suppresses over one thousand mRNAs, in addition to canonical noncoding RNAs, in quiescence. In quiescence, a minority of the mRNAs affected by the NNS-nuclear exosome pathway are the same as those identified when glucose was removed, demonstrating a previously unidentified role for the pathway. RNA sequencing through the diauxic shift revealed at least two distinct time points at which the nuclear exosome controls the abundance of mRNAs involved in protein production, cellular organization, and metabolism, for optimal quiescence entry. Both transcription and post-transcriptional regulation are dramatically reprogrammed in quiescence, shifting the balance of noncoding and coding transcripts. The nuclear exosome and NNS are crucial for proper regulation of both mRNAs and ncRNAs in quiescence and through quiescence entry.
Project description:A defining characteristic of quiescent cells is their low level of gene activity compared to growing cells. Using a yeast model for cellular quiescence, we compared the genome-wide profiles of multiple histone modifications between growing and quiescent cells, and correlated these profiles with the presence of RNA polymerase II and its transcripts. Quiescent cells retained several forms of histone methylation normally associated with transcriptionally active chromatin and had many transcripts in common with growing cells. Quiescent cells also contained high levels of RNA polymerase II, but only low levels of the canonical initiating and elongating forms of the polymerase. The data suggest that the transcript and histone methylation marks in quiescent cells were either inherited from growing cells or established early during the development of quiescence and then retained in this non-growing cell population. This might ensure that quiescent cells can rapidly adapt to a changing environment to resume growth. RNA-seq analysis was performed in yeast Log-phase cells and purified Quiescent yeast cells and the transcriptomes in each were compared. The RNA data was correlated with genomic RNA polymerase II and histone H3 methylation occupancy profiles in the log and quiescent cells.
Project description:A defining characteristic of quiescent cells is their low level of gene activity compared to growing cells. Using a yeast model for cellular quiescence, we compared the genome-wide profiles of multiple histone modifications between growing and quiescent cells, and correlated these profiles with the presence of RNA polymerase II and its transcripts. Quiescent cells retained several forms of histone methylation normally associated with transcriptionally active chromatin and had many transcripts in common with growing cells. Quiescent cells also contained high levels of RNA polymerase II, but only low levels of the canonical initiating and elongating forms of the polymerase. The data suggest that the transcript and histone methylation marks in quiescent cells were either inherited from growing cells or established early during the development of quiescence and then retained in this non-growing cell population. This might ensure that quiescent cells can rapidly adapt to a changing environment to resume growth.
Project description:In this project, we employed a dynamic mass spectrometry-based proteomic approach to obtain global maps of basal autophagic flux in human primary fibroblasts (HCA2-hTert). The data provide a comparison of protein degradation rates between dividing and quiescent HCA2-hTert cells. To further investigate the role of autophagy in up-regulated protein degradation, protein degradation rates were also measured in autophagy-deficient (Atg5-/-) in both dividing and quiescent cells. Steady-state protein level changes in dividing and quiescent cells were measured by standard SILAC. To investigate the role of PSME1 in proteasome activity regulation, protein degradation rates in PSME1 knockdown cell line were measured by SILAC. Stable isotope labeling The media utilized for isotopic labeling was Eagle’s minimum essential medium (ATCC) supplemented with 15% dialyzed fetal bovine serum (Thermo Scientific), 100 U/ml penicillin, and 100 U/ml streptomycin. Both wildtype and Atg5-/- Cells were gradually adapted to this media and prepared for labeling experiments. Cells were then plated at a density of 500,000 cells per 10 cm plate. One day after plating, the dividing cultures were switched to MEM labeling media for SILAC (Thermo Scientific) supplemented with L-arginine:HCl (13C6, 99%) and L-lysine:2HCl (13C6, 99%, Cambridge Isotope Laboratories) at concentrations of 0.1264 g/l and 0,087 g/l and 15% dialyzed fetal bovine serum (Thermo Scientific). Cells were collected after 0, 1, 2, and 3 days of labeling, washed with PBS and cell pellets were frozen prior to further analysis. 8 days after plating, the confluent quiescent cultures were switched to MEM labeling media for SILAC (Thermo Scientific) supplemented with L-arginine:HCl (13C6, 99%) and L-lysine:2HCl (13C6, 99%; Cambridge Isotope Laboratories) at concentrations of 0.1264 g/l and 0.087 g/l and 15% dialyzed fetal bovine serum (Thermo Scientific). Cells were collected after 0, 2, 4, and 6 days of labeling, washed with PBS and cell pellets were frozen prior to further analysis. In order to measure changes in steady-state protein levels by standard SILAC, WT cells were gradually adapted to Eagle’s minimum essential medium (ATCC) supplemented with 15% dialyzed fetal bovine serum (Thermo Scientific), 100 U/ml penicillin, and 100 U/ml streptomycin. Then, WT cells were passaged in MEM labeling media for SILAC (Thermo Scientific) supplemented with L-arginine:HCl (13 C6, 99%) and L-lysine:2HCl (13 C6, 99%; Cambridge Isotope Laboratories) at concentrations of 0.1264 g/l and 0.087 g/l and 15% dialyzed fetal bovine serum (Thermo scientific) for eight passages. Cells were then plated at a density of 500,000 cells per 10-cm plate. 2 days after plating, dividing cells were collected and washed with PBS, and cell pellets were frozen prior to further analysis. Following extraction (see below), equal protein amounts of dividing and quiescent WT cells were mixed before mass spectrometric analysis. To measure protein degradation in PSME1 knockdown cell line, 8 days after plating, the confluent quiescent cultures were switched to MEM labeling media for SILAC (Thermo Scientific) supplemented with L-arginine:HCl (13C6, 99%) and L-lysine:2HCl (13D4, 96%-98%; Cambridge Isotope Laboratories) at concentrations of 0.1264 g/l and 0.087 g/l and 15% dialyzed fetal bovine serum (Thermo Scientific). Cells were collected after 3 days of labeling, washed with PBS and cell pellets were frozen prior to further analysis.