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Time dynamics of quantitative protein and mRNA levels reveals extensive translational regulation after stress

ABSTRACT: Eukaryotic cells are constantly challenged by the presence of reactive oxygen species, which play an important role in aging and human disease progression. In particular, acute oxidative stress can lead to extensive damage to cellular DNA, proteins, and lipids and can trigger a response that remodels the transcriptional and translational state of the cell. Although a number of previous studies have profiled the relative changes in mRNA and protein and more studies revealing the dynamics of transcription and translation in response to stress are starting to emerge, a quantitative view of this response has been lacking. Here, we have applied quantitative methods to characterize the time dynamics of mRNA and protein levels in the oxidative stress response of the fission yeast Schizosaccharomyces pombe, which has allowed us to perform dynamic modeling of responsive genes in units of copies per cell. Analysis of the resulting time dynamics provided a new genome-wide view of the scale, timing and rates of transcription and translation in the transient response. The majority of dynamic genes were observed to be responsive in their mRNA or protein levels alone implying extensive translational regulation. Nevertheless, modeling of genes with responsive mRNA and protein levels showed that protein levels could, in a majority of these cases, be accurately predicted with constant translation and decay rates while a minority benefited from explicit translation delay parameters. A number of independent features, e.g. measures of codon bias, ribosome occupancy, etc., were found to be less correlated to maximally perturbed protein levels than steady-state levels. Codon bias measures were more correlated than mRNA levels to quantitative protein levels at both perturbed and un-perturbed states. Measures of translation activity, on the other hand, were only significantly correlated at steady state.

ORGANISM(S): Schizosaccharomyces pombe Saccharomyces cerevisiae

PROVIDER: GSE62120 | GEO | 2015/03/01

SECONDARY ACCESSION(S): PRJNA263246

REPOSITORIES: GEO

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Project description:Eukaryotic cells are constantly challenged by the presence of reactive oxygen species, which play an important role in aging and human disease progression. In particular, acute oxidative stress can lead to extensive damage to cellular DNA, proteins, and lipids and can trigger a response that remodels the transcriptional and translational state of the cell. Although a number of previous studies have profiled the relative changes in mRNA and protein and more studies revealing the dynamics of transcription and translation in response to stress are starting to emerge, a quantitative view of this response has been lacking. Here, we have applied quantitative methods to characterize the time dynamics of mRNA and protein levels in the oxidative stress response of the fission yeast Schizosaccharomyces pombe, which has allowed us to perform dynamic modeling of responsive genes in units of copies per cell. Analysis of the resulting time dynamics provided a new genome-wide view of the scale, timing and rates of transcription and translation in the transient response. The majority of dynamic genes were observed to be responsive in their mRNA or protein levels alone implying extensive translational regulation. Nevertheless, modeling of genes with responsive mRNA and protein levels showed that protein levels could, in a majority of these cases, be accurately predicted with constant translation and decay rates while a minority benefited from explicit translation delay parameters. A number of independent features, e.g. measures of codon bias, ribosome occupancy, etc., were found to be less correlated to maximally perturbed protein levels than steady-state levels. Codon bias measures were more correlated than mRNA levels to quantitative protein levels at both perturbed and un-perturbed states. Measures of translation activity, on the other hand, were only significantly correlated at steady state. In total 32 samples: 11 for stressed time series R1, 11 for stressed time series R2, 5 for control time series C1 and 5 for control time series C2

Project description:Quantitative studies of the P. falciparum transcriptome have shown that the tightly controlled progression of the parasite through the intraerythrocytic developmental cycle (IDC) is accompanied by a continuous gene expression cascade where most expressed genes exhibit a single transcriptional peak. Since proteins represent the decisive business end of gene expression, understanding the correlation between mRNA and protein levels is crucial for inferring biological activity from transcriptional gene expression data. While pertinent studies on other organisms show that as little as 20-40% of protein abundance variation may be attributable to corresponding mRNA levels, the situation in Plasmodium is further complicated by the dynamic nature of the cyclic gene expression cascade where the mRNA levels of most genes change constantly during the IDC. In this study, we simultaneously determined mRNA and protein abundance profiles for P. falciparum parasites during the IDC at 2-hour resolution based on spotted oligonucleotide microarrays and 2D-protein gels in combination with DIGE fluorescent dyes. Intriguingly, most proteins are represented by more than one isoform, presumably due to post-translational modifications. Analysis of 366 protein abundance profiles and the corresponding mRNA levels shows that in 67.2% of cases the protein abundance peaks at least 8 hours after the mRNA level peak. While it may be tempting to interpret this as evidence for widespread post-transcriptional gene regulation additional analyses including computer modeling demonstrate that in >60% of these cases the observed protein profiles including the peak lag times could arise as a consequence of the corresponding mRNA levels when simple translation and degradation dynamics are assumed. We further characterize and illustrate these dynamics and show that even human host proteins within the parasite may be subject to similar dynamics as their parasite counterparts. 24 timepoint samples were harvested from a tightly synchronous 6.5 liter biofermenter culture of P. falciparum (Dd2) at 2-hour intervals during one entire intraerythrocytic developmental cycle and compared against a 3D7 RNA reference pool.

Project description:Cell growth rate is regulated in response to resource availability including the abundance, and molecular form, of essential nutrients. In the model eukaryotic cell, Saccharomyces cerevisiae (budding yeast), the molecular form of environmental nitrogen impacts both cell growth rate and mRNA expression. Disentangling causal relationships between nitrogen availability, cell growth rate and differential gene expression poses a considerable challenge. Using experimental control of cell growth rate using chemostats, we studied the effect of variation in environmental nitrogen on differential gene expression. We find that the primary determinant of nitrogen-regulated gene expression is nitrogen abundance whereas variation in nitrogen source affects the expression of only a small number of transcripts with highly specialized functions. To study the dynamics of nitrogen-responsive gene expression we perturbed steady-state nitrogen-limited chemostat cultures by addition of either proline or glutamine. Addition of either proline or glutamine to cells growing in nitrogen-limited chemostats results in repression of the nitrogen catabolite repression (NCR) regulon consistent with nitrogen abundance, and not nitrogen source, being the primary determinant of nitrogen-regulated gene expression. We find that a transition from nitrogen-limited to nitrogen-replete conditions is accompanied by rapid induction of transcripts required for protein translation. We identified a reciprocal relationship between specific regulons required for protein translation (RP and RiBi) and the NCR regulon. Using mathematical modeling we find evidence that cells adopt a metabolically inefficient growth mode during this transition. By means of high resolution time series analysis we find evidence that rapid, and potentially accelerated, mRNA degradation plays an important role in remodeling gene expression programs in response to change in environmental nitrogen. We propose that the evolutionarily conserved TORC1 signaling pathway orchestrates the balance between protein translation and assimilation of nitrogen sources at the transcriptional level to optimize rates of cell proliferation. A total of of 102 samples were analyzed in different nitrogen-limited conditions using chemostats in both steady-state and dynamic conditions. A common reference obtained from an ammonium-limited chemostat growing at a dilution rate of 0.12/hr was used for all two color hybridization experiments.

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Time dynamics of quantitative protein and mRNA levels reveals extensive translational regulation after stress

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