Project description:Translational buffering refers to the regulation of ribosome occupancy to offset the effects of transcriptional variation. While previous work reported translational buffering in a limited set of conditions, it remains unknown whether this is an intrinsic property of specific genes across a large number of different cell types. To identify genes exhibiting this phenomenon on a global scale and across different experimental conditions, we uniformly analyzed 1515 matched ribosome profiling and RNA-seq datasets from human and mouse tissues or cell lines. This resource enabled us to determine the set of genes exhibiting translational buffering by comparative analysis of variation at ribosome occupancy and the RNA levels across cell types and the relationship between mRNA abundance and translation efficiency. We demonstrate that translational buffering is a conserved property of genes using homologous gene pairs from humans and mice. Genes exhibiting translational buffering have lower variation in protein abundance in cancer cell lines, primary human tissues and mouse samples. Moreover, we observed that translationally buffered genes are more likely to be haploinsufficient and triplosensitive suggesting a demand for stringent dosage limits in these genes. We hypothesized two models of translational buffering, namely “differential accessibility model” and “change in translation initiation rate model”. Our experiment suggests that some transcripts conform to the former and others align with the alternate model. Overall, our work broadens the catalog of genes subjected to translational buffering, underscores the characteristics of genes that demonstrate this phenomenon and additionally provides an insight into the rationale driving this effect.
Project description:Differences in gene regulation between human and closely related species influence phenotypes that are distinctly human. While gene regulation is a multi-step process, the majority of research concerning divergence in gene regulation among primates has focused on transcription. To gain a comprehensive view of gene regulation, we surveyed genome-wide ribosome occupancy, which reflects levels of protein translation, in lymphoblastoid cell lines derived from human, chimpanzee and rhesus macaque. We further integrated mRNA and protein level measurements collected from matching cell lines. We find that, in addition to transcriptional regulation, the major factor determining protein level divergence between human and closely related species is post-translational buffering. Inter-species divergence in transcription is generally propagated to the level of protein translation. In contrast, gene expression divergence is often attenuated post-translationally, potentially mediated through post-translational modifications. Results from our analysis indicate that post-translational buffering is a conserved mechanism that led to relaxation of selective constraint on transcript levels in humans.
Project description:Transcript buffering entails reciprocal modulation of mRNA synthesis and degradation to maintain stable RNA levels under varying cellular conditions. Current models depict a global connection between mRNA synthesis and degradation, but underlying mechanisms remain unclear. Here we show that changes in RNA metabolism following depletion of TIP60/KAT5, the acetyltransferase subunit of the NuA4 transcriptional coactivator complex, reveal that transcript buffering occurs at a gene-specific level. By combining RNA sequencing of nuclear, cytoplasmic, and newly synthesised transcript fractions with biophysical modelling in mouse embryonic stem cells, we demonstrate that transcriptional changes caused by TIP60 depletion are offset by corresponding changes in RNA nuclear export and cytoplasmic stability, indicating gene-specific buffering. Disruption of the unrelated ATAC coactivator complex also causes gene-specific transcript buffering. We propose that cells dynamically adjust RNA splicing, export, and degradation in response to individual RNA synthesis alterations, thereby sustaining cellular homeostasis.
Project description:Disruptions of protein homeostasis in the endoplasmic reticulum (ER) elicit activation of the unfolded protein response (UPR), a translation- and transcription-coupled proteostatic stress response pathway. The primary translational control arm of the UPR is initiated by the PERK-dependent phosphorylation of eIF2α, leading to a large-scale reprogramming of translation and subsequent activation of an ATF4-mediated transcriptional program. It has remained challenging, however, to accurately evaluate the contribution of each component of the eIF2α/ATF4 pathway to the remodelling of transcription and translation. Here, we have used mouse embryonic fibroblasts containing either a knock-in of the non-phosphorylatable eIF2α S51A mutant or knock-out for ATF4 by ribosome profiling and mRNA-seq to define the specific contributions of eIF2α phosphoryation and ATF4 in controlling the translational and transcriptional components of the UPR. These studies show that the transcriptional and translational targets of each P-eIF2α, ATF4, and the other UPR gene expression programs overlapped extensively, leading to a core set of UPR genes whose robust expression in response to ER stress is driven by multiple mechanisms. The identification of other, more factor-specific targets illustrated the potential for functional specialization of the UPR. As the UPR progressed temporally, cells employed distinct combinations of transcriptional and translational mechanisms, initiated by different factors, to adapt to ongoing stress. These effects were accompanied by a buffering effect where changes in mRNA levels were coupled to opposing changes in ribosome loading, a property which makes cooperation between transcription and translation essential to confer robust protein expression. Translational analysis by ribosome profiling and mRNA-seq of PERK pathways mutants during the UPR. Mouse embryonic fibroblasts (MEFs) lacking components of the PERK pathway (eIF2a phosphorylation and ATF4) were subjected to ER stress and analyzed by ribosome profiling.
Project description:Aneuploidy, i.e., variation in the number of individual chromosomes (chromosomal aneuploidy) or chromosome segment (segmental aneuploidy) is associated with developmental abnormalities and reduced fitness in all species examined, is the leading cause of miscarriages and mental retardations and a hallmark of cancer. Despite their documented importance in disease the effects of aneuploidies on the transcriptome remains largely unknown. Here we have examined the expression output in seven deficiency heterozygotes as single deficiencies and in all pairwise combinations. The results show that genes in one copy are buffered, i.e., are expressed above the expected 50% expression level compared to wild type and the buffering is general and not influenced by additional haploid regions. Long genes are significantly better buffered than short genes and our analysis suggests that gene length is the primary determinant for the degree of buffering. For short genes the degree of buffering depends on expression level and expression pattern. Furthermore, the results show that in deficiency heterozygotes the expression of genes involved in proteolysis is enhanced and negatively correlates with the degree of buffering. Our results suggest that proteolysis is a general response induced by aneuploidy.
Project description:Aneuploidy, i.e., variation in the number of individual chromosomes (chromosomal aneuploidy) or chromosome segment (segmental aneuploidy) is associated with developmental abnormalities and reduced fitness in all species examined, is the leading cause of miscarriages and mental retardations and a hallmark of cancer. Despite their documented importance in disease the effects of aneuploidies on the transcriptome remains largely unknown. Here we have examined the expression output in seven deficiency heterozygotes as single deficiencies and in all pairwise combinations. The results show that genes in one copy are buffered, i.e., are expressed above the expected 50% expression level compared to wild type and the buffering is general and not influenced by additional haploid regions. Long genes are significantly better buffered than short genes and our analysis suggests that gene length is the primary determinant for the degree of buffering. For short genes the degree of buffering depends on expression level and expression pattern. Furthermore, the results show that in deficiency heterozygotes the expression of genes involved in proteolysis is enhanced and negatively correlates with the degree of buffering. Our results suggest that proteolysis is a general response induced by aneuploidy. We prepared total RNA from flies heterozygous for seven different deletions, Df(3R)ED10953, Df(2L)ED4559, Df(2R)ED1770, Df(2R)ED1612, Df(2L)ED3, Df(3R)ED5071 or Df(3R)ED7665 in two or three single biological replicates or in pairwise combinations, as well as from six biological replicates of wild type control flies.
Project description:Translational control plays a central role in regulation of gene expression and can lead to significant divergence between mRNA- and protein-abundance. Here we used genome-wide approaches combined with time-course analysis to measure the mRNA-abundance, mRNA-translation rate and protein expression during the transition of naïve-to-primed mouse embryonic stem cells (ESCs). We find that the ground state ESCs cultured with GSK3-, MEK-inhibitors and LIF (2iL) display higher ribosome density on a selective set of mRNAs. This set of mRNAs undergo strong translational buffering to maintain stable protein expression levels in 2iL-ESCs. Importantly, we show that the global alteration of cellular proteome during the transition of naïve to primed pluripotency is largely accompanied by transcriptional rewiring. Thus, we provide a comprehensive and detailed overview of the global changes in gene expression in different states of ESCs and dissect the relative contributions of RNA-transcription, translation and regulation of protein stability in controlling protein abundance.
Project description:Translational control plays a central role in regulation of gene expression and can lead to significant divergence between mRNA- and protein-abundance. Here we used genome-wide approaches combined with time-course analysis to measure the mRNA-abundance, mRNA-translation rate and protein expression during the transition of naïve-to-primed mouse embryonic stem cells (ESCs). We find that the ground state ESCs cultured with GSK3-, MEK-inhibitors and LIF (2iL) display higher ribosome density on a selective set of mRNAs. This set of mRNAs undergo strong translational buffering to maintain stable protein expression levels in 2iL-ESCs. Importantly, we show that the global alteration of cellular proteome during the transition of naïve to primed pluripotency is largely accompanied by transcriptional rewiring. Thus, we provide a comprehensive and detailed overview of the global changes in gene expression in different states of ESCs and dissect the relative contributions of RNA-transcription, translation and regulation of protein stability in controlling protein abundance.