Project description:Ribosome-associated quality control pathways respond to defects in translational elongation to recycle arrested ribosomes and degrade aberrant polypeptides and mRNAs. Loss of an individual tRNA gene leads to ribosomal pausing that is resolved by the translational GTPase GTPBP2, and in its absence causes neuron death. Here we show that loss of the homologous protein GTPBP1 during tRNA deficiency in the mouse brain also leads to codon-specific ribosome pausing and neurodegeneration, suggesting that these non-redundant translational GTPases function in the same pathway to mitigate ribosome pausing. Ribosome stalling in the mutant brain led to activation of the integrated stress response (ISR) mediated by GCN2 and decreased mTORC1 signaling. However, in contrast to the ISR, which enhanced neuron survival, reduced mTORC1 signaling increased neuronal death. Our data demonstrate that GTPBP1 functions as an important quality control mechanism during translation elongation and suggest that translational signaling pathways intricately interact to regulate neuronal homeostasis during defective translation elongation.
Project description:The cGAS-STING pathway, a central component of the innate immune system, senses cytosolic DNA and induces interferon-stimulated genes (ISGs) to mediate inflammation. Here we report the unexpected discovery that cGAS senses dysfunctional translation. Purified ribosomes interact with and stimulate recombinant cGAS catalytic activity in vitro. Disruption of the ribosome-associated protein quality control pathway, which detects and resolves ribosome collisions, results in cGAS- and STING-dependent ISG expression, and cause the re-localization of cGAS from the nucleus to the cytosol. Other orthogonal perturbations that lead to elevated levels of collided ribosomes cause re-localization of cGAS as well. Thus, the cGAS-STING pathway senses and responds to translation stress. These findings have implications for the inflammatory responses to viral infection and tumorigenesis, both of which substantially reprogram cellular protein synthesis.
Project description:The cGAS-STING pathway, a central component of the innate immune system, senses cytosolic DNA and induces interferon-stimulated genes (ISGs) to mediate inflammation. Here we report the unexpected discovery that cGAS senses dysfunctional protein production. Purified ribosomes interact with and stimulate the catalytic activity of recombinant cGAS in vitro. Disruption of the ribosome-associated protein quality control pathway, which detects and resolves ribosome collisions, results in cGAS- and STING-dependent ISG expression, and causes the re-localization of cGAS from the nucleus to the cytosol. Indeed, cGAS preferentially binds collided ribosomes in vitro, and other orthogonal perturbations that lead to elevated levels of collided ribosomes cause re-localization of cGAS as well. Thus, the cGAS-STING pathway senses and responds to translation stress. These findings have implications for the inflammatory responses to viral infection and tumorigenesis, both of which substantially reprogram cellular protein synthesis.
Project description:Low Klf4 expression reproducibly gives rise to a homogeneous population of partially reprogrammed iPSCs. Upregulation of Klf4 allows these cells to resume reprogramming, indicating that they are paused iPSCs that remain on the path towards pluripotency. Paused iPSCs with different Klf4 expression levels remain at distinct intermediate stages of reprogramming.
Project description:Cultured pluripotent stem cells are a cornerstone of regenerative medicine due to their ability to give rise to all cell types of the body. While pluripotent stem cells can be propagated indefinitely in vitro, pluripotency is paradoxically a very transient state in vivo, lasting 2-3 days around the time of blastocyst implantation. The exception to this rule is embryonic diapause, a reversible state of suspended development triggered by unfavorable conditions. Diapause is a strategy widely employed across the animal kingdom, including in mammals, but its regulation remains poorly understood. Here we report that inhibition of mechanistic target of rapamycin (mTor), a major nutrient sensor and promoter of growth, induces reversible pausing of mouse blastocyst development and allows their prolonged culture ex vivo. Paused blastocysts remain pluripotent and competent to give rise to embryonic stem (ES) cells and mice. We show that both natural diapause blastocysts in vivo and paused blastocysts ex vivo display pronounced reductions in mTor activity, translation and transcription. In addition, pausing can be induced directly in cultured ES cells and sustained for weeks in the absence of cell death or deviations from cell cycle distributions. We show that paused ES cells remain pluripotent, display a remarkable global suppression of transcription, and maintain a gene expression signature of diapaused blastocysts. These results allow for the first time the sustained suspension of development of a mammalian embryo in the laboratory, and shed light on the regulation of diapause and the origins of ES cells. Our findings have important implications in the fields of assisted reproduction, regenerative medicine, cancer, metabolic disorders and aging.
Project description:Translation initiation is considered overall rate-limiting for protein biosynthesis, whereas the impact of non-uniform ribosomal elongation rates is largely unknown. Using a modified ribosome profiling protocol based on footprints from two closely packed ribosomes (disomes), we have mapped ribosomal collisions transcriptome-wide in mouse liver. We uncover that the stacking of an elongating onto a paused ribosome occurs frequently and scales with translation rate, trapping ~10% of translating ribosomes in the disome state. A distinct class of pause sites, independent of translation rate, is indicative of deterministic pausing signals. We find pause sites associated with specific codons, amino acids, and peptide motifs, and with structural features of the nascent polypeptide, suggestive of programmed pausing as a widespread mechanism associated with protein folding. Evolutionary conservation at disome sites and experiments indicate functional relevance of translational pausing. Collectively, our disome profiling approach allows novel and unexpected insights into gene regulation occurring at the step of translation elongation.
Project description:A total of 10 cDNA libraries were constructed, representing 3 and 2 independent biological replicates of S. aureus strain KES34 (unmodified ribosomes) and KES30 (m6A2058-modified ribosomes), respectively. Translational efficiency (RPF/mRNA ratios), total mRNA abundance and ribosome density of each ORFs were calculated.