Project description:Mammalian preimplantation development is associated with marked metabolic robustness, and embryos can develop under a wide variety of nutrient conditions, including even the complete absence of soluble amino acids. Here we show that mouse embryonic stem cells (ESCs) capture the unique metabolic state of preimplantation embryos and proliferate in the absence of several essential amino acids. Amino acid independence is enabled by constitutive uptake of exogenous protein through macropinocytosis, alongside a robust lysosomal digestive system. Following transition to more committed states, ESCs reduce digestion of extracellular protein and instead become reliant on exogenous amino acids. Accordingly, amino acid withdrawal selects for ESCs that mimic the preimplantation epiblast. More broadly, we find that all lineages of preimplantation blastocysts exhibit constitutive macropinocytic protein uptake and digestion. Taken together, these results highlight exogenous protein uptake and digestion as an intrinsic feature of preimplantation development and provide insight into the catabolic strategies that enable embryos to sustain viability before implantation.
Project description:Messenger RNA (mRNA) translation can lead to higher rates of mRNA decay, suggesting a role for the ribosome in mRNA destruction. Furthermore, features of an mRNA, such as codon identities, that are directly probed by the ribosome also correlate with mRNA decay rates. Specifically, many amino acids are encoded by synonymous codons, and some synonymous codons are decoded by more abundant tRNAs leading to more optimal translation and increased mRNA stability. In addition to different translation rates, the presence of individual codons can lead to higher or lower rates of amino acid misincorporation which could potentially lead to protein misfolding if an individual amino acid makes many critical contacts in a structure. Here, we directly test whether amino acid misincorporation affects mRNA stability, taking advantage of an aminoglycoside antibiotic (G418) which promotes higher error rates in the ribosome. We observe that G418 decreases firefly luciferase mRNA stability in an in vitro system, and we similarly observe that G418 reduces mRNA stability in mouse embryonic stem cells (mESCs). G418-sensitive mRNAs are enriched for suboptimal hydrophobic amino acid codons as well as other codons that are known to result in higher rates of amino acid misincorporation. Since protein folding is highly sensitive to the identity of hydrophobic amino acids, these results strongly suggest that defects in protein folding are linked to mRNA decay.
Project description:Recent observations about how cells sense amino acids have argued for preeminent roles of mTOR and the stress kinase GCN2 in allowing cells to estimate their amino acid needs. Here we used models of programmed immune microenvironments where helper T cells have to sense how much amino acids are available to engage in antigen-fueled proliferation. Contrary to current models, T cells activate mTOR in the competency phase of the cell cycle regardless of amino acid amounts, GCN2 or surface TCR. Instead, we found T cells use an amino acid sensing system to target IL-2-induced STAT5 phosphorylation at the restriction point of cell cycle commitment. mTOR activity is subsequently reduced and specifically connected to SREBP activation. T cells can be pushed into cycle by increasing IL-2 even when no amino acids are available. Collectively, our studies reveal helper T cells use sequential and distinct pathways to measure local amino acid concentrations.
Project description:Microorganisms can restructure their transcriptional output to adapt to environmental conditions by sensing endogenous metabolite pool. In this study, an Agilent customized microarray representing approximately 4,106 genes was used to study temporal transcript profiles of Bacillus subtilis in response to valine, glutamate and glutamine pulses. Amino-acid-regulated genes were identified having significantly changed expression at one or more time points in response to pulses of valine, glutamate, and glutamine, respectively, and Val-, Glu and Gln-specific genes were further distinguished from them. Different amino acid treatments were compared in terms of both the global temporal profiles and the 5-minute quick regulations, and between-experiment differential genes were identified. The highlighted genes were analyzed based on diverse sources of gene functions using a variety of computational tools, including T-profiler analysis, hierarchical clustering and enrichment of functional categories. The results revealed the common and distinct modes of action of these three amino acids, and should help to elucidate the specific signaling mechanism of each amino acid as an effector. Three amino acids (Glutamate, Glutamine, and Valine) were adopted to perturb the culture of subtilis. Four time-points were investigated for each perturbation. There are two replicates for the first time-point of Valine-treatment experiment.