Signal propagation from the cell membrane to a promoter can induce gene expression. To examine signal transmission through sub-cellular compartments and its effect on transcription levels in individual cells within a population, we used the Wnt/β-catenin signaling pathway as a model system. Wnt signaling orchestrates a response through nuclear accumulation of β-catenin in the cell population. However, quantitative live-cell measurements in individual cells showed variability in nuclear β-catenin accumulation, which could occur in two waves, followed by slow clearance. Nuclear accumulation dynamics were initially rapid, cell cycle independent and differed substantially from LiCl stimulation, presumed to mimic Wnt signaling. β-catenin levels increased simultaneously at adherens junctions and the centrosome, and a membrane-centrosome transport system was revealed. Correlating β-catenin nuclear dynamics to cyclin D1 transcriptional activation showed that the nuclear accumulation rate of change of the signaling factor, and not actual protein levels, correlated with the transcriptional output of the pathway.DOI: http://dx.doi.org/10.7554/eLife.16748.001
20In the current study, we present a new and facile synthesis of N doped C-dots (N@C-dots) by 21 hydrothermally reacting an aqueous solution of Bovine Serum Albumin (BSA). The as-prepared 22 quantum dots (QDs) exhibited high quantum yield (44 %), high photostability, colloidal stability, 23 and high functionalization efficiency. In addition to their low cost, the N@C-dots have 24 demonstrated a non-toxic and long-lasting effect when applied for imaging human cells (human 25 osteosarcoma (U2OS) cells). Importantly, with high physiological stability, excellent 26 biocompatibility, and homogenous distribution, the N@C-dot suspension were exploited for high 27 quality cell imaging and to model the biological effects at the nuclear level. Moreover, the water-28 soluble N@C-dots are nontoxic to the selected cell line in our preliminary evaluation.Recently, doping of C-dots with hetero-atoms (metal and non-metal) has been reported to 20 provide very high quantum yield (more than 20%). In spite of the controversy regarding the 21 mechanism of the photoluminescence (PL) of doped C-dots, it is widely accepted that surface 22
Summary The transcriptional response of β-actin to extra-cellular stimuli is a paradigm for transcription factor complex assembly and regulation. Serum induction leads to a precisely timed pulse of β-actin transcription in the cell population. Actin protein is proposed to be involved in this response, but it is not known whether cellular actin levels affect nuclear β-actin transcription. We perturbed the levels of key signaling factors and examined the effect on the induced transcriptional pulse by following endogenous β-actin alleles in single living cells. Lowering serum response factor (SRF) protein levels leads to loss of pulse integrity, whereas reducing actin protein levels reveals positive feedback regulation, resulting in elevated gene activation and a prolonged transcriptional response. Thus, transcriptional pulse fidelity requires regulated amounts of signaling proteins, and perturbations in factor levels eliminate the physiological response, resulting in either tuning down or exaggeration of the transcriptional pulse.
Edited by Wilhelm JustStress granules are cytoplasmic structures that form in response to a variety of cellular stresses. They contain mRNAs and many proteins including numerous types of RNA-binding proteins, and have been studied in connection to major cellular events such as protein synthesis as well as disease. Despite the well-known fact that stress granules encapsulate mRNPs (mRNA-protein complexes), much of the research has naturally focused on the protein components of stress granules. The specific details of mRNP entry into and exit from stress granules and the functional reasons for these dynamics are not fully understood. Here, we review studies that have concentrated on the aspects of mRNP accumulation in stress granules and produced quantitative data concerning mRNP/stress granule interactions.
Discriminating between the mRNA and protein outputs of each of the alleles of an endogenous gene in intact cells, is a difficult task. To examine endogenous transcripts originating from a specific allele, we applied Central Dogma tagging (CD-tagging), which is based on a tag insertion into an endogenous gene by creation of a new exon. Previously, CD-tagging was used to tag endogenous proteins. Here we developed a CD-tagging-MS2 approach in which two tags were inserted in tandem; a fluorescent protein tag in conjunction with the mRNA MS2 tag used for tagging mRNAs in cells. A cell clone library of CD-tagged-MS2 genes was generated, and protein and mRNA distributions were examined and characterized in single cells. Taking advantage of having one allele tagged, we demonstrate how the transcriptional activity of all alleles, tagged and untagged, can be identified using single molecule RNA fluorescence in situ hybridization (smFISH). Allele-specific mRNA expression and localization were quantified under normal and stress conditions. The latter generate cytoplasmic stress granules (SGs) that can store mRNAs, and the distribution of the mRNAs within and outside of the SGs was measured. Altogether, CD-tagging-MS2 is a robust and inexpensive approach for direct simultaneous detection of an endogenous mRNA and its translated protein product in the same cell.
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