We developed a genetically encoded, highly specific fluorescent probe for detecting hydrogen peroxide (H(2)O(2)) inside living cells. This probe, named HyPer, consists of circularly permuted yellow fluorescent protein (cpYFP) inserted into the regulatory domain of the prokaryotic H(2)O(2)-sensing protein, OxyR. Using HyPer we monitored H(2)O(2) production at the single-cell level in the cytoplasm and mitochondria of HeLa cells treated with Apo2L/TRAIL. We found that an increase in H(2)O(2) occurs in the cytoplasm in parallel with a drop in the mitochondrial transmembrane potential (DeltaPsi) and a change in cell shape. We also observed local bursts in mitochondrial H(2)O(2) production during DeltaPsi oscillations in apoptotic HeLa cells. Moreover, sensitivity of the probe was sufficient to observe H(2)O(2) increase upon physiological stimulation. Using HyPer we detected temporal increase in H(2)O(2) in the cytoplasm of PC-12 cells stimulated with nerve growth factor.

Photosensitizers are chromophores that generate reactive oxygen species (ROS) upon light irradiation. They are used for inactivation of specific proteins by chromophore-assisted light inactivation (CALI) and for light-induced cell killing in photodynamic therapy. Here we report a genetically encoded photosensitizer, which we call KillerRed, developed from the hydrozoan chromoprotein anm2CP, a homolog of green fluorescent protein (GFP). KillerRed generates ROS upon irradiation with green light. Whereas known photosensitizers must be added to living systems exogenously, KillerRed is fully genetically encoded. We demonstrate the utility of KillerRed for light-induced killing of Escherichia coli and eukaryotic cells and for inactivating fusions to beta-galactosidase and phospholipase Cdelta1 pleckstrin homology domain.

Green fluorescent protein (GFP) and GFP-like proteins represent invaluable genetically encoded fluorescent probes. In the last few years a new class of photoactivatable fluorescent proteins (PAFPs) capable of pronounced light-induced spectral changes have been developed. Except for tetrameric KFP1 (ref. 4), all known PAFPs, including PA-GFP, Kaede, EosFP, PS-CFP, Dronpa, PA-mRFP1 and KikGR require light in the UV-violet spectral region for activation through one-photon excitation--such light can be phototoxic to some biological systems. Here, we report a monomeric PAFP, Dendra, derived from octocoral Dendronephthya sp. and capable of 1,000- to 4,500-fold photoconversion from green to red fluorescent states in response to either visible blue or UV-violet light. Dendra represents the first PAFP, which is simultaneously monomeric, efficiently matures at 37 degrees C, demonstrates high photostability of the activated state, and can be photoactivated by a common, marginally phototoxic, 488-nm laser line. We demonstrate the suitability of Dendra for protein labeling and tracking to quantitatively study dynamics of fibrillarin and vimentin in mammalian cells.

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The decrease of TCR diversity with aging has never been studied by direct methods. In this study, we combined high-throughput Illumina sequencing with unique cDNA molecular identifier technology to achieve deep and precisely normalized profiling of TCR β repertoires in 39 healthy donors aged 6–90 y. We demonstrate that TCR β diversity per 106 T cells decreases roughly linearly with age, with significant reduction already apparent by age 40. The percentage of naive T cells showed a strong correlation with measured TCR diversity and decreased linearly up to age 70. Remarkably, the oldest group (average age 82 y) was characterized by a higher percentage of naive CD4+ T cells, lower abundance of expanded clones, and increased TCR diversity compared with the previous age group (average age 62 y), suggesting the influence of age selection and association of these three related parameters with longevity. Interestingly, cross-analysis of individual TCR β repertoires revealed a set >10,000 of the most representative public TCR β clonotypes, whose abundance among the top 100,000 clones correlated with TCR diversity and decreased with aging.

Deep profiling of antibody and T cell-receptor repertoires by means of high-throughput sequencing has become an attractive approach for adaptive immunity studies, but its power is substantially compromised by the accumulation of PCR and sequencing errors. Here we report MIGEC (molecular identifier groups-based error correction), a strategy for high-throughput sequencing data analysis. MIGEC allows for nearly absolute error correction while fully preserving the natural diversity of complex immune repertoires.

In recent years diverse photolabeling techniques using green fluorescent protein (GFP)-like proteins have been reported, including photoactivatable PA-GFP, photoactivatable protein Kaede, the DsRed 'greening' technique and kindling fluorescent proteins. So far, only PA-GFP, which is monomeric and gives 100-fold fluorescence contrast, could be applied for protein tracking. Here we describe a dual-color monomeric protein, photoswitchable cyan fluorescent protein (PS-CFP). PS-CFP is capable of efficient photoconversion from cyan to green, changing both its excitation and emission spectra in response to 405-nm light irradiation. Complete photoactivation of PS-CFP results in a 1,500-fold increase in the green-to-cyan fluorescence ratio, making it the highest-contrast monomeric photoactivatable fluorescent protein described to date. We used PS-CFP as a photoswitchable tag to study trafficking of human dopamine transporter in living cells. At moderate excitation intensities, PS-CFP can be used as a pH-stable cyan label for protein tagging and fluorescence resonance energy transfer applications.

Photobleaching of green fluorescent protein (GFP) is a widely used approach for tracking the movement of subcellular structures and intracellular proteins. Although photobleaching is a powerful technique, it does not allow direct tracking of an object's movement and velocity within a living cell. Direct tracking becomes possible only with the introduction of a photoactivated fluorescent marker. A number of previous studies have reported optically induced changes in the emission spectra of fluorescent proteins. However, the ideal photoactivated fluorescent marker should be a nonfluorescent tag capable of "switching on" (i.e., becoming fluorescent) in response to irradiation by light of a particular wavelength, intensity, and duration. In this report, we generated a mutant of Anemonia sulcata chromoprotein asCP. The mutant protein is capable of unique irreversible photoconversion from the nonfluorescent to a stable bright-red fluorescent form ("kindling"). This "kindling fluorescent protein" (KFP1) can be used for precise in vivo photolabeling to track the movements of cells, organelles, and proteins. We used KFP1 for in vivo cell labeling in mRNA microinjection assays to monitor Xenopus laevis embryo development and to track mitochondrial movement in mammalian cells.