Genetically encodable bioluminescent system from fungi.

Bioluminescence is found across the entire tree of life, conferring a spectacular set of visually oriented functions from attracting mates to scaring off predators. Half a dozen different luciferins, molecules that emit light when enzymatically oxidized, are known. However, just one biochemical pathway for luciferin biosynthesis has been described in full, which is found only in bacteria. Here, we report identification of the fungal luciferase and three other key enzymes that together form the biosynthetic cycle of the fungal luciferin from caffeic acid, a simple and widespread metabolite. Introduction of the identified genes into the genome of the yeast Pichia pastoris along with caffeic acid biosynthesis genes resulted in a strain that is autoluminescent in standard media. We analyzed evolution of the enzymes of the luciferin biosynthesis cycle and found that fungal bioluminescence emerged through a series of events that included two independent gene duplications. The retention of the duplicated enzymes of the luciferin pathway in nonluminescent fungi shows that the gene duplication was followed by functional sequence divergence of enzymes of at least one gene in the biosynthetic pathway and suggests that the evolution of fungal bioluminescence proceeded through several closely related stepping stone nonluminescent biochemical reactions with adaptive roles. The availability of a complete eukaryotic luciferin biosynthesis pathway provides several applications in biomedicine and bioengineering.

CD8+ T cells with characteristic T cell receptor beta motif are detected in blood and expanded in synovial fluid of ankylosing spondylitis patients.

Objective: The risk of AS is associated with genomic variants related to antigen presentation and specific cytokine signalling pathways, suggesting the involvement of cellular immunity in disease initiation/progression. The aim of the present study was to explore the repertoire of TCR sequences in healthy donors and AS patients to uncover AS-linked TCR variants. Methods: Using quantitative molecular-barcoded 5'-RACE, we performed deep TCR ß repertoire profiling of peripheral blood (PB) and SF samples for 25 AS patients and 108 healthy donors. AS-linked TCR variants were identified using a new computational approach that relies on a probabilistic model of the VDJ rearrangement process. Results: Using the donor-agnostic probabilistic model, we reveal a TCR ß motif characteristic for PB of AS patients, represented by eight highly homologous amino acid sequence variants. Some of these variants were previously reported in SF and PB of patients with ReA and in PB of AS patients. We demonstrate that identified AS-linked clones have a CD8+ phenotype, present at relatively low frequencies in PB, and are significantly enriched in matched SF samples of AS patients. Conclusion: Our results suggest the involvement of a particular antigen-specific subset of CD8+ T cells in AS pathogenesis, confirming and expanding earlier findings. The high similarity of the clonotypes with the ones found in ReA implies common mechanisms for the initiation of the diseases.

MAGERI: Computational pipeline for molecular-barcoded targeted resequencing.

Unique molecular identifiers (UMIs) show outstanding performance in targeted high-throughput resequencing, being the most promising approach for the accurate identification of rare variants in complex DNA samples. This approach has application in multiple areas, including cancer diagnostics, thus demanding dedicated software and algorithms. Here we introduce MAGERI, a computational pipeline that efficiently handles all caveats of UMI-based analysis to obtain high-fidelity mutation profiles and call ultra-rare variants. Using an extensive set of benchmark datasets including gold-standard biological samples with known variant frequencies, cell-free DNA from tumor patient blood samples and publicly available UMI-encoded datasets we demonstrate that our method is both robust and efficient in calling rare variants. The versatility of our software is supported by accurate results obtained for both tumor DNA and viral RNA samples in datasets prepared using three different UMI-based protocols.

Dynamics of Individual T Cell Repertoires: From Cord Blood to Centenarians.

The diversity, architecture, and dynamics of the TCR repertoire largely determine our ability to effectively withstand infections and malignancies with minimal mistargeting of immune responses. In this study, we have employed deep TCRß repertoire sequencing with normalization based on unique molecular identifiers to explore the long-term dynamics of T cell immunity. We demonstrate remarkable stability of repertoire, where approximately half of all T cells in peripheral blood are represented by clones that persist and generally preserve their frequencies for 3 y. We further characterize the extremes of lifelong TCR repertoire evolution, analyzing samples ranging from umbilical cord blood to centenarian peripheral blood. We show that the fetal TCR repertoire, albeit structurally maintained within regulated borders due to the lower numbers of randomly added nucleotides, is not limited with respect to observed functional diversity. We reveal decreased efficiency of nonsense-mediated mRNA decay in umbilical cord blood, which may reflect specific regulatory mechanisms in development. Furthermore, we demonstrate that human TCR repertoires are functionally more similar at birth but diverge during life, and we track the lifelong behavior of CMV- and EBV-specific T cell clonotypes. Finally, we reveal gender differences in dynamics of TCR diversity constriction, which come to naught in the oldest age. Based on our data, we propose a more general explanation for the previous observations on the relationships between longevity and immunity.

Fluorescent proteins and their applications in imaging living cells and tissues.

Green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its homologs from diverse marine animals are widely used as universal genetically encoded fluorescent labels. Many laboratories have focused their efforts on identification and development of fluorescent proteins with novel characteristics and enhanced properties, resulting in a powerful toolkit for visualization of structural organization and dynamic processes in living cells and organisms. The diversity of currently available fluorescent proteins covers nearly the entire visible spectrum, providing numerous alternative possibilities for multicolor labeling and studies of protein interactions. Photoactivatable fluorescent proteins enable tracking of photolabeled molecules and cells in space and time and can also be used for super-resolution imaging. Genetically encoded sensors make it possible to monitor the activity of enzymes and the concentrations of various analytes. Fast-maturing fluorescent proteins, cell clocks, and timers further expand the options for real time studies in living tissues. Here we focus on the structure, evolution, and function of GFP-like proteins and their numerous applications for in vivo imaging, with particular attention to recent techniques.

Application of nonsense-mediated primer exclusion (NOPE) for preparation of unique molecular barcoded libraries.

BACKGROUND: Recently we proposed efficient method to exclude undesirable primers at any stage of amplification reaction, here termed NOPE (NOnsense-mediated Primer Exclusion). According to this method, added oligonucleotide overlapping with the 3'-end of unwanted amplification primer (NOPE oligo) simultaneously provides a template for its elongation. This elongation disrupts specificity of unwanted primer, preventing its further participation in PCR. The suggested approach allows to rationally manage the course of PCR reactions in order to facilitate analysis of complex DNA mixtures as well as to perform multistage PCR bypassing intermediate purification steps. RESULTS: Here we apply NOPE method to DNA library preparation for the high-throughput sequencing (HTS) with the PCR-based introduction of unique molecular identifiers (UMI). We show that NOPE oligo efficiently neutralizes UMI-containing oligonucleotides after introduction of UMI into sample DNA molecules, thus allowing to proceed with further amplification steps without purification and associated loss of starting material. At the same time, NOPE oligo does not affect the efficiency of target PCR amplification. CONCLUSION: We describe a simple, robust and cheap modification of UMI-labeled HTS libraries preparation procedure, that allows to bypass purification step and thus to preserve starting material which may be limited, e.g. circulating tumor DNA, circulating fetal DNA, or small amounts of isolated cells of interest. Furthermore, demonstrated simplicity and robustness of NOPE method should make it popular in various PCR protocols.

Towards error-free profiling of immune repertoires.

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.

Intracellular pH imaging in cancer cells in vitro and tumors in vivo using the new genetically encoded sensor SypHer2.

BACKGROUND: Measuring intracellular pH (pHi) in tumors is essential for the monitoring of cancer progression and the response of cancer cells to various treatments. The purpose of the study was to develop a method for pHi mapping in living cancer cells in vitro and in tumors in vivo, using the novel genetically encoded indicator, SypHer2. METHODS: A HeLa Kyoto cell line stably expressing SypHer2 in the cytoplasm was used, to perform ratiometric (dual excitation) imaging of the probe in cell culture, in 3D tumor spheroids and in tumor xenografts in living mice. RESULTS: Using SypHer2, pHi was demonstrated to be 7.34±0.11 in monolayer HeLa cells in vitro under standard cultivation conditions. An increasing pHi gradient from the center to the periphery of the spheroids was displayed. We obtained fluorescence ratio maps for HeLa tumors in vivo and ex vivo. Comparison of the map with the pathomorphology and with hypoxia staining of the tumors revealed a correspondence of the zones with higher pHi to the necrotic and hypoxic areas. CONCLUSIONS: Our results demonstrate that pHi imaging with the genetically encoded pHi indicator, SypHer2, can be a valuable tool for evaluating tumor progression in xenograft models. GENERAL SIGNIFICANCE: We have demonstrated, for the first time, the possibility of using the genetically encoded sensor SypHer2 for ratiometric pH imaging in cancer cells in vitro and in tumors in vivo. SypHer2 shows great promise as an instrument for pHi monitoring able to provide high accuracy and spatiotemporal resolution.

Fluorescent ratiometric pH indicator SypHer2: Applications in neuroscience and regenerative biology.

BACKGROUND: SypHer is a genetically encoded fluorescent pH-indicator with a ratiometric readout, suitable for measuring fast intracellular pH shifts. However, the relatively low brightness of the indicator limits its use. METHODS: Here we designed a new version of pH-sensor called SypHer-2, which has up to three times brighter fluorescence in cultured mammalian cells compared to the SypHer. RESULTS: Using the new indicator we registered activity-associated pH oscillations in neuronal cell culture. We observed prominent transient neuronal cytoplasm acidification that occurs in parallel with calcium entry. Furthermore, we monitored pH in presynaptic and postsynaptic termini by targeting SypHer-2 directly to these compartments and revealed marked differences in pH dynamics between synaptic boutons and dendritic spines. Finally, we were able to reveal for the first time the intracellular pH drop that occurs within an extended region of the amputated tail of the Xenopus laevis tadpole before it begins to regenerate. CONCLUSIONS: SypHer2 is suitable for quantitative monitoring of pH in biological systems of different scales, from small cellular subcompartments to animal tissues in vivo. GENERAL SIGNIFICANCE: The new pH-sensor will help to investigate pH-dependent processes in both in vitro and in vivo studies.

Soluble OX40L favors tumor rejection in CT26 colon carcinoma model.

OX40 receptor-expressing regulatory T cells (Tregs) populate tumors and suppress a variety of immune cells, posing a major obstacle for cancer immunotherapy. Different ways to functionally inactivate Tregs by triggering OX40 receptor have been suggested, including anti-OX40 antibodies and Fc:OX40L fusion proteins. To investigate whether the soluble extracellular domain of OX40L (OX40Lexo) is sufficient to enhance antitumor immune response, we generated an OX40Lexo-expressing CT26 colon carcinoma cell line and studied its tumorigenicity in immunocompetent BALB/c and T cell deficient nu/nu mice. We found that soluble OX40L expressed in CT26 colon carcinoma favors the induction of an antitumor response which is not limited just to cells co-expressing EGFP as an antigenic determinant, but also eliminates CT26 cells expressing another fluorescent protein, KillerRed. Tumor rejection required the presence of T lymphocytes, as indicated by the unhampered tumor growth in nu/nu mice. Subsequent re-challenge of tumor-free BALB/c mice with CT26 EGFP cells resulted in no tumor growth, which is indicative of the formation of immunological memory. Adoptive transfer of splenocytes from mice that successfully rejected CT26 OX40Lexo EGFP tumors to naïve mice conferred 100% resistance to subsequent challenge with the CT26 EGFP tumor.

Age-related decrease in TCR repertoire diversity measured with deep and normalized sequence profiling.

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 ß repertoires in 39 healthy donors aged 6-90 y. We demonstrate that TCR ß diversity per 10(6) 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 ß repertoires revealed a set >10,000 of the most representative public TCR ß clonotypes, whose abundance among the top 100,000 clones correlated with TCR diversity and decreased with aging.

Live-Cell STED Microscopy with Genetically Encoded Biosensor.

Of the various super-resolution techniques, stimulated emission depletion (STED) microscopy achieves the best temporal resolution at high spatial resolution, enabling live-cell imaging beyond the diffraction limit. However, STED and most other super-resolution imaging methods utilize a particular type of information extractable from the raw data, namely the positions of fluorophores. To expand on the use of super-resolution techniques, we report here the live-cell STED microscopy of a dynamic biosensor. Using the fluorescent H2O2 sensor HyPer2 for subdiffraction imaging, we were able not only to image filaments with superior resolution by localizing emission but also to trace H2O2 produced within living cell by monitoring brightness of the probe. STED microscopy of HyPer2 demonstrates potential utility of FP-based biosensors for super-resolution experiments in situ and in vivo.

The Chemical Basis of Fungal Bioluminescence.

Many species of fungi naturally produce light, a phenomenon known as bioluminescence, however, the fungal substrates used in the chemical reactions that produce light have not been reported. We identified the fungal compound luciferin 3-hydroxyhispidin, which is biosynthesized by oxidation of the precursor hispidin, a known fungal and plant secondary metabolite. The fungal luciferin does not share structural similarity with the other eight known luciferins. Furthermore, it was shown that 3-hydroxyhispidin leads to bioluminescence in extracts from four diverse genera of luminous fungi, thus suggesting a common biochemical mechanism for fungal bioluminescence.

Flavoprotein miniSOG as a genetically encoded photosensitizer for cancer cells.

BACKGROUND: Genetically encoded photosensitizers are a promising optogenetic instrument for light-induced production of reactive oxygen species in desired locations within cells in vitro or whole body in vivo. Only two such photosensitizers are currently known, GFP-like protein KillerRed and FMN-binding protein miniSOG. In this work we studied phototoxic effects of miniSOG in cancer cells. METHODS: HeLa Kyoto cell lines stably expressing miniSOG in different localizations, namely, plasma membrane, mitochondria or chromatin (fused with histone H2B) were created. Phototoxicity of miniSOG was tested on the cells in vitro and tumor xenografts in vivo. RESULTS: Blue light induced pronounced cell death in all three cell lines in a dose-dependent manner. Caspase 3 activation was characteristic of illuminated cells with mitochondria- and chromatin-localized miniSOG, but not with miniSOG in the plasma membrane. In addition, H2B-miniSOG-expressing cells demonstrated light-induced activation of DNA repair machinery, which indicates massive damage of genomic DNA. In contrast to these in vitro data, no detectable phototoxicity was observed on tumor xenografts with HeLa Kyoto cell lines expressing mitochondria- or chromatin-localized miniSOG. CONCLUSIONS: miniSOG is an excellent genetically encoded photosensitizer for mammalian cells in vitro, but it is inferior to KillerRed in the HeLa tumor. GENERAL SIGNIFICANCE: This is the first study to assess phototoxicity of miniSOG in cancer cells. The results suggest an effective ontogenetic tool and may be of interest for molecular and cell biology and biomedical applications.

Red-shifted fluorescent aminated derivatives of a conformationally locked GFP chromophore.

A novel class of fluorescent dyes based on conformationally locked GFP chromophore is reported. These dyes are characterized by red-shifted spectra, high fluorescence quantum yields and pH-independence in physiological pH range. The intra- and intermolecular mechanisms of radiationless deactivation of ABDI-BF2 fluorophore by selective structural locking of various conformational degrees of freedom were studied. A unique combination of solvatochromic and lipophilic properties together with "infinite" photostability (due to a dynamic exchange between free and bound dye) makes some of the novel dyes promising bioinspired tools for labeling cellular membranes, lipid drops and other organelles.

Yellow fluorescent protein phiYFPv (Phialidium): structure and structure-based mutagenesis.

The yellow fluorescent protein phiYFPv (λem(max) ≃ 537 nm) with improved folding has been developed from the spectrally identical wild-type phiYFP found in the marine jellyfish Phialidium. The latter fluorescent protein is one of only two known cases of naturally occurring proteins that exhibit emission spectra in the yellow-orange range (535-555 nm). Here, the crystal structure of phiYFPv has been determined at 2.05 Å resolution. The `yellow' chromophore formed from the sequence triad Thr65-Tyr66-Gly67 adopts the bicyclic structure typical of fluorophores emitting in the green spectral range. It was demonstrated that perfect antiparallel π-stacking of chromophore Tyr66 and the proximal Tyr203, as well as Val205, facing the chromophore phenolic ring are chiefly responsible for the observed yellow emission of phiYFPv at 537 nm. Structure-based site-directed mutagenesis has been used to identify the key functional residues in the chromophore environment. The obtained results have been utilized to improve the properties of phiYFPv and its homologous monomeric biomarker tagYFP.

Next generation sequencing for TCR repertoire profiling: platform-specific features and correction algorithms.

The TCR repertoire is a mirror of the human immune system that reflects processes caused by infections, cancer, autoimmunity, and aging. Next generation sequencing (NGS) is becoming a powerful tool for deep TCR profiling; yet, questions abound regarding the methodological approaches for sample preparation and correct data interpretation. Accumulated PCR and sequencing errors along with library preparation bottlenecks and uneven PCR efficiencies lead to information loss, biased quantification, and generation of huge artificial TCR diversity. Here, we compare Illumina, 454, and Ion Torrent platforms for individual TCR profiling, evaluate the rate and character of errors, and propose advanced platform-specific algorithms to correct massive sequencing data. These developments are applicable to a wide variety of next generation sequencing applications. We demonstrate that advanced correction allows the removal of the majority of artificial TCR diversity with concomitant rescue of most of the sequencing information. Thus, this correction enhances the accuracy of clonotype identification and quantification as well as overall TCR diversity measurements.

Targeted depletion of TRBV9+ T cells as immunotherapy in a patient with ankylosing spondylitis.

Autoimmunity is intrinsically driven by memory T and B cell clones inappropriately targeted at self-antigens. Selective depletion or suppression of self-reactive T cells remains a holy grail of autoimmune therapy, but disease-associated T cell receptors (TCRs) and cognate antigenic epitopes remained elusive. A TRBV9-containing CD8+ TCR motif was recently associated with the pathogenesis of ankylosing spondylitis, psoriatic arthritis and acute anterior uveitis, and cognate HLA-B*27-presented epitopes were identified. Following successful testing in nonhuman primate models, here we report human TRBV9+ T cell elimination in ankylosing spondylitis. The patient achieved remission within 3 months and ceased anti-TNF therapy after 5 years of continuous use. Complete remission has now persisted for 4 years, with three doses of anti-TRBV9 administered per year. We also observed a profound improvement in spinal mobility metrics and the Bath Ankylosing Spondylitis Metrology Index (BASMI). This represents a possibly curative therapy of an autoimmune disease via selective depletion of a TRBV-defined group of T cells. The anti-TRBV9 therapy could potentially be applicable to other HLA-B*27-associated spondyloarthropathies. Such targeted elimination of the underlying cause of the disease without systemic immunosuppression could offer a new generation of safe and efficient therapies for autoimmunity.

Structural basis for bathochromic shift of fluorescence in far-red fluorescent proteins eqFP650 and eqFP670.

The crystal structures of the far-red fluorescent proteins (FPs) eqFP650 (λ(ex)(max)/λ(em)(max) 592/650 nm) and eqFP670 (λ(ex)(max)/λ(em)(max) 605/670 nm), the successors of the far-red FP Katushka (λ(ex)(max)/λ(em)(max) 588/635 nm), have been determined at 1.8 and 1.6 Å resolution, respectively. An examination of the structures demonstrated that there are two groups of changes responsible for the bathochromic shift of excitation/emission bands of these proteins relative to their predecessor. The first group of changes resulted in an increase of hydrophilicity at the acylimine site of the chromophore due to the presence of one and three water molecules in eqFP650 and eqFP670, respectively. These water molecules provide connection of the chromophore with the protein scaffold via hydrogen bonds causing an ~15 nm bathochromic shift of the eqFP650 and eqFP670 emission bands. The second group of changes observed in eqFP670 arises from substitution of both Ser143 and Ser158 by asparagines. Asn143 and Asn158 of eqFP670 are hydrogen bonded with each other, as well as with the protein scaffold and with the p-hydroxyphenyl group of the chromophore, resulting in an additional ~20 nm bathochromic shift of the eqFP670 emission band as compared to eqFP650. The role of the observed structural changes was verified by mutagenesis.

Light-induced blockage of cell division with a chromatin-targeted phototoxic fluorescent protein.

Proteins of the GFP (green fluorescent protein) family are widely used as passive reporters for live cell imaging. In the present study we used H2B (histone H2B)-tKR (tandem KillerRed) as an active tool to affect cell division with light. We demonstrated that H2B-tKR-expressing cells behave normally in the dark, but transiently cease proliferation following green-light illumination. Complete light-induced blockage of cell division for approx. 24 h was observed in cultured mammalian cells that were either transiently or stably transfected with H2B-tKR. Illuminated cells then returned to normal division rate. XRCC1 (X-ray cross complementing factor 1) showed immediate redistribution in the illuminated nuclei of H2B-tKR-expressing cells, indicating massive light-induced damage of genomic DNA. Notably, nondisjunction of chromosomes was observed for cells that were illuminated during metaphase. In transgenic Xenopus embryos expressing H2B-tKR under the control of tissue-specific promoters, we observed clear retardation of the development of these tissues in green-light-illuminated tadpoles. We believe that H2B-tKR represents a novel optogenetic tool, which can be used to study mitosis and meiosis progression per se, as well as to investigate the roles of specific cell populations in development, regeneration and carcinogenesis in vivo.