LSSmScarlet, dCyRFP2s, dCyOFP2s and CRISPRed2s, Genetically Encoded Red Fluorescent Proteins with a Large Stokes Shift

Genetically encoded red fluorescent proteins with a large Stokes shift (LSSRFPs) can be efficiently co-excited with common green FPs both under single- and two-photon microscopy, thus enabling dual-color imaging using a single laser. Recent progress in protein development resulted in a great variety of novel LSSRFPs; however, the selection of the right LSSRFP for a given application is hampered by the lack of a side-by-side comparison of the LSSRFPs' performance. In this study, we employed rational design and random mutagenesis to convert conventional bright RFP mScarlet into LSSRFP, called LSSmScarlet, characterized by excitation/emission maxima at 470/598 nm. In addition, we utilized the previously reported LSSRFPs mCyRFP1, CyOFP1, and mCRISPRed as templates for directed molecular evolution to develop their optimized versions, called dCyRFP2s, dCyOFP2s and CRISPRed2s. We performed a quantitative assessment of the developed LSSRFPs and their precursors in vitro on purified proteins and compared their brightness at 488 nm excitation in the mammalian cells. The monomeric LSSmScarlet protein was successfully utilized for the confocal imaging of the structural proteins in live mammalian cells and multicolor confocal imaging in conjugation with other FPs. LSSmScarlet was successfully applied for dual-color two-photon imaging in live mammalian cells. We also solved the X-ray structure of the LSSmScarlet protein at the resolution of 1.4 Å that revealed a hydrogen bond network supporting excited-state proton transfer (ESPT). Quantum mechanics/molecular mechanics molecular dynamic simulations confirmed the ESPT mechanism of a large Stokes shift. Structure-guided mutagenesis revealed the role of R198 residue in ESPT that allowed us to generate a variant with improved pH stability. Finally, we showed that LSSmScarlet protein is not appropriate for STED microscopy as a consequence of LSSRed-to-Red photoconversion with high-power 775 nm depletion light.

Tracing of intracellular pH in cancer cells in response to Taxol treatment

Genetically encoded pH-sensors are the promising instrument for intracellular pH (pHi) registration. In tumor tissue the reversed pH gradient is known to be the important hallmark of cancer and regulator of tumor response on chemotherapy. However the effect of chemotherapeutic drugs on the pHi of tumor cells is largely unknown. Here we using genetically encoded ratiometric pH-sensor SypHer2 were able to monitor pHi in vitro in cell monolayer and tumor spheroids and in vivo in tumor xenografts. In tumor cell monolayer different pHi dynamic was revealed in the dying cell and division-arrested surviving cells. The treatment effect of taxol varied in monolayer and tumor spheroids and pHi changes were able to reflect these difference. The tend to pHi decrease in respect to taxol in vivo matched with results obtained for the cell monolayer. Also in both cases the cell cycle-arrest was the main treatment effect in contrast to tumor spheroid, where the cell death was the primary result. These findings elucidate the significance of pHi in the mechanisms of taxol action on cervical cancer cells and will be valuable for development of new approaches for cancer treatment.

Semicontinuous system for the production of recombinant mCherry protein in Chlamydomonas reinhardtii

Biotechnology advances have allowed bacteria, yeasts, plants, mammalian and insect cells to function as heterologous protein expression systems. Recently, microalgae have gained attention as an innovative platform for recombinant protein production, due to low culture media cost, compared to traditional systems, as well as the fact that microalgae such as Chlamydomonas reinhardtii are considered safe (GRAS) by the Food and Drug Administration (FDA). Previous studies showed that recombinant protein production in traditional platforms by semicontinuous process increased biomass and bio product productivity, when compared to batch process. As there is a lack of studies on semicontinuous process for recombinant protein production in microalgae, the production of recombinant mCherry fluorescent protein was evaluated by semicontinuous cultivation of Chlamydomonas reinhardtii in bubble column photobioreactor. This semicontinuous cultivation process was evaluated in the following conditions: 20%, 40%, and 60% culture portion withdrawal. The highest culture withdrawal percentage (60%) provided the best results, as an up to 161% increase in mCherry productivity (454.5 RFU h-1 - Relative Fluorescence Unit h-1 ), in comparison to batch cultivation (174.0 RFU h-1 ) of the same strain. All cultivations were carried out for 13 days, at pH 7, temperature 25°C and, by semicontinuous process, two culture withdrawals were taken during the cultivations. Throughout the production cycles, it was possible to obtain biomass concentration up to 1.36 g L-1 .

Fabrication Method of a High-Density Co-Culture Tumor-Stroma Platform to Study Cancer Progression

Cancer has now been established as one of the most common chronic diseases due to high mortality rate. The early stage of non-invasive tumors can now be successfully treated leading to have high survival rates; however, the late stage invasive and metastatic tumors still suffer from poor treatment outcomes. Among multiple contributing factors, the role of tumor microenvironment and its complexities has been well recognized in cancer progression. Stromal cells including cancer-associated fibroblasts (CAFs), endothelial cells, adipocytes, immune cells as well as extracellular matrix (ECM) continuously interact with malignant cells and regulate various hallmarks of cancer including tumor growth, invasion, and intravasation. To better understand the role of the interaction between tumor cells and their surrounding microenvironment, numerous model systems ranging from two-dimensional (2D) assays to 3D hydrogels and in vivo murine xenografts have been utilized. While each one of these model systems exhibit certain advantages in studying biological facets of tumor progression, they are often limited to perform well-controlled mechanistic studies due to various factors including lack of tumor-stroma organotypic organization and presence of confounding biochemical and biophysical factors within the tumor microenvironment. In this regard, in the past few years, 3D in vitro microengineered model systems are becoming instrumental to precisely mimic the complexities of the native tumor microenvironment to conduct fundamental and well-designed studies for multiple purposes ranging from biological discovery to therapeutic screening. These model systems include microfluidics, micro-patterned features, and 3D organoids. In this chapter, we will outline the fabrication strategy of our microengineered 3D co-culture tumor-stromal model which comprises high-density array of tumor seeded microwells surrounded by stromal cells, such as CAFs encapsulated within collagen-based hydrogel. The developed platform provides excellent spatial organization of tumor and stromal entities with designated initial architecture and cellular positioning, therefore enabling to study the specific role of cell-cell and cell-ECM interaction on tumor proliferation/expansion, cancer cell migration as well as stromal activation. The developed platform is compatible with standard biological assays enabling gene and protein expression analyses across different types of cancer and co-culture of tumor and stromal cells.

Fungal Bioreporters to Monitor Outcomes of Aspergillus: Host-Cell Interactions

Fluorescence-based techniques enable researchers to monitor physiologic processes, specifically fungal cell viability and death, during cellular encounters with the mammalian immune system with single event resolution. By incorporating two independent fluorescent probes in fungal organisms either prior to, or ensuing experimental infection in mice or in cultured leukocytes, it is possible to distinguish and quantify live and killed fungal cells to interrogate genetic, pharmacologic, and cellular determinants that shape host-fungal cell outcomes. This chapter reviews the techniques and applications of fluorescent fungal reporters of viability, with emphasis on the filamentous mold Aspergillus fumigatus.

Fungal Bioreporters to Monitor Outcomes of Blastomyces: Host-Cell Interactions

Fluorescence-based techniques enable researchers to monitor physiologic processes, specifically fungal cell viability and death, during cellular encounters with the mammalian immune system with single event resolution. By incorporating two independent fluorescent probes in fungal organisms either prior to, or ensuing experimental infection in mice or in cultured leukocytes, it is possible to distinguish and quantify live and killed fungal cells to interrogate genetic, pharmacologic, and cellular determinants that shape host-fungal cell outcomes. This chapter reviews the techniques and applications of fluorescent fungal reporters of viability, with emphasis on the North American endemic dimorphic fungus, Blastomyces dermatitidis.

Overcoming chromoprotein limitations by engineering a red fluorescent protein

Chromoproteins (CPs) are widely-used visual reporters of gene expression. We previously showed that, for coloration in Escherichia coli, CPs had to be overexpressed and that this caused large fitness costs with the most useful (darkly colored) CPs. These fitness costs were problematic because passage of plasmids encoding darkly colored CPs in liquid culture frequently resulted in loss of color due to mutations. Unexpectedly, an early variant of the monomeric red fluorescent protein 1 (mRFP1) gene that was codon-optimized for E. coli (abbreviated mRFP1E) was found here to be an ideal replacement for CP genes. When we subcloned mRFP1E in the same way as our CP genes, it produced a similarly dark color, yet affected E. coli fitness minimally. This finding facilitated testing of several hypotheses on the cause of CP cytotoxicities by gel electrophoresis and size-exclusion chromatography: toxicities correlated with the combination of amounts of expression, oligomerization and inclusion bodies, not isoelectric point. Finally, a semi-rational mutagenesis strategy created several mRFP1 protein variants with different colors without altering the fitness cost. Thus, these mutants and mRFP1E are suitable for comparative fitness costs between different strains of E. coli. We conclude that our new mRFP1E series overcomes prior limitations of CPs.

A general strategy to red-shift green fluorescent protein-based biosensors

Compared with green fluorescent protein-based biosensors, red fluorescent protein (RFP)-based biosensors are inherently advantageous because of reduced phototoxicity, decreased autofluorescence and enhanced tissue penetration. However, existing RFP-based biosensors often suffer from small dynamic ranges, mislocalization and undesired photoconversion. In addition, the choice of available RFP-based biosensors is limited, and development of each biosensor requires substantial effort. Herein, we describe a general and convenient method, which introduces a genetically encoded noncanonical amino acid, 3-aminotyrosine, to the chromophores of green fluorescent protein-like proteins and biosensors for spontaneous and efficient green-to-red conversion. We demonstrated that this method could be used to quickly expand the repertoire of RFP-based biosensors. With little optimization, the 3-aminotyrosine-modified biosensors preserved the molecular brightness, dynamic range and responsiveness of their green fluorescent predecessors. We further applied spectrally resolved biosensors for multiplexed imaging of metabolic dynamics in pancreatic β-cells.

Photodynamic Activation of Cholecystokinin 1 Receptor with Different Genetically Encoded Protein Photosensitizers and from Varied Subcellular Sites

Cholecystokinin 1 receptor (CCK1R) is activated by singlet oxygen (¹O₂) generated in photodynamic action with sulphonated aluminum phthalocyanine (SALPC) or genetically encoded protein photosensitizer (GEPP) KillerRed or mini singlet oxygen generator (miniSOG). A large number of GEPP with varied ¹O₂ quantum yields have appeared recently; therefore, in the present work, the efficacy of different GEPP to photodynamically activate CCK1R was examined, as monitored by Fura-2 calcium imaging. KillerRed, miniSOG, miniSOG2, singlet oxygen protein photosensitizer (SOPP), flavin-binding fluorescent protein from Methylobacterium radiotolerans with point mutation C71G (Mr4511^C71G), and flavin-binding fluorescent protein from Dinoroseobacter shibae (DsFbFP) were expressed at the plasma membrane (PM) in AR4-2J cells, which express endogenous CCK1R. Light irradiation (KillerRed: white light 85.3 mW‧cm^-2, 4' and all others: LED 450 nm, 85 mW·cm^-2, 1.5') of GEPP_PM-expressing AR4-2J was found to all trigger persistent calcium oscillations, a hallmark of permanent photodynamic CCK1R activation; DsFbFP was the least effective, due to poor expression. miniSOG was targeted to PM, mitochondria (MT) or lysosomes (LS) in AR4-2J in parallel experiments; LED light irradiation was found to all induce persistent calcium oscillations. In miniSOG_PM-AR4-2J cells, light emitting diode (LED) light irradiation-induced calcium oscillations were readily inhibited by CCK1R antagonist devazepide 2 nM; miniSOG_MT-AR4-2J cells were less susceptible, but miniSOG_LS-AR4-2J cells were not inhibited. In conclusion, different GEPP_PM could all photodynamically activate CCK1R. Intracellular GEPP photodynamic action may prove particularly suited to study intracellular GPCR.

Brown Adipose Tissue: A Potential Site for Islet Transplantation

BACKGROUND

Islet transplantation is a promising treatment in patients with complicated diabetes. The ideal transplant site that can extend islet graft survival and reduce the required number of engrafted islets remains to be established.

METHODS

Donor islets were isolated from red fluorescent protein (RFP) mice and transplanted into interscapular brown adipose tissue (BAT) or unilateral inguinal white adipose tissue of age-matched diabetic RFP mice. Blood glucose and body weight of the mice were monitored, and vitality and function of ectopic RFP islets were detected by fluorescence imaging, histological examination, and intraperitoneal glucose tolerance test (GTT).

RESULTS

BAT enabled the marginal number of grafted islets (80 islets) to restore blood glucose, insulin level, and GTT to normal values in all diabetic recipient mice in the short term after graft, and maintained these values for 1 year at the end of the experiment. Importantly, in the short term after transplantation, abundant extra- and intraislet neovasculatures were observed in BAT, but not in white adipose tissue, which allowed the ectopic islets to retain typical architecture and morphology and contributed to the normal GTT. Moreover, the islet-engrafted BAT displayed normal structure and morphology without significant immunocyte infiltration, and the recipient mice also showed normal lipid levels in the blood.

CONCLUSIONS

BAT remarkably enhances the viability and biological function of the transplanted ectopic islets. Moreover, the anatomical location of BAT lends itself to biopsy, removal, and islet retransplantation, which strongly suggests the BAT as a potential desirable site for islet transplantation in basic and clinical research.

Development of an endothelial cell-restricted transgenic reporter rat: a resource for physiological studies of vascular biology

Here, we report the generation of a Cre-recombinase (iCre) transgenic rat, where iCre is driven using a vascular endothelial-cadherin (CDH5) promoter. The CDH5 promoter was cloned from rat pulmonary microvascular endothelial cells and demonstrated ~60% similarity to the murine counterpart. The cloned rat promoter was 2,508 bp, it extended 79 bp beyond the transcription start site, and it was 22,923 bp upstream of the translation start site. The novel promoter was cloned upstream of codon-optimized iCre and subcloned into a Sleeping Beauty transposon vector for transpositional transgenesis in Sprague-Dawley rats. Transgenic founders were generated and selected for iCre expression. Crossing the CDH5-iCre rat with a tdTomato reporter rat resulted in progeny displaying endothelium-restricted fluorescence. tdTomato fluorescence was prominent in major arteries and veins, and it was similar in males and females. Quantitative analysis of the carotid artery and the jugular vein revealed that, on average, more than 50% of the vascular surface area exhibited strong fluorescence. tdTomato fluorescence was observed in the circulations of every tissue tested. The microcirculation in all tissues tested displayed homogenous fluorescence. Fluorescence was examined across young (6-7.5 mo), middle (14-16.5 mo), and old age (17-19.5 mo) groups. Although tdTomato fluorescence was seen in middle- and old-age animals, the intensity of the fluorescence was significantly reduced compared with that seen in the young rats. Thus, this endothelium-restricted transgenic rat offers a novel platform to test endothelial microheterogeneity within all vascular segments, and it provides exceptional resolution of endothelium within-organ microcirculation for application to translational disease models.NEW & NOTEWORTHY The use of transgenic mice has been instrumental in advancing molecular insight of physiological processes, yet these models oftentimes do not faithfully recapitulate human physiology and pathophysiology. Rat models better replicate some human conditions, like Group 1 pulmonary arterial hypertension. Here, we report the development of an endothelial cell-restricted transgenic reporter rat that has broad application to vascular biology. This first-in-kind model offers exceptional endothelium-restricted tdTomato expression, in both conduit vessels and the microcirculations of organs.

Photoelectric Silk via Genetic Encoding and Bioassisted Plasmonics

Genetically encoded photoelectric silk that can convert photons to electrons (light to electricity) over a wide visible range in a self-power mode is reported. As silk is a versatile host material with electrical conductivity, biocompatibility, and processability, a photoelectric protein is genetically fused with silk by silkworm transgenesis. Specifically, mKate2, which is conventionally known as a far-red fluorescent protein, is used as a photoelectric protein. Characterization of the electrochemical and optical properties of mKate2 silk allows designing a photoelectric measurement system. A series of in situ photocurrent experiments support the sensitive and stable performance of photoelectric conversion. In addition, as a plasmonic nanomaterial with a broad spectral resonance, titanium nitride (TiN) nanoparticles are biologically hybridized into the silk glands, taking full advantage of the silkworms' open circulatory system as well as the absorption band of mKate2 silk. This biological hybridization via direct feeding of TiN nanoparticles further enhances the overall photoelectric conversion ability of mKate2 silk. It is envisioned that the biologically derived photoelectric protein, its ecofriendly scalable production by transgenic silkworms, and the bioassisted plasmonic hybridization can potentially broaden the biomaterial choices for developing next-generation biosensing, retina prosthesis, and neurostimulation applications.

The signal peptide of Cry1Ia can improve the expression of eGFP or mCherry in Escherichia coli and Bacillus thuringiensis and enhance the host's fluorescent intensity

BACKGROUND

The signal peptides (SPs) of secretory proteins are frequently used or modified to guide recombinant proteins outside the cytoplasm of prokaryotic cells. In the periplasmic space and extracellular environment, recombinant proteins are kept away from the intracellular proteases and often they can fold correctly and efficiently. Consequently, expression levels of the recombinant protein can be enhanced by the presence of a SP. However, little attention has been paid to the use of SPs with low translocation efficiency for recombinant protein production. In this paper, the function of the signal peptide of Bacillus thuringiensis (Bt) Cry1Ia toxin (Iasp), which is speculated to be a weak translocation signal, on regulation of protein expression was investigated using fluorescent proteins as reporters.

RESULTS

When fused to the N-terminal of eGFP or mCherry, the Iasp can improve the expression of the fluorescent proteins and as a consequence enhance the fluorescent intensity of both Escherichia coli and Bt host cells. Real-time quantitative PCR analysis revealed the higher transcript levels of Iegfp over those of egfp gene in E. coli TG1 cells. By immunoblot analysis and confocal microscope observation, lower translocation efficiency of IeGFP was demonstrated. The novel fluorescent fusion protein IeGFP was then used to compare the relative strengths of cry1Ia (Pi) and cry1Ac (Pac) gene promoters in Bt strain, the latter promoter proving the stronger. The eGFP reporter, by contrast, cannot indicate unambiguously the regulation pattern of Pi at the same level of sensitivity. The fluorescent signals of E. coli and Bt cells expressing the Iasp fused mCherry (ImCherry) were also enhanced. Importantly, the Iasp can also enhanced the expression of two difficult-to-express proteins, matrix metalloprotease-13 (MMP13) and myostatin (growth differentiating factor-8, GDF8) in E. coli BL21-star (DE3) strain.

CONCLUSIONS

We identified the positive effects of a weak signal peptide, Iasp, on the expression of fluorescent proteins and other recombinant proteins in bacteria. The produced IeGFP and ImCherry can be used as novel fluorescent protein variants in prokaryotic cells. The results suggested the potential application of Iasp as a novel fusion tag for improving the recombinant protein expression.

A human embryonic stem cell reporter line for monitoring chemical-induced cardiotoxicity

AIMS

Human embryonic stem cells (hESCs) can be used to generate scalable numbers of cardiomyocytes (CMs) for studying cardiac biology, disease modelling, drug screens, and potentially for regenerative therapies. A fluorescence-based reporter line will significantly enhance our capacities to visualize the derivation, survival, and function of hESC-derived CMs. Our goal was to develop a reporter cell line for real-time monitoring of live hESC-derived CMs.

METHODS AND RESULTS

We used CRISPR/Cas9 to knock a mCherry reporter gene into the MYH6 locus of hESC lines, H1 and H9, enabling real-time monitoring of the generation of CMs. MYH6:mCherry+ cells express atrial or ventricular markers and display a range of cardiomyocyte action potential morphologies. At 20 days of differentiation, MYH6:mCherry+ cells show features characteristic of human CMs and can be used successfully to monitor drug-induced cardiotoxicity and oleic acid-induced cardiac arrhythmia.

CONCLUSION

We created two MYH6:mCherry hESC reporter lines and documented the application of these lines for disease modelling relevant to cardiomyocyte biology.

Atrial-Specific Gene Delivery Using an Adeno-Associated Viral Vector

RATIONALE

Somatic overexpression in mice using an adeno-associated virus (AAV) as gene transfer vectors has become a valuable tool to analyze the roles of specific genes in cardiac diseases. The lack of atrial-specific AAV vector has been a major obstacle for studies into the pathogenesis of atrial diseases. Moreover, gene therapy studies for atrial fibrillation would benefit from atrial-specific vectors. Atrial natriuretic factor (ANF) promoter drives gene expression specifically in atrial cardiomyocytes.

OBJECTIVE

To establish the platform of atrial specific in vivo gene delivery by AAV-ANF.

METHODS AND RESULTS

We constructed AAV vectors based on serotype 9 (AAV9) that are driven by the atrial-specific ANF promoter. Hearts from mice injected with AAV9-ANF-GFP (green fluorescent protein) exhibited strong and atrial-specific GFP expression without notable GFP in ventricular tissue. In contrast, similar vectors containing a cardiac troponin T promoter (AAV9-TNT4-GFP) showed GFP expression in all 4 chambers of the heart, while AAV9 with an enhanced chicken β-actin promoter (AAV-enCB-GFP) caused ubiquitous GFP expression. Next, we used Rosa26^mT/mG (membrane-targeted tandem dimer Tomato/membrane-targeted GFP), a double-fluorescent Cre reporter mouse that expresses membrane-targeted tandem dimer Tomato before Cre-mediated excision, and membrane-targeted GFP after excision. AAV9-ANF-Cre led to highly efficient LoxP recombination in membrane-targeted tandem dimer Tomato/membrane-targeted green fluorescent protein mice with high specificity for the atria. We measured the frequency of transduced cardiomyocytes in atria by detecting Cre-dependent GFP expression from the Rosa26^mT/mG allele. AAV9 dose was positively correlated with the number of GFP-positive atrial cardiomyocytes. Finally, we assessed whether the AAV9-ANF-Cre vector could be used to induce atrial-specific gene knockdown in proof-of-principle experiments using conditional JPH2 (junctophilin-2) knockdown mice. Four weeks after AAV9-ANF-Cre injection, a strong reduction in atrial expression of JPH2 protein was observed. Furthermore, there was evidence for abnormal Ca²⁺ handling in atrial myocytes isolated from mice with atrial-restricted JPH2 deficiency.

CONCLUSIONS

AAV9-ANF vectors produce efficient, dose-dependent, and atrial-specific gene expression following a single-dose systemic delivery in mice. This vector is a novel reagent for both mechanistic and gene therapy studies on atrial diseases.

Cell density-dependent auto-inducible promoters for expression of recombinant proteins in Pseudomonas putida

Inducible promoters such as Plac are of limited usability for industrial protein production with Pseudomonas putida. We therefore utilized cell density-dependent auto-inducible promoters for recombinant gene expression in P. putida KT2440 based on the RoxS/RoxR Quorum Sensing (QS) system of the bacterium. To this end, genetic regions upstream of the RoxS/RoxR-regulated genes ddcA (PR ox132 ) and PP_3332 (PR ox306 ) were inserted into plasmids that mediated the expression of superfolder green fluorescent protein (sfGFP) and surface displayed mCherry, confirming their promoter functionalities. Mutation of the Pribnow box of PR ox306 to the σ70 consensus sequence (PR ox3061 ) resulted in a more than threefold increase of sfGFP production. All three promoters caused cell density-dependent expression, starting transcription at optical densities (OD578 ) of approximately 1.0 (PR ox132 , PR ox306 ) or 0.7 (PR ox3061 ) as determined by RT-qPCR. The QS dependency of PR ox306 was further shown by cultivating P. putida in media that had already been used for cultivation and thus contained bacterial signal molecules. The longer P. putida had grown in these media before, the earlier protein expression in freshly inoculated P. putida appeared with PR ox306 . This confirmed previous findings that a bacterial compound accumulates within the culture and induces protein expression.

A fluorescent reporter assay of differential gene expression response to insulin in hepatocytes

Insulin regulates multiple hepatic metabolic pathways in a seemingly heterogeneous manner. To understand this heterogeneity, we hypothesized that different subpopulations of hepatocytes have different sensitivity to insulin. To test this hypothesis, we developed a fluorescent reporter in which the insulin-responsive fatty acid synthase (FAS) promoter drove expression of a time-dependent fluorescent protein ("timer") and characterized timer expression in flow-sorted cell populations. In Hepa1c1c7 and AML12 hepatocytes, we found that different cell populations express distinct timer fluorescence following insulin treatment, consistent with cellular heterogeneity in the response to insulin. RNA measurements indicated an enrichment of forkhead box O transcription factors in cells with a greater response to insulin. Moreover, we found evidence of increased Akt activation. These data are consistent with a heterogeneous cellular response to insulin and raise the possibility that these different subpopulations underlie the peculiar pathophysiology of hepatic insulin resistance.

Theophylline-inducible riboswitch accurately regulates protein expression at low level in Escherichia coli

OBJECTIVES

Fine-tuning of enzyme expression at low levels is an important challenge for metabolic engineers. Here, theophylline-inducible riboswitch for translational regulation was evaluated. The background expression, translation rate, and time delay for its induction was reported.

RESULTS

To evaluate the effect of the amount of mRNA on its translation rate, transcription of the riboswitch RNA with red fluorescent protein (RFP) was controlled by the lac system with addition of isopropyl β-D-1-thiogalactopyranoside in Escherichia coli. Regardless of the amount of riboswitch mRNA, the translation of RFP was completely suppressed without theophylline during both growth and stationary phases. Furthermore, a strong positive correlation between theophylline concentration (0 to 1 mM) and specific RFP production rate was observed. The specific RFP production rate with the riboswitch was approximately 2.3% of that without the riboswitch. Furthermore, 60 min of time delay for RFP expression was observed after adding theophylline during the stationary phase.

CONCLUSION

Theophylline-inducible riboswitch precisely controls protein translation at low expression levels with significantly low background expression. It can emerge as a powerful tool for fine tuning of enzyme expression.

In vivo measurements reveal a single 5'-intron is sufficient to increase protein expression level in Caenorhabditis elegans

Introns can increase gene expression levels using a variety of mechanisms collectively referred to as Intron Mediated Enhancement (IME). IME has been measured in cell culture and plant models by quantifying expression of intronless and intron-bearing reporter genes in vitro. We developed hardware and software to implement microfluidic chip-based gene expression quantification in vivo. We altered position, number and sequence of introns in reporter genes controlled by the hsp-90 promoter. Consistent with plant and mammalian studies, we determined a single, natural or synthetic, 5'-intron is sufficient for the full IME effect conferred by three synthetic introns, while a 3'-intron is not. We found coding sequence can affect IME; the same three synthetic introns that increase mcherry protein concentration by approximately 50%, increase mEGFP by 80%. We determined IME effect size is not greatly affected by the stronger vit-2 promoter. Our microfluidic imaging approach should facilitate screens for factors affecting IME and other intron-dependent processes.

Recombinant Ca2+-regulated photoproteins of ctenophores: current knowledge and application prospects

Bright bioluminescence of ctenophores is conditioned by Ca²⁺-regulated photoproteins. Although they share many properties characteristic of hydromedusan Ca²⁺-regulated photoproteins responsible for light emission of marine animals belonging to phylum Cnidaria, a substantial distinction still exists. The ctenophore photoproteins appeared to be extremely sensitive to light-they lose the ability for bioluminescence on exposure to light over the entire absorption spectrum. Inactivation is irreversible because keeping the inactivated photoprotein in the dark does not recover its activity. The capability to emit light can be restored only by incubation of inactivated photoprotein with coelenterazine in the dark at alkaline pH in the presence of oxygen. Although these photoproteins were discovered many years ago, only the cloning of cDNAs encoding these unique bioluminescent proteins in the early 2000s has provided a new impetus for their studies. To date, cDNAs encoding Ca²⁺-regulated photoproteins from four different species of luminous ctenophores have been cloned. The amino acid sequences of ctenophore photoproteins turned out to completely differ from those of hydromedusan photoproteins (identity less than 29%) though also similar to them having three EF-hand Ca²⁺-binding sites. At the same time, these photoproteins reveal the same two-domain scaffold characteristic of hydromedusan photoproteins. This review is an attempt to systemize and critically evaluate the data scattered through various articles regarding the structural features of recombinant light-sensitive Ca²⁺-regulated photoproteins of ctenophores and their bioluminescent and physicochemical properties as well as to compare them with those of hydromedusan photoproteins. In addition, we also discuss the prospects of their biotechnology applications.

Neuropathic Pain Up-Regulates Hypothalamo-Neurohypophysial and Hypothalamo-Spinal Oxytocinergic Pathways in Oxytocin-Monomeric Red Fluorescent Protein 1 Transgenic Rat

Despite the high incidence of neuropathic pain, its mechanism remains unclear. Oxytocin (OXT) is an established endogenous polypeptide produced in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus. OXT, which is synthesized by OXT neurons in the SON and the magnocellular part of the PVN (mPVN), is delivered into the posterior pituitary (PP), then released into the systemic blood circulation. Meanwhile, OXT-containing neurosecretory cells in the parvocellular part of the PVN (pPVN) are directly projected to the spinal cord and are associated with sensory modulation. In this study, the OXT system in the hypothalamo-neurohypophysial and hypothalamo-spinal pathway was surveyed using a rat neuropathic pain model induced by partial sciatic nerve ligation (PSL). In the present study, we used transgenic rats expressing an OXT-monomeric red fluorescent protein 1 (mRFP1) fusion gene. In a neuropathic pain model, mechanical allodynia was observed, and glial cell activation was also confirmed via immunohistochemistry. In this neuropathic pain model, a significant increase in the OXT-mRFP1 expression was observed in the PP, the SON, mPVN, and pPVN. Furthermore, OXT-mRFP1 granules with positive fluorescent reaction were remarkably increased in laminae I and II of the ipsilateral dorsal horn. Although the plasma concentrations of OXT did not significantly change, a significant increase of the mRNA levels of OXT and mRFP1 in the SON, mPVN, and pPVN were observed. These results suggest that neuropathic pain induced by PSL upregulates hypothalamic OXT synthesis and transportation to the OXTergic axon terminals in the PP and spinal cord.

Melleolides impact fungal translation via elongation factor 2

Melleolides from the honey mushroom Armillaria mellea represent a structurally diverse group of polyketide-sesquiterpene hybrids. Among various bioactivites, melleolides show antifungal effects against Aspergillus and other fungi. This bioactivity depends on a Δ2,4-double bond present in dihydroarmillylorsellinate (DAO) or arnamial, for example. Yet, the mode of action of Δ2,4-unsaturated, antifungal melleolides has been unknown. Here, we report on the molecular target of DAO in the fungus Aspergillus nidulans. Using a combination of synthetic chemistry to create a DAO-labelled probe, protein pulldown assays, MALDI-TOF-based peptide analysis and western blotting, we identify the eukaryotic translation elongation factor 2 (eEF2) as a binding partner of DAO. We confirm the inhibition of protein biosynthesis in vivo with an engineered A. nidulans strain producing the red fluorescent protein mCherry. Our work suggests a binding site dissimilar from that of the protein biosynthesis inhibitor sordarin, and highlights translational elongation as a valid antifungal drug target.

Identification and subcellular location of an RNA silencing suppressor encoded by mulberry crinkle leaf virus

Mulberry crinkle leaf virus (MCLV) is a novel geminivirus recently identified from the woody plant mulberry (Morus alba L.). Little is known about the functions of the proteins encoded by the MCLV genome. Here, all the MCLV-encoded proteins were examined for the ability to suppress gene silencing by an agroinfiltration assay in combination with northern blot analysis of green fluorescent protein (GFP) mRNA and western blot analysis. Of the six proteins, only one protein, V3, which has been predicted to play a role in viral movement, was found to suppress the gene silencing induced by a sense GFP gene in Nicotiana benthamiana 16c. The minimal amino acid sequence of V3 that maintains suppressor activity was also determined by constructing truncated mutants lacking different lengths of the amino acid sequences at the N- or C-terminus of the V3 protein. The results showed that the 94 N-terminal amino acid residues of V3 are sufficient to maintain V3 suppressor activity. In addition, the subcellular location of the V3 protein was investigated by confocal laser scanning microscopy after the expression of a V3-RFP fused protein in leaf epidermal cells of N. benthamiana. The results indicated that the V3 protein localized not only to the cytoplasm but also to the nucleus of N. benthamiana, implying that V3 can shuttle between the nucleus and the cytoplasm. Deletion mutant analysis indicated that a putative nuclear localization signal (NLS) between aa 118-134 might be responsible for the nuclear distribution of the V3 protein. Given the importance of RNA silencing in plant-virus interactions, the identification of a silencing suppressor of MCLV should be valuable in understanding the pathogenicity and molecular biology of this virus.

Calcium Imaging of Microglial Network Activity in Stroke

Calcium signaling plays a significant role in microglial activation. Genetically encoded calcium indicators (GECI) have been widely used for calcium imaging studies in many brain cell types, including neurons, astrocytes, and oligodendrocytes. However, microglial calcium imaging approaches have been hampered by idiosyncrasies of their gene expression and malleable cell properties. The generation of PC::G5-tdT, a Polr2a locus-based conditional mouse reporter of calcium, facilitated the deployment of GECI in microglia. When crossed with the Iba1(Aif1)-IRES-Cre line, all brain microglia of the progeny are labeled with the calcium indicator variant GCaMP5G and the red fluorescent protein tdTomato. This reporter system has enabled in vivo studies of intracellular calcium in large microglial cell populations in cerebral pathologies such as ischemic stroke. In this chapter, we outline specific guidelines for genetic, surgical, imaging, and data analysis aspects of microglial calcium monitoring of the ischemic cortex following middle cerebral artery occlusion.

Labeling Microglia with Genetically Encoded Calcium Indicators

Genetically encoded calcium indicators (GECIs) have become widely used for Ca²⁺ imaging in cultured cells as well as in living organisms. Transduction of microglia with viral vectors encoding GECIs provides a convenient means to label microglia for in vivo Ca²⁺ imaging. We describe a method using microglia-specific microRNA-9-regulated viral vector, to label microglial cells with a ratiometric GECI (Twitch-2B). This method enables longitudinal recording of both transient and sustained elevations of Ca²⁺ in microglia in live animals.

Selective overexpression of cytoglobin in stellate cells attenuates thioacetamide-induced liver fibrosis in mice

Cytoglobin (CYGB), discovered in hepatic stellate cells (HSCs), is known to possess a radical scavenger function, but its pathophysiological roles remain unclear. Here, for the first time, we generated a new transgenic (TG) mouse line in which both Cygb and mCherry reporter gene expression were under the control of the native Cygb gene promoter. We demonstrated that the expression of Cygb-mCherry was related to endogenous Cygb in adult tissues by tracing mCherry fluorescence together with DNA, mRNA, and protein analyses. Administration of a single dose (50 mg/kg) of thioacetamide (TAA) in Cygb-TG mice resulted in lower levels of alanine transaminase and oxidative stress than those in WT mice. After 10 weeks of TAA administration, Cygb-TG livers exhibited reduced neutrophil accumulation, cytokine expression and fibrosis but high levels of quiescent HSCs. Primary HSCs isolated from Cygb-TG mice (HSCCygb-TG) exhibited significantly decreased mRNA levels of α-smooth muscle actin (αSMA), collagen 1α1, and transforming growth factor β-3 after 4 days in culture relative to WT cells. HSCsCygb-TG were resistant to H2O2-induced αSMA expression. Thus, cell-specific overexpression of Cygb attenuates HSC activation and protects mice against TAA-induced liver fibrosis presumably by maintaining HSC quiescence. Cygb is a potential new target for antifibrotic approaches.

Advantages of patient-derived orthotopic mouse models and genetic reporters for developing fluorescence-guided surgery

Fluorescence-guided surgery can enhance the surgeon's ability to achieve a complete oncologic resection. There are a number of tumor-specific probes being developed with many preclinical mouse models to evaluate their efficacy. The current review discusses the different preclinical mouse models in the setting of probe evaluation and highlights the advantages of patient-derived orthotopic xenografts (PDOX) mouse models and genetic reporters to develop fluorescence-guided surgery.

Lineage tracing aged mouse kidneys shows lower number of cells of renin lineage and reduced responsiveness to RAAS inhibition

Blocking the renin-angiotensin-aldosterone system (RAAS) remains a mainstay of therapy in hypertension and glomerular diseases. With the population aging, our understanding of renin-producing cells in kidneys with advanced age is more critical than ever. Accordingly, we administered tamoxifen to Ren1cCreERxRs-tdTomato-R mice to permanently fate map cells of renin lineage (CoRL). The number of Td-tomato-labeled CoRL decreased significantly in aged mice (24 mo of age) compared with young mice (3.5 mo of age), as did renin mRNA levels. To determine whether aged CoRL responded less to RAAS blockade, enalapril and losartan were administered over 25 days following uninephrectomy in young and aged mice. The number of CoRL increased in young mice in response to enalapril and losartan. However, this was significantly lower in aged mice compared with young mice due to limited proliferation, but not recruitment. Gene expression analysis of laser-captured CoRL showed a substantial increase in mRNA levels for proapoptotic and prosenescence genes, and an increase in a major prosenescence protein on immunostaining. These results show that CoRL are lower in aged mice and do not respond to RAAS inhibition to the same extent as young mice.

Hypersensitive assessment of aryl hydrocarbon receptor transcriptional activity using a novel truncated cyp1a promoter in zebrafish

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent organic pollutant (POP), an unintentional byproduct of various industrial processes, and a human carcinogen. The expression of the cytochrome P450 1A (cyp1a) gene is upregulated in the presence of TCDD through activating the aryl hydrocarbon receptor pathway in a dose-dependent manner. Several essential response elements, including the 8 potential xenobiotic response elements in the cyp1a promoter region, have been identified to be the main functional parts for the response to TCDD. Thus, we aimed to develop a convenient and sensitive biomonitoring tool to examine the level of POPs in the environment and evaluate its potential human health risks by TCDD. Here, we established a transgenic zebrafish model with a red fluorescent reporter gene ( mCherry) using the truncated cyp1a promoter. Under exposure to TCDD, the expression pattern of mCherry in the reporter zebrafish mirrored that of endogenous cyp1a mRNA, and the primary target tissues for TCDD were the brain vessels, liver, gut, cloaca, and skin. Our results indicated that exposure of the embryos to TCDD at concentrations as low as 0.005 nM for 48 h, which did not elicit morphologic abnormalities in the embryos, markedly increased mCherry expression. In addition, the reporter embryos responded to other POPs, and primary liver cell culture of zebrafish revealed that Cyp1a protein was mainly expressed in the cytoplasm of liver cells. Furthermore, our transgenic fish embryos demonstrated that TCDD exposure can regulate the expression levels of several tumor-related factors, including epidermal growth factor, TNF-α, C-myc, proliferating cell nuclear antigen, TGF-β, serine/threonine kinase (Akt), and phosphorylated Akt, suggesting that our transgenic fish can be used as a sensitive model to evaluate the carcinogenicity induced by TCDD exposure.-Luo, J.-J., Su, D.-S., Xie, S.-L., Liu, Y., Liu, P., Yang, X.-J., Pei D.-S. Hypersensitive assessment of aryl hydrocarbon receptor transcriptional activity using a novel truncated cyp1a promoter in zebrafish.

Visualizing Soluble Protein Mutants by Using Monomeric Red Fluorescent Protein as a Reporter for Directed Evolution

Directed evolution-based protein engineering usually generates large library contained insoluble mutants because of structural disturbance by mutation. To reduce the workload and costs, it is crucial to identify and eliminate those insoluble variants prior to dedicated analysis. Here, we demonstrate a method to visualize soluble protein mutants by using monomeric red fluorescent protein (mRFP) as a fusion tag. A plasmid was devised to express nicotinic acid mononucleotide adenylyltransferase (NadD) fused with a GGGS-linked mRFP tag at the C-terminus. The plasmid was subjected to site saturation mutagenesis within the nadD gene, used to transform Escherichia coli DH10B competent cells, leading to colonies with different red intensities. It was found that the fluorescence intensity of the cell culture correlated positively with the content of NadD-mRFP mutant in the supernatant. Mutation at position 132 led to a library of which most colonies lost the red phenotype, indicating that the position had a key role for proper protein folding. Similarly, mRFP enabled identification of soluble mutants of other enzymes including 1-deoxy-D-xylulose-5-phosphate reductoisomerase and phosphite dehydrogenase. These data suggested that mRFP can serve as a fusion reporter for visualizing soluble protein mutants to facilitate more efficient library screening in directed evolution.

Expression of fluorescent proteins in Lactobacillus rhamnosus to study host-microbe and microbe-microbe interactions

Probiotic Lactobacillus strains are widely used to benefit human and animal health, although the exact mechanisms behind their interactions with the host and the microbiota are largely unknown. Fluorescent tagging of live probiotic cells is an important tool to unravel their modes of action. In this study, the implementation of different heterologously expressed fluorescent proteins for the labelling of the model probiotic strains Lactobacillus rhamnosusGG (gastrointestinal) and Lactobacillus rhamnosusGR-1 (vaginal) was explored. Heterologous expression of mTagBFP2 and mCherry resulted in long-lasting fluorescence of L. rhamnosusGG and GR-1 cells, using the nisin-controlled expression (NICE) system. These novel fluorescent strains were then used to study in vitro aspects of their microbe-microbe and microbe-host interactions. Lactobacillus rhamnosusGG and L. rhamnosusGR-1 expressing mTagBFP2 and mCherry could be visualized in mixed-species biofilms, where they inhibited biofilm formation by Salmonella Typhimurium-gfpmut3 expressing the green fluorescent protein. Likewise, fluorescent L. rhamnosusGG and L. rhamnosusGR-1 were implemented for the visualization of their adhesion patterns to intestinal epithelial cell cultures. The fluorescent L. rhamnosus strains developed in this study can therefore serve as novel tools for the study of probiotic interactions with their environment.

AAV-mediated gene delivery of the calreticulin anti-angiogenic domain inhibits ocular neovascularization

Ocular neovascularization is a common pathological feature in diabetic retinopathy and neovascular age-related macular degeneration that can lead to severe vision loss. We evaluated the therapeutic efficacy of a novel endogenous inhibitor of angiogenesis, the calreticulin anti-angiogenic domain (CAD180), and its functional 112-residue fragment, CAD-like peptide 112 (CAD112), delivered using a self-complementary adeno-associated virus serotype 2 (scAAV2) in rodent models of oxygen-induced retinopathy and laser-induced choroidal neovascularization. The expression of CAD180 and CAD112 was elevated in human umbilical vein endothelial cells transduced with scAAV2-CAD180 or scAAV2-CAD112, respectively, and both inhibited angiogenic activity in vitro. Intravitreal gene delivery of scAAV2-CAD180 or scAAV2-CAD112 significantly inhibited ischemia-induced retinal neovascularization in rat eyes (CAD180: 52.7% reduction; CAD112: 49.2% reduction) compared to scAAV2-mCherry, as measured in retinal flatmounts stained with isolectin B4. Moreover, the retinal structure and function were unaffected by scAAV2-CAD180 or scAAV2-CAD112, as measured by optical coherence tomography and electroretinography. Moreover, subretinal delivery of scAAV2-CAD180 or scAAV2-CAD112 significantly attenuated laser-induced choroidal neovascularization in mouse eyes compared to scAAV2-mCherry, as measured by fundus fluorescein angiography (CAD180: 62.4% reduction; CAD112: 57.5% reduction) and choroidal flatmounts (CAD180: 40.21% reduction; CAD112: 43.03% reduction). Gene delivery using scAAV2-CAD180 or scAAV2-CAD112 has significant potential as a therapeutic option for the management of ocular neovascularization.

Generation and characterization of a fowl adenovirus 9 dual-site expression vector

Fowl adenoviruses (FAdVs) are widely considered as excellent platforms for vaccine development and gene therapy. We improved on our right-end partial TR-2 deleted or a left-end 2.3 kb deleted vectors by developing a single, dual-site delivery vector. We demonstrated that, in addition to ORF11, the right end ORF17 is also dispensable. To further improve the capacity and flexibility of the FAdV-9 based vector system, we generated an infectious recombinant FAdV-9 dual-site expression clone lacking 1.9 kb of the left end and replaced with mCherry under the control of a native promoter, and 3.6 kb of the right-end replaced with an EGFP expression cassette. Five intermediate FAdmid clones were successfully constructed: a) pFAdV-9Δ0-2RED (mCherry replacing the left end 2.2 kb ORF0 to 2); b) pFAdV-9RED (mCherry replacing the left end 1.9 kb ORF1 to 2); c) pFAdV-9Δ17 (deletion of ORF17 and 393 bp downstream untranslated region); d) pFAdV-9GFP (EGFP expression cassette replacing the right end 3.6 kb) and e) pFAdV-9Dual (both mCherry in the left end and the EGFP expression cassette in the right end of our vector). Our novel FAdV-9 dual-site vaccine vector, produced infectious virus and expressed either one or both mCherry and EGFP.

Stably Fluorescent Cell Line of Human Ovarian Epithelial Cancer Cells SK-OV-3ip-red

Stable red fluorescing line of human ovarian epithelial cancer cells SK-OV-3ip-red was generated expressing gene coding for protein TurboFP635 (Katushka) fluorescing in the far-red spectrum region with excitation and emission peaks at 588 and 635 nm, respectively. Fluorescence of SK-OV-3ip-red line remained high during long-term cell culturing and after cryogenic freezing. The obtained cell line SK-OV-3ip-red can serve a basis for a model of a scattered tumor with numerous/extended metastases and used both for testing anticancer drugs inhibiting metastasis growth and for non-invasive monitoring of the growth dynamics with high precision.

Optogenetic manipulation of anatomical re-entry by light-guided generation of a reversible local conduction block

Aims

Anatomical re-entry is an important mechanism of ventricular tachycardia, characterized by circular electrical propagation in a fixed pathway. It's current investigative and therapeutic approaches are non-biological, rather unspecific (drugs), traumatizing (electrical shocks), or irreversible (ablation). Optogenetics is a new biological technique that allows reversible modulation of electrical function with unmatched spatiotemporal precision using light-gated ion channels. We therefore investigated optogenetic manipulation of anatomical re-entry in ventricular cardiac tissue.

Methods and results

Transverse, 150-μm-thick ventricular slices, obtained from neonatal rat hearts, were genetically modified with lentiviral vectors encoding Ca2+-translocating channelrhodopsin (CatCh), a light-gated depolarizing ion channel, or enhanced yellow fluorescent protein (eYFP) as control. Stable anatomical re-entry was induced in both experimental groups. Activation of CatCh was precisely controlled by 470-nm patterned illumination, while the effects on anatomical re-entry were studied by optical voltage mapping. Regional illumination in the pathway of anatomical re-entry resulted in termination of arrhythmic activity only in CatCh-expressing slices by establishing a local and reversible, depolarization-induced conduction block in the illuminated area. Systematic adjustment of the size of the light-exposed area in the re-entrant pathway revealed that re-entry could be terminated by either wave collision or extinction, depending on the depth (transmurality) of illumination. In silico studies implicated source-sink mismatches at the site of subtransmural conduction block as an important factor in re-entry termination.

Conclusions

Anatomical re-entry in ventricular tissue can be manipulated by optogenetic induction of a local and reversible conduction block in the re-entrant pathway, allowing effective re-entry termination. These results provide distinctively new mechanistic insight into re-entry termination and a novel perspective for cardiac arrhythmia management.

Analysis of Stroma Labeling During Multiple Passage of a Sarcoma Imageable Patient-Derived Orthotopic Xenograft (iPDOX) in Red Fluorescent Protein Transgenic Nude Mice

A patient-derived orthotopic xenograft (PDOX) model of undifferentiated pleomorphic sarcoma (UPS) was previously established that acquired red fluorescent protein (RFP)-expressing stroma by growth in an RFP transgenic nude mouse. In the present study, an imageable PDOX model (iPDOX) of UPS was established by orthotopic implantation in the biceps femoris of transgenic RFP nude mice. After the tumors grew to a diameter of 10 mm, they were harvested and the brightest portion of the tumors were subsequently orthotopically transplanted to both RFP and non-colored nude mice. The UPS PDOX tumor was again transplanted to RFP transgenic and non-colored nude mice, and finally a 3rd passage was made in the same manner. Five UPS tumors from each passage in both RFP and non-colored mouse models were harvested. The FV1,000 confocal microscope was used to visualize and quantitate the RFP area of the resected tumors. The average percent fluorescent area in the first passage of RFP mice was 34 ± 22%; in the second passage, 34 ± 20%; and 36 ± 11% in the third passage of RFP transgenic nude mice. The average tumor RFP area in the first passage from RFP mice to non-colored mice was 20 ± 7%; in the second passage, 28 ± 11%; in the third passage was 27 ± 13%. The present results demonstrate the extensive and stable acquisition of stroma by the UPS-tumor growing orthotopically in transgenic RFP nude mice (iPDOX). This model can be used for screening for effective drugs for individual patients and drug discovery. J. Cell. Biochem. 118: 3367-3371, 2017. © 2017 Wiley Periodicals, Inc.

Heterogeneity of Stop Codon Readthrough in Single Bacterial Cells and Implications for Population Fitness

Gene expression noise (heterogeneity) leads to phenotypic diversity among isogenic individual cells. Our current understanding of gene expression noise is mostly limited to transcription, as separating translational noise from transcriptional noise has been challenging. It also remains unclear how translational heterogeneity originates. Using a transcription-normalized reporter system, we discovered that stop codon readthrough is heterogeneous among single cells, and individual cells with higher UGA readthrough grow faster from stationary phase. Our work also revealed that individual cells with lower protein synthesis levels exhibited higher UGA readthrough, which was confirmed with ribosome-targeting antibiotics (e.g., chloramphenicol). Further experiments and mathematical modeling suggest that varied competition between ternary complexes and release factors perturbs the UGA readthrough level. Our results indicate that fluctuations in the concentrations of translational components lead to UGA readthrough heterogeneity among single cells, which enhances phenotypic diversity of the genetically identical population and facilitates its adaptation to changing environments.

Sox10+ Cells Contribute to Vascular Development in Multiple Organs-Brief Report

OBJECTIVE

Previous genetic lineage tracing studies showed that Sox10+ cells differentiate into vascular mural cells, limited to neural crest-derived blood vessels in craniofacial tissues, aortic arch, pulmonary arch arteries, brachiocephalic, carotid arteries, and thymus. The purpose of this study was to investigate the contribution of Sox10+ cells to the vascular development in other tissues and organs and their relationship with neural crest.

APPROACH AND RESULTS

Using genetic lineage tracing technique based on Cre/LoxP system, we examined blood vessels in the adult organs of the mice expressing Sox10-Cre/Rosa-LoxP-red fluorescent protein or Wnt1-Cre/Rosa-LoxP-red fluorescent protein by immunohistological analysis. In addition to previously reported tissues and organs derived from neural crest, we showed that Sox10+ cells also contributed to vascular mural cells in the lung, spleen, and kidney, which are derived from non-neural crest origin as evidenced by red fluorescent protein-negative blood vessels in these 3 organs of Wnt1-Cre/Rosa-LoxP-red fluorescent protein mice.

CONCLUSIONS

This study demonstrates that Sox10+ cells contribute to pericytes and smooth muscle cells in most parts of the body, including those from neural crest and non-neural crest, which has significant implications in vascular remodeling under physiological and pathological conditions.

Live Cell Imaging: Assessing the Phototoxicity of 488 and 546 nm Light and Methods to Alleviate it

In live cell imaging of fluorescent proteins, phototoxicity of the excitation light can be problematical. Cell death is obvious, but reduced cell viability can make the interpretation of observations error prone. We characterized the phototoxic consequences of 488 and 546 nm light on untransformed human cells and tested methods that have or could be used to alleviate photodamage. Unlabeled RPE1 cells were given single 0.5-2.5 min irradiations in early G1 from a mercury arc lamp on a fluorescence microscope. Four hundred eighty-eight nanometer light produced a dose-dependent decrease in the percentage of cells that progressed to mitosis, slowing of the cell cycle for some of those entering mitosis, and a ∼12% incidence of cell death for the highest dose. For 546 nm light we found a 10-15% reduction in the percentage of cells entering mitosis, no strong dose dependency, and a ∼2% incidence of cell death for the longest irradiations. For cells expressing GFP-centrin1 or mCherry-centrin1, fewer entered mitosis for each dose than unlabeled cells. For constant total dose 488 nm light irradiations of unlabeled cells, reducing the intensity 10-fold or spreading the exposures out as a series of 10 sec pulses at 1 min intervals produced a minor and not consistent improvement in the percentage of cells entering mitosis. Reducing oxidative processes, by culturing at ∼3% oxygen or adding the reducing agent Trolox noticeably increased the fraction of cells entering mitosis. Thus, for long-term imaging there can be value to using RFP constructs and for GFP-tagged proteins reducing oxidative processes. J. Cell. Physiol. 232: 2461-2468, 2017. © 2016 Wiley Periodicals, Inc.

Increasing the yield of middle silk gland expression system through transgenic knock-down of endogenous sericin-1

Various genetically modified bioreactor systems have been developed to meet the increasing demands of recombinant proteins. Silk gland of Bombyx mori holds great potential to be a cost-effective bioreactor for commercial-scale production of recombinant proteins. However, the actual yields of proteins obtained from the current silk gland expression systems are too low for the proteins to be dissolved and purified in a large scale. Here, we proposed a strategy that reducing endogenous sericin proteins would increase the expression yield of foreign proteins. Using transgenic RNA interference, we successfully reduced the expression of BmSer1 to 50%. A total 26 transgenic lines expressing Discosoma sp. red fluorescent protein (DsRed) in the middle silk gland (MSG) under the control of BmSer1 promoter were established to analyze the expression of recombinant. qRT-PCR and western blotting showed that in BmSer1 knock-down lines, the expression of DsRed had significantly increased both at mRNA and protein levels. We did an additional analysis of DsRed/BmSer1 distribution in cocoon and effect of DsRed protein accumulation on the silk fiber formation process. This study describes not only a novel method to enhance recombinant protein expression in MSG bioreactor, but also a strategy to optimize other bioreactor systems.

Memory formation orchestrates the wiring of adult-born hippocampal neurons into brain circuits

During memory formation, structural rearrangements of dendritic spines provide a mean to durably modulate synaptic connectivity within neuronal networks. New neurons generated throughout the adult life in the dentate gyrus of the hippocampus contribute to learning and memory. As these neurons become incorporated into the network, they generate huge numbers of new connections that modify hippocampal circuitry and functioning. However, it is yet unclear as to how the dynamic process of memory formation influences their synaptic integration into neuronal circuits. New memories are established according to a multistep process during which new information is first acquired and then consolidated to form a stable memory trace. Upon recall, memory is transiently destabilized and vulnerable to modification. Using contextual fear conditioning, we found that learning was associated with an acceleration of dendritic spines formation of adult-born neurons, and that spine connectivity becomes strengthened after memory consolidation. Moreover, we observed that afferent connectivity onto adult-born neurons is enhanced after memory retrieval, while extinction training induces a change of spine shapes. Together, these findings reveal that the neuronal activity supporting memory processes strongly influences the structural dendritic integration of adult-born neurons into pre-existing neuronal circuits. Such change of afferent connectivity is likely to impact the overall wiring of hippocampal network, and consequently, to regulate hippocampal function.

Long-Term Expression of a Fluorescent Reporter Gene via Direct Injection of Plasmid Vector into Mouse Skeletal Muscle: Comparison of Human Creatine Kinase and Cmv Promoter Expression Levels in Vivo

Expression of a fluorescent reporter gene has been studied using two alternate promoters to transcribe the green fluorescent protein (gfp) from Aequorea victoria. The human cytomegalovirus (CMV) enhancer/promoter or the human muscle-specific creatine kinase promoter (CKM) were inserted along with the gfp cDNA into a plasmid expression vector based on a modified adeno-associated virus genome. Naked plasmid DNA was injected into the hamstring muscle of mdx mice and gfp gene expression determined from frozen muscle sections taken at 4, 14, and 42 days postinjection. Fluorescence patterns obtained by photomicroscopy and quantitative fluorescence measurements indicated a near-linear increase in the accumulation of the gfp in skeletal muscle during the length of the study, with gfp expression at 42 days being roughly four times the values obtained at 4 days. The levels of expression of gfp from the CKM construct were consistantly higher than for the CMV construct. The CKM promoter/expression vector combination demonstrates significant potential for simple, direct delivery and long-term, high-level expression of genes in skeletal muscle.

Construction of a viral T2A-peptide based knock-in mouse model for enhanced Cre recombinase activity and fluorescent labeling of podocytes

Podocyte injury is a key event in glomerular disease leading to proteinuria and opening the path toward glomerular scarring. As a consequence, glomerular research strives to discover molecular mechanisms and signaling pathways affecting podocyte health. The hNphs2.Cre mouse model has been a valuable tool to manipulate podocyte-specific genes and to label podocytes for lineage tracing and purification. Here we designed a novel podocyte-specific tricistronic Cre mouse model combining codon improved Cre expression and fluorescent cell labeling with mTomato under the control of the endogenous Nphs2 promoter using viral T2A-peptides. Independent expression of endogenous podocin, codon improved Cre, and mTomato was confirmed by immunofluorescence, fluorescent activated cell sorting and protein analyses. Nphs2pod.T2A.ciCre.T2A.mTomato/wild-type mice developed normally and did not show any signs of glomerular disease or off-target effects under basal conditions and in states of disease. Nphs2pod.T2A.ciCre.T2A.mTomato/wild-type-mediated gene recombination was superior to conventional hNphs2.Cre mice-mediated gene recombination. Last, we compared Cre efficiency in a disease model by mating Nphs2pod.T2A.ciCre.T2A.mTomato/wild-type and hNphs2.Cre mice to Phb2fl/fl mice. The podocyte-specific Phb2 knockout by Nphs2pod.T2A.ciCre.T2A.mTomato/wild-type mice resulted in an aggravated glomerular injury as compared to a podocyte-specific Phb2 gene deletion triggered by hNphs2.Cre. Thus, we generated the first tricistronic podocyte mouse model combining enhanced Cre recombinase efficiency and fluorescent labeling in podocytes without the need for additional matings with conventional reporter mouse lines.

Labeling the Stroma of a Patient-Derived Orthotopic Xenograft (PDOX) Mouse Model of Undifferentiated Pleomorphic Soft-Tissue Sarcoma With Red Fluorescent Protein for Rapid Non-Invasive Imaging for Drug Screening

Our laboratory pioneered patient-derived orthotopic xenograft (PDOX) mouse models using surgical orthotopic implantation (SOI). PDOX models are patient-like, in contrast to the ectopic subcutaneous-transplant cancer models. In the present study, we demonstrate that an undifferentiated pleomorphic soft-tissue sarcoma (UPS-STS) PDOX model acquired bright RFP-expressing stroma through one passage in red fluorescent protein (RFP) transgenic mice, which upon passage to non-colored nude mice was non-invasively imageable. A PDOX nude mouse model of UPS-STS was established in the biceps femoris of nude mice. After the tumors grew to a diameter of 10 mm, the tumors were subsequently passaged to RFP transgenic mice, and after tumor growth were then passaged to non-transgenic nude mice. Tumors were divided into small fragments and transplanted in the biceps femoris at each passage. The OV100 Small Animal Fluorescence Imaging System and FV1000 laser scanning confocal microscope were used to image RFP fluorescence in the UPS-STS PDOX models. UPS-STS PDOX tumors, previously grown in RFP transgenic nude mice for only one passage, had very bright fluorescence and after passage to non-transgenic nude mice maintained the bright fluorescence and were non-invasively imageable. FV1000 confocal imaging revealed diffusely distributed bright RFP stromal cells in the PDOX tumor, both in RFP transgenic mice and after passage to non-transgenic mice. These results demonstrate a powerful method to make the PDOX UPS-STS model brightly fluorescent for non-invasive imaging, as well as for confocal microscopy of individual stromal cells associated with the tumor. The RFP-labeled UPS PDOX has the potential to rapidly screen for novel effective agents for individual patients, including stroma-targeting drugs, whereby the stromal cells are a visual target. J. Cell. Biochem. 118: 361-365, 2017. © 2016 Wiley Periodicals, Inc.

Comparison of Tumor Recurrence After Resection of Highly- and Poorly-Metastatic Triple-negative Breast Cancer in Orthotopic Nude-Mouse Models

BACKGROUND

Triple-negative breast cancer (TNBC), defined by the absence of receptors for estrogen, progesterone and human epithelial receptor 2, is a recalcitrant disease in need of effective therapy. We previously isolated highly-metastatic variants of the human TNBC cell line MDA-MB-231 using serial orthotopic implantation in nude mice.

MATERIALS AND METHODS

In the present report, we compared local and metastatic recurrence in lymph nodes in orthotopic nude-mouse models after bright-light surgery (BLS) of tumors from highly-metastatic variants or poorly-metastatic parental MDA-MB-231-RFP cells. Orthotopic tumors from parental MDA-MB-231 or highly-metastatic MDA-MB-231 were resected under bright light similar to an operating room.

RESULTS

After resection of primary tumors, local recurrence from highly-metastatic MDA-MB-231 cells grew more rapidly than did parental MDA-MB-231 cells. Lymph-node metastasis from highly-metastatic MDA-MB-231 cells occurred after primary tumor resection much more extensively than after parental MDA-MB-231 tumors were resected.

CONCLUSION

The results of the present report suggest that conventional surgery under bright light was unable to control highly-metastatic compared with poorly-metastatic MDA-MB-231 TNBC.

Imaging the microenvironment of pancreatic cancer patient-derived orthotopic xenografts (PDOX) growing in transgenic nude mice expressing GFP, RFP, or CFP

We have developed a multi-color, imageable, orthotopic mouse model for individual patients with pancreatic cancer. The tumors are labeled by first passaging them orthotopically through transgenic nude mice expressing green fluorescent protein (GFP), red fluorescent protein (RFP), or cyan fluorescent protein (CFP). Passage of the tumors in these colored transgenic mice labels the stromal cells of the tumor. The cancer cells in the PDOX are labeled in situ with GFP by telomerase-dependent adenovirus OBP-401. The models are termed imageable patient-derived orthotopic xenografts (iPDOX). The tumors acquired brightly-fluorescent stromal cells from the transgenic host mice, which were stably associated with the tumors through multiple passages. The colored fluorescent protein-expressing stromal cells included cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). This model enables powerful color-coded imaging of the interaction of cancer and stromal cells during tumor progression and treatment.

A Robotic Platform for High-throughput Protoplast Isolation and Transformation

Over the last decade there has been a resurgence in the use of plant protoplasts that range from model species to crop species, for analysis of signal transduction pathways, transcriptional regulatory networks, gene expression, genome-editing, and gene-silencing. Furthermore, significant progress has been made in the regeneration of plants from protoplasts, which has generated even more interest in the use of these systems for plant genomics. In this work, a protocol has been developed for automation of protoplast isolation and transformation from a 'Bright Yellow' 2 (BY-2) tobacco suspension culture using a robotic platform. The transformation procedures were validated using an orange fluorescent protein (OFP) reporter gene (pporRFP) under the control of the Cauliflower mosaic virus 35S promoter (35S). OFP expression in protoplasts was confirmed by epifluorescence microscopy. Analyses also included protoplast production efficiency methods using propidium iodide. Finally, low-cost food-grade enzymes were used for the protoplast isolation procedure, circumventing the need for lab-grade enzymes that are cost-prohibitive in high-throughput automated protoplast isolation and analysis. Based on the protocol developed in this work, the complete procedure from protoplast isolation to transformation can be conducted in under 4 hr, without any input from the operator. While the protocol developed in this work was validated with the BY-2 cell culture, the procedures and methods should be translatable to any plant suspension culture/protoplast system, which should enable acceleration of crop genomics research.

Efficient Production of Fluorescent Transgenic Rats using the piggyBac Transposon

Rats with fluorescent markers are of great value for studies that trace lineage-specific development, particularly those assessing the differentiation potential of embryonic stem cells (ESCs). The piggyBac (PB) transposon is widely used for the efficient introduction of genetic modifications into genomes, and has already been successfully used to produce transgenic mice and rats. Here, we generated transgenic rats carrying either the desRed fluorescent protein (RFP) gene or the enhanced green fluorescent protein (eGFP) gene by injecting pronuclei with PB plasmids. We showed that the transgenic rats expressed the RFP or eGFP gene in many organs and had the capability to transmit the marker gene to the next generation through germline integration. In addition, rat embryonic stem cells (ESCs) carrying an RFP reporter gene can be derived from the blastocysts of the transgenic rats. Moreover, the RFP gene can be detected in chimeras derived from RFP ESCs via blastocyst injection. This work suggests that PB-mediated transgenesis is a powerful tool to generate transgenic rats expressing fluorescent proteins with high efficiency, and this technique can be used to derive rat ESCs expressing a reporter protein.

Mitochondria-targeted DsRed2 protein expression during the early stage of bovine somatic cell nuclear transfer embryo development

Somatic cell nuclear transfer (SCNT) has been widely used as an efficient tool in biomedical research for the generation of transgenic animals from somatic cells with genetic modifications. Although remarkable advances in SCNT techniques have been reported in a variety of mammals, the cloning efficiency in domestic animals is still low due to the developmental defects of SCNT embryos. In particular, recent evidence has revealed that mitochondrial dysfunction is detected during the early development of SCNT embryos. However, there have been relatively few or no studies regarding the development of a system for evaluating mitochondrial behavior or dynamics. For the first time, in mitochondria of bovine SCNT embryos, we developed a method for the visualization of mitochondria and expression of fluorescence proteins. To express red fluorescence in mitochondria of cloned embryos, bovine ear skin fibroblasts, nuclear donor, were stably transfected with a vector carrying mitochondria-targeting DsRed2 gene tagged with V5 epitope (mito-DsRed2-V5 tag) using lentivirus-mediated gene transfer because of its ability to integrate in the cell genome and the potential for long-term transgene expression in the transduced cells and their dividing cells. From western blotting analysis of V5 tag protein using mitochondrial fraction and confocal microscopy of red fluorescence using SCNT embryos, we found that the mitochondrial expression of the mito-DsRed2 protein was detected until the blastocyst stage. In addition, according to image analysis, it may be suggested possible use of the system for visualization of mitochondrial localization and evaluation of mitochondrial behaviors or dynamics in early development of bovine SCNT embryos.

Utilizing FUCCI reporters to understand pluripotent stem cell biology

The fluorescence ubiquitination cell cycle indicator (FUCCI) system provides a powerful method to evaluate cell cycle mechanisms associated with stem cell self-renewal and cell fate specification. By integrating the FUCCI system into human pluripotent stem cells (hPSCs) it is possible to isolate homogeneous fractions of viable cells representative of all cell cycle phases. This method avoids problems associated with traditional tools used for cell cycle analysis such as synchronizing drugs, elutriation and temperature sensitive mutants. Importantly, FUCCI reporters allow cell cycle events in dynamic systems, such as differentiation, to be evaluated. Initial reports on the FUCCI system focused on its strengths in reporting spatio-temporal aspects of cell cycle events in living cells and developmental models. In this report, we describe approaches that broaden the application of FUCCI reporters in PSCs through incorporation of FACS. This approach allows molecular analysis of the cell cycle in stem cell systems that were not previously possible.