See the Unseen: Red-Emissive Carbon Dots for Visualizing the Nucleolar Structures in Two Model Animals and In Vivo Drug Toxicity.

Nucleolus, which participates in many crucial cellular activities, is an ideal target for evaluating the state of a cell or an organism. Here, bright red-emissive carbon dots (termed CPCDs) with excitation-independent/polarity-dependent fluorescence emission are synthesized by a one-step hydrothermal reaction between congo red and p-phenylenediamine. The CPCDs can achieve wash-free, real-time, long-term, and high-quality nucleolus imaging in live cells, as well as in vivo imaging of two common model animals-zebrafish and Caenorhabditis elegans (C. elegans). Strikingly, CPCDs realize the nucleolus imaging of organs/flowing blood cells in zebrafish at a cellular level for the first time, and the superb nucleolus imaging of C. elegans suggests that the germ cells in the spermatheca probably have no intact nuclei. These previously unachieved imaging results of the cells/tissues/organs may guide the zebrafish-related studies and benefit the research of C. elegans development. More importantly, a novel strategy based on CPCDs for in vivo toxicity evaluation of materials/drugs (e.g., Ag+ ), which can visualize the otherwise unseen injuries in zebrafish, is developed. In conclusion, the CPCDs represent a robust tool for visualizing the structures and dynamic behaviors of live zebrafish and C. elegans, and may find important applications in cell biology and toxicology.

Nucleus-targeting pH-Responsive carbon dots for fast nucleus pH detection.

Nucleus pH is closely linked to many diseases such as aging, heart disease, skeletal myopathies, cancer, Alzheimer's disease, etc. Nevertheless, fluorescent sensors that can directly monitor nucleus pH changes have not yet been reported. Here, we first reported a green emissive carbon dots (CDs) for nucleus pH detection in living cells. CDs can selectively target nucleus with high accumulation at nucleolus due to their high affinity towards RNA once entering cells by lipid raft mediated endocytosis. Without washing, CDs at 5 µg/mL was enough to lighten nucleus within 10 min with the fluorescence on ever after 24 h incubation, achieving fast, wash-free, and long-term nucleus/nucleolus imaging. Meanwhile, the luminescent intensity of CDs was reduced gradually when pH changed continuously from 1 to 12, showing a pH-responsive fluorescence property with two linear ranges of pH 2-7 and pH 7-12. With their nucleus-targeting ability and pH-dependent photoluminescent property, CDs was successfully leveraged for nucleus pH detection in A549 cells and for in vivo pH sensing in zebra fish. CDs present a promising and powerful fluorescent sensor for nucleus imaging and nucleus pH sensing in living cells on the way to understand nucleus-related biological events.

Chitosan-modified fluorescent dye for simple, fast, and in-situ measurement of fungal cell growth in the presence of insoluble compounds.

The measurement of fungal cell growth in submerged culture systems containing insoluble compounds is essential yet difficult due to the interferences from the insoluble compounds like biopolymers. Here, we developed a fluorescent strategy based on chitosan-modified fluorescein isothiocyanate (GC-FITC) to monitor the cell growth of lignocellulosic fungi cultivated on biopolymers. GC-FITC could stain only lignocellulosic fungi (Tricoderma reesei, Penicillium oxalicum, Aspergillus nidulans, and Neurospora crassa), but not biopolymers (cellulose, xylan, pectin, or lignin), excluding the interferences from these insoluble biopolymer. Moreover, a linear relationship was observed between the fluorescence intensity of GC-FITC absorbed by lignocellulosic fungi and the biomass of lignocellulosic fungi. Therefore, GC-FITC was leveraged to monitor the cell growth of lignocellulosic fungi when using biopolymers like cellulose as the carbon sources, which is faster, more convenient, time-saving, and cost-effective than the existing methods using protein/DNA content measurement. GC-FITC offers a powerful tool to detect fungal growth in culture systems with insoluble materials.

Carbon dots for multicolor cell imaging and ultra-sensitive detection of multiple ions in living cells: One Stone for multiple Birds.

Given the significant impact of ions on environment pollution and human health, it is urgently needed to establish effective and convenient ion detection approaches, particularly in living cells. In this paper, we constructed multicolor N-doped-carbon dots (mPD-CDs) by facile one-step hydrothermal carbonization of m-phenylenediamine (mPD). mPD-CDs were successfully deployed for multicolor cellular imaging for animal cells, fungi, and bacteria in a wash-free way with high photostability and satisfactory biocompability. Moreover, mPD-CDs can be used as a fluorescent sensing probe for ultrasensitive detection of both iodide ion (I-) and typical heavy metals such as cadmium (Cd2+), copper (Cu2+), mercury (Hg2+), gadolinium (Gd3+), ferrous ion (Fe2+), Zinc (Zn2+), and ferric ion (Fe3+). This is the first report using CDs as optical sensing probe for the detection of Gd3+, and for detection of Fe3+ with fluorescence "turn on". More significantly, with these versatile and fascinating properties, we applied mPD-CDs for intracellular ion detection in living cells like Hep G2 and S. cerevisiae, and zebra fish. Altogether, mPD-CDs displayed great potential for multicolor cell imaging and the multiple ion detection in vitro and in vivo, presenting a promising strategy for in-situ ultrasensitive sensing of multiple metal ions in the environment and the biological systems.

Transmembrane transport process and endoplasmic reticulum function facilitate the role of gene cel1b in cellulase production of Trichoderma reesei.

BACKGROUND: A total of 11 ß-glucosidases are predicted in the genome of Trichoderma reesei, which are of great importance for regulating cellulase biosynthesis. Nevertheless, the relevant function and regulation mechanism of each ß-glucosidase remained unknown. RESULTS: We evidenced that overexpression of cel1b dramatically decreased cellulase synthesis in T. reesei RUT-C30 both at the protein level and the mRNA level. In contrast, the deletion of cel1b did not noticeably affect cellulase production. Protein CEL1B was identified to be intracellular, being located in vacuole and cell membrane. The overexpression of cel1b reduced the intracellular pNPGase activity and intracellular/extracellular glucose concentration without inducing carbon catabolite repression. On the other hand, RNA-sequencing analysis showed the transmembrane transport process and endoplasmic reticulum function were affected noticeably by overexpressing cel1b. In particular, some important sugar transporters were notably downregulated, leading to a compromised cellular uptake of sugars including glucose and cellobiose. CONCLUSIONS: Our data suggests that the cellulase inhibition by cel1b overexpression was not due to the ß-glucosidase activity, but probably the dysfunction of the cellular transport process (particularly sugar transport) and endoplasmic reticulum (ER). These findings advance the knowledge of regulation mechanism of cellulase synthesis in filamentous fungi, which is the basis for rationally engineering T. reesei strains to improve cellulase production in industry.

Intron retention coupled with nonsense-mediated decay is involved in cellulase biosynthesis in cellulolytic fungi.

BACKGROUND: Knowledge on regulatory networks associated with cellulase biosynthesis is prerequisite for exploitation of such regulatory systems in enhancing cellulase production with low cost. The biological functions of intron retention (IR) and nonsense-mediated mRNA decay (NMD) in filamentous fungi is lack of study, let alone their roles in cellulase biosynthesis. RESULTS: We found that major cellulase genes (cel7a, cel7b, and cel3a) exhibited concomitant decrease in IR rates and increase in their gene expression in T. reesei under cellulase-producing condition (cellulose and lactose) that was accompanied with a more active NMD pathway, as compared to cellulase non-producing condition (glucose). In the presence of the NMD pathway inhibitor that successfully repressed the NMD pathway, the mRNA levels of cellulase genes were sharply down-regulated, but the rates of IR in these genes were significantly up-regulated. Consistently, the cellulase activities were severely inhibited. In addition, the NMD pathway inhibitor caused the downregulated mRNA levels of two important genes of the target of rapamycin (TOR) pathway, trfkbp12 and trTOR1. The absence of gene trfkbp12 made the cellulase production in T. reesei more sensitive to the NMD pathway inhibitor. CONCLUSIONS: All these findings suggest that the IR of cellulase genes regulates their own gene expression by coupling with the NMD pathway, which might involve the TOR pathway. Our results provide better understanding on intron retention, the NMD pathway, and cellulase production mechanism in filamentous fungi.

Plant-derived Ca, N, S-Doped carbon dots for fast universal cell imaging and intracellular Congo red detection.

Congo red (CR) is a hazardous pigment, posing increasing dangerous to the environment and human health. However, the in-situ detection of CR in living cells has not been reported, as far as we know. Here, negatively-charged green-emitting Ca, N, S-doped carbon dots (Mis-mPD-CDs) were fabricated from plant and m-phenylenediamine (mPD) by facile one-step hydrothermal carbonization. Mis-mPD-CDs were capable of rapidly detecting CR on the basis of their fluorescence quenching by CR due to the inner filter effect. This CR detection based on Mis-mPD-CDs displayed a linear range of 0.2-1.2 µM and a low limit of detection (58 nM), and was not interfered by metal ions, important biological molecules, and other dyes, showing high sensitivity and selectivity. More interestingly, Mis-mPD-CDs can rapidly enter and label animal cells (A549, 4T1, and HUVEC), fungi (S. cerevisiae, C. albicans, and T. reesei), and bacteria (E. coli and S. aureus) for long term with high stability and appealing biocompatibility. Based on these compelling characteristics, we applied Mis-mPD-CDs for sensing and imaging CR in living cells (A549, C. albicans, E. coli, and S. aureus) and zebra fish. On the other hand, the quantitative detection of CR by Mis-mPD-CDs was realized in real samples like fish tissues and industrial wastewater. This is the first report on applying CDs for rapid CR detection in living cells and in vivo. Mis-mPD-CDs provides a novel efficient platform for probing intracellular CR, expanding the applications of CDs as biosensors for toxic dyes.

Glutamine involvement in nitrogen regulation of cellulase production in fungi.

BACKGROUND: Cellulase synthesized by fungi can environment-friendly and sustainably degrades cellulose to fermentable sugars for producing cellulosic biofuels, biobased medicine and fine chemicals. Great efforts have been made to study the regulation mechanism of cellulase biosynthesis in fungi with the focus on the carbon sources, while little attention has been paid to the impact and regulation mechanism of nitrogen sources on cellulase production. RESULTS: Glutamine displayed the strongest inhibition effect on cellulase biosynthesis in Trichoderma reesei, followed by yeast extract, urea, tryptone, ammonium sulfate and L-glutamate. Cellulase production, cell growth and sporulation in T. reesei RUT-C30 grown on cellulose were all inhibited with the addition of glutamine (a preferred nitrogen source) with no change for mycelium morphology. This inhibition effect was attributed to both L-glutamine itself and the nitrogen excess induced by its presence. In agreement with the reduced cellulase production, the mRNA levels of 44 genes related to the cellulase production were decreased severely in the presence of glutamine. The transcriptional levels of genes involved in other nitrogen transport, ribosomal biogenesis and glutamine biosynthesis were decreased notably by glutamine, while the expression of genes relevant to glutamate biosynthesis, amino acid catabolism, and glutamine catabolism were increased noticeably. Moreover, the transcriptional level of cellulose signaling related proteins ooc1 and ooc2, and the cellular receptor of rapamycin trFKBP12 was increased remarkably, whose deletion exacerbated the cellulase depression influence of glutamine. CONCLUSION: Glutamine may well be the metabolite effector in nitrogen repression of cellulase synthesis, like the role of glucose plays in carbon catabolite repression. Glutamine under excess nitrogen condition repressed cellulase biosynthesis significantly as well as cell growth and sporulation in T. reesei RUT-C30. More importantly, the presence of glutamine notably impacted the transport and metabolism of nitrogen. Genes ooc1, ooc2, and trFKBP12 are associated with the cellulase repression impact of glutamine. These findings advance our understanding of nitrogen regulation of cellulase production in filamentous fungi, which would aid in the rational design of strains and fermentation strategies for cellulase production in industry.

CRISPR-Cas13a mediated nanosystem for attomolar detection of canine parvovirus type 2.

Canine parvovirus type 2 (CPV-2) infection is the most lethal disease of dogs with higher mortality in puppies worldwide. In today's world, dogs are an integral part of our communities as well as dogs breeding and rearing has become a lucrative business. Therefore, a fast, accurate, portable, and cost-effective CPV-2 detection method with the ability for on-site detection is highly desired. In this study, we for the first time proposed a nanosystem for CPV-2 DNA detection with RNA-guided RNA endonuclease Cas13a, which upon activation results in collateral RNA degradation. We expressed LwCas13a in prokaryotic expression system and purified it through nickel column. Activity of Cas13a was verified by RNA-bound fluorescent group while using a quenched fluorescent probe as signals. Further Cas13a was combined with Recombinase polymerase amplification (RPA) and T7 transcription to establish molecular detection system termed specific high-sensitivity enzymatic reporter un-locking (SHERLOCK) for sensitive detection of CPV-2 DNA. This nanosystem can detect 100 amol/L CPV-2 DNA within 30 min. The proposed nanosystem exhibited high specificity when tested for CPV-2 and other dog viruses. This CRISPR-Cas13a mediated sensitive detection approach can be of formidable advantage during CPV-2 outbreaks because it is time-efficient, less laborious and does not involve the use of sophisticated instruments.