No abstract

The nucleolus, the locus of ribosome biogenesis, was found to be the predominant intracellular target of a new fluorescent probe, V-P1. In solution, the probe demonstrated both a selectivity to RNA G-quadruplexes and a sensitivity to the viscosity, while G-quadruplex binding did not disturb the viscosity sensing. In cells, confocal and fluorescence lifetime imaging, combined with digestion and competition experiments lend support to the hypothesis of an RNA-based G-quadruplex as the intracellular target, postulated to be nucleolar ribosomal RNA (rRNA). The probe demonstrated a high sensitivity to viscosity in both the cytoplasm and the nuclear compartment and was used to precisely interrogate the viscosity changes resulting from diverse stimuli, such as temperature, monensin treatment and etoposide-induced apoptosis. Owing to the putative rRNA Gquadruplex binding in vitro and in vivo, and further combined with a relatively low degree of toxicity, the dye enables the interrogation of cytoplasm and intranuclear viscosity changes under diverse conditions and could find applications in studying the influence and significance of cytoplasm and intranuclear viscosity as well as in gaining insight into the native secondary structure of rRNA in nucleoli.

The redox-regulator glutathione (GSH) maintains a specific redox potential to sustain routine cellular activity from oxidative damage. In the early stage of the cell cycle process, the glutathione levels increase in the nuclei for protecting the DNA replication process from reactive oxygen species (ROS). In the first attempt, we developed a new ratiometric fluorescent probe that has provided information about glutathione levels in the nuclei. The UV−vis. absorption of probe GScp has shown a hypsochromic shift from 410 to 350 nm in the presence of GSH. In fluorescence titration, we observed that fluorescence emission of the GScp switched from 510 to 460 nm in the presence of GSH. The self-calibrated probe GScp has shown nearly optimal reversibility in GSH redox dynamics with the dissociation constant 2.47 mM. The probe is ideal for GSH tracking in live cells, as its toxicity has within the safe zone. The probe GScp has validated GSH levels in nucleoli by providing fluorescence images in blue-channel. This finding inspires us to use for validation of GSH dynamics in the nucleoli in the cell cycle process.

No abstract

As both host and pathogen require iron for survival, iron is an important regulator of host-pathogen interactions. However, the molecular mechanism by which how the availability of iron modulates host innate immunity against bacterial infections remains largely unknown. Using the metazoan Caenorhabditis elegans as a model, we demonstrate that infection with a pathogenic bacterium Salmonella enterica serovar Typhimurium induces autophagy by inactivating the target of rapamycin (TOR). Although the transcripts of ftn-1 and ftn-2 encoding two H-ferritin subunits are upregulated upon S. Typhimurium infection, the ferritin protein is kept at a low level due to its degradation mediated by autophagy. Autophagy, but not ferritin, is required for defense against S. Typhimurium infection under normal circumstances. Increased abundance of iron suppresses autophagy by activating TOR, leading to an increase in the ferritin protein level. Iron sequestration, but not autophagy, becomes pivotal to protect the host from S. Typhimurium infection in the presence of exogenous iron. Our results show that TOR acts as a regulator linking iron availability with host defense against bacterial infection.