Besides degrading aberrant mRNAs that harbor a premature translation termination codon (PTC), nonsense-mediated mRNA decay (NMD) also targets many seemingly "normal" mRNAs that encode for full-length proteins. To identify a bona fide set of such endogenous NMD targets in human cells, we applied a meta-analysis approach in which we combined transcriptome profiling of knockdowns and rescues of the three NMD factors UPF1, SMG6, and SMG7. We provide evidence that this combinatorial approach identifies NMD-targeted transcripts more reliably than previous attempts that focused on inactivation of single NMD factors. Our data revealed that SMG6 and SMG7 act on essentially the same transcripts, indicating extensive redundancy between the endo-and exonucleolytic decay routes. Besides mRNAs, we also identified as NMD targets many long noncoding RNAs as well as miRNA and snoRNA host genes. The NMD target feature with the most predictive value is an intron in the 3 ′ UTR, followed by the presence of upstream open reading frames (uORFs) and long 3 ′ UTRs. Furthermore, the 3 ′ UTRs of NMD-targeted transcripts tend to have an increased GC content and to be phylogenetically less conserved when compared to 3 ′ UTRs of NMD insensitive transcripts.

Realization of the immense potential of nanomaterials for biomedical applications will require a thorough understanding of how they interact with cells, tissues, and organs. There is evidence that, depending on their physicochemical properties and subsequent interactions, nanomaterials are indeed taken up by cells. However, the subsequent release and/or intracellular degradation of the materials, transfer to other cells, and/or translocation across tissue barriers are still poorly understood. The involvement of these cellular clearance mechanisms strongly influences the long-term fate of used nanomaterials, especially if one also considers repeated exposure. Several nanomaterials, such as liposomes and iron oxide, gold, or silica nanoparticles, are already approved by the American Food and Drug Administration for clinical trials; however, there is still a huge gap of knowledge concerning their fate in the body. Herein, clinically relevant nanomaterials, their possible modes of exposure, as well as the biological barriers they must overcome to be effective are reviewed. Furthermore, the biodistribution and kinetics of nanomaterials and their modes of clearance are discussed, knowledge of the long-term fates of a selection of nanomaterials is summarized, and the critical points that must be considered for future research are addressed.

The long-term fate of biomedically relevant nanoparticles (NPs) at the single cell level after uptake is not fully understood yet. We report that lysosomal exocytosis of NPs is not a mechanism to reduce the particle load. Biopersistent NPs such as nonporous silica and gold remain in cells for a prolonged time. The only reduction of the intracellular NP number is observed via cell division, e.g., mitosis. Additionally, NP distribution after cell division is observed to be asymmetrical, likely due to the inhomogeneous location and distribution of the NP-loaded intracellular vesicles in the mother cells. These findings are important for biomedical and hazard studies as the NP load per cell can vary significantly. Furthermore, we highlight the possibility of biopersistent NP accumulation over time within the mononuclear phagocyte system.