The ectopic expression of transcription factors can reprogram differentiated tissue cells into induced pluripotent stem cells. However, this is a slow and inefficient process, depending on the simultaneous delivery of multiple genes encoding essential reprogramming factors and on their sustained expression in target cells. Moreover, once cell reprogramming is accomplished, these exogenous reprogramming factors should be replaced with their endogenous counterparts for establishing autoregulated pluripotency. Complete and designed removal of the exogenous genes from the reprogrammed cells would be an ideal option for satisfying this latter requisite as well as for minimizing the risk of malignant cell transformation. However, no single gene delivery/expression system has ever been equipped with these contradictory characteristics. Here we report the development of a novel replication-defective and persistent Sendai virus (SeVdp) vector based on a noncytopathic variant virus, which fulfills all of these requirements for cell reprogramming. The SeVdp vector could accommodate up to four exogenous genes, deliver them efficiently into various mammalian cells (including primary tissue cells and human hematopoietic stem cells) and express them stably in the cytoplasm at a prefixed balance. Furthermore, interfering with viral transcription/replication using siRNA could erase the genomic RNA of SeVdp vector from the target cells quickly and thoroughly. A SeVdp vector installed with Oct4/Sox2/Klf4/c-Myc could reprogram mouse primary fibroblasts quite efficiently; ϳ1% of the cells were reprogrammed to Nanog-positive induced pluripotent stem cells without chromosomal gene integration. Thus, this SeVdp vector has potential as a tool for advanced cell reprogramming and for stem cell research. The generation of induced pluripotent stem (iPS)3 cells by reprogramming tissue cells with defined factors opened the door for realizing the medical application of patient-derived engineered stem cells (1). iPS cells were established originally by the ectopic expression of multiple transcription factors (e.g. Oct3/4, Sox2, Klf4, and c-Myc) using a retroviral vector (1). Since then, researchers have established iPS cells by several different approaches (and by their combination), including gene transfer, protein transduction, and treatment with chemical compounds (2). However, because of superior reproducibility and efficacy, ectopic expression of reprogramming factors by gene transfer is still the primary method of choice.Various lines of evidence indicate that efficient cell reprogramming requires the sustained and simultaneous expression of several (usually 4) exogenous factors for at least 10 -20 days (3). On the other hand, after reprogramming has been completed, these exogenous factors should be replaced promptly with their endogenous counterparts if the cells are to acquire autoregulated pluripotency (3). For this reason, retroviral and lentiviral vectors have been used preferentially; chromosomal insertion of the vector genome allow...

The mechanisms of the molecular and dissociative adsorption of formic acid HCOOH on a ZnO(101̄0) surface were investigated by means of the ab initio molecular orbital method using a Zn4O4 cluster embedded in an electrostatic field represented by 464 point charges at the crystal ZnO lattice positions. cis-Formic acid molecularly adsorbs on a ZnO(101̄0) surface without activation energy. It dissociates into a formate anion HCOO- and a proton H+ with an activation energy of 11.7 kcal/mol. The formate anion is geometrically stable in the bridging structure of two Zn atoms and the unidentate structure of a Zn atom interacting with a surface OH species. The adsorption energy is about 80 kcal/mol for both structures. In contrast, the bidentate structure is about 24 kcal/mol less stable. Possible reaction pathways for the dissociation of the O−H bond of cis-formic acid were also examined. trans-Formic acid is dissociatively adsorbed on a ZnO(101̄0) surface to form a formate anion and a surface OH species without activation energy. The initial formate anion generated from trans-formic acid continues to interact with the surface OH species. This interaction produces the stability of the unidentate structure. Interconversion between the unidentate and bridging structures was also examined. The formate anion can be easily tilted on the surface by a small perturbation, leading to increased interaction between the formate species and the surface.

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