Recent landmark experiments have shown that transient overexpression of a small number of transcription factors can reprogram differentiated cells into induced pluripotent stem (iPS) cells that resemble embryonic stem (ES) cells. These iPS cells hold great promise for medicine because they have the potential to generate patient-specific cell types for cell replacement therapy and produce in vitro models of disease, without requiring embryonic tissues or oocytes. Although current iPS cell lines resemble ES cells, they have not passed the most stringent test of pluripotency by generating full-term or adult mice in tetraploid complementation assays, raising questions as to whether they are sufficiently potent to generate all of the cell types in an organism. Whether this difference between iPS and ES cells reflects intrinsic limitations of direct reprogramming is not known. Here we report fertile adult mice derived entirely from iPS cells that we generated by inducible genetic reprogramming of mouse embryonic fibroblasts. Producing adult mice derived entirely from a reprogrammed fibroblast shows that all features of a differentiated cell can be restored to an embryonic level of pluripotency without exposure to unknown ooplasmic factors. Comparing these fully pluripotent iPS cell lines to less developmentally potent lines may reveal molecular markers of different pluripotent states. Furthermore, mice derived entirely from iPS cells will provide a new resource to assess the functional and genomic stability of cells and tissues derived from iPS cells, which is important to validate their utility in cell replacement therapy and research applications.

SUMMARY In the retina, rod and cone photoreceptors form distinct connections with different classes of downstream bipolar cells. However, the molecular mechanisms responsible for their selective connectivity are unknown. Here we identify a cell-adhesion protein, ELFN1, to be essential for the formation of synapses between rods and rod ON-bipolar cells in the primary rod pathway. ELFN1 is expressed selectively in rods where it is targeted to the axonal terminals by the synaptic release machinery. At the synapse, ELFN1 binds in trans to mGluR6, the postsynaptic receptor on rod ON-bipolar cells. Elimination of ELFN1 in mice prevents the formation of synaptic contacts involving rods, but not cones, allowing a dissection of the contributions of primary and secondary rod pathways to retinal circuit function and vision. We conclude that ELFN1 is necessary for the selective wiring of rods into the primary rod pathway and is required for high sensitivity of vision.

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A straightforward protocol for the site-specific incorporation of a 19F label into any protein in vivo is described. This is done using a plasmid containing an orthogonal aminoacyl-tRNA synthetase/tRNA(CUA) that incorporates L-4-trifluoromethylphenylalanine in response to the amber codon UAG. This method improves on other in vivo methods because the 19F label is incorporated into only one location on the protein of interest and that protein can easily be produced in large quantities at low cost. The protocol for producing 19F-labeled protein is similar to expressing protein in Escherichia coli and takes 4 d to obtain pure protein starting from the appropriate vectors.

Posttranslational modification of tyrosine residues in proteins, to produce 3-nitrotyrosine (3-NT), is associated with over 50 disease states including transplant rejection, lung infection, central nervous system and ocular inflammation shock, cancer, and neurological disorders (for example, Alzheimer's disease, Parkinson's disease, and stroke). The levels of 3-NT increase in aging tissue, and levels of 3-NT in proteins are a predictor of disease risk. Here we report the evolution and characterization of an aminoacyl-tRNA synthetase/tRNA pair for the cotranslational, site-specific incorporation of 3-NT into proteins at genetically encoded sites. To demonstrate the utility of our approach for studying the effect on protein function of nitration on sites defined in vivo, we prepared manganese superoxide dismutase (MnSOD) that is homogeneously nitrated at a site known to be modified in disease-related inflammatory responses, and we measured the effect of this defined modification on protein function.