Expression of TAT recombinant Oct4, Sox2, Lin28, and Nanog proteins from baculovirus-infected Sf9 insect cells. 
Somatic cell reprogramming has generated enormous interest, following the first report of generation of induced pluripotent stem cells (iPSCs) from mouse fibroblasts, but the integration of viral transgenes into the genome is unlikely to be accepted.  Given these safety considerations, a method for virus-free transient gene expression from suspension-adapted Sf9 insect cells was developed.  Here, we expressed transactivator of transcription (TAT)-fused proteins, Sox2, Oct4, Lin28, and Nanog in Sf9 cells using the baculovirus expression vector system (BEVS).  The molecular weights of the TAT-Sox2, TAT-Oct4, TAT-Lin28, and TAT-Nanog fusion proteins were 36kD, 40kD, 24kD, and 36kD, respectively.  Further investigation indicated that most of the recombinant proteins remained in the nuclei of the Sf9 insect cells and were therefore unavailable for purification and cellular reprogramming.  Once this problem has been solved, it seems likely that protein expressed from baculovirus-infected Sf9 insect cells will be the method of choice for cellular reprogramming.