Hi thanks for your answer. I detected GFP with fluorescence microscopy in vitro and in vivo. I transfeted a psiSTRIKE (shRNA) vector with a gene for hMGFP, which is Monster Green Fluorescent Protein, improved variant of GFP with less cytotocity. Downstream from the hMGFP gene there is an ubiquitary CMV-Promotor.
I cotransfected Cos-7 cells with vectors for target protein and psiSTRIKE (shRNA) vectors. My observations shows that cells that doesn't show green fluorescence also have a reduced protein level. So I supposed, that those cells could have uptaken a psiSTRIKE vector that produce shRNAs but not enough hMGFP for a proper fluorescence. Another interpretation would be the export of siRNAs from positive transfected cells into the medium and the uptake by others. But I don't know enough about DNA export and uptake. I know there are core pores in the nucleus membrane that recognize NLS signal from core proteins, and also mRNA export into the cytoplasma, but is there a similar mechanism/transporter/porine for DNA/mRNA export in the cytoplasmic membrane¿ I read in a publication of Elbashir et al. that it is possible for lung cells and different tumor cells to uptake siRNAs without being transfected. So the Cos-7 are kidney cells, immortalized by a tumor process, could this be the answer?
