Efficient Non-Viral Transfection of Mouse and Human Embryonic Stem Cells.

BACKGROUND: Development of efficient non-viral gene transfer technologies for embryonic stem (ES) cells is urgently needed for various existing and new ES cell-based research strategies. In this study we investigated mRNA electroporation as a tool for short-term gene transfer in both mouse and human ES cells.

METHODS: Culture and mRNA electroporation conditions for feeder-free cultured mouse and human ES cells were optimized on three mouse ES cell lines (E14, R1 and HM-1) and one human ES cell line (H9). After electroporation with EGFP mRNA, transfected ES cell populations were analyzed by FACS for EGFP expression, viability and phenotype. Also, stably-transfected mouse ES cell lines containing Lox-P or FRT-flanked reporter genes were electroporated with mRNA encoding Cre- or FLPe-recombinase proteins. Monitoring recombination efficiency was done based on the appearance and/or disappearance of fluorescent reporter genes, as determined by FACS analysis. ES cells that underwent recombination were further analyzed for potential to differentiate towards the neural lineage and differentiated cells were analyzed by FACS for expression of neural markers.

RESULTS: (A) Electroporation of EGFP mRNA in mouse ES cells resulted in high level transgene expression (>90% EGFP positive cells) combined with low electroporation-induced cell mortality (>90% viable cells). Moreover, the electroporation procedure did not influence ES cell phenotype and further cell culture of undifferentiated ES cell populations. Electroporation of mRNA encoding Cre- or FLPe-recombinase proteins in stably-transfected mouse ES cell lines containing LoxP- or FRT-flanked reporter genes resulted in a recombination efficiency of respectively 75% and 90%. Moreover, these recombination events did not have influence on ES cell phenotype, viability, growth potential, and their ability to differentiate towards neural cell types upon retinoic acid stimulation. (B) Although human ES cells are much more sensitive as compared to mouse ES cells, we were able to develop improved culture and electroporation conditions for feeder-free maintained H9 human ES cells, which resulted in high level transgene expression (>90% EGFP+ cells) combined with high cell viability (>90% viable cells) after EGFP mRNA electroporation.

CONCLUSIONS: RNA electroporation is a highly efficient method for short-term genetic loading of both mouse and human ES cells. Ongoing research now focuses on either short-term (via direct mRNA electroporation) or sustained (via mRNA-based FLPe-recombination) expression of transcription factors in ES cells and their influence on cell-fate within in vitro cultured embryoid bodies.