Prevention of Transgene Silencing During Human PluripotentStem Cell Differentiation
While high and stable transgene expression can be achieved in undifferentiated pluripotent stem cells, conventional transgene expression systems are often silenced upon differentiation. Silencing occurs with both randomly integrated transgenes, introduced via transposase or lentiviral methods, and with transgenes targeted to specific genomic sites, including at commonly used safe harbor loci. The challenge to robustly express experimental transgenes in differentiated pluripotent stem cells is a major bottleneck in the field for applications such as CRISPR screening. Here, we conducted a comparative analysis to systematically evaluate the impact of various promoters, transcriptional regulatory elements, insulators, and genomic integration sites on transgene silencing during neuronal differentiation. Our findings reveal that specific combinations of promoters and transcriptional stability elements are able to prevent transgene silencing during differentiation, whereas chromatin insulators had less impact on silencing and three novel safe harbor integration sites performed similarly to the CLYBL locus. Guided by these insights we developed the PiggyBac vector TK4, which showed complete resistance to transgene silencing across various neuronal and microglial differentiation protocols from six different pluripotent stem cell lines, as independently confirmed by seven different laboratories. This construct will be highly useful for assays requiring stable transgene expression during differentiation, and holds the potential for broad applications in various research fields.