Robust gene expression control in human cells with a novel universal TetR aptamer splicing module

Fine-tuning of gene expression is desirable for a wide range of applications in synthetic biology. In this context, RNA regulatory devices provide a powerful and highly functional tool. We developed a versatile, robust and reversible device to control gene expression by splicing regulation in human cells using an aptamer that is recognized by the Tet repressor TetR. Upon insertion in proximity to the 5' splice site, intron retention can be controlled via the binding of TetR to the aptamer. Although we were able to demonstrate regulation for different introns, the genomic context had a major impact on regulation. In consequence, we advanced the aptamer to develop a splice device. Our novel device contains the aptamer integrated into a context of exonic and intronic sequences that create and maintain an environment allowing a reliable and robust splicing event. The exon-born, additional amino acids will then be cleaved off by a self-cleaving peptide. This design allows portability of the splicing device, which we confirmed by demonstrating its functionality in different gene contexts. Intriguingly, our splicing device shows a high dynamic range and low basal activity, i.e. desirable features that often prove a major challenge when implementing synthetic biology in mammalian cell lines.