siRNA-mediated knockdown of endogenous MBNL proteins promotes NF1 exon 23a skipping. Co-transfection of HeLa Cells with either Control siRNA (300 pmoles) or MBNL1 (200 pmoles) plus MBNL2 (100 pmoles) siRNAs. HeLa Cells were mock transfected with no siRNA for a negative control. Total RNA was isolated from the transfected cells and semi-quantitative RT-PCR was performed using the primers designed in exons 23 and 24 (Figure 1A). The average percentage NF1 exon 23a inclusion was determined from two independent experiments. RT-PCR was performed to determine changes in MBNL1 and MBNL2 mRNA levels upon siRNA knockdown with Beta Actin as a loading control.