Fig 1: Correction of DM1 hallmarks by DMPK-promoter silencing with CRISPRi in DM1 patient-derived myotubes(A) DMPK RNA quantification by qRT-PCR in DM1 myotubes (myoDM1) treated with the guides targeting the DMPK promoter (sgDMPK_2, _5, and _12) compared with non-target guides (sgNT1 to 3). The values of non-treated DM1 cells are displayed as references. The relative DMPK mRNA levels were normalized to the HPRT housekeeping gene. Statistics: one-way ANOVA followed by post hoc Tukey test for relative DMPK RNA level. ****p < 0.0001. Data are shown as the mean ± SD, n = 6 replicate transductions. (B) Observations of the nuclear relocalization of the MBNL1 protein alongside the reduction of the CUGexp foci in DM1 myotubes treated with sgDMPK_2 targeting the DMPK promoter versus the non-target guide, sgNT1. The foci were detected by FISH (in red), MBNL1 proteins were labeled by immunofluorescence (in green), and nuclei were visualized by DAPI (in blue). A Nikon Ti2 confocal microscope and a Yokogawa CSU-W1 spinning disk were used at 100× original magnification. Scale bar, 10 µm. (C–E) Correction of splicing defects by DMPK silencing in DM1 myotubes (myoDM1). The level of exon inclusion corresponding to the percentage splice in (PSI) index for BIN1 exon 11 (C), DMD exon 78 (D), and LDB3 exon 11 (E) was determined for DM1 myotubes expressing guides targeting the DMPK promoter (sgDMPK_2, _5, and _12) or non-target guides (sgNT1 to 3) by RT-PCR followed by gel electrophoresis. The values of non-treated DM1 or WT (myoWT) cells are added as references. Representative electrophoretic profiles are displayed below the charts. Statistics: one-way ANOVA followed by post hoc Tukey tests; **p < 0.01; ***p < 0.001; ****p < 0.0001. Data are shown as the mean ± SD, n = 6 replicate transductions.