Restoration of FMR1 and FMRP levels through CGG repeat contraction via R-loop formation at the CGG repeat site. Kinase inhibitors upregulate DNA demethylases TET1 and TET2, leading to FMR1 promoter and CGG repeat demethylation. This demethylation initiates FMR1 transcription and facilitates the R-loop formation that is mediated by RNA polymerase II. Subsequent resolution of these R-loops through the MSH2-mediated MMR pathway results in CGG repeat contraction, FMR1 reactivation, and restoration of FMRP levels. Additionally, induction of R-loops using dCas9 and gRNA targeting the CGG repeats also promotes CGG contraction and restores FMR1 and FMRP levels, indicating that R-loop formation at the CGG repeat site is both necessary and sufficient for repeat contraction. Created with BioRender.com.
