A novel pathogenic mutation of MeCP2 impairs chromatin association independent of protein levels

Loss-of-function mutations in MECP2 cause Rett Syndrome (RTT), a severe neurological disorder that mainly affects girls. Mutations in MECP2 do occur in males occasionally and typically cause severe encephalopathy and premature lethality. Recently, we identified a missense mutation c.353G>A, p.Gly118Glu (G118E) in a young boy who suffered from progressive motor dysfunction and developmental delay. To determine whether this variant causes the clinical symptoms and study its functional consequences, we established two disease models, including patient-derived iPSCs and a knock-in mouse line. Given that G118E mutation is in the DNA binding domain of MeCP2 and could potentially disrupt its chromatin association, we performed Cut&Run using WT and G118E mouse cortical tissue to characterize the genome wide binding pattern of WT and mutant MeCP2 proteins. We observed a reduction of DNA binding of G118E MeCP2 in the known MeCP2 target loci, as well as in a genome-wide manner. Cleavage Under Targets & Release Using Nuclease (CUT&RUN) was performed using mouse cortical tissues collected from 3 Mecp2-G118E mice and 3 wild-type littermates.