TALEN-mediated MeCP2 Gene Mutagenesis in Rhesus and Cynomolgus Monkeys

We report Transcription Activator-like Effector Nucleases (TALEN)-mediated mutagenesis of the Rett Syndrome gene, methyl-CpG binding protein 2 (Mecp2), in nonhuman primates (NHPs). Microinjection of Mecp2-targeting TALEN plasmids into rhesus and cynomolgus zygotes caused 40-50% of the embryos harboring mutations when examined beyond 8-cell stage. The surrogate pregnancy rates were 28.6% (2/7) and 16.7% (1/6) for rhesus and cynomolgus, respectively. The 2 rhesus surrogates went through miscarriage at 30- and 63/64-days of gestation. Analyses of two 63/64-day-old liter-mate embryos indicated both were male and carried MeCP2 mutations, yet chimeric. Mutation rate was higher in one embryonic brain than the other. RNA sequencing and anatomical analyses indicated that the brain with higher-degree mutations was underdeveloped, which, together with mid-gestation-stage male lethality likely recapitulate the disease. One live delivery of a female cynomolgus monkey occurred after 162 days of gestation, with abundant mutagenesis in peripheral tissues examined. We conclude that TALEN-mediated mutagenesis greatly facilitates disease modeling in NHPs. Examination of 25 different tissues transcriptome from the two aborted male rhesus monkeys