Human opsin restoration by histone methylation using methyltransferase fusion protein SETD7-dCas9

Epigenetic modulation enables precise gene regulation without altering DNA sequences. While histone acetylation has been widely utilized for gene activation, the therapeutic potential of histone methylation remains underexplored. In this study, we developed a new epigenetic activator by fusing the histone methyltransferase SETD7 to deactivated Cas9 (dCas9). The optimized SETD7-dCas9 fusion protein successfully induced H3K4 mono-methylation and activated transcription at multiple target loci. We further established a prediction model using promoter CpG methylation status to identify genes most responsive to SETD7-dCas9-mediated activation. To evaluate therapeutic relevance, we targeted the medium-wavelength-sensitive opsin gene (<i>OPN1MW</i>), which is crucial for cone photoreceptor function as a strategy for treating retinitis pigmentosa. SETD7-dCas9-mediated activation of <i>OPN1</i> <i>MW</i> restored light absorption properties comparable with rhodopsin, effectively compensating for rhodopsin deficiency in an <i>in vitro</i> disease model. These findings demonstrate the potential of histone methylation-based gene activation as a mutation-independent therapeutic strategy. The SETD7-dCas9 system represents a promising epigenome editing platform for precision gene regulation in diverse diseases.