Abstract
Epigenetic modification plays a key role in gene regulation. CRISPRoff and CRISPRon, based on Nuclease-dead Cas9 (dCas9), can achieve precise, reversible regulation of gene expression without changing the DNA sequence, which is better than traditional cutting technology. This article systematically compares the two sets of systems. At the molecular level, the differences in composition and mechanism between the two are analyzed. CRISPRoff achieves long-lasting silencing through the coordinated activity of its effector domains writing trimethylation of histone H3 at lysine 9 (H3K9me3) and DNA methylation; CRISPRon achieves reversible activation through demethylation and collaborative transcription activation. On this basis, this article reviews the application of the two in disease treatment, including CRISPRoff targeting Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) for the treatment of familial hypercholesterolemia (FH), CRISPRon targeting the Forkhead Box P3 (FOXP3) Regulatory T-Cell-Specific Demethylated Region (TSDR) demethylation to stabilize regulatory T cells (Tregs) and exploring the synergistic prospects of the two in chimeric antigen receptor T-cell (CAR-T cell) remodeling. This article clarifies the applicable boundaries and complementary relationship between the two and provides a theoretical direction for tool selection and collaborative strategies. However, there are still problems to be solved in this field, such as in vivo collaborative application and delivery efficiency. Future research should focus on the development of efficient delivery systems and verify the feasibility of collaborative strategies in in vivo models to promote clinical transformation.