As one of the most popular tools for genome editing, CRISPR/Cas9 system has been widely used in gene targeting, transcriptional regulation, epigenetic modification, even in gene therapy and drug delivery. Although CRISPR/Cas9 system provides a simple, specific and high efficient platform, it still has some limitations. Recently, several modified versions of CRISPR/Cas systems (Cpf1, C2c2, dCas9 and dC2c2) have been remarkably developed for more powerful and customizable genome editing and function studies. In this review, we summarized the key findings and progress on Cas9 and modified Cas proteins, which would help to better understand CRISPR/ Cas systems and advanced future studies on their applications.
