Aptamer- and Ribozyme-Engineered sgRNAs for Conditional Control of CRISPR/Cas9 Function

The clustered regularly interspaced short palindromic repeats CRISPR-associated protein 9 (CRISPR/Cas9) system has emerged as a versatile platform for genome editing, transcriptional regulation, and chromosomal imaging. Recent advances in synthetic biology have enabled the engineering of single guide RNA (sgRNA) to confer conditional responsiveness on the CRISPR/Cas9 system. By integrating functional nucleic acid elements, such as aptamers, ribozymes, and aptazymes, into specific structural regions of the sgRNA, researchers have developed systems that respond to a variety of molecular signals, including small molecules, proteins, and endogenous metabolites. These engineered sgRNAs enable spatiotemporal control of gene editing, activation, repression, and imaging in both prokaryotic and eukaryotic cells. This review summarizes the structural principles, design strategies, and applications of condition-responsive CRISPR/Cas9 systems, highlighting their potential in synthetic biology, disease modeling, and therapeutic development. Current challenges and future directions for improving the specificity, efficiency, and applicability of these systems are also discussed.