CRISPR activation reveals SOX5/6/9 as key transcriptional regulators directing iPSC-derived cells toward a notochordal lineage.

Intervertebral disc (IVD) degeneration, a leading cause of chronic lower back pain, is associated with loss of vacuolated notochordal cells (NCs) and fibrotic remodeling of the nucleus pulposus. Emerging therapies increasingly focus on NCs, which are rare but therapeutically relevant cells for regenerating degenerated IVDs. In this study, we used CRISPR-based transactivation (CRISPRa) to direct the differentiation of human induced pluripotent stem cells (iPSCs) into the NC lineage. We tested CRISPRa-mediated activation of NOTO, TBXT, FOXA2, SOX5, SOX6, and SOX9, coupled with single-cell sequencing of Aggrecan-2A-mScarlet reporter iPSCs. This approach identified the SOX5/6/9 combination (SOX-trio) as critical for promoting NC lineage commitment. The SOX-trio yielded the largest cell population expressing a range of genes previously associated with NC identity, including SHH, FOXA1, FOXA2, FOXJ1, FN1, ALCAM, KRT8, and KRT18. Our study demonstrates the integration of CRISPRa with single-cell technologies as a powerful platform for investigating and enriching iPSC-derived NCs, supporting future regenerative strategies across various fields.