Putting stem cells back to sleep during precise genome editing
In stem cells, it’s easier to break a gene with CRISPR genome editing than to fix it. A recent “Cell Reports” paper by the Corn lab figures out why and devises a way to precisely repair genes in bone marrow stem cells. The approach could lead to cures for disorders such as sickle cell disease.
Genome editing often takes the form of either error-prone sequence disruption via non-homologous end joining (NHEJ) or sequence replacement via homology directed repair (HDR). While NHEJ is effective in many contexts, HDR is often difficult in primary cells. The Corn lab and collaborators used a combination of immunophenotyping, next generation sequencing, and single-cell RNA-sequencing to investigate and reprogram genome editing outcomes in subpopulations of adult human CD34+ hematopoietic stem and progenitor cells (HSPCs). They found that quiescent stem-enriched cells utilize NHEJ and exhibit almost no HDR. By contrast, non-quiescent cells with the same immunophenotype utilize both NHEJ and HDR. Inducing quiescence prior to editing with a small molecule cocktail results in complete loss of HDR in all cell subtypes. The group developed a new strategy of controlled cycling and quiescence that yields a 6-fold increase in the HDR/NHEJ ratio in quiescent stem cells ex vivo and in vivo. These results highlight the tension between editing and fundamental cellular physiology and suggests strategies to manipulate quiescent cells for research and therapeutic genome editing.
Link to the paper in external page "Cell Reports".