Inhibiting POLQ-mediated alternative NHEJ enhances CRISPR/Cas9 mediated precise genome editing in CHO cells

Abstract

CRISPR/Cas9 mediated precise gene editing requires homology-directed repair (HDR), which occurs less frequently than non-homologous end-joining (NHEJ) including the canonical NHEJ and alternative NHEJ (Alt-EJ) in mammalian cells, especially in CHO cells that inherent resist HDR. To solve the above hurdle, here we for the first time show that knockout the DNA polymerase {theta} (POL{theta}), which is essential for Alt-EJ, significantly increases the knock-in efficiency by nearly forty-fold in CHO cells via eGFP reporter system and does not affect the normal growth and proliferation of cells. Meanwhile, even when transfecting simple circular, without negative element homologous template DNA donor and CRISPR/Cas9 plasmid to two different genomic sites, the knock-in rate of 4kb donor integration can still reach a mean of over 80% (29/36) and 2.7% (1/36) of the selected cell colonies in POLQ-/- CHO cells, however, no positive knock-in cell colonies was obtained in wild-type CHO cells which respectively selected 62 cell colonies and 36 cell colonies. Furthermore, we show that POLQ promotes random integration in CHO cells. Finally, RNA-sequence analysis reveals not significant altered DNA repair, metabolism, apoptosis, and cell cycle in POLQ-/- cells. These findings open a new target gene POLQ to overcome bottlenecks of the precision genome editing.