DNA knock-in system
The present disclosure relates to an efficient genome editing technique. In one aspect, the technique can greatly improve the efficiency of homologous recombination during intracellular targeting, including gene targeting. Using this technique, genetically modified cell lines, rat, mouse, zebrafish, and fertilized eggs of other species can be quickly and efficiently generated.
1. A method of inserting a donor sequence at a predetermined insertion site on a chromosome in an eukaryotic cell, comprising:
a) introducing into the cell a first sequence-specific nuclease that cleaves the chromosome at the insertion site;
b) introducing into the cell a circular donor construct;
c) introducing into the cell an exonuclease; and
d) introducing into the cell a second sequence-specific nuclease;
wherein the circular donor construct is cleaved within the cell by the second sequence-specific nuclease to produce a linear nucleic acid,
wherein the linear nucleic acid comprises a 5′ homology arm, the donor sequence, and a 3′ homology arm, wherein the 5′ homology arm is homologous to a sequence upstream of the nuclease cleavage site on the chromosome and wherein the 3′ homology arm is homologous to a sequence downstream of the nuclease cleavage site on the chromosome;
wherein the 5′ homology arm and the 3′ homology arm are proximal to the 5′ and 3′ ends of the linear nucleic acid, respectively,
wherein the circular donor construct comprises a 5′ flanking sequence upstream of the 5′ homology arm and a 3′ flanking sequence downstream of the 3′ homology arm,
wherein the second sequence-specific nuclease cleaves the circular donor construct at both of the 5′ flanking sequence and the 3′ flanking sequence, thereby producing the linear nucleic acid,
wherein the donor sequence is inserted into the chromosome at the insertion site through homologous recombination, and
wherein the 5′ flanking sequence and the 3′ flanking sequence each comprises a sequence selected from the group consisting of SEQ ID NOs: 3-20.
2. The method of claim 1 , wherein the first sequence-specific nuclease is zinc finger nuclease (ZFN).
3. The method of claim 1 , wherein the first sequence-specific nuclease is a transcription activator-like effector nuclease (TALEN).
4. The method of claim 1 , wherein the first sequence-specific nuclease is an RNA-guided nuclease.
5. The method of claim 4 , wherein the RNA-guided nuclease is Cas.
6. The method of claim 5 , wherein the RNA-guided nuclease is Cas9.
7. The method of claim 4 , further comprising introducing into the cell a first guide RNA recognizing the insertion site.
8. The method of claim 1 , wherein the first sequence-specific nuclease is introduced into the cell as a protein, mRNA, or cDNA.
9. The method of claim 1 , wherein the 5′ homology arm and the 3′ homology arm are at least 200 bp.
10. The method of claim 1 , wherein the exonuclease is a 5′ to 3′ exonuclease.
11. The method of claim 1 , wherein the second sequence-specific nuclease is an RNA-guided nuclease, and wherein the method further comprises introducing into the cell a second guide RNA recognizing both of the flanking sequences.
12. A method of generating a genetically modified non-human animal comprising a donor sequence inserted at a predetermined insertion site on the chromosome of the non-human animal, comprising introducing the cell generated by the method of claim 1 into a carrier non-human animal to produce the genetically modified non-human animal.
13. The method of claim 12 , wherein the cell is a zygote or a pluripotent stem cell.
14. A kit for inserting a donor sequence at an insertion site on a chromosome in an eukaryotic cell, comprising:
a) a first sequence-specific nuclease that cleaves the chromosome at the insertion site;
b) a circular donor construct;
c) an exonuclease; and
d) a second sequence-specific nuclease;
wherein the circular donor construct can be cleaved within the eukaryotic cell by the second sequence-specific nuclease to produce a linear nucleic acid,
wherein the linear nucleic acid comprises a 5′ homology arm, the donor sequence, and a 3′ homology arm, wherein the 5′ homology arm is homologous to a sequence upstream of the nuclease cleavage site on the chromosome and wherein the 3′ homology arm is homologous to a sequence downstream of the nuclease cleavage site on the chromosome;
wherein the circular donor construct comprises a 5′ flanking sequence upstream of the 5′ homology arm and a 3′ flanking sequence downstream of the 3′ homology arm;
wherein the 5′ homology arm and the 3′ homology arm are proximal to the 5′ and 3′ ends of the linear nucleic acid, respectively;
wherein the second sequence-specific nuclease is capable of cleaving the circular donor construct at both of the 5′ flanking sequence and the 3′ flanking sequence, thereby producing the linear nucleic acid; and
wherein the 5′ flanking sequence and the 3′ flanking sequence each comprises a sequence selected from the group consisting of SEQ ID NOs: 3-20.
15. The method of claim 1 , wherein the 5′ flanking sequence or the 3′ flanking sequence is about 1 to about 500 bp.
16. The method of claim 10 , wherein the exonuclease is a herpes simplex virus type 1 (HSV-1) exonuclease.
17. The method of claim 16 , wherein the exonuclease is UL12.
18. The method of claim 1 , wherein the first sequence-specific nuclease and the second sequence-specific nuclease are both ZFNs, both TALENs, or both RNA-guide nucleases.
19. A method of inserting a donor sequence at a predetermined insertion site on a chromosome in an eukaryotic cell, comprising:
a) introducing into the cell a sequence-specific RNA-guided nuclease;
b) introducing into the cell a circular donor construct;
c) introducing into the cell a first guide RNA recognizing the insertion site;
d) introducing into the cell a second guide RNA recognizing a cleavage site on the circular donor construct; and
e) introducing into the cell an exonuclease;
wherein upon cleavage within the cell by the sequence-specific RNA-guided nuclease the circular donor construct produces a linear nucleic acid comprising a 5′ homology arm, the donor sequence, and a 3′ homology arm,
wherein the 5′ homology arm is homologous to a sequence upstream of the nuclease cleavage site on the chromosome and wherein the 3′ homology arm is homologous to a sequence downstream of the nuclease cleavage site on the chromosome;
wherein the 5′ homology arm and the 3′ homology arm are proximal to the 5′ and 3′ ends of the linear nucleic acid, respectively;
wherein the circular donor construct comprises a 5′ flanking sequence upstream of the 5′ homology arm and a 3′ flanking sequence downstream of the 3′ homology arm;
wherein the sequence-specific RNA-guided nuclease cleaves the circular donor construct at both of the 5′ flanking sequence and the 3′ flanking sequence, thereby producing the linear nucleic acid,
wherein the donor sequence is inserted into the chromosome at the insertion site through homologous recombination, and
wherein the 5′ flanking sequence and the 3′ flanking sequence each comprises a sequence selected from the group consisting of SEQ ID NOs: 3-20.