CRISPR Cas9 Gene Editing - CRISPR Library Screening - Gene Knockout Cell Line - Knock in Cell Line - Cas12a – EDITGENE

Maintaining the activity of cell cultures is crucial. Cells should not be allowed to reach confluence for more than 24 hours. Frozen new cells can restore transfection activity. The optimal cell plating density varies for different cell types or applications; however, for adherent cells, a confluence of 70% to 90% or a density of 5×10^5 to 2×10^6 suspended cells/ml typically yields good transfection results. It is important to ensure that cells are not fully confluent or in a fixed phase during transfection.

Both double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) targets can activate the trans-cleaving activity (also known as collateral cleavage) of Cas12a, similar to Cas12b. However, the efficiency differs: ssDNA targets activate Cas12b trans-cleaving activity more efficiently than dsDNA targets, while dsDNA targets activate Cas12a trans-cleaving activity more efficiently than ssDNA targets.

CRISPR detection reagents:
1.The RPA isothermal amplification kit can be stored at -20°C for long-term storage.
2.Target plasmids can be stored at -20°C for long-term use.
3.Cas proteins are sensitive to repeated freeze-thaw cycles; it is recommended to aliquot into multiple tubes and store at -80°C, retrieving them as needed for experiments. For short-term use, they can be stored at -20°C.
4.crRNA is prone to degradation and should be stored at -80°C if not used in the short term.
5. Probes, being double-stranded DNA, are relatively stable and can be stored at -20°C.

The main differences among Cas9, Cas12, and Cas13 lie in their action mechanisms:
· Cas12 is activated to cleave ssDNA trans-cleaving after binding with guide RNA and target DNA.
· Cas13 is activated to cleave ssRNA trans-cleaving after binding with guide RNA and target RNA.
· Cas9 has not been reported to exhibit trans-cleaving activity.

1.Design an efficient crRNA sequence. Proper design and structure prediction using online resources can help select suitable crRNA to achieve good trans-cleavage activity of the Cas enzyme.
2.Choose an appropriate signal reporter substrate. Research indicates that using a 15 nt single-stranded DNA (ssDNA) as a reporter substrate maximizes the cleavage reaction rate of Cas12a, significantly enhancing the reaction rate compared to the commonly used 5-nt ssDNA.
3.Optimize reaction conditions and buffers. Adjusting the CRISPR reaction parameters, such as the ratio of Cas enzyme to crRNA, the concentration of the Cas enzyme, and the reaction temperature, can improve detection performance to some extent.

1.The design process can follow these steps:
1.Identify the target gene sequence.
2.Specify the Cas protein being used. Different Cas proteins require corresponding PAM (Protospacer Adjacent Motif) sequences; for instance, Cas12a needs the "TTTV" PAM sequence for target recognition.
3.Select the crRNA targeting region. Choose a 20 nt nucleotide sequence on the target gene that is adjacent to the PAM site and pairs with the complementary strand of the crRNA.
4.Combine the selected 20 nt target sequence (variable part) with the scaffold sequence (fixed part) to design the crRNA sequence.
5.Use online tools such as CRISPR design tools (e.g., CRISPOR, Benchling, etc.) to assist in designing crRNA. These tools can predict the efficiency and specificity of the sgRNA, helping to avoid potential off-target effects.
6.After completing the design, the synthetic crRNA sequence can be ordered from a synthetic biology company.

Selecting a suitable gene delivery system requires a comprehensive assessment based on specific experimental conditions, research objectives, and cell types. Quantitatively comparing various systems in terms of delivery efficiency, cytotoxicity, and stability is an important step in determining the choice.
Viral delivery systems are suitable for experiments that require high delivery efficiency and sustained gene expression, especially when cells can tolerate higher levels of cytotoxicity and immune responses. If lower cytotoxicity and immune response, along with ease of use and cost-effectiveness, are priorities, then a liposome-based gene delivery system should be chosen. For high delivery efficiency that involves delivering large DNA fragments, and if the user can accept a higher operational complexity, a gene gun delivery system is an optional method. If high delivery efficiency is needed while maintaining relative simplicity and no special equipment is required, then the electroporation delivery system may be a suitable choice.

When selecting a vector, consider the purpose of the experiment and the type of host cells. For example, plasmid vectors are commonly used for gene expression or amplification in bacteria, while viral vectors are more suitable for gene transfer in mammalian cells. Additionally, the vector's promoter, replicon, and antibiotic selection markers should be chosen based on specific requirements.

During vector amplification, Escherichia coli (E. coli) strains are typically used. The commonly used strain for most non-recombinant vectors is DH5α, which is suitable for most applications. For recombinant vectors, such as lentiviral vectors and transposon vectors, the Stbl3 strain can be used for amplification. Stbl3 is a specialized E. coli strain derived from HB101, which has a mutation in the recombinase gene recA13, effectively suppressing recombination of long fragment terminal repeat regions and reducing the likelihood of erroneous recombination.

When selecting a vector, consider the purpose of the experiment and the type of host cells. For example, plasmid vectors are commonly used for gene expression or amplification in bacteria, while viral vectors are more suitable for gene transfer in mammalian cells. Additionally, the vector's promoter, replicon, and antibiotic selection markers should be chosen based on specific requirements.

During vector amplification, Escherichia coli (E. coli) strains are typically used. The commonly used strain for most non-recombinant vectors is DH5α, which is suitable for most applications. For recombinant vectors, such as lentiviral vectors and transposon vectors, the Stbl3 strain can be used for amplification. Stbl3 is a specialized E. coli strain derived from HB101, which has a mutation in the recombinase gene recA13, effectively suppressing recombination of long fragment terminal repeat regions and reducing the likelihood of erroneous recombination.

During vector amplification, Escherichia coli (E. coli) strains are typically used. The commonly used strain for most non-recombinant vectors is DH5α, which is suitable for most applications. For recombinant vectors, such as lentiviral vectors and transposon vectors, the Stbl3 strain can be used for amplification. Stbl3 is a specialized E. coli strain derived from HB101, which has a mutation in the recombinase gene recA13, effectively suppressing recombination of long fragment terminal repeat regions and reducing the likelihood of erroneous recombination.

During vector amplification, Escherichia coli (E. coli) strains are typically used. The commonly used strain for most non-recombinant vectors is DH5α, which is suitable for most applications. For recombinant vectors, such as lentiviral vectors and transposon vectors, the Stbl3 strain can be used for amplification. Stbl3 is a specialized E. coli strain derived from HB101, which has a mutation in the recombinase gene recA13, effectively suppressing recombination of long fragment terminal repeat regions and reducing the likelihood of erroneous recombination.

Lentiviruses have high transduction efficiency and the ability to maintain stable gene expression over the long term, making them particularly suitable for cell types that are difficult to transfect. Furthermore, lentiviruses can integrate exogenous genes into the host genome, ensuring prolonged gene expression.

4.Poor cell condition after lentiviral infection may be caused by various factors. Here are some possible reasons and corresponding solutions: 1.High viral titer: High titers of lentivirus may cause cytotoxicity, preventing normal cell growth. Solution: Lower the viral titer and conduct a series of dilution experiments to find a titer that effectively transduces without adversely affecting cell growth. 2.Poor cell condition: The health status of cells before infection can affect growth after infection. Solution: Ensure cells are in optimal condition for infection, for example, by changing to fresh culture medium 24 hours before infection and ensuring appropriate cell density. 3.Toxicity of gene expression mediated by the virus: The gene carried by the lentiviral vector may be toxic to the cells, affecting their growth. Solution: If possible, use a control vector to determine if the problem is related to gene expression, and select appropriate vectors or genes for research. 4.Excessive antibiotic selection pressure: If antibiotics are used to select transfected cells, excessive concentrations of antibiotics may inhibit cell growth. Solution: Optimize the antibiotic concentration and use gradient experiments to determine the optimal concentration.