CRISPR/Cas9 Knockout Animal Model

Reagents and chemicals

• Use validated sgRNA or crRNA:tracrRNA targeting the gene of interest, Cas9 mRNA or Cas9 protein, nuclease-free preparation conditions, embryo culture medium, and embryo-transfer materials; donor DNA is not required for simple knockout models but is used in knock-in or floxed-allele protocols^{[3][4][5][6][8][9]}.

Antibodies, probes, dyes, or kits

• Use PCR primers for target-site amplification, Sanger sequencing or high-throughput amplicon sequencing reagents for genotyping, and protein-level assays such as Western blot or immunostaining when the knockout study validates loss of the encoded protein^[5][7][10].

Equipment and instruments

• Published workflows use micromanipulation and microinjection systems for pronuclear or cytoplasmic zygote injection, electroporators for RNP delivery into intact zygotes, embryo culture equipment, surgical embryo-transfer equipment, and sequencing instruments for founder genotyping^{[3][4][5][6][7][9]}.

Preparation Steps

• Design sgRNA against an exon whose disruption is expected to abolish gene function, prepare Cas9/sgRNA as mRNA plus sgRNA or preassembled Cas9 ribonucleoprotein, and validate target activity by sequencing-based genotyping after embryo or founder recovery rather than relying only on design prediction^{[3][4][5][6][7]}.

• Prepare fertilized one-cell embryos from the selected animal strain or species and maintain embryos under the culture conditions reported for that species; mouse and rat studies commonly use zygote-stage delivery, while species-specific timing has been reported for gerbil and honeybee embryos^{[3][4][5][6][7][11][12]}.

Operation Steps

• For microinjection-based knockout generation, inject Cas9 mRNA with sgRNA or Cas9 protein with sgRNA/crRNA:tracrRNA into one-cell embryos, culture injected embryos to confirm viability, transfer viable embryos into pseudopregnant recipients, and collect founder animals for genotyping^{[3][7][8][9][11]}.

• For electroporation-based knockout generation, expose intact zygotes to Cas9/sgRNA RNP under published electroporation conditions; mouse CRISPR-EZ and TAKE studies reported efficient RNP delivery into zygotes, and rat zygote electroporation produced knockout founders in the analyzed animals^[4][5][6].

• When mosaicism is a concern, use multiple adjacent sgRNAs targeting a key exon or perform careful founder genotyping, because zygotic CRISPR editing can generate different alleles within the same F0 animal and multiple-sgRNA strategies have been used to increase complete exon disruption^[3][7].

Data Acquisition and Analysis

• Genotype founders by PCR amplification across the target locus followed by Sanger sequencing, cloning plus sequencing, or amplicon deep sequencing; classify alleles as frameshift, in-frame indel, larger deletion, biallelic mutation, monoallelic mutation, or mosaic mutation^{[3][4][5][7][12]}.

• Confirm functional knockout by measuring loss or reduction of the encoded protein when suitable antibodies or assays exist, and validate phenotype only after matching genotype to molecular readouts and appropriate wild-type or uninjected controls^[7][10][11].

• Assess potential off-target editing using predicted off-target-site sequencing or broader sequencing approaches when the study design requires founder-line validation; published CjCas9 knockout mice used targeted deep sequencing and whole-genome sequencing and reported no detected off-target mutations in analyzed founder animals^[13].

Problem: Low founder editing rate.

• Possible Cause: Inefficient delivery or inactive guide RNA.
• Literature-supported Solution: Use experimentally validated sgRNA and consider Cas9 RNP electroporation or optimized zygote microinjection, because published mouse and rat studies reported efficient knockout generation using these delivery formats^[4][5][6].

Problem: High mosaicism in F0 animals.

• Possible Cause: Editing occurs after the first embryonic cell division.
• Literature-supported Solution: Genotype founders carefully and consider multiple adjacent sgRNAs targeting one critical exon, which was reported to improve complete knockout generation in mouse and monkey embryos^[7].

Problem: Founder has DNA mutation but unclear protein loss.

• Possible Cause: In-frame indels or monoallelic disruption may not abolish protein expression.
• Literature-supported Solution: Confirm knockout at the protein or phenotype level when possible, as reported in Scd1 knockout mice and Cst3 knockout gerbils^[10][11].

Problem: Conditional-allele generation is inefficient.

• Possible Cause: Two independent donor insertions in cis are rare.
• Literature-supported Solution: Avoid assuming that two-donor floxing will work efficiently, because a multi-center study found 15 correct conditional alleles among 1,718 live-born mice and reported higher efficiency for one-donor approaches^[14].