Gene knockout (KO) refers to a gene editing technique that permanently inactivates the function of a specific gene in an organism's genome through targeted deletion, insertion, or replacement, mediated by homologous recombination or nuclease-induced DNA double-strand break repair mechanisms.
 

Among these, homologous recombination-mediated gene knockout is one of the classic implementation methods.
 

This method is based on the DNA homologous recombination mechanism, where exogenous DNA undergoes recombination with homologous sequences at the target site in the host genome to achieve knockout or replacement of the target gene. Its core principle is that when the introduced exogenous DNA fragment shares highly homologous sequences with the genomic target site, the cell's homologous recombination repair pathway is activated, prompting the precise replacement of the original genomic fragment with the exogenous DNA, thereby achieving targeted disruption or modification of the gene of interest.

Image source: iGEM
 

Key steps include:
 

1.Targeting Vector Design and Construction:​ Design DNA fragments (homology arms, typically 1-2 kb) highly homologous to the upstream and downstream regions of the target site, with a positive/negative selection marker (e.g., Neo⁺/TK⁻) inserted in between. Prepare the transfection plasmid after linearization via enzyme digestion.
 

2.ES Cell Transfection and Homologous Recombination:​ Introduce the linearized vector into mouse embryonic stem cells (mES cells) via electroporation. Utilizing the cell's intrinsic homologous recombination repair mechanism, achieve precise replacement of the target gene with the exogenous sequence, thereby disrupting its function.
 

3.Screening and Model Establishment:​ Obtain correctly recombined ES clones through drug selection and molecular identification (e.g., Southern blot, PCR). Generate mice via blastocyst injection and embryo transfer. Following successful generation of genetically modified mice, genotype the offspring.
 

The advantages of this method lie in its high precision and predictability, enabling the deletion, replacement, or insertion of large DNA fragments. The established models have stable genetic backgrounds, and the modifications are heritable, making them the cornerstone for long-term, systematic biological research.
 

Genotype Analysis
 

When performing knockout validation at the animal level, heterozygous and homozygous genotypes are typically obtained. Among these, homozygous knockouts with complete loss of function mainly include two categories:
 

1.Homozygote (HO):​ Both alleles carry identical frameshift mutations (e.g., both with a 4 bp deletion), resulting in a consistent genotype and homogeneous genetic background. This is the ideal material for functional comparisons and standardized analysis.
 

2.Compound Heterozygote:​ Both alleles carry frameshift mutations, but of different types (e.g., one with a 1 bp deletion, the other with a 5 bp deletion). Since both lead to frameshifts and premature translation termination, they are functionally equivalent to homozygotes, meaning the target gene's function is completely lost. This is widely recognized in the literature.

Core: Both involve biallelic frameshift mutations and are functionally equivalent. The difference lies in whether the mutant sequences are identical. Homozygotes are ideal experimental materials, while compound heterozygotes are commonly obtained qualified knockout clones.
 

Technological Applications
 

Gene knockout serves as a bridge connecting gene sequences to biological functions, and its applications profoundly influence modern life science and medical research:
 

Gene Function Research:​ Directly reveals the role of a gene in biological processes such as development and metabolism.
 

Deciphering Disease:​ By knocking out specific genes, construct models that highly mimic human diseases (e.g., cancer, genetic disorders), making it a powerful tool for studying disease pathogenesis.
 

"Litmus Test" for Drug Discovery:​ The most direct evidence for validating a novel drug target is whether the disease phenotype can be reversed or ameliorated after knocking out that target gene. It is a crucial step in translating a target hypothesis into a tangible therapy.
 

MingCeler Biotech's TurboMice™ technology overcomes the technical challenges of long mouse model generation cycles and low success rates for complex models, enabling editing at nearly any target gene locus. It can generate complete homozygous gene-edited mouse models directly from embryonic stem cells in as little as two months. MingCeler Biotech​ can customize various gene knockout mouse models according to client needs. Inquiries are welcome.