Engineered mice are rodents whose genetic material has been intentionally altered by scientists. These modifications allow researchers to study specific genes or disease processes in a living system, providing insights difficult to obtain otherwise. The development of these models has advanced biomedical research, offering a valuable tool for understanding human health and disease.
Understanding Engineered Mice
An engineered mouse is an animal with targeted changes to its DNA, precisely modified by scientists. This intentional alteration allows researchers to investigate gene function or create animal models that mimic human diseases. Genetic modifications can involve adding new material, inactivating existing genes, or changing specific sequences within a gene.
One type is a transgenic mouse, which has foreign DNA (a transgene) integrated into its genome. This foreign DNA can come from another species or be a modified version of a mouse gene, often leading to the overexpression of a particular protein or the expression of a new protein. Conversely, knockout mice are engineered to have a specific gene inactivated or “knocked out,” often by deleting a portion of the gene. This allows scientists to observe the consequences of a gene’s absence, helping to determine its normal function.
Knock-in mice represent a more precise form of genetic alteration where a specific gene is replaced or modified within its native location. This can involve inserting a human gene into the mouse genome, replacing a mouse gene with its human counterpart, or introducing a specific mutation to study its effects. These mice provide researchers with versatile tools to explore biological questions.
Methods of Engineering Mice
Creating engineered mice involves advanced molecular biology techniques to introduce desired genetic changes into the mouse genome. Pronuclear injection is a common method used to generate transgenic mice. This technique involves injecting a purified DNA construct directly into one of the pronuclei of a fertilized mouse egg. The injected eggs are then transferred into a surrogate mother, and the resulting pups integrate the foreign DNA randomly into their genome, becoming transgenic.
For more targeted genetic modifications, such as creating knockout or knock-in mice, techniques like homologous recombination and CRISPR-Cas9 are employed. Homologous recombination involves introducing a DNA construct into mouse embryonic stem (ES) cells, where it can precisely replace or alter a specific gene. These modified ES cells are then injected into early mouse embryos, which develop into chimeric mice that may pass the genetic modification to their offspring.
The CRISPR-Cas9 system has advanced mouse engineering due to its efficiency and precision. This technology uses a guide RNA to direct the Cas9 enzyme to a specific DNA sequence, where it creates a double-strand break. This break can be repaired by the cell’s natural mechanisms, either by introducing random insertions or deletions (leading to gene inactivation) or by incorporating a provided DNA template for precise gene replacement or modification. CRISPR-Cas9 allows for faster and more cost-effective generation of complex mouse models, including those with multiple gene modifications or specific point mutations.
Applications in Scientific Research
Engineered mice are widely used in scientific research to understand complex biological processes and to develop new treatments for human diseases. One of their primary applications is in modeling human diseases, such as cancer, Alzheimer’s disease, cystic fibrosis, and various neurological disorders. For example, mice with mutations in the APC gene are used to study colorectal cancer, while models with specific amyloid precursor protein genes help investigate Alzheimer’s. These models allow scientists to observe disease progression, identify underlying mechanisms, and test potential therapies in a living system.
These mice are also instrumental in understanding the function of individual genes. By inactivating or modifying a specific gene, researchers can observe the resulting changes in the mouse’s physiology or behavior, thereby inferring the gene’s role in normal biological processes. This “reverse genetics” approach helps define gene function. For instance, scientists can study how certain DNA sequences regulate gene expression in specific tissues or at particular developmental stages.
Furthermore, engineered mice are important tools in drug discovery and development. They enable researchers to identify and validate drug targets, assess the selectivity of new compounds, and predict potential toxicity or side effects before human trials. For example, humanized mouse models, where a mouse gene is replaced with its human counterpart, can be used to test drugs that specifically interact with human proteins. This allows for preclinical testing of novel therapeutic agents, accelerating the progression of promising drug candidates through the development pipeline.