Novel method for genetic manipulation of single cells
- Dr. Johanna Walter
Are numerous new animal experiments looming?
Researchers from ETH Zurich recently published a study in which they genetically modified cells in the brains of mice. New about the method is that individual cells were manipulated in various ways. The researchers anticipate insights into genetically related diseases and have applied for a patent for the method. The nationwide organization Doctors Against Animal Experiments (DAAE) is concerned that this method could lead to countless additional animal experiments and sees no benefit from it.
The method is based on viruses that introduce components of the so-called genetic scissors CRISPR/Cas into the cells of the "experimental" animals. These viruses are injected into the tail vein of the mice. Once inside the cells of the animals, the genetic scissors seek specific regions of the genetic material and selectively deactivate them. In the study that has now been published, viruses were used to deactivate 29 different genes, with only one gene being deactivated in each respective cell. As a result, there was a random distribution of cells in the brains of the animals, each with one of the 29 genes deactivated (1). Four weeks after the injection, the mice were killed, their brains were removed, and the genetically modified cells isolated from brain samples. These cells were then examined to determine the changes resulting from the deactivation of the respective gene (2).
"Such experiments are also possible with cell cultures. Here, too, many different genes can be simultaneously deactivated, and then an examination can be conducted to determine the consequences of the loss of a single gene for the cell - without any need for an animal to suffer," explains Dr. Johanna Walter, scientific officer at DAAE. "The advantage of using the genetic scissors directly in a living brain is not clear," Walter adds.
Researchers typically justify their animal experiments by claiming that certain effects, such as behavioral changes, can only be measured in a living animal. However, this is not the case here; no examinations are conducted on the live animals, but rather, only individual cells from the killed animals are analyzed. Instead, the animal experiments are justified by arguing that cells in culture behave differently than in a living organism. In doing so, the experimenters not only disregard the differences between humans and animals but also modern cell culture approaches like organoids, in which cells grow in a three-dimensional structure consisting of multiple cell types, thereby simulating the conditions in a living organism.
The deletion syndrome 22q11, in which a small segment of genetic information is missing on chromosome 22 and which the researchers have now examined in mice, has already been studied by other scientists using organoids derived from cells donated by human volunteers. These organoids were also treated with the genetic scissors. This method is well-known to the researchers at ETH Zurich: While they justify their experiments on mice by claiming that cells behave differently in cell culture, they still refer to the study with human organoids, as it would confirm their own results. Furthermore, experiments with brain organoids are also conducted at the ETH Zurich, in the same department and at the same address, in which the mouse brains were genetically modified using the CRISPR/Cas genetic scissors. In one experiment, for instance, 36 genes associated with autism were examined (3). "Why experiments are being conducted in the brains of mice when the same research questions can be addressed with organoids is completely incomprehensible," criticizes Walter. "These experiments do not provide insights into the mechanisms of the disease. Instead, a live animal is being used as a 'cultivation vessel' for genetically modified cells in experiments that could have been carried out in cell culture - as one could easily determine by looking into the neighboring laboratory," Walter continues.
There is an entire range of animal-free methods for investigating the contribution of genes to the development of diseases. In addition to the previously mentioned cell culture techniques like organoids, computer models can also be used to predict the activity of individual genes based on tiny amounts of patient-specific material (4). Many more examples of modern, animal-free research methods that provide human-relevant results can be found in the Non-Animal Technologies (NAT) database of DAAE (5).
"The belief of many researchers that experiments conducted in animals are somehow superior is not only peculiar but deeply ingrained. We continue to work on breaking this dogma and convincing scientists of the effectiveness of animal-free methods. Especially animal experiments, for which mature animal-free methods exist and are known to the experimenters, should no longer be approved, or presented as successful through publication of the results in prestigious journals," urges Walter.
- ETH Zurich: Genetically modifying individual cells in animals, press release, 20.09.2023 (retrieved 25.10.2023)
- Santinha A.J. et al. Transcriptional linkage analysis with in vivo AAV-Perturb-seq. Nature 2023; 622:367–375
- ETH Zurich: A human model for autism, press release, 13.09.2023 (retrieved 25.10.2023)
- Baur B et al. Predicting patient-specific enhancer-promoter interactions. Cell Reports Methods 2023; 3(9):100594
- NAT database https://nat-database.org