MIT researchers produce liver tumors in mice - adults
The sequencing of the genomes of tumor cells revealed thousands of mutations associated with cancer. One way to discover the role of these mutations is to breed a strain of mice that carry the genetic defect - but breeding of these mice is an expensive long-term process
Now, MIT researchers found an alternative .: They have shown that a gene editing system called CRISPR can introduce carcinogenic mutations in the livers of adult mice, allowing scientists to detect these mutations much faster.
in a study appearing in the Aug. 6 issue of Nature , the researchers generated liver tumors in adult mice by disrupting the tumor suppressor genes p53 and PTEN. They are currently working on ways to provide the components necessary for CRISPR other organs, allowing them to investigate the mutations found in other types of cancer.
hundreds "The sequencing of the human tumors revealed oncogenes and tumor suppressor genes in different combinations. The flexibility of this technology, as delivery is better in the future, give you a way to test very these combinations quickly, "says the Institute Professor Phillip Sharp, author of the paper.
Tyler Jacks, director of MIT's Koch Institute for Integrative Cancer Research and David H. Koch Professor of Biology, is the senior author of the paper. The main authors are Koch Institute postdocs Wen Xue, Sidi Chen and Hao Yin.
gene disruption
CRISPR based on the cellular machinery that bacteria use to defend themselves against the virus infection. The researchers copied this bacterial system to create complex editing gene that include an enzyme called DNA-cutting case.9 linked to a short RNA strand guide which is programmed to bind to a specific sequence of the genome, called case.9 where to make its cut.
In some cases, the researchers simply snip a portion of a gene to disrupt its function; in others, they also introduce a DNA template strand that encodes a novel sequence to replace the deleted DNA.
To investigate the potential utility of CRISPR to create cancer mouse models, the researchers used the first knockdown p53 and PTEN, which protect cells from becoming cancerous by controlling cell growth. Previous studies have shown that genetically engineered mice with mutations in these two genes will develop cancer within a few months.
The studies of these genetically modified mice have given many important discoveries, but the process requires introduction of mutations in embryonic stem cells, can take more than a year and costing hundreds of thousands of dollars . "It is a very long process, and the genes that you work longer and more complex it becomes," said Jacks.
Using enzymes targeted cases to cut extracts of p53 and PTEN , researchers capable of disrupting both genes in about 3 percent of liver cells, enough to produce liver tumors within three months.
many possible models
the researchers also used CRISPR to create a mouse model with an oncogene called beta-catenin, which makes them more likely to become cancer cells if additional mutations occur later. to create this model, researchers had cut the normal version of the gene and replace it with an overactive form, which managed about 0.5 percent of hepatocytes (cells that make up the bulk of the liver).
ability to not only remove genes but to replace them with modified versions "really opens up all sorts of new possibilities when you think about the types of genes that you would mutate in the future," said Jacks. "As long as the function of loss and gain of function are possible."
Using CRISPR to generate tumors should help scientists to study how quickly the different genetic mutations interact to produce cancer, and the effects of potential drugs on tumors with a specific genetic profile.
"This is a game changer for the production of modified strains of human cancer," says Ronald DePinho, director of the University of Texas MD Anderson Cancer Center, who was not part of the team research. in gene function completely ablation "CRISPR / case.9 offers the possibility in the adult mouse. Improvement potential of this powerful technology will be realized with improved delivery methods, the test CRISPR / case.9 efficiency in other organs and tissues, and the use of CRISPR / case.9 in tumor prone environments. "
in this study, the researchers presented the genes necessary for CRISPR by injections into the veins in mice tails. Although this is an effective way to get the genetic material in the liver, it would not work for other organs of interest. However, nanoparticles and other delivery methods being developed for DNA and RNA may be more effective to target other organs, says Sharp .
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