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One-Step Generation of Transgenic Mice in Just Weeks

By May 7, 2013

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The lab of Rudolf Jaenisch, who developed the first transgenic mouse in 1974, has developed a new approach to genetically engineer mice in just weeks, rather than years which are currently needed. This new technique does not rely on engineering embryonic stem (ES) cells, but rather, directly introduces the genetic changes in developing mouse embryos. In addition to making production of transgenic mice and rats for laboratory research faster and easier, it should also work with other types of organisms whose embryonic cells are difficult to engineer and manipulate.

The new approach takes advantage of a unique response bacterial developed as a defense against invading viruses. Bacteria can target and cut the DNA of invading viruses. To do this, they use short sequences of DNA that match some part of the DNA of the invading virus. Many bacteria seem to have a "catalog" of short stretches of DNA that match parts of many different types of viruses. These regions of DNA were dubbed Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) when they were first discovered.

Researchers found that they could co-opt this bacterial defense system to target and inactivate specific genes in more advanced non-bacterial cells. To do this, they only needed to introduce the gene that cuts the targeted viral DNA in bacteria--the CRISPR-associated protease (Cas). Basically, it seems that almost any gene in most cells can be cut by introducing DNA that makes the Cas protein and a CRISPR construct with a short sequence that recognize some small part the gene. Even though a cell will fix a gene that has been cut, it does not get fixed correctly (because of the way Cas cuts it).  Then, the gene will no longer work, so it has been "knocked out".

Inactivating or "knocking out" genes is a common approach researchers use to understand how particular genes function and also generate mice or rat strains that model various human diseases. One of the big difficulties of engineering animals with certain genes knocked out, though, is that almost all genes come in pairs--one from each parent. Both copies of a gene need to be inactivated to fully knockout a gene. Unless the knock out technique is very efficient, this is rare. However, the CRISPR approach seems to be exceptionally effective.

In a Cell publication this week, the researchers in Dr. Jaenisch's lab describe how they were able to simultaneously and specifically knock out two genes with a single injection of a mouse embryo. Further, they also used the technique to produce embryonic mouse stem cells with disruptions of 5 distinct genes simultaneously. Mice produced using these embryonic stem cells would then carry all 5 of these mutations.

For a more information, you can read the press release from the Whitehead Institute at MIT describing the paper.

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