TALENs (Transcription Activator-Like Effector Nucleases) | Gene Editing Explained

0:00-1:38 | What are TALENs?
1:38-2:58 | How do TALENs work?
2:58-4:30 | Why are TALENs useful?

TALENs or Transcription Activator-Like Effector Nucleases! What are they, how do they work and why are they useful? TALENs are one of the 3 most common techniques, along with zinc finger nucleases or ZFNs and CRISPR-Cas9, that we currently use in gene editing. In fact one simplified way to think of all three of these methods is as iterative versions of gene editing where ZFNs are the most crude or basic version and CRISPR-Cas9 is the most commonly utilized, due to its simplicity, versatility and precision.

So what are TALENs? Tal effectors are proteins that are secreted by Xanthomonas bacteria (plant bacteria) when these infect plants. These TALEs contain highly conserved repeats. This repeat variable diresidue or RVDs as it is also called acts as a sort of key, allowing for very specific binding to a specific section of DNA. TALENs are made by fusing these TALEs with Fok1 endonuclease, used to cut the DNA at the particular point we wish to cut it at. Putting it another way, fusing the TALEs and Fok1 endonuclease together, allows us to create a highly specific “gene scissor”. If you have watched my video on zinc finger nucleases this Fok1 enzyme probably sounds familiar since it is used for the exact same purpose in that technique as well.

But what about how these TALENs actually work in action? Well to use this technique the TALEN construct specific for the DNA sequence in question first has to be engineered. Then this construct is inserted into a plasmid (this part of an eukaryotic cell) and transfected or inserted into the cell. The TALEN catches a ride with the plasmid. Once inside the DNA of the plasmid gets expressed and with it the TALEN and in this manner it is free to enter the nuclease. Once inside of the nucleus it binds to its specific section of DNA thanks to the repeat variable residues or RVD which again works similar to a key and a lock. Then the Fok1 creates a cut into the DNA. This process happens on the other side of the double stranded DNA at the same time, creating a double stranded break in the DNA. By varying exactly how the TALENs cut the DNA and whether or not it does so in the presence of an alternative DNA strand a gene can either be deleted or altered. Again, very similar to how zinc finger nuclease gene editing works.

Gene editing is a rather controversial topic. However, a large part is due to the massive impact it could have on society both good and bad but mostly good in my opinion. However, due to the share power this technique provides it is very understandable and perhaps even admirable that the initial reaction of many people when discussing this topic is caution. The ethics of genetic editing is a massive topic and one I might cover in a future video. At this point though, only one thing is certain, genetic engineering is not going anywhere. It is simply to useful for us to ignore, the question rather is, to what extent should we limit its uses.