Cloning Dinosaurs

There seems to be some excitement over an ancient DNA cloning paper in PLoS One, titled: Resurrection of DNA Function In Vivo from an Extinct Genome. The news reports have titles like, The Jurassic Code: Resurrecting the Planet's Extinct Species -Can It Be Done? or Bringing back the dinosaurs?) implying scientists won another big fight in the battle for Jurassic Park.

It might be an interesting publication, but I have some issues with the reporting.

First of all, the group did not clone a gene. A gene is a stretch of DNA that creates the initial template for a protein (RNA). What Pask and colleagues extracted and put into mice was an "enhancer". Enhancers are not part of the template (DNA->RNA->Protein), but they point RNA producing enzymes where to start "transcribing". So, when you put an "enhancer" in front of a "protein coding gene", it will be transcribed.

The blue color in mice is actually coming from betagalactosidase, the gene placed under the control of the Tasmanian Tiger enhancer region. beta-galactosidase or LacZ is commonly used as reporter gene, since when you add the necessary subtrate it says "Hello World!" via the blue color.

And then there is the issue bringing an extinct animal back (hence the dino comments). Enhancers are usually short DNA pieces, which can remain intact in fragmented DNA samples. Genes are usually big and complex. Unfortunately, enhancers by themselves, without any data on their location in the genome don't carry much information. Genes on the other hand, can tell us how a certain mechanism works in that particular organism.

Also, the researchers cloned the piece of DNA based on similarities between species. The problem here is that, if we decide to resurrect an extinct animal, we might actually need the non-conserved, i.e. species specific pieces of DNA.

The similarity based selection also diminishes significance of Tasmanian Tiger enhancer functioning in mice. We (all living organisms) come from the same root. Therefore, our genes resemble and depending on how far apart we are on the evolutionary scale, can substitute for each other. Some human genes function in mice and even in yeast. The more similar the DNA sequences are the better chance they will be interchangeable.

Finally, this study is not the first of its kind. One of the references brings up a PNAS paper from 1989 by Svante Pääbo, in which he reports his experience in extracting DNA from tissue samples as old as 13000 years. The same researcher also extracted and cloned 3.4kb (kilobases) of DNA from a 2400 mummy.

Looks like it is going to be a while until we get to take the family out to Jurassic Park for the weekend (and then horribly killed).