Giovanna Di Sauro

How many of you remember Jurassic Park? If you do, you would probably also remember that resuscitating a species which has undergone extinction long ago would basically be impossible because of, among other things, DNA degradation. But what about species that are more recent, and whose tissue samples have been carefully stored? We know that ancient DNA can now be better sequenced (think of frozen mammoths and Neanderthal bones). Will the day come when we will be able to resuscitate them?

A new paper published in PLOS One named “Resurrection of DNA Function In Vivo from an Extinct Genome” shows that it is possible to “resuscitate”, if not the entire organism, at least a piece of its genome – one whose function is conserved in species that are still among us. To show this, the researchers behind the paper picked the genome of a species whose last exemplar died in captivity in 1936, and which constitutes an example of marsupial carnivores: the Tasmanian tiger.

To do this, the authors extracted DNA from three century-old pouch young stored in alcohol, and a dried pelt. The extraction methods including classic ethanol precipitations and sucrose gradients (to eliminate contaminants). As usual in this cases, the DNA resulted to be fragmented, but the researchers were aided in their effort to verify their results by the presence of different DNA sources, and the choice of a well-characterized sequence, the transcriptional enhancer of a collagen gene (Col2a1). Comparing the results obtained from PCR reactions run on DNA extracted from the three different sources helped assure that the DNA was not contaminated (as human collagen genes would be similar, but not identical, to those belonging to the Tasmanian tigers).

The researchers then decided to study the function of this element (reconstituted by PCR) in vivo. Multiple copies of the enhancers were added in front of the he human β-globin basal promoter fused to lacZ and followed by a polyadenylation signal – therefore producing a chimeric reporter gene to use in their assays. This reporter would reveal the expression pattern of the genetic element, as well as the strength of expression in developing tissues. This reporter construct was then injecting in murine zygotic pronuclei, and its expression assayed at different stages of mouse development.

As you can see from the third figure in the paper, you can see that the reporter is most strongly expressed in regions where cartilage is forming – the skull, the tail, and the developing limbs. In section g, you can even distinguish the digits in the developing mouse forelimb. These results indicate that, regardless of some variation in the strength of the expression, the transgene made out of the “extinct DNA” is expressed in the same pattern as that if the endogenous transgene – which is also expressed at sites of cartilage development and growth. This therefore means that the function of the modern murine element, and the one belonging to the extinct Tasmanian tiger, is actually conserved. It also suggests that this method could be used to analyze the function of genomic material extracted from extinct specimens in vivo.

While this does not mean that we will be able to resuscitate the Tasmanian tiger any time soon (if not at all), it gives us another glimpse on the practical power of evolutionary theory, and the incredible genetic conservation among species, even those that evolved quite separately from each other.

Pask, A.J., Behringer, R.R., Renfree, M.B., Svensson, E.I. (2008). Resurrection of DNA Function In Vivo from an Extinct Genome. PLoS ONE, 3(5), e2240. DOI: 10.1371/journal.pone.0002240

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