Lesterman @ stock.adobe.com
Humanity is in jeopardy from the accelerating decline of the Earth’s natural life-support systems. With the intent to reverse the human impact on nature, ongoing research is being developed, aiming to bring back extinct species and re-introduce them into their natural habitat through the power of technologies such as CRISPR.
De-extinction, also known as resurrection biology or species revivalism, is the process of creating an organism or breeding population through techniques such as gene-editing. By collecting the DNA of an extinct species, and combining it with the DNA of other species, typically that of the nearest living relative, the missing structure of the extinct species can be patched by mimicking the relative species DNA. Scientists have explored several approaches to increase the efficiency of this process through CRISPR-Cas9, but epigenetics and the environment will also play critical roles in the conditioning and survival of species.
Until now, scientists have not been able to grow de-extinct species cells in a test tube. Once they overcome this issue, the next step is to inject the DNA editing tool into an embryo. However, scientists ran into problems here too: they had to rely on viruses to deliver the CRISPR machinery, which makes the package too large to be safely injected. One solution could be to engineer an entirely new species, each harboring genetic material that allows for easier DNA editing.
CRISPR-Cas9 was originally discovered as part of the naturally occurring bacterial immune system. The technique enables scientists to use custom-built "guide" RNAs to target a sequence of DNA to modify, delete, or insert new sequences into it to create new heritable genomes without introducing foreign genetic material. The Cas protein effectively acts as a scissor in the genome editing process. Once the DNA has been targeted and cut, scientists can "use the cell's own DNA repair machinery to add or delete pieces of genetic material, or to make changes to the DNA by replacing an existing segment with a customized DNA sequence."
However, if cuts are made in the wrong place in the sequence, this may result in unwanted mutations which may or may not be altered later using epigenetic manipulation. But the goal is to recreate and reassamble the relevant genome from extinct organisms in related extant species to create a genetic sequence which can be passed on, thereby resurrecting the extinct species.
Scientists and researchers are currently working towards the de-extinction of the extinct passenger pigeon by creating a living pigeon model that carries the Cas9 gene in its reproductive cells. Progress has been reported and work continues to generate Cas9 capable of producing transgenic offspring.
Stem Cell Manufacturing has also featured in de-extinction programs, the first success being the bucardo, or Pyrenean ibex in 2003. While the animal only survived for a matter of minutes, this technology has since progressed and may be viable to resurrect the woolly mammoth, or the white rhinoceros, considered functionally extinct. Stem Cell Manufacturing is a method of manufacturing stem cell tissue through bioprocessing tools that extract cells from an organism and culture them in a laboratory setting. The process involves producing cells to form tissue, and then turning the stem cells into functioning cells in order to create an embryo, effectively growing species from the "test tube."
DNA Barcoding is another emerging technology that may play a role in de-extinction. This is a method by which sequences of DNA are converted into unique barcodes for researchers to catalog, differentiate and identify plant and animal species. Being able to detect differences between species at a finer scale has already led to the discovery of new species based on their genetic divergence, including a new species of aloe, African leaf-nosed bats, and chameleons. An extensive library of DNA barcodes, such as those held in Germplasm Banks, helps identify new species and better understand the extent to which species may be on the brink of extinction.
Apart from fueling the imaginations of Hollywood directors, de-extinction might be most useful to maintain a stable supply of food such as bananas, rice, chocolate, and certain grape varieties that could be at risk of extinction because of a limited genetic pool and low diversity.
There are certainly advantages in bringing back "keystone species," such as to provide ecosystems services to improve habitats that have been degraded either by human activity or through loss of a keystone species . But the evolution of this technology also brings up ethical questions. Even if we beat evolution on the front end by bringing back extinct species, what will happen when evolution takes over with the resurrected species? Is it possible to know how local natural environments will change with a species brought back to life? Is it ethical to repair the actions of our ancestors when they may cause different consequences?
A balance will need to be struck between the costs involved in resurrecting species, the benefits that can be reasonably be expected, and unknown or unforseeable costs in taking such an action.