• Featured in:
  • Stem Cells in Focus on March 2021, in its original copyedited form
  • Popular Science on August 2022, to comment on recent progress on the topic

“It’s like witnessing a funeral,” a spectator whispers as the Tasmanian artist Lucienne Rickard chafes a rubber eraser against a pencil portrait of the swift parrot, a critically endangered bird that seasonally migrates from mainland Australia to Tasmania. In her series “Extinction Studies”, Rickard was drawing and then erasing meticulous replicas of extinct and threatened species to alert her viewers of the ongoing assault on Earth’s biodiversity (Figure 1). Even the loss of a single species like the swift parrot can leave a large void in nature. Beyond their majestic beauty, migratory birds have been shown to promote biodiversity by transporting nutrients and other organisms, by coupling otherwise disparate communities, and by influencing the genetic mixing of resident populations. If nothing is done, the swift parrot’s foreseeable extinction will upset the balance of the forest ecosystem in which it dwells.

Figure 1: In the series “Extinction Studies,” Lucienne Rickard draws realistic, large-scale images of endangered and extinct species, and then erases them to represent their loss. Using the same piece of paper, the remnants and impressions of the previous species can be seen under the new sketch. Shown here is the Caribbean Monk Seal, now extinct after humans exploited them for their skins and oil and decimated their food source by overfishing.

Photo credit: Lucienne Rickard, Extinction Studies project at the Tasmanian Museum and Art Gallery, supported by Detached Cultural Organisation. For more information, please see the artist’s Instagram account: @luciennerickard.

Many other animals are facing eradication as the Earth undergoes its sixth mass extinction. In the past century alone, we have lost the same number of species that would typically go extinct over the course of 10,000 years. This calamitous decline in biodiversity is mainly caused by humans, through habitat degradation, pollution, factory farming and animal exploitation. Nevertheless, we can still slow down the annihilation of species through conscious environmental preservation, and remarkably, stem cell research.

The role of stem cell research in species conservation is best exemplified by efforts to save the beloved rhino, whose populations have been driven to the brink of extinction by illegal poaching. Loss of the rhinoceros would jeopardize the grassland habitats of Africa and Asia where these megaherbivores play key roles in shaping the earth and vegetation upon which many other species depend. The most pressing case is that of the Northern White Rhino, which at present, has only two known living individuals left in the entire world, both infertile females (Figure 2). Because previous attempts at breeding this species in captivity were unsuccessful, researchers are currently using assisted reproductive technology and novel stem cell techniques to try to save the rhinos.

Figure 2: Nola, the last Northern White Rhino in the United States, died in 2015 but her cells live on in the form of induced pluripotent stem cells made by researchers from the San Diego Zoo Institute for Conservation Research, USA in collaboration with the Scripps Research Institute, USA.

Photo credit: San Diego Zoo Global.

In anticipation, scientists have collected sperm and eggs from the last few surviving Northern White Rhinos, which they used to successfully produce five Northern White Rhino embryos through in vitro fertilization (IVF). The researchers are now hoping that the closely-related Southern White Rhino can function as a surrogate mother for these embryos and bear healthy Northern White Rhino calves. However, the remaining supply of eggs is very limited and collecting more would put the health of the last remaining females at risk. Scientists have hence turned to stem cell research to try to create additional Northern White Rhino embryos, which could eventually help create a self-sustaining population.

In a landmark study in 2006, Japanese scientist Shinya Yamanaka developed a method to revert a skin cell back to an embryonic stem cell state by cellular reprogramming. This creates what are known as induced pluripotent stem cells (iPSCs), which can give rise to all of the cell types in an organism. The first Northern White Rhino iPSCs were reprogrammed in 2011, and today, there are iPSCs from 12 Northern White Rhinos, 8 of which are not familially related. This last point is important because to establish a healthy population, sufficient genetic diversity must be present. The successful creation of iPSCs from the Northern White Rhino jumpstarted efforts to preserve other endangered species using stem cells, including the Sumatran Rhino, estimated at fewer than 80 in existence.

The next step in this conservation effort is to figure out how iPSCs can be grown into a live healthy organism. Scientists reckon that this can be done in two ways. First is to induce iPSCs to develop and mature into a full embryo. To date, this feat has been successfully performed in mice, but iPSC-derived embryos often end up with developmental defects. The second option is to coax iPSCs to produce mature sperm and eggs for IVF. This process requires a complex multi-step differentiation protocol that while yet to be accomplished, is very well-studied in mouse cells. Further research is thus required not only to improve and fully realize these techniques, but also to extend these discoveries to other species like the rhino, which might not necessarily be responsive to the same protocols used for mice. Until then, Northern White Rhino iPSCs are being maintained safely in the laboratory where they will be available once science advances.

Cellular reprogramming can be performed on virtually any cell from any species. This technology is therefore as applicable to extinct species as it is to endangered ones, as long as a viable cell is still available. Fortunately, this actually is the case for many recently extinct species, thanks to frozen tissue banks such as The Frozen Zoo in San Diego, CA, USA, which has already preserved cells from more than 10,000 individuals representing 1,000+ species. With this in mind, scientists have begun research on reviving ecologically important extinct animals such as the passenger pigeon (a migratory bird like the swift parrot) and the wooly mammoth (a megaherbivore like the rhino).

As a final note, it is important to remember that even with stem cells, the preservation and revival of species still relies on the perpetuation of habitats in which they can thrive. So let’s do our part in protecting planet Earth. It’s our only home, and saving the creatures that make it wondrous means saving ourselves, too.