Although only females remain, the end of the northern white rhino is not yet sealed: Researchers have reported successes in the goal of preserving the species using stem cell technology. They succeeded in producing so-called pluripotent stem cells from frozen skin cells of a specimen that had already died. Scientists hope it can now be used to produce rhino eggs.
Habitat loss, and above all the desirable horn, was the deaths of the northern white rhino (Ceratotherium simum cottoni). Then, in 2018, the news broke that seemed to seal the species’ fate: the last bull died. Only Madam Rhino, Fatu and Negin, remained. As a result, the possibilities of natural reproduction are no longer available. However, the friends of the charismatic bachiderm did not want to give up: for the continued existence of the species, all records of breeding technology under the framework of the International BioRescue Consortium are withdrawn.
The scientists follow two strategies: Assisted reproductive methods aim to ensure offspring, and they also want to produce stem cells and egg cells in the laboratory from the skin cells of the northern white rhino. In terms of assisted reproduction, the team has already come a long way: The egg cells were taken from the rhinoceros Fatu and fertilized in the laboratory with thawed sperm from the last bull. Meanwhile, 14 embryos have emerged that are now stored in liquid nitrogen. They will soon be transplanted into surrogate mothers of southern white rhinos to produce offspring.
The second approach is necessary
However, this is not enough to provide a basis for the survival of the species. “Nagin and Fatu are very closely related and their genes are partially identical,” says Thomas Hildebrandt, BioRescue Project Director, of the Leibniz Institute for Animal and Wildlife Research. “Because of its age and poor reproductive system, we were also unable to obtain any eggs from survivors from which embryos could be successfully formed. So all 14 embryos are from VAT. So we urgently need a complementary strategy for gamete generation – ie egg and sperm cells – than a much larger number of individuals.”
So the team is also pursuing a stem cell strategy. The team led by Vera Zwizza of the Max Delbrück Center for Molecular Medicine in Berlin (MDC) has taken a major step forward. As they explain, special units are needed to produce egg cells: the so-called pluripotent stem cells (iPS cells), which can theoretically be obtained from any cell in the body. In developing their method, Zywitza and her colleagues are working closely with researchers who have already succeeded in mice: In 2016, a team led by Katsuhiko Hayashi of Japan’s Kyushu University succeeded in producing egg cells from rodent skin cells, artificially inseminating them and giving them female eggs to grow mice. This resulted in healthy and fertile offspring.
However, the rhino is not a mouse – transmission of the method has proven difficult. However, the BioRescue team has now succeeded in producing rhinoceros iPS cells from the skin. The starting material came from a rhino cow Napier, which died in a zoo in 2015. As the researchers report, they have succeeded in a technique called adhesive reprogramming. In doing so, they first introduced additional genetic information into skin cells via special DNA carriers – so-called plasmids. They mediated functions that were eventually able to convert skin cells into so-called induced pluripotent stem cells. “The successful transformation to the naive state of pluripotency provided a promising starting point for the generation of germline cells,” says Ziwiza.
chance of survival
The cells generated by the plasmid method are well suited to research stem cells in rhinos and to better understand their different states. However, they cannot be used to generate germ cells because they still contain foreign, destroyed genetic material, the scientists explained. However, according to an MDC report, the team has now also succeeded in generating iPS cells using an alternative method. Reprogramming factors were not introduced by plasmids, but with the help of RNA viruses. The statement says these new iPS cells no longer contain anything that doesn’t belong. This substance can now be used to produce oocyte progenitor cells.
The researchers report that another component essential to the project’s success could also arise from iPS cells: ovarian tissue. As they explain, progenitor cells only mature into egg cells if they are surrounded by this substance. “So we have to make the progenitor cells as well as the ovarian tissue,” Ziwiza says. The BioRescue team is also in close contact with Katsuhiko Hayashi. Because he had already succeeded in producing ovarian tissue from mouse stem cells.
“Functional oocytes of the northern white rhino – it will be the culmination of our research work,” says Sebastian Dickey of the Max Delbrück Center. According to him, the successes can also serve as a model: if reproduction from stem cells in rhinos is successful, then other endangered species or species that have already been exterminated by humans can also be revived in this way. Raw materials are often readily available: cell cultures of more than 1,000 endangered species are stored in the frozen zoo at the Beckmann Conservation Research Center in San Diego and in the Biobank of the Wildlife Research Institute in Berlin. In conclusion, however, Diecke stresses: “However, I would prefer that our approach never be used, and more done to conserve the species before it’s too late,” says the scientist.
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