Fatu and Najin are the last two northern white rhinoceroses in the world, and they are both females. As a result, they can no longer reproduce naturally, and face an imminent threat of extinction. In order to assure that this subspecies will not disappear forever, the international BioRescue consortium is attempting to create artificial egg cells by using skin cells of these rhinos.
The scientists aim to first convert the skin cells into stem cells, and then into germ cells, or gametes, which could finally be matured into functional egg cells. These could be implanted in surrogate female southern white rhinos – a species closely related to the northern white rhinos.
Although this method seems highly futuristic for many scientists, there is in fact a precedent: in 2016, Professor Katsuhiko Hayashi from Kyushu University in Japan managed to successfully transform skin into egg cells in mice, and to successfully fertilize several females, which ultimately gave birth to 11 healthy and fertile offspring. Even if the percentage of offspring was lower than with conventional artificial insemination, the fact that they developed normally and did not die prematurely make scientists optimistic that the same method could soon save northern white rhinos from extinction.
“Considering that Hayashi spent many years researching this method, we can be proud if, in three years’ time, we understand the process and have managed to produce mature northern white rhino progenitor germ cells,” said the head of the research team Sebastian Diecke, a professor at the Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC) in Berlin. “If we are able to then mature these into functional egg cells, that would naturally be the crowning achievement of our research.”
In a new study published in the journal Nature Scientific Reports, Professor Diecke and his team have revealed that they managed to take an important step in this direction by creating induced pluripotent stem (iPS) cells from northern white rhino skin cells, which could eventually develop into immature eggs cells, or oocytes.
“Our paper sheds new light on pluripotency – the ability of stem cells to differentiate into all cells of the body,” said lead author Dr. Vera Zywitza, a postdoctoral researcher at MDC. “It therefore represents an important milestone on the road to artificially generated rhino oocytes.”
Although the iPS cells cannot yet be used to create germline cells due to the fact that they contain persistent foreign genetic material that the scientists were forced to add in order to prevent cell death, they can still shed much light on the nature of rhino stem cells and help scientists understand the molecular mechanisms that take place in such cells.
“For example, we can study why the gestation period of a rhinoceros is 16 months whereas that of a mouse is only 21 days, or how organs develop in different species. This teaches us a lot about evolution,” Dr. Zywitza said.
Further research is needed to clear the iPS cells from the foreign genetic factors that they now contain and make them grow into egg cells. Once this process is complete, the northern white rhino is sure to be saved from extinction.
Image Credit: Jan Zwilling, IZW