Scientists announce major breakthrough in efforts to save endangered white rhino

Northern White Rhino females Fatu and Nájin in the Ol Pejeta Conservancy in Kenya

An international team of scientists working to save the northern white rhino from extinction has announced a major breakthrough. They have succeeded in cultivating primordial germ cells, the precursors of rhino eggs and sperm, from stem cells. I discussed the latest achievement with Jan Stejskal of Dvůr Králové Zoo, which is spearheading the international effort to save the rhinos:

“Basically, what is necessary to for us to save the northern white rhino, is to produce embryos, and there are two ways to achieve that.

“One is to collect the eggs from the last living donors that are now in Kenya and the other way is to produce eggs through reprogramming tissue in vitro.

Sebastian Diecke and Vera Zywitza from Max Delbrück Center | Photo: Jan Zwilling,  BioRescue/Zoo Dvůr Králové

“We started work on producing eggs in a laboratory environment years ago. The first step was to derive so-called induced pluripotent stem cells from a tissue sample. This was done in the Max Delbruck Centre in Berlin.

“Now, our colleagues in Osaka have made another breakthrough. They succeeded in creating primordial germ cells from these induced pluripotent stem cells. So it is one more step, and a very important one, on the way to acquire eggs in a laboratory.”

What other steps are needed to complete the process of creating artificial eggs and sperm?

“Now we have to learn how to turn these primordial germ cells into eggs and sperm. What might be interesting to your listeners is that primordial germ cells still contain two sets of chromosomes. So our colleagues have to learn how to produce cells that would have only one set of chromosomes.”

As you have already said, you do have one donor of natural egg cells, one of the two surviving female rhinos called Fatu. Why is it important to have egg cells from other specimen?

Masafumi Hayashi from the Osaka University | Photo: Antony Mwangi,  BioRescue/Zoo Dvůr Králové

“You are right, there are two last living females, Najim and Fatu. Unfortunately, Najim is no longer providing oocytes or eggs of the quality that would be sufficient to create embryos.

“That means we only have one female left. So far, we have made 23 embryos. But if we look at the genetic variability of these embryos, it is not sufficient for establishing a population.

“If we learn how to make eggs and sperm through stem-cell associated technique, it will allow us to use genetic material from 12 individuals. With 12 individuals, we will have enough genetic variability to establish a new population.

Katsuhiko Hayashi from the University of Osaka | Photo: Jan Zwilling,  BioRescue/Zoo Dvůr Králové

“So this is one positive outcome of the latest achievement in Osaka. The other one is that when we learn how to make these embryos, we actually could make much more of them available for embryo transfers.

“Because the next step is that we have to put this embryo into a surrogate mother, because none of the females of the northern white rhino are able to carry the pregnancy to term.”

As you said, you have already produced white rhino embryos by in vitro fertilisation, which you plan to implant in the womb of a close relative, the southern white rhino. When will that take place?

“I would be really happy to know this, but because this is research on the edge of our current knowledge, we can’t really say when exactly we will succeed.

Jan Stejskal with Fatu | Photo: Ami Vitale

“On the other hand, let’s say the steps we have achieved already could give us some optimism. The primordial germ cells were made within about three years, so we hope that we could be able to make eggs and sperm in the laboratory in three or four years from now.

“Regarding a successful embryo transfer, let’s hope that we could achieve it in one year from now. And then, if we look at the length of the rhino pregnancy, which is about 16 months, if everything goes well, I think we could expect a rhino to be born through this chain of procedures in three or four years from now.”