Hybrid embryos of the “functionally extinct” northern white rhino created in lab

In a first, rhinoceros embryos have been developed in vitro to be ready for implantation.

In a new study, researchers have taken a step towards saving the world’s most endangered mammal by creating a hybrid embryo of the northern white rhinoceros (NWR) and a closely related species, the southern white rhinoceros (SWR).

A long time ago, the northern species was separated from the southern by a physical barrier, the Rift Valley. They lived in different areas and developed a different physiology and genetic code.

The recent death of the last NWR male has left only two females as the remaining members of the northern species.

Luckily, researchers had collected sperm from NWR males while still alive. Now this sperm fertilized eggs of the closely related SWR in vitro. The hybrid embryos have been developed to blastocyst stage and then frozen for possible implantation into a SWR female. Despite the successful development of hybrid embryos, researchers eventually want to create pure NWR embryos using eggs from last two females in Kenya.

We spoke to study authors Cesare Galli and Thomas Hildebrandt about the work.

ResearchGate: What motivated this study? Why is it significant?

Thomas Hildebrandt: What we are developing within our international research team is unique. It is a blueprint on how to bring back technically extinct species. Of course, it would be better to never have to use this tool, to be so intelligent to never let a species get to a point of no return.

Cesare Galli: This study is significant because it’s a science and fact-based approach to conservation that is both measurable and reproducible. Classic conservation approaches have failed because of the opposition of conservation scientists to new technology. You can gauge this with the reviewer’s comments published with the paper.

RG: What were you able to achieve in your study?

Galli: For the first time we took an egg collected from an SWR female through maturation, fertilization and culture to the blastocyst stage where it can then be cryopreserved – frozen – or used to make stem cells. Embryos at this stage have a 50 percent chance to deliver a baby when implanted into the uterus.

RG: What challenges come with In vitro fertilization for the white northern white rhinoceros (NWR) compared to other large mammals, like horses?

Hildebrandt: Firstly, it is very difficult to pick up the oocytes from rhinos - we are the only ones on this planet who can do so. Then the transport into the laboratory can harm the cells. In the lab these cells are different to cells from horses and the standard protocol for horses cannot be applied. For example, the zona pellucida is different and to apply a sperm into an egg cell is very fragile and complicated.

Courtesy of Simon Greenwood.

RG: Now that there are only two female NWRs left is there added time pressure to continue the species?

Galli: The aging of the animals does not help reproduction so the sooner we can access these animals to collect the eggs and work on them the better. But it will be a “mission impossible” type of job.

Hildebrandt: So far, we are astonished by how far we have come. The only limiting factor in our fight against time are financial resources. This project is underfinanced, although it will have a major impact in the future. People think we have enough money but the reality is that it’s the dedication of the team that keeps this project running.

RG: Are you confident the NWR can be saved using this method?

Hildebrandt: Yes, but the artificial reproduction work has to be accompanied by an induced pluripotent stem cells (iPS) approach to have the best possible genetic variation for the founder population.

RG: What’s next for this research? Do you have timeline for implantation?

Hildebrandt: The next steps are to perform an ovum pick up in Kenya using the last two NWR females, apply NWR sperm and create pure NWR embryos.

RG: What does your study mean for animal conservation efforts more generally?

Galli: It means that there is an option that can be used when the conditions and the numbers of an animal become critical. This approach can be translated to other mammals with the necessary research and development.

Hildebrandt: This study means that we have a tool to bring back doomed species. But bringing them back only makes sense if society is willing to accept these species and provide them with protected habitat.

Featured image courtesy of Lucas Alexander.