It’s too late for conservation efforts to save the northern white rhino, but with recent scientific advancements there may still be hope to bring back this beloved species. In a recently published paper, scientist Marisa Korody and her colleagues at the San Diego Zoo Global (US) and Scripps Research’s Department of Molecular Medicine (US) describe their exciting advances in using stem cells to make relive the northern white rhino.
The northern white rhino is functionally extinct, which means there aren’t enough rhinos left to save the species. In fact, there are only two northern white rhinos left: a mother and a daughter. But for decades, scientists have kept cell samples from 15 northern white rhinos containing enough genetic material to potentially bring this species back from the brink. These preserved samples contain fibroblasts – the type of skin cells that secrete collagen – from white rhinos. Thanks to new methods developed by these scientists, fibroblast cells can be converted into something much more valuable: induced pluripotent stem cells. These stem cells can differentiate into any type of cell in the body, including heart cells, muscle cells, and reproductive cells.
In theory, by converting fibroblasts into reproductive cells, scientists could create genetically unique rhino embryos. Along with other assisted reproductive technologies, scientists could implant a new embryo into a closely related southern white rhino, where the baby northern white rhino could develop as an otherwise normal pregnancy. By completing this process multiple times, scientists might be able to establish a stable population of northern white rhinos.
In 2011, this research team generated induced pluripotent stem cells from samples of another endangered species, but unfortunately, as this process was found to harm recipient genomes, this method was largely unsuccessful. Despite this setback, in 2015 the authors met with colleagues around the world to consider ways to save the northern white rhino, and they concluded that methods involving induced pluripotent stem cells may still be the most promising solution. Over the following years, scientists worked to improve their methods, and these improvements are documented in their recent article. These experiments represent the first step in a long-term plan to bring back the northern white rhino through assisted reproduction techniques.
From the start, scientists faced a whole host of challenges. Through trial and error, they altered the cell growth medium, optimizing it for rhino cells. Using their improved growth medium, the scientists were able to generate induced pluripotent stem cell lines from 11 rhinos. This has never been done before and represents a huge step forward in the recovery of this species.
Before trying to make their first rhino, scientists had to stress these induced pluripotent stem cells and sequence their genomes to determine if the cell quality is good enough to potentially produce new viable rhinos. They maintained colonies of these cells in long-term cultures and exposed these colonies to different conditions to provide insight into the resilience of these cells. These tests demonstrated that long-term culture did not affect the potential of these cells to differentiate into cardiac lineage cells, confirming that these cells are stable over the long term. The researchers also confirmed that these pluripotent cells could potentially produce gametes, eggs and sperm used for sexual reproduction. These advances indicate that with these newly developed protocols, induced pluripotent stem cells are a promising tool that could one day help recover the northern white rhino.
While this study includes some exciting results, there is still a lot of work to be done. For example, scientists now need to sequence the genomes of northern and southern white rhinos so that other researchers can analyze the ability of stem cells to stay the same over time. Despite the work that remains to be done, these promising advances could one day help the northern white rhino population to recover. This method can also work to save other threatened or extinct species, as long as the necessary genetic material is available. In the long term, these scientists plan to continue a series of experiments that could ultimately bring this beloved rhino, and potentially other endangered species, back from the brink of extinction.