Stem Cells and Genetic Rescue of Critically Endangered Species
Utilizing stem cells to restore genetic variation lost from critically small populations of endangered species is one aspect of a multifaceted strategy for preventing extinction. With only seven surviving individuals, including only four that are potentially reproductively capable, the northern white rhinoceros may technically already be over the brink of extinction.
Our Frozen Zoo® contains viable cell cultures, frozen in liquid nitrogen, from 12 northern white rhino individuals, beginning with a female, Lucy, whose cells were frozen in April 1979. In 2011, we reached a milestone: in a collaboration with Dr. Jeanne Loring’s laboratory at the Scripps Research Institute in La Jolla, we generated stem cells from the critically endangered northern white rhino and the endangered African primate, the drill. These stem cells are pluripotent, meaning that they can produce any tissue in the body and represent both a scientific and conservation milestone.
We have developed a plan for genetic rescue of the Northern white rhinoceros, and having a “crash” of Northern white rhino pluripotent cells is an important part of that plan. With donated funding to advance our efforts in genetic rescue of northern white rhinos, we aim to develop pluripotent stem cells from all twelve northern white rhino individuals whose cells are banked in the Frozen Zoo®.
Technical advances are being reported and improvements made for stem cell development in humans and mice. We and our colleagues in the Loring Lab hope to benefit from these advances and generate stem cells from all the northern white rhinos in the Frozen Zoo®, as well as other species.
As stem cell studies have progressed, we are looking to use whole genome sequencing studies to shed light on the genetic diversity in northern white and southern white rhinos, and compare these related forms of rhino at the DNA sequence level.
Meanwhile, our collaboration with the Scripps Research Institute broadens in scope as efforts to produce pluripotent stem cells from other species advance. Susanne Montague in the Loring lab has established a pluripotent stem cell line from a Somali wild ass, a critically endangered species. The San Diego Zoo Safari Park is one of the few institutions in the world breeding this rare African equid, which is believed to number less than 600 individuals in the wild.
The captive breeding program for Somali wild ass is based on a limited number founder animals and the sustainability of the captive population may depend upon incorporation of genetic diversity from cell cultures, such as those that have been established in the Frozen Zoo®. Restoration of genetic diversity from cryobanked cells is likely to be easier to accomplish with pluripotent stem cells. Our future efforts for fulfilling the plan for genetic rescue of the northern white rhinoceros other critically endangered species will depend on further advances in genetic and reproductive technologies utilizing stem cells, but the reward may well be preventing extinction of some very special species.
By Oliver Ryder, Ph.D., Director of Genetics, Kleberg Chair