Stem Cell Science Offers Hope for Conservation

It is remarkable that our Frozen Zoo® now contains frozen cell cultures of more than 9,000 individual birds, reptiles, amphibians, mammals and, even, fish. Adding in the number of frozen biopsies that may be expanded to produce cell cultures, the Frozen Zoo® contains more than 10,000 individual animals of over 1,000 species. Nowhere else does such an amazing collection exist.

Over the years, we have established and frozen cell cultures mostly derived from small—or even minute—skin biopsies. Skin cells grown from these biopsies have a more technical name: fibroblasts. They can be thawed and grown, producing more cells, which can be harvested for a variety of studies, or frozen again to have more cells available for later use.

The stunning finding that fibroblasts could be used to clone the animal from which they were derived, as was the case with Dolly the sheep and ten more mammalian species, brought new considerations to the conservation role of the Frozen Zoo®.

Equally astounding was the finding that stimulating the action of as few as four genes can induce fibroblasts to become stem cells capable of producing all the cell types in the body (called pluripotent stem cells). Or, in the case of the mouse, a single stem cell can direct the development of a whole new mouse.

Through collaborative efforts between the Genetics Division of the San Diego Zoo Institute for Conservation Research and The Scripps Research Institute (TSRI), the first pluripotent stem cells generated from fibroblasts in the Frozen Zoo® was announced in 2011.

Scientists at Dr. Jeanne Loring’s laboratory at TSRI received cells from a highly endangered African primate, the drill, and the most endangered species of rhinoceros, the northern white rhino from the Frozen Zoo®. Our hopes are that stem cell technologies might eventually benefit health management of endangered species, and that they might be used in assisted reproductive technologies to contribute to population management recovery efforts in zoos.

Approaches to treatment involving stem cells offer the possibility for improved quality of life and increased reproductive potential for the small zoo-based population of drills, a species challenged by diabetes in zoo populations.

The northern white rhino is nearing the end of its existence as a species because the small group of living animals has limited reproductive potential, and they do not constitute a sufficient population to recover the species. 

In addition, five of the seven living animals are related. But the Frozen Zoo® has cell cultures from 13 northern white rhinos, including unrelated individuals from whom cells have been banked over the last four decades. These cultures represent a far larger gene pool than the surviving individuals.

The collaboration with Dr. Inbar Ben-Nun and colleagues at Dr. Loring’s lab is being extended to additional species. In theory, the stem cells could produce eggs and sperm, previously demonstrated in the laboratory’s mice.

The vast knowledge of the biology and ability to manipulate the reproduction of the lab mouse stands in stark contrast to the state of rhinoceros reproductive management. Although strides are being made in assisted reproduction in other species of rhinos, prospects are precarious to develop sufficient technology that will forestall extinction in the northern white rhino. Many conservationists have given up hope.

The development of stem cells from these rhinos offers a glimmer of optimism that rises out of the liquid nitrogen freezers of the Frozen Zoo®. For other mammal species on the brink of extinction, banked fibroblasts from genetically valuable animals represent the potential to rescue populations depleted of genetic variation.

Oliver Ryder, Ph.D., director of Genetics Division and Kleberg Chair.