Stem Cell Technique Could Preserve Endangered Bird Species

Birds are a critical part of the global ecosystem; they enable our food production through consumption of agricultural pests like aphids and rodents, and control the spread of diseases by eating insects like mosquitos and ticks. However, around 15 percent of all bird species now face risk of extinction—in Hawaii alone, 33 of the state's 45 native species are critically endangered.

Caltech researchers have now developed technology to freeze and preserve stem cells from birds that can then be reconstituted to help propagate populations.

The work was conducted by Caltech postdoctoral scholar Xi Chen as a collaboration between the USC laboratory of Qi-Long Ying and the Caltech laboratory of Carlos Lois, research professor of biology. The study is described in a paper in the journal Nature Biotechnology on September 30.

"Preservation of animal species is not just some hippie pursuit—it has real economic and public health consequences," Lois says. "Losing species is a domino effect. For example, birds eat insects like mosquitos, so fewer birds mean more mosquitos, which could mean spreading more diseases like West Nile virus and malaria. Each animal's role in nature has far-reaching repercussions, which often affect human health and the general functioning of our society."

While the technology to sequence a bird's entire genome is readily available, simply having a genetic sequence does not mean you can produce an animal from it—you need cells. As an analogy, one can imagine having all of the instructions on how to build a car but not having a factory with the machinery or materials necessary to do so.

In mammals, embryos develop for a few days as a collection of cells that can be grown outside of the female (in vitro), before they are eventually implanted into the uterus where they develop. The technology to freeze, revive, and grow mammals from embryos cultured in vitro has existed for many species for more than 30 years. But preserving bird embryos is not currently possible because they grow inside of eggs, and it is not possible to freeze entire eggs and then revive them.

To address this bottleneck, the new technique allows scientists to grow stem cells (cells with the ability to develop into specialized types) in culture from different bird species; the stem cells are taken from a nascent embryo, propagated in vitro in the lab for up to several months, and then frozen. They can then be thawed and grown again at a later date and inserted into an egg, which is then incubated to develop the animal.

As working with endangered animals is high risk, the team demonstrated proof of concept in common bird species such as quail, pheasant, turkey, goose, chicken, peafowl, duck, and ostrich. The Lois lab is currently collaborating with the San Diego Zoo to apply similar techniques to preserve stem cells from wild bird species, including some that are critically endangered.

"Currently, protecting remaining individuals is our only strategy to prevent bird extinction," Lois says. "However, despite intensive conservation efforts, many species continue to vanish. The techniques we're developing will enable reconstituting birds from stored cells of endangered species, even after extinction, creating a permanent repository for species restoration."

The paper is titled "Derivation of embryonic stem cells across avian species." In addition to Chen and Lois, Caltech co-authors are graduate student Martin Tran and visiting research scientist Carol Readhead. Additional co-authors are Zheng Guo, Xinyi Tong, Xizi Wang, Xugeng Liu, Ping Wu, Christina Wu, Lin Cao, Yixin Huang, Han Zeng, Nima Adhami, Sirjan Mor, Cheng-Ming Choung, and Qi-Long Ying of USC; Rusty Lansford of Children's Hospital Los Angeles; and Hiroki Nagai and Guojun Sheng of Kumamoto University in Japan. Funding was provided by the National Institutes of Health. Carlos Lois is an affiliated faculty member with the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech.