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Which Came First, the Chicken or the Egg?

Media Contact:
Jennifer Martin, CSREES Staff (202) 720-8188

Stacy Kish, CSREES Staff (202) 690-5716
August 7, 2006

Scientists are side stepping this age old question by using primordial germ cells (PGCs) to create unique genetically modified chickens. During embryonic development, PGCs are one of the earliest cells to differentiate becoming either the sperm or eggs in the adult vertebrate. Scientists believe manipulating PGCs will provide a new avenue to genetically modify chickens for agricultural and pharmaceutical applications.

In chickens, PGCs segregate from body cells after 18 hours of incubation. Between 48 and 72 hours of incubation, PGCs migrate to the gonad where they begin to mature and differentiate to produce either sperm or eggs in adults. The chicken is an ideal candidate for this research because chicken eggs provide easy access to the earliest stages of embryo development.

Marie-Cecile van de Lavoir and collegues at Origen Therapeutics in collaboration with scientists from the University of California – Davis, isolated and cultured the chicken PGC line. After a series of analyses, the scientists found that the majority of the cultured PGCs maintained their germ cell characteristics after 197 days in culture. This ground breaking outcome documents the first successful culture of PGCs for any species.

The scientists also demonstrated that genetic modifications can be introduced into the chicken genome using PGCs. A gene encoding for the production of a green fluorescent protein, called GFP, was introduced into the chicken primordial germ cells. The scientists grew the germ cells carrying the genetic modification under cultured conditions in order to create a population of germ cells expressing GFP. The modified germ cells were injected into embryos at an early stage of development and incubated to hatch. The resulting chickens were reared to sexual maturity and produced offspring. A proportion of the offspring inherited the ability to produce GFP and subsequently passed this trait to their offspring following the classic laws of inheritance.

This cutting edge research provides scientists new opportunities to genetically modify PGCs to create genetically modified strains of chickens for industrial, agricultural, and pharmaceutical applications. This knowledge will also expand on experiments designed to understand the molecular events that control the growth of embryos from a single cell into a fully formed organism. The results of this research are presented in an article entitled, ‘Germline transmission of genetically modified primordial germ cells' featured in the June 8 th edition of the journal Nature.

The USDA's Cooperative State Research, Education and Extension Service funded this research through its Small Business Innovative Research Program (SBIR). The SBIR program makes competitively awarded grants to qualified small businesses to support high quality, advanced concepts research related to important scientific problems and opportunities in agriculture that could lead to significant public benefit if successful.

CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education, and extension programs in the Land-Grant University System and other partner organizations. For more information, visit http://www.csrees.usda.gov.

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