Egg yolks turned out to be a key ingredient for cultivating bird embryonic stem cells (ESCs) in the lab. Using a growing medium of egg yolk along with a few other key factors, a USC Stem Cell-led team of scientists has succeeded in deriving and maintaining authentic ESCs from chickens and seven other bird species. The team first optimized conditions to support ESCs from chickens, the most well-studied avian species. Starting with cells from the early embryonic stage known as the blastoderm, they added two chemicals known to encourage ESC formation by inhibiting signals that sometimes promote stem cell differentiation. The first chemical, IWR-1, inhibits cell signals related to the proteins Wnt and β-catenin, and the second chemical, Gö6983, inhibits cell signals from the protein kinase C family. When exposed to these two chemicals, the chicken cells exhibited genetic markers of stem cell pluripotency but still could not be maintained in the lab long-term. The scientists then made a game-changing observation: when the blastoderm cells were transferred from their eggs along with larger amounts of yolk, they tended to self-renew better in the lab. The scientists began to suspect that the missing ingredient in their ESC-promoting cocktail was a natural component of egg yolk. A careful study of the yolk revealed that it does indeed contain a protein, ovotransferrin, that completed their cocktail and enabled them to derive and maintain ESCs from several chicken breeds. The researchers found that different species required variations of the cocktail, but they successfully derived and maintained true self-renewing and pluripotent ESCs from chicken, quail, pheasant, turkey, duck, goose, peafowl, and ostrich. These bird ESCs hold tremendous promise for applications ranging from studying embryonic development to producing lab-grown poultry to reviving endangered or even extinct birds.
