Transplantation of human embryonic stem cells to the chick embryo.

The traditional methods of studying the differentiation of human embryonic stem cells (hESCs) are to differentiate them in vitro or in immune-deficient mice as teratomas. The chick embryo is a well-studied and accessible experimental system that has been shown to permit the development of mammalian cells, including murine embryonic stem cells. We therefore performed experiments transplanting colonies of hESCs into organogenesis-stage chick embryos, hoping this might provide a novel system for studying the developmental programs and decisions of these important cells. hESCs, constitutively expressing green fluorescent protein or labeled with the dye CFDA, were used to allow the following the hESC in living embryos. As a first step, we chose to transplant hESCs into the trunk of chick embryos, both into and instead of developing somites. Our first results showed that hESCs survive, migrate, and integrate into the tissues of the chick embryo. Some of the hESCs differentiate and the type of embryonic microenvironment that the implanted cells were exposed to modified their differentiation. Therefore, this hESC-chick embryo system has potential for complementing studies in rodents and in vitro, and uniquely, to shed light on early processes in the development of human cells in the embryonic context.