AVIAN EMBRYONIC STEM CELLS, PRIMORDIAL GERM CELLS AND TRANSGENIC CHICKENS

Abstract

Transgenic animals have become important tools for biological research. In mammals, several methods are available to introduce foreign DNA into the mammalian genome. Gene transfer in birds is a relatively complicated process because of the unique aspects of avian reproduction, and avian transgenics has largely been limited to the use of retroviral/lentiviral vectors. However, the temporal and spatial aspects of the development of avian primordial cells (PGCs) provides easy access to the germline and several methods can be used to produce germline chimeras. Initially, the ability to make germline chimeras has given rise to efforts to establish avian embryonic stem cells (ESCs)lines. In the chick, ESCs can be cultured from the area pellucida of the unincubated embryo. These cells show several features of stem cells including the capacity to give rise to all somatic tissues. However, competency to give rise to the germline has been difficult to achieve, most likely due to the mechanisms of avian germline development. As an alternative to embryonic stem cells, the long term culture of avian PGCs hold significant promise for non-viral methods of manipulating the avian genome. Using a combination of STO feeder layers, conditioned media, fibroblast growth factor-2 and stem cell factor, stable lines of chick PGCs have been established from single embryos. These lines express several markers of germ cells and have been in continuous culture for over a year. Many of the lines retain their ability to populate the germinal ridge when injected into early embryos and can give rise to functional gametes at sexual maturity. Like that observed in mammals, under specific culture conditions, PGCs can give rise to embryonic germ (EG) cells. However, as observed with ESCs, avian EG cells only give rise to somatic cells. Hence, the long-term culture of primordial germ cells opens new applications for avian germ cell biology, avian transgenics, germplasm preservation and stem cell biology.