Isolation and Culture of Mouse Germ Cells

The isolation and culture of germ cells has allowed both the analysis of gene expression in these cells as well as studies of their behavior and growth requirements. Some of the factors found to be important for the in vitro culture of germ cells have subsequently been found to be physiologically relevant to germ cell growth and development in vivo. For example, leukemia inhibitory factor (LIF) was identified as a potent germ cell survival factor and mitogen in culture (1 ). Subsequently, targeted disruption of the signaling component of the LIF receptor, gp130 , demonstrated the importance of this signaling pathway for germ cell development in the embryo (2 ). Cultures of primordial germ cells (PGCs) have also been used as a model system in which to study cell migration and invasiveness (3 ). More recently, the ability of PGCs to give rise to pluripotent stem cells, similar to embryonic stem (ES) cells, has been revealed in culture (4 ,5 ). The development of these cells from human PGCs represents an important advance in the study of human embryology (6 ). Similarly, recent developments in spermatogonial transplantation (7 ,8 ) have opened up new and exciting avenues for the study of this important lineage. The ability of isolated spermatogonia to repopulate the testis tubule and give rise to mature sperm provides a rigorous transplantation system in which to test many hypotheses about spermatogonial growth and differentiation. In effect, it provides for those working on spermatogonial stem cells the same experimental system that has been available for many years for those working on hemopoietic stem cells. This experimental paradigm has accelerated efforts to develop a culture system for spermatogonia similar to that used to such good effect for the analysis of