Primordial Germ Cell-Derived Hemopoiesis

Summary

A new concept for the initiation of hemopoiesis is presented in which the primordial germ cell (PGC) is viewed as the hemopoietic-initiating cell. Evidence from developmental biology and hematology is presented indicating an intimate link between the PGC population and hemopoiesis. Results are described showing that PGCs can be cultured in vitro and induced into cells of the hemopoietic system. These including erythropoietic cells as well as multipotential stem cells and the most primitive hemopoietic stem cell detected in vitro, the cobblestone area-forming cell. Finally, a pathway for the initiation of hemopoiesis from the primordial germ cell is presented.

In 1971, Metcalf and Moore¹ wrote “It is unfortunate that the role of the mammalian yolk sac has been underestimated, relegated to the status of an atavistic organ of transitory importance in mammalian development and considered a classic example of ontogeny recapitulation phylogeny. In two particular aspects, in the development of the haemopoietic system and in the production of primordial germ cells, such pessimism is hardly warranted, and there arte excellent grounds for believing that the yolk sac has a unique role to play in the development of these two systems. In both instances this may be dut to early development of the yolk sac in an extraembryonic situation removed from the pressures of early embryonic differentiation. It would be singulary siastrous for the development of the embryo and the survival of the species if the first hemopoietic stem cells amd primordial germ cells were to rapidly and completely succumb to differentiation pressures, such as exist within the early embryonic environment”. These authors go on to state that “…haemopoietic potential is determined at the very early pre-primitive strek blastoderm stage, and is relatively uninfluenced by the course of the subsequent movement of the tissue to its definitive site. It is generally accepted that the mesodermal cells that ultimately form blood islands originate from epiblast, invaginate through the primitive streak and produce, by lateral migration, the middle germ layer.”