Correlates between hematopoiesis and neuropoiesis: Neural stem cells

There are many parallels between the neuropoietic and lymphohematopoietic s ystems. The lymphohematopoietic stem/progenitor cell system has been extens ively characterized, but there are still major questions relating to the de finitive stem cell assay, the structure of the system (i.e., hierarchical v ersus cell cycle-based), and the nature of differentiation (i.e., stochasti c versus deterministic). Recent data have established the existence of an e pidermal growth factor (EGF)-responsive neural stem cell in adult mice. We have studied these neural progenitor/stem cells in fetal (day 15) and 2-day postnatal mice and established a single-cell progenitor assay and a variet y of putative uni-, bi-, and tripotential stem cells that form in response to EGF, Neurospheres are the EGF-responsive neural units that grow in liqui d culture, and we have found that cells derived from these neurospheres exp ress a wide array of cytokines and their receptors, This will provide a win dow on the hemopoietic progenitor system analogous to that created by the d escription of in vitro growth of clonal hematopoietic progenitors.