Abstract
There are many parallels between the neuropoietic and lymphohematopoietic systems. The lymphohematopoietic stem/progenitor cell system has been extensively characterized, but there are still major questions relating to the definitive stem cell assay, the structure of the system (i.e., hierarchical versus cell cycle–based), and the nature of differentiation (i.e., stochastic versus deterministic). Recent data have established the existence of an epidermal 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 variety of putative uni-, bi-, and tripotential stem cells that form in response to EGF. Neurospheres are the EGF-responsive neural units that grow in liquid culture, and we have found that cells derived from these neurospheres express a wide array of cytokines and their receptors. This will provide a window on the hemopoietic progenitor system analogous to that created by the description of in vitro growth of clonal hematopoietic progenitors.
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