CLONAL AND POPULATION ANALYSES DEMONSTRATE THAT AN EGF-RESPONSIVE MAMMALIAN EMBRYONIC CNS PRECURSOR IS A STEM-CELL

In cultures of embryonic striatum, we previously reported that EGF ind uces the proliferation of single precursor cells, which give rise to s pheres of undifferentiated cells that can generate neurons and glia. W e report here that, in vitro, these embryonic precursor cells exhibit properties and satisfy criteria representative of stem cells. The EGF- responsive cell was able to generate the three major phenotypes of the mammalian CNS-neurons, astrocytes, and oligodendrocytes. Approximatel y 90% of both primary spheres and secondary expanded clones, derived f rom the primary spheres, contained all three cell types. The increase in frequency of EGF-generated spheres, from 1% in primary culture to c lose to 20% in secondary culture, and the large number of clonally der ived secondary spheres that could be generated from a single primary s phere indicate that EGF induces both renewal and expansion of the prec ursor cell itself. In population studies, the EGF-responsive cells wer e carried through 10 passages, resulting in a 10(7)-fold increase in c ell number, without losing their proliferative and multilineage potent ial. Thus, this study describes the first demonstration, through clona l and population analyses in vitro, of a mammalian CNS stem cell that proliferates in response to an identified growth factor (EGF) and prod uces the three principal cell types of the CNS. (C) 1996 Academic Pres s, Inc.