The neocortex of the adult brain consists of neurons and glia that are gene
rated by precursor cells of the embryonic ventricular zone. In general, gli
a are generated after neurons during development(1), but radial glia are an
exception to this rule. Radial glia are generated before neurogenesis and
guide neuronal migration(2). Radial glia are mitotically active throughout
neurogenesis(3), and disappear or become astrocytes when neuronal migration
is complete(4,5). Although the lineage relationships of cortical neurons a
nd glia have been explored(6,7), the clonal relationship of radial glia to
other cortical cells remains unknown. It has been suggested that radial gli
a may be neuronal precursors(5,8-10), but this has not been demonstrated in
vivo. We have used a retroviral vector encoding enhanced green fluorescent
protein to label precursor cells in vivo and have examined clones 1-3 days
later using morphological, immunohistochemical and electrophysiological te
chniques. Here we show that clones consist of mitotic radial glia and postm
itotic neurons, and that neurons migrate along clonally related radial glia
. Time-lapse images show that proliferative radial glia generate neurons. O
ur results support the concept that a lineage relationship between neurons
and proliferative radial glia may underlie the radial organization of neoco
rtex.