Migratory paths and phenotypic choices of clonally related cells in the avian optic tectum.

We used retrovirus-mediated gene transfer to study the migration of clonally related cells in the developing chicken optic tectum. Clonal cohorts initially form radial arrays in the ventricular zone (approximately E5), but eventually divide into three separate migratory streams. In the first migration, a minor population of cells migrates tangentially along axon fascicles in medio-laterally directed files (approximately E6-E7); these eventually differentiate into multipolar efferent cells. After E7, the majority of cells in each clone migrate radially along fascicles of radial glia to form the tectal plate, wherein they differentiate into neurons and astrocytes. Around E9, a set of small cells leaves the radial arrays in superficial layers to form a second tangential migration; at least some of these differentiate into astrocytes. Thus, as the tectum develops, cells derived from a single multipotential precursor migrate along three separate pathways, follow separate guidance cues, and adopt distinct phenotypes.