THE DISPERSION OF CLONALLY RELATED CELLS IN THE DEVELOPING CHICK TELENCEPHALON

Lineage analysis in the chick telencephalon was carried out using a li brary of retroviral vectors. Clones were analyzed in posthatch day 14- 21 animals for the phenotype and final locations of sibling cells. Clo nes often contained multiple types of neurons and glia. Clones of more than four cells almost always crossed functional boundaries. They wer e dispersed primarily along the rostrocaudal axis or in multiple direc tions, e.g., along the rostrocaudal and mediolateral axes. In order to begin to understand how the final patterns of dispersion were reached , embryonic tissue was examined. Radial migration, apparently supporte d by radial glial cells, occurred within the proliferative zones in al l clones. In contrast to the migration of cells in the mammalian telen cephalon, no tangential migration within the proliferative zones was o bserved at any age examined. However, beginning at embryonic day 4.5, tangential migration in the mantle zone in multiple directions was obs erved among the majority of clones. This type of migration occurred as soon as a mantle zone became apparent. It appeared that the tangentia l migration was not along radial glial processes. As in the mammalian telencephalon and chick diencephalon, dispersion among clonally relate d cells in the chick telencephalon is frequent, is extensive, and resu lts from tangential migration in a variety of directions. (C) 1998 Aca demic Press.