A SUBSET OF CLONES IN THE CHICK TELENCEPHALON ARRANGED IN ROSTROCAUDAL ARRAYS

Background: Different areas of the vertebrate central nervous system a ppear to follow different rules during development for determining the position of sibling cells. For example, in the chick hindbrain, clone s are frequently confined to a single functional unit that derives fro m a single rhombomere. In contrast, clones in the mammalian cerebral c ortex often cross functional boundaries because of the extensive migra tion of sibling cells in orthogonal directions. We have investigated w hether the pattern of clonal distribution in the chick telencephalon i s similar to that of the hindbrain or to the more functionally analogo us mammalian cerebral cortex. Progenitor cells in the chick telencepha lon were marked using a retroviral library encoding alkaline phosphata se and over 10(5) distinct molecular tags. Patterns of dispersion were detected using alkaline phosphatase histochemistry, followed by the r ecovery and sequencing of the molecular tag. We also analyzed the phen otypes of cells that occurred within the clones. Results: A subset of progenitors gave rise to clones that were found in rostrocaudal arrays resembling tubes. Arrays were restricted in the mediolateral and dors oventral planes but could span up to 4 mm in the rostrocaudal directio n. They were found throughout the telencephalon and a single clone oft en spanned more than one telencephalic nucleus. Rostrocaudal clones co mprised 60 % of clones containing five or more cells and contained man y different types of neurons, astrocytes, oligodendrocytes, or various combinations of these cell types. Conclusions: Telencephalic progenit ors are multipotent, producing progeny that become distinct cell types . Clonally related cells can migrate rostrocaudally within domains tha t are restrained in the mediolateral and dorsoventral directions. A su bset of rostrocaudal clones resemble those seen in the mammalian cereb ral cortex, with respect to the Grossing of functional boundaries, but all rostrocaudal clones differ from the cerebral cortical clones in t he pattern of spread of sibling cells, with the rostrocaudal clones be ing more constrained in the mediolateral and dorsoventral directions. A role for lineage in the patterning of the chick forebrain is support ed by these observations. In addition, these data suggest a role for c ues within the telencephalic marginal zone that serve to guide clones in their rostrocaudal migration.