Radial and horizontal deployment of clonally related cells in the primate neocortex: relationship to distinct mitotic lineages.

To analyze cell lineage in the rhesus monkey necorotex, we used recombinant retroviruses to label individual progenitor cells in the ventricular zone (VZ), then determined histochemically the distribution of their progeny during and after the period of cortical neurogenesis. Distribution patterns of labeled cells in the VZ suggested the coexistence of asymmetrically and symmetrically dividing progenitor cells, indicating that both postmitotic and mitotic progeny are produced during cortical neurogenesis. In the cortex, several distinct patterns of clonal distribution were observed and interpreted as follows: clones aligned radially suggested that asymmetrically dividing progenitors generate sequential "siblings" that migrate, in tandem, along a common radial path to the cortex. In contrast, clones oriented horizontally within a single lamina suggested that symmetric divisions produce multiple, laterally displaced progenitors which, in turn, simultaneously generate "cousin" cells that migrate, in concert, to the same cortical layer. Thus, we propose that different mitotic lineages, which coexist in the monkey VZ, produce distinct radial or laminar patterns of clone deployment that foreshadow the cytological organization of the adult neocortex.