Clonal dispersion in proliferative layers of developing cerebral cortex

Abstract

IN the adult cerebral cortex, many retrovirally labelled clones are widely dispersed¹, though the mechanisms of this dispersion are not well understood. Here we investigate the temporal sequence of clonal dispersion after labelling progenitors of rat cortical cells with replication-incompetent retroviruses at early stages of cortical neurogenesis, 14–15 days after conception (E14/15). The location of labelled daughter cells was determined 3, 6 or 10 days later. Labelled sibling cells were radially arrayed three days after infection (E18). In contrast, by six days after infection (E20/21), 43% of cortical clones were dispersed non-radially by at least 500 μm. Four of these widespread clones were dispersed longitudinally by ≤2 mm, implying sustained rates of dispersion of >15μm per hour. Dispersed sibling cells occurred within proliferative zones of the forebrain in 35% of widely dispersed clones, suggesting that some dispersion reflects movement of dividing cells. Some clones dispersed beyond the neocortex into the olfactory bulb. Progenitor cell dispersion represents a previously unrecognized mode of migration by which sibling cells become widely dispersed in the developing forebrain.