Fig. 2.

Ikaros-expressing progenitor cells generate projection neurons of all laminar fates. (A and B) BAC-Ikaros-Cre transgenic mouse crossed to the R26-YFP reporter mouse was used for lineage analysis of neurons produced from Ikaros-expressing progenitor cells. A low recombination rate gives rise to distinguishable clones of progenitor cells and their progeny at E13.5. (C–F) In the adult brain, progeny of Ikaros-Cre–expressing progenitor cells (YFP⁺) were mainly neurons (NeuN⁺) and found throughout the layers of the cortex. (D and E) YFP⁺ progeny in deep cortical layers frequently expressed Foxp2 and Tbr1, two transcription factors expressed in layer 6 projection neurons. (F) YFP⁺ neurons in the upper layers were often positive for Cux1, a marker of cortical projection neurons in layers 2–3. (Scale bars: A–F, 100 μm; D′–F′, 50 μm.)