Figure 6.

Sox4 is present in dividing cortical cells and selectively colabels with Ngn2. A, B, In clonal cultures that allow both progenitor division and neuronal differentiation, cells transfected with a ubiquitous YFP plasmid and a neuron-specific dsRed plasmid may be a Green⁺Magenta⁻ progenitor or a Green⁺Magenta⁺ neuron (A). Quantification reveals that in this culture system, elevation of Sox11, but not Sox4, results in a higher proportion of transfected cells becoming neurons, whereas reduction of Sox11 or Sox4 results in a smaller proportion of transfected cells becoming neurons (B). C, E14.5 cortex, prepared for mitotic analysis with cells labeled for BrdU (blue, injected at E13.5) and counterstained with Ki67 (green) and Sox4 (magenta). BrdU⁺Ki67⁻ cells were dividing at E13.5, but had exited the cell cycle by E14.5, whereas BrdU⁺Ki67⁺ cells remained mitotically active at E14.5. Sox4⁺ cells (solid circles in C) tended to continue dividing, whereas Sox4⁻ cells (dashed circles in C) tended to exit the cell cycle. D, E, Costaining of Sox11 (D) and Sox4 (E) (both magenta) with Ngn2 (green) at E14.5 reveals little overlap with Sox11 but considerable colabeling with Sox4. Arrowheads indicate white cells expressing both Sox11 or Sox4 and Ngn2. Scale bars: A, 16 μm; C–E, 20 μm.