Figure 3

The number of deep layer, Tbr1+ neurons continues to increase throughout the neurogenic period in the Dicer null cortex. (A) Time course of Tbr1 (layer 6 transcription factor) and Satb2 (layer 2 to 4 transcription factor) expression in the developing cerebral cortex. In the wild-type the generation of deep layer neurons plateaus by E15.5 when the late born Satb2+ population begins expanding. Conversely, in the Dicer null cortex, the number of Tbr1+ cells increases throughout development and only a very limited number of upper layer neurons are produced during the neurogenic period. (B, C) Quantification of Tbr1 (B) and Satb2 (C) positive nuclei showed significant increases in Tbr1 nuclei number in the Dicer null at E17.5 (P = 0.005) and P0 (P = 0.01) and significant decreases in Satb2+ nuclei number at E15.5 (P = 0.002), E17.5 (P = 0.003) and P0 (P = 0.007). Counts were performed on three sections from two wild-type and two Dicer null cortices at each timepoint. Scale bars: 50 μm.