Figure 2. The distribution of Tbr2+ cells during cortical development is similar in ferrets and rats, but different in macaques.

(a–c) Coronal sections of somatosensory cortex from E80 macaque, P2 ferret and E20 rat immunostained for Tbr2 (red) and counterstained with DAPI (blue). Images are displayed at the same scale. In each species a dense inner band of Tbr2+ cells was located within the cell dense zone surrounding the lateral ventricle visualized with DAPI. The diffuse outer band of Tbr2 expression was located within a striated zone marked by streams of cells organized in tangential clusters. (d–f) Graphs showing changes in the distribution of Tbr2+ cells during development of the cerebral cortex. The stage of development is shown at the bottom of the graphs, and the approximate cortical layer generated at each stage of development is indicated along the top of each graph. (d) In macaque the distribution of Tbr2+ cells progressively shifted to the outer subventricular zone (oSVZ) during development. By E80, during genesis of layer 4 neurons [20], 59% of Tbr2+ cells were located in the oSVZ. (e) The distribution of Tbr2+ cells in the gyrencephalic ferret shifted to the oSVZ more slowly in comparison to macaque. At P2 during genesis of layer 2 neurons [19], 62% of Tbr2+ cells remained in the inner SVZ (iSVZ). (f) The distribution of Tbr2+ cells in the lissencephalic rat was similar to that of the gyrencephalic ferret. At E20 during genesis of upper layer neurons [21], the majority of Tbr2+ cells (59%) were located in the iSVZ, and 17% were located in the oSVZ. Legend indicates histological zones: VZ: blue; iSVZ: red; oSVZ: green. Scale bar in (a) applies to (a–c).