The distribution of Tbr2+ mitoses shifts to the outer subventricular zone (oSVZ) during early stages of cortical development in macaque, but not in ferret or rat.

<p>(<b>a–c</b>) Images taken from coronal sections of the E80 macaque, P2 ferret, and E20 rat oSVZ. Tissue was immunostained for 4A4 (green), Tbr2 (red) and counterstained with DAPI (blue). Boxes to the right highlight examples of 4A4+ mitotic cells that either do not express Tbr2 (#1) or that do express Tbr2 (#2). (<b>d–f</b>) Graphs showing changes in the distribution of Tbr2+ mitoses during development of the somatosensory 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. (<b>d</b>) At E50 in the macaque all Tbr2+ mitoses were located in the inner SVZ (iSVZ). There was a steady decrease in the proportion of Tbr2+ divisions occurring in the iSVZ. By E80 the majority of Tbr2+ mitoses (76%) had shifted to the oSVZ. (<b>e</b>) In ferret the majority of Tbr2+ mitoses were located in the iSVZ throughout neurogenesis in the somatosensory cortex. At P2, during neurogenesis of layer 2 neurons <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030178#pone.0030178-Noctor4" target="_blank">[19]</a>, 73% of Tbr2+ mitoses were still located in the iSVZ. (<b>f</b>) The pattern observed in rat was similar to that of the ferret. The majority of Tbr2+ mitoses were located in the iSVZ throughout the period of cortical neurogenesis. At P2, during production of layer 2 neurons <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030178#pone.0030178-Bayer1" target="_blank">[21]</a>, there was a similar number of Tbr2+ mitoses located in the rat iSVZ (74%) as was observed in the ferret. Legend indicates histological zones: VZ: blue; iSVZ: red; oSVZ: green.</p>