Fig. 3

Individual Sox9+ Progenitors Produce Symmetric and Asymmetric Clones Spanning Cortical Layers. (a) By utilizing the Sox9 ^CreER;MADM system, tamoxifen injection at E11.5 yields sparse labeling of Sox9+ progenitors, which allows for clonal analysis of neurons derived from a single progenitor. Simplified dot representation of Sox9+ progenitor-derived clone overlaid onto sagittal section of E19.5 brain, reveals the cortical clone’s location. (b) Magnification of inset area displays example Sox9+ progenitor-derived cortical clone, comprised of EGFP (green) and tdTomato (red) expressing neurons. (c) Identical clone is portrayed in simplified dot representation to resolve cell position in relation to cortical lamina. (d-l) Representations of Sox9+ progenitor-derived clones demonstrate the size and laminar spread of neurons observed for each of these clones. Note certain clones display relatively equal numbers of EGFP and tdTomato expressing neurons implying a symmetric pattern of cell division, while other clones show proportions that imply asymmetric division. (m) Each clone was analyzed in order to assess number of neurons present in superficial layers (2–4), deep layer 5, and deep layer 6 (as no neurons were observed in layer 1). Pie chart displays the percentage of clones in which neurons were observed in cortical layers 2–6, layers 2–5 only (no neurons in layer 6), and layer 6 only (no neurons in layers 2–4 or layer 5). (n) Histogram displays the average number of neurons observed in each clone throughout layers 2–6, as well as within superficial layers 2–4, deep layer 5, and deep layer 6. (o) E19.5 brain section, including Sox9+ progenitor-derived clone (EGFP, green; tdTomato, red), immuno-labeled for Ctip2 (cyan), a layer 5 neuronal marker. (p-q) Magnification of inset area in o demonstrates molecular heterogeneity of neurons within a single Sox9+ progenitor-derived clone. A number of the neurons within the clone express Ctip2 (arrows, bottom), while others do not (arrowheads, top)