Figure 8

Changes in cortical progenitor cell multipotency following loss of Dicer function. The neurogenic period in mice begins at around E11 and ends at E17. Over this period all of the different classes of cortical projection neurons are generated in a fixed temporal order beginning with Tbr1+, layer 6 and subplate neurons. By E14.5 layer 6 neuron-genesis is waning and cortical progenitors are primarily producing CTIP2+ layer 5 cortical neurons. Finally, at around E15.5, upper layer genesis (characterised by expression of BRN2, CUX1 and Satb2) begins. Dicer null cortical progenitors fail to adhere to this stereotyped production of cortical projection neurons and generate Tbr1+ neurons throughout the neurogenesis period at the expense of other cell types. Despite this apparent lack of multipotency in the neuronal lineage Dicer null stem cells maintain the ability to undergo the higher order neurogliogenic switch to produce astrocytes.