In vivo CTIP1 knock-down in layer 5 PNs and its overexpression in layer 6 PNs lead to reciprocal changes in TBR1 expression. A, C, Coronal sections of brains in utero electroporated at E13.5 and analyzed at P0. A, Confocal images of layer 5 neurons are shown; electroporated neurons express GFP. CTIP1 knockdown associates to an increase in the number of cells expressing TBR1 in layer 5 PNs (n = 5 brains) relative to control condition. pshCTIP1 effect on TBR1 expression is reversed by the coelectroporation of a plasmid expressing a CTIP1 variant engineered to be insensitive to shCTIP1 (pmutCTIP1; n = 5 brains). Notched arrowheads point electroporated cells expressing TBR1. C, Confocal images of layer 6 neurons overexpressing CTIP1 by electroporation of pmutCTIP1. Cells electroporated with pmutCTIP1 are identified by the expression of the MYC epitope. Overexpression of CTIP1 in layer 6 PNs leads to a decrease in the number of cells expressing TBR1 (n = 6 brains) relative to control condition. The empty expression vector (pCAGIG-IRES-GFP) was used as control. Notched arrowheads point electroporated cells expressing TBR1. B, D, Quantification of experiments showed in A and C, respectively. The results are expressed as the percentage of GFP-positive cells that also express TBR1 in layer 5 (B) or in layer 6 (D). Error bars represent ± SD. Student's t test ***p < 0.001. Scale bar, 25 μm.