Incomplete molecular differentiation of CSMNs in Ldb2-deficient mutants. In situ hybridization on coronal P1 sections reveals loss of the differentiation markers Foxo1 (A–D′), Foxp2 (E–H′), Diap3 (I–L′), and Igfbp4 (M–P′) in layer 5 of motor cortex (arrows) in Ldb1/2-DKO mice. Note that layer 6 expression of Foxp2 is not affected by the loss of Ldb genes, confirming the specific roles of Ldb1/2 in layer 5 neurons. Scale bars: 1 mm in (P, main panels), 0.2 mm in (P′, inset panels).