How master splicing regulators cross talk with each other and to what extent transcription regulators are differentially spliced remain unclear in the developing brain. Here, cell-type–specific RNA-Seq analyses of the developing neocortex uncover variable expression of the Rbfox1/2/3 genes and enriched alternative splicing events in transcription regulators, altering protein isoforms or inducing nonsense-mediated mRNA decay. Transient expression of Rbfox proteins in radial glial progenitors induces neuronal splicing events preferentially in transcription regulators such as Meis2 and Tead1. Surprisingly, Rbfox proteins promote the inclusion of a mammal-specific alternative exon and a previously undescribed poison exon in Ptbp1. Simultaneous ablation of Rbfox1/2/3 in the neocortex downregulates neuronal isoforms and disrupts radial neuronal migration. Furthermore, the progenitor isoform of Meis2 promotes Tgfb3 transcription, while the Meis2 neuron isoform promotes neuronal differentiation. These observations indicate that transcription regulators are differentially spliced between cell types in the developing neocortex. (The sex has not been reported to affect cortical neurogenesis in mice, and embryos of both sexes were studied without distinguishing one or the other.)