Transcriptional repressor involved in multiple aspects of cortical development, including neuronal migration, laminar and areal identity, and axonal projection (PubMed:9883721, PubMed:11239428, PubMed:21285371). As transcriptional repressor of FEZF2, it blocks the formation of the corticospinal (CS) tract from layer 6 projection neurons, thereby restricting the origin of CS axons specifically to layer 5 neurons (PubMed:21285371). Homodimer (By similarity). Part of a complex containing CASK, TBR1 and TSPYL2; may modulate gene expression in response to neuronal synaptic activity (PubMed:15066269). Forms homodimers (By similarity). Interacts with FOXP2 (By similarity). Interacts with FOXP1 (By similarity). Interacts with BCL11A (By similarity). Expressed in the developing and adult cortex (PubMed:11239428). Expressed in the olfactory bulbs (PubMed:9883721). First detected around day 10 of embryonic development in the preplate, at day 12.5, in the cortical plate and intermediate zone, and from day 16.5 to 18.5, in a rostro-caudal gradient in the subplate. In the thalamus, expression is first observed at postnatal stage, P7, and weak expression continues in later postnatal and adult stages. Homozygous mutant mice do not nurse and die between postnatal days 1 and 3 (PubMed:9883721, PubMed:11239428). Brains are smaller than those of heterozygous or wild-type littermates, olfactory bulbs are small and olfactory bulb projection neurons are absent (PubMed:9883721). Mutant mice show severe defects of cortical development (PubMed:11239428).