Neurod2/6 transcription factors control basal progenitor differentiation and sequential production of neocortical cell subtypes

Neurod2 and Neurod6 (Neurod2/6) are key transcription factors that promote neuronal differentiation, however, their role in the developing neocortex is not fully understood. Both genes have similar expression patterns during development as well as binding motifs. In order to investigate their role in cortical neurogenesis, we generated a mouse model deficient for both Neurod2/6. Here we demonstrate that differentiation of Tbr2-positive (Tbr2+) basal progenitors (BPs), but not Pax6+ apical progenitors, was severely defected, resulting in ectopically expanded BPs in perinatal Neurod2/6 deficient brains. The sequential fate specification of cortical neurons was also impaired in the absence of Neurod2/6. Ectopic Tbr2+ BPs expressed multiple proliferation markers and were able to self-renew. Olig2+ glial precursors were consequently over-produced in Neurod2/6 deficient brains. Restoration of Neurod2/6 in the double deficient brains downregulated Tbr2 expression, and exhibited substantial rescue effects on defected laminar subtype specification and excessive gliogenesis. Our work indicates that Neurod2/6 regulate BP differentiation and sequential production of cortical cell subtypes via inhibiting Tbr2-dependent genetic program.