Gli3 is required for maintenance and fate specification of cortical progenitors

Gli3, one of three vertebrate Gli transcription factors in Hedgehog (Hh) pathway, is processed into a repressor form (Gli3R) in the absence of Hh signal and acts as the major negative transducer of the pathway. Although the role of Gli3 in embryonic patterning has been extensively studied, its role in cortical neurogenesis, especially in the regulation of neural progenitors in proliferation and cell fate specification, is largely unknown. To bypass the patterning defects caused by loss of Gli3, we conditionally deleted Gli3 after patterning was complete in mouse. Our results from birthdating and in utero electroporation experiments demonstrate that the Gli3, specifically Gli3R, is critical for specifying the fate of cortical neurons that are generated following a stereotypical temporal order. Moreover, Gli3 is required for maintaining the cortical progenitors in active cell cycle, suggesting that cells may acquire differentiated status as they turn off Gli3 expression during neurogenesis.