Fig. 6. Summary of the specific roles of the Pax6 DNA-binding domains in telencephalic development. Analysis of the Pax6^Aey18–/– mutant showed that the PD of Pax6 (A,B) is important for the regulation of neurogenesis, proliferation and regionalization in the developing telencephalon and that it contributes to the formation of the pallio-subpallial boundary. The lack of a phenotype in neurogenesis and proliferation in the forebrain of Pax6^4Neu–/– mice showed that the HD has no role in these processes (A), but is involved in some aspects of the pallio-subpallial boundary formation (SFRP2 expression). The Pax6(5a) isoform (B) is generated by alternative splicing leading to the insertion of a 14 AA insert in the N-terminal PAI subdomain of the PD, abolishing DNA binding and thereby favoring DNA binding via the RED domain. Retroviral overexpression revealed the anti-proliferative role of the Pax6(5a) isoform in cortical cells.