For the development of the central nervous system, a large variety of neuronal cell types are needed to be generated at defined times and locations. Cajal-Retzius (CR) cells are the first neurons generated during corticogenesis and appear to play key roles in the laminar organization of the cortex. However, the molecular mechanism underlying the generation of CR cells is poorly understood. We have already shown that Dmrta1 (double-sex and mab-3 related transcription factor-like family A1) is expressed in neural stem/progenitor cells in the neocortex and regulates proneural genes downstream of Pax6. To further reveal functions of Dmrt genes in neurogenesis of the neocortex, we generated Dmrta1 KO mice and found reduction of Reelin-positive CR cells in Dmrta1 KO (knockout) mice compared with wild type (WT) mice. The possibility that Dmrt3, another Dmrt family molecule, compensates the loss of function of Dmrta1 cannot be excluded because Dmrta1 single KO mice still retained approximately 70% of CR cells compared to WT mice. Therefore, we examined Dmrt3 KO to find the reduction of CR cells in the neocortex of Dmrt3 KO mice. To more directly explore the relationship among Dmrt family members in CR cell development, additional experiments using Dmrta1 and Dmrt3 double-KO mice are now in progress.