Comprehensive characterization of migration profiles of murine cerebral cortical neurons during development using FlashTag labeling

In mammalian cerebral neocortex, different regions have different cytoarchitecture, neuronal birthdates and functions. In most regions, neuronal migratory profiles have been speculated similar to each other based on observations using thymidine analogues. Few reports investigated regional migratory differences from mitosis at the ventricular surface. Here, in mice, we applied FlashTag technology, in which dyes are injected intraventricularly, to describe migratory profiles. We revealed a mediolateral regional difference in migratory profiles of neurons that is dependent on the developmental stages, e.g., neurons labeled at E12.5-15.5 reached their destination earlier dorsomedially than dorsolaterally even where there were underlying ventricular surfaces, reflecting sojourning below the subplate. This difference was hardly recapitulated by thymidine analogues, which visualize neurogenic gradient, suggesting biological significance different from neurogenic gradient. These observations advance understanding of cortical development, portraying strength of FlashTag in studying migration, and are thus a resource for studies of normal and abnormal neurodevelopment.