Neuronal birthdate-specific gene transfer with adenoviral vectors.

The multilayered structure of the cerebral cortex has been studied in detail. Early-born neurons migrate into the inner layer and late-born neurons migrate into more superficial layers, thus establishing an inside-out gradient. The progenitor cells appear to acquire layer-specific properties at the time of neuronal birth; however, the molecular mechanisms of cell-fate acquisition are still unclear, because it has been difficult to identify a cohort of birthdate-related progenitor cells. Using replication-defective adenoviral vectors, we successfully performed "pulse gene transfer" into progenitor cells in a neuronal birthdate-specific manner. When adenoviral vectors were injected into the midbrain ventricle of mouse embryos between embryonic day 10.5 (E10.5) and E14.5, the adenoviral vectors introduced a foreign gene into a specific cohort of birthdate-related progenitor cells. The virally infected cohorts developed normally into cortical neurons and formed the canonical cortical layers in an inside-out manner. This technique allows us to distinguish a cohort of birthdate-related progenitor cells from other progenitor cells with different birthdates and to introduce a foreign gene into specific subsets of cortical layers by performing adenoviral injection at specific times. This adenovirus-meditated gene transfer technique will enable us to examine the properties of each subset of progenitor cells that share the same neuronal birthdate.