• apical progenitors
• corticogenesis
• developmental neuroscience
• differentiation
• fate plasticity
• migration
• neurogenesis
• radial glia
• temporal patterning

Apical progenitor cells residing in the ventricular zone generate all the diverse neuronal subtypes of the neocortex, in a tightly controlled temporal order, regulated by a complex interplay between intrinsic and extrinsic factors. At each cell cycle, apical progenitors are faced with the choice between the generation of other progenitors – apical or basal – and neurons. In time, self-renewed apical progenitors undergo a progression in competence states, determining the neuronal subtype to be generated, modulated by dynamically changing environmental cues. To date, these phenomena have only been investigated with suboptimal temporal or spatial resolution. Thus, it hasn’t been possible yet to fully address important questions about fate decisions and fate plasticity of apical progenitors. Here, a new technique, called FlashTag, was used to label isochronic cohorts of early and late apical progenitors, with unprecedented specificity in space and time. This allowed tracking their heterogeneous progeny, revealing differential patterns of fate decisions and migration kinetics. It also allowed probing the fate plasticity of late progenitors through heterochronic transplantation into early hosts, showing a surprising degree of responsiveness to the new environment.