Apical progenitors remain multipotent throughout cortical neurogenesis

We used FlashTag, a method to pulse-label and isolate APs in the mouse neocortex with high temporal resolution, to fate-map neuronal progeny following heterochronic transplantation of APs into younger embryos. We find that unlike differentiated IPs, which lose the ability to generate deep layer neurons when transplanted into a younger host, APs are temporally uncommitted and become molecularly respecified to generate normally earlier-born neuron types. These results indicate that AP temporal identity progression occurs in the absence of detectable fate restriction and reveal that differentiation status, rather than embryonic age, is the core determinant of temporal plasticity in the mammalian neocortex. Overall design: Patch-seq RNA sequencing of apical progenitors transplanted into a younger host.