Temporal patterning of apical progenitors and their daughter neurons in the developing neocortex

During cortical development, distinct subtypes of glutamatergic neurons are sequentially born and differentiate from dynamic populations of progenitors. How progenitors and their daughter cells are temporally patterned remains unknown. Here, we trace the transcriptional trajectories of successive generations of apical progenitors (APs) and isochronic cohorts of their daughter neurons in the developing mouse neocortex using high temporal resolution parallel single-cell RNA sequencing. We identify and functionally characterize a core set of evolutionarily-conserved temporally patterned genes which drive APs from internally-driven states to more exteroceptive states, revealing a progressively increasing role for extracellular signals as corticogenesis unfolds. These embryonic age-dependent AP molecular states are reflected in their neuronal progeny as successive ground states, onto which essentially conserved early post-mitotic differentiation programs are applied. Thus, temporally unfolding molecular birthmarks present in progenitors act in their post-mitotic progeny as seeds for adult neuronal diversity. Overall design: Investigation of the transcriptional dynamics in time-locked cohorts of cortical cells across embryonic neurogenesis. Flashtag is injected at 4 ages (E12, E13, E14, E15), and cells collected 1H, 24H, 96H after birth (= a total of 12 conditions) and analyzed by single cell transcriptomics.