Figure 3. The cell cycle of cortical progenitors change during development.

Cortical progenitors undergo symmetric divisions during E10-12 and at this stage have a long S-phase of around 8 hours. The transition to neurogenic divisions results in a shortened S-phase and as progenitors undergo differentiation the G1 phase lengthens. Chromatin states involving high mobility group A proteins are also important for maintaining an open chromatin conformation in early cortical progenitors. Genome maintenance is paramount in early-born apical neural progenitors, and an increased S-phase length likely allows enhanced genome surveillance to ensure a pristine genome. Cortical layers form progressively from E12; VZ is the ventricular zone. DNA repair via homologous recombination (HR) and non-homologous end-joining (NHEJ) is important to ensure genome integrity during progenitor proliferation and differentiation. Figure adapted from reference 25.