The E3 ubiquitin ligase APC/C-Cdh1 coordinates neurogenesis and cortical size during development

The morphology of the adult brain is the result of a delicate balance between the symmetric divisions to maintain the progenitor cell pool, and the asymmetric divisions to generate a newly differentiated neuron. Neurogenesis is a complex process that relies on an as yet unknown molecular switch that tightly coordinates the cell cycle exit with the start of the differentiation process. The cell cycle length is a key factor that determines the balance between the maintenance of progenitor cells and neuronal differentiation. In fact, neurogenesis in the cerebral cortex is stimulated by lengthening the G1 phase and delayed by shortening it. The anaphase-promoting complex/cyclosome (APC/C) cofactor, Cdh1, regulates mitosis exit and G1-phase length in proliferating cells. Here we assessed whether APC/C-Cdh1 activity would be responsible for the switch from progenitor cells cycling to neurogenesis in the cerebral cortex. We use an embryo-restricted Cdh1 knockout mouse model and show that functional APC/C-Cdh1 ubiquitin ligase activity is required for both terminal differentiation of cortical neurons in vitro and neurogenesis in vivo. Further, genetic ablation of Cdh1 impairs the ability of APC/C to promote neurogenesis by delaying the exit of the progenitor cells from the cell cycle. This causes replicative stress and p53-mediated apoptotic death resulting in decreased number of cortical neurons and cortex size. These results demonstrate that APC/C-Cdh1 coordinates cortical neurogenesis and size, thus posing Cdh1 in the molecular pathogenesis of congenital neurodevelopmental disorders, such as microcephaly.