Differentiation of human embryonic stem cells into Corticofugal projection neurons
Understanding how neuronal diversity is achieved within the cerebral cortex remains a major challenge in neuroscience. The surge of human embryonic stem cells (hESCs) as a novel model system provides a unique opportunity to study human corticogenesis in vitro and€ identify the mechanisms that promote neuronal differentiation to achieve neuronal diversity in the human brain. Here, we demonstrate the derivation of corticofugal neurons from a genetically engineered Fezf2-YFP hESC reporter line, and uncover two distinct Fezf2 subpopulations that are reminiscent of the 2 Fezf2-expressing neuronal subtypes in the developing mouse brain. Fezf2 is a transcription factor that is both necessary and sufficient for the specification of subcerebral projection neurons in mouse. Its role in human corticogenesis is still unknown. However, the high conservation of FEZF2 protein between mouse and human suggest that Fezf2 is a specific marker of human cerebral neurons as well. Two hypotheses drove our research: 1) Extrinsic factors that modulate in vivo developmental signaling pathways play a critical role in the differentiation of hESCs to a corticofugal fate in vitro; 2) Human embryonic stem cell-derived neurons can survive in vivo and extend axonal projections to specific targets in the rodent brain. Our research shows that hESCs-derived corticofugal neurons are an effective model system to investigate the molecular pathways that regulate human cortical differentiation, axon extension and survival, an endeavor that was until now proscribed due to the manipulation of human embryos.