hPSC-derived corticogenesis generates pyramidal neurons that integrate into brain networks in vivo

Background and novelty The cerebral cortex is the most complex structure of our brain. During evolution, the relative size of the cortex has increased considerably among higher mammals and new cortical areas involved in higher evolved functions have emerged. The study of human cortical development has major implications for brain evolution and cortical related diseases, but has remained elusive due to paucity of experimental models.
Here, we describe an intrinsic pathway of corticogenesis from human embryonic (ESC) and induced pluripotent (iPSC) stem cells leading to the sequential generation of first forebrain progenitors and later pyramidal neurons of all six layers identities in a time-dependent fashion, highly reminiscent of the in vivo situation.
Experimental approach
We describe an in vitro model for the directed differentiation of human pluripotent stem cells in a monolayer fashion and devoided of morphogens, but supplemented with noggin, and inhibitor of the BMP pathway, that has been shown to be required for neuroectoderm specification. Specified progenitors and neurons are later transplanted into mouse newborn brain and analysed after several months in vivo by immunofluorescence analysis and by patch-clamp recordings.
Results and discussion
Following the in vitro differentiation, human pluripotent stem cells efficiently differentiated into forebrain and telencephalic progenitors based on the expression of various genes tested by immunofluorescence, quantitative PCR and microarray analysis. At later stages, these cells exited cell cycle and became cortical pyramidal neurons, as attested by their pyramidal morphology, but also by the expression of various markers of cortical neurons and cortical layer specific genes. The cortical neurons present markers of connectivity and a mature electrophisiological profile at later stages. Moreover, following grafting into the mouse newborn cortex, the human ESC- derived neurons extended axons to endogenous cortical targets, present numerous synapses and functionally integrated into the host.