In vivo modeling of human neuron dynamics and Down syndrome.

Harnessing the potential of human stem cells for modeling the physiology and diseases of cortical circuitry requires monitoring cellular dynamics in vivo. We show that human induced pluripotent stem cell (iPSC)-derived cortical neurons transplanted into the adult mouse cortex consistently organized into large (up to ~100 mm3) vascularized neuron-glia territories with complex cytoarchitecture. Longitudinal imaging of >4000 grafted developing human neurons revealed that neuronal arbors refined via branch-specific retraction; human synaptic networks substantially restructured over 4 months, with balanced rates of synapse formation and elimination; and oscillatory population activity mirrored the patterns of fetal neural networks. Lastly, we found increased synaptic stability and reduced oscillations in transplants from two individuals with Down syndrome, demonstrating the potential of in vivo imaging in human tissue grafts for patient-specific modeling of cortical development, physiology, and pathogenesis.This work was supported by the Medical Research Council (V.D.P.); the GABBA Ph.D. program (FCT fellowship PD/BD/52198/2013), the Rosetrees Trust, and ARUK (R.R.); the UK Dementia Research Institute (grant code DRIImp17/18 Q3 to S.J.B.); a Wellcome Senior Investigator award (F.J.L.); and the Alborada Trust of the ARUK Stem Cell Research Centre (M.P. and F.J.L.)