Human cells and tissue may be available post-mortem, however, these cannot be used to observe complex biological activities for mechanistic studies.14 Particularly for the study of brain, this limitation severely restrains the exploration of complex neuronal network activity, brain development and related neurodegenerative disorders. Studies have reported human-mouse chimeric models with human cells transplanted into mouse.15, 16 This transplantation system allows us to more closely evaluate donor cellular dynamics in vivo.17, 18 Similarly, neurons differentiated from human induced pluripotent stem cells (iPSC) are often co-cultured with mouse glial cells for metabolic and trophic support19, 20 as mouse glia enhance maturation of human induced neurons.21 Gene expression studies from either xenograft transplants or co-cultures include sequences from multiple species that need to be resolved.
