HUMAN CORTICOSPINAL CONNECTOIDS TO MODEL DEVELOPMENT AND DISEASES

Voluntary movement relies on the corticospinal tract, a tightly regulated pathway that carries commands from the cerebral cortex to spinal cord neurons through long-range axons. Developmental, degenerative, and traumatic insults can disrupt this circuit and compromise motor functions. To study this system, we developed an innovative 3D human in vitro model of the corticospinal tract. Firstly, we generated brain and spinal cord organoids from healthy human iPSCs. Brain organoids progressively shifted from neural progenitor to neuronal marker expression and were enriched in neurons with distinct cortical identities. Spinal cord organoids were patterned toward a motor neuron fate and showed high expression of mature motor neuronal markers. To model corticospinal connectivity, we used a microfluidic device with two chambers connected by a central channel provided by Prof. Yoshiho Ikeuchi (Institute of Industrial Science, University of Tokyo) and produced as described in Osaki et al. (DOI: 10.3791/61544 ). Then, we placed brain and spinal cord organoids in opposing compartments allowing axons to project toward each other. This approach resulted in corticospinal connectoids with a robust axonal bundle spanning between the two organoids. Imaging analysis of the bundle revealed strong neurofilament and HOMER1B/C expression, supporting axonal identity and synapse formation. We expect this platform to be applicable to amyotrophic lateral sclerosis and spinal cord injury, allowing us to evaluate the emergence of pathological phenotypes. Overall, this system provides a versatile platform to investigate human corticospinal development and disease, supporting target discovery and the evaluation of therapeutic strategies.