Brain organoid assemblies, by integrating organoids from different brain regions (e.g., the cortex-hippocampus system), can simulate tau protein propagation in AD, the transregional propagation of tau from the hippocampus to the neocortex, and the regulatory role of APOE4 in microglia (Knopman et al., 2021; van der Kant et al., 2020; Koutsodendris et al., 2023). Here, MAPT is linked to Alzheimer disease.