Gene-Edited Fluorescent and Mixed Cerebral Organoids

Cerebral organoids are a promising model to study human brain function and disease, although the high inter-organoid variability is still challenging. To overcome this limitation, we introduce the method of labeled mixed organoids generated from two different human induced pluripotent stem cell (hiPSC) lines, which enables the identification of cells from different origin within a single organoid. The method combining gene editing and organoid differentiation offers a unique tool to study gene function in a complex human three-dimensional model. Using a CRISPR-Cas9 gene-editing approach, different fluorescent proteins were fused to β-actin or lamin B1 in hiPSCs, and mixtures of differently edited cells were seeded to induce cerebral organoid differentiation. Consequently, the development of the organoids was detectable by live confocal fluorescence microscopy of whole organoids and immunofluorescence staining in fixed samples. We demonstrate that a direct comparison of the individual cells is possible by having the edited and the control (or the two differentially labeled) cells within the same organoid, thus overcoming the inter-organoid inhomogeneity limitations. Furthermore, the approach enables mosaic analysis of mutant clones in a wild-type three-dimensional cellular environment. It paves the way for the reliable analysis of human genetic disorders using organoids and the gain of fundamental understanding of the molecular mechanisms underlying pathological conditions.