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Brain organoids have been proposed as suitable human brain model candidates for a variety of applications. However, the lack of appropriate maturation limits the transferability of such functional tools. Here, we present a method to facilitate neuronal maturation by integrating astrocyte-secreted factors into hPSC-derived 2D and 3D neural culture systems. We demonstrate that protein- and nutrient-enriched astrocyte-conditioned medium (ACM) accelerates neuronal differentiation with enlarged neuronal layer and the overproduction of deep-layer cortical neurons. We captured the elevated changes in the functional activity of neuronal networks within ACM-treated organoids using comprehensive electrophysiological recordings. Furthermore, astrocyte-secreted cues can induce lipid droplet accumulation in neural cultures, offering protective effects in neural differentiation to withstand cellular stress. Together, these data indicate the potential of astrocyte secretions to promote neural maturation. Subject terms: Neurological models, Neuronal development

Human brain development relies on a finely tuned balance between the proliferation and differentiation of neural progenitor cells, followed by the migration, differentiation, and connectivity of post-mitotic neurons with region-specific identities. These processes are orchestrated by gradients of morphogens, such as FGF8. Disruption of this developmental balance can lead to brain malformations, which underlie a range of complex neurodevelopmental disorders, including epilepsy, autism, and intellectual disabilities. Studying the early stages of human brain development, whether under normal or pathological conditions, remains challenging due to ethical and technical limitations inherent to working with human fetal tissue. Recently, human brain organoids have emerged as a powerful in vitro alternative, allowing researchers to model key aspects of early brain development while circumventing many of these constraints. Unlike traditional 2D cultures, where neural progenitors and neurons are grown on flat surfaces, 3D organoids form floating self-organizing aggregates that better replicate the cellular diversity and tissue architecture of the developing brain. However, 3D organoid protocols often suffer from significant variability between batches and individual organoids. Furthermore, few existing protocols directly manipulate key morphogen signaling pathways or provide detailed analyses of the resulting effects on regional brain patterning. • To address these limitations, we developed a hybrid 2D/3D approach for the rapid and efficient induction of telencephalic organoids that recapitulate major steps of anterior brain development. Starting from human induced pluripotent stem cells (hiPSCs), our protocol begins with 2D neural induction using small-molecule inhibitors to achieve fast and homogenous production of neural progenitors (NPs). After dissociation, NPs are reaggregated in Matrigel droplets and cultured in spinning mini-bioreactors, where they self-organize into neural rosettes and neuroepithelial structures, surrounded by differentiating neurons. Activation of the FGF signaling pathway through the controlled addition of FGF8 to the culture medium will modulate regional identity within developing organoids, leading to the formation of distinct co-developing domains within a single organoid. Our protocol combines the speed and reproducibility of 2D induction with the structural and cellular complexity of 3D telencephalic organoids. The ability to manipulate signaling pathways provides an additional opportunity to further increase system complexity, enabling the simultaneous development of multiple distinct brain regions within a single organoid. This versatile system facilitates the study of key cellular and molecular mechanisms driving early human brain development across both telencephalic and non-telencephalic areas. Key features • This protocol builds on the method established by Chambers et al. [1] for generating 2D neural progenitors, followed by dissociation and reaggregation into 3D brain organoids. • For optimal growth and maturation, telencephalic organoids are cultured in spinning mini-bioreactors [2] or on orbital shakers. • The protocol enables the generation of telencephalic neural progenitors in 10 days and produces 3D telencephalic organoids containing neocortical neurons within one month of culture. • Addition of morphogens in the culture medium (example: FGF8) enhances cellular heterogeneity, promoting the emergence of distinct brain domains within a single organoid.

Neuropsychiatric disorders remain difficult to treat due to complex and poorly understood mechanisms. NeuroPainting is a high-content morphological profiling assay based on Cell Painting and optimized for human stem cell–derived neural cell types, including neurons, progenitors, and astrocytes. The assay quantifies over 4000 features of cell structure and organelle organization, generating a dataset suitable for phenotypic screening in neural models. Here, we show that, in studies of the 22q11.2 deletion—a strong genetic risk factor for schizophrenia—we observe cell-type-specific effects, particularly in astrocytes, including mitochondrial disruption, altered endoplasmic reticulum organization, and cytoskeletal changes. Transcriptomic analysis shows reduced expression of cell adhesion genes in deletion astrocytes, consistent with post-mortem brain data. Integration of RNA and morphology data suggests a link between adhesion gene dysregulation and mitochondrial abnormalities. These results illustrate how combining image-based profiling with gene expression analysis can reveal cellular mechanisms associated with genetic risk in neuropsychiatric disease. Here, authors use NeuroPainting, a high-content imaging assay, to reveal cell-type-specific effects of 22q11.2 deletion in neural cells, linking adhesion gene dysregulation to mitochondrial and structural abnormalities, especially in astrocytes.