Temporal Proteomic and PTMomic Atlas of Cerebral Organoid Development

Cerebral organoids (CBOs) are generated from pluripotent stem cells that undergo neuroectoderm specification and neuronal differentiation in three dimensions. The developing neurons in CBOs migrate and self-organize into cerebral cortex-like layers, mimicking human brain development. CBOs develop according to intrinsic signaling mechanisms and offer unique insights into mechanisms of early human brain development. This process requires coordinated spatiotemporal regulation of protein expression and function, where the latter can be achieved by post-translational modifications (PTMs) on proteins. Despite the importance of proteins in brain development and function, profiling of protein abundance and the involvement of PTMs in CBO development remain underexplored. To gain insight into protein and PTM abundance in CBOs, we performed a high-resolution temporal analysis of CBOs up to day 200 using proteomics, PTMomics and metabolomics. We quantified more than 9,300 proteins and various neurodevelopmentally relevant PTMs (including phosphorylation, lysine acetylation, sialylated N-glycosylation, and cysteine modifications). We demonstrate that protein abundance and dynamic PTMs show significant temporal changes during CBO development related to neuronal differentiation and energy metabolism, whereas calcium signaling is mainly regulated by dynamic PTMs. We further show that synaptic protein content correlated with neurotransmitter levels, and we detected astroglia beyond day 100. Lastly, comparative analysis showed proteomic similarities between CBOs and human fetal brain tissue, supporting the physiological relevance of CBOs. Overall, our study presents a temporal atlas of protein and PTM abundance in CBOs and provides a valuable resource for studying neurodevelopment in neural organoids. ### Competing Interest Statement The authors have declared no competing interest.