This thesis elucidates the role of excitatory/inhibitory (E/I) balance in neurodevelopmental disorders (NDDs), with a specific focus on identifying mechanisms dependent on the sialyltransferase ST3GAL3. By integrating theoretical frameworks with human-induced pluripotent stem cell (iPSC) modeling and CRISPR/Cas9 genome editing, the research investigates E/I dysregulation in a human-specific context. The work first establishes a conceptual framework by positioning E/I imbalance as a transdiagnostic pathophysiological mechanism underlying the shared and distinct features of NDDs, such as autism spectrum disorder (ASD), ADHD, and epilepsy. Recognizing the limitations of existing models, the thesis evaluates iPSC technology as a platform to recapitulate human neurodevelopment. It compares directed and induced differentiation strategies and highlights the power of integrating these models with high-throughput tools like multi-electrode array (MEA) recordings and single-cell transcriptomics. The experimental core of the thesis involves the generation and validation of an isogenic ST3GAL3 null mutant iPSC line using CRISPR/Cas9. ST3GAL3 was selected due to its clinical associations with intellectual disability and ADHD. Functional analysis of ST3GAL3-deficient cortical neurons via MEA technology revealed a significant E/I imbalance, characterized by increased network excitability and aberrant burst patterns. Complementary transcriptomic analyses identified the downregulation of key genes involved in both glutamatergic and GABAergic synaptic signaling, suggesting that ST3GAL3 is essential for maintaining homeostatic synaptic activity and plasticity. Collectively, these findings offer novel mechanistic insights into how molecular disruptions in ST3GAL3 culminate in systems-level alterations. By transitioning from theory to empirical human-based experimentation, this research identifies ST3GAL3 as a pivotal regulator of synaptic function and a potential therapeutic target for NDDs.
David Diouf (Thu,) studied this question.