CHARACTERIZATION OF KABUKI SYNDROME TYPE 1 IPSCS, NEURONAL PROGENITORS AND HIPPOCAMPAL NEURONS

Kabuki syndrome type 1 (KS1) is a rare congenital disorder caused by mutations in the KMT2D gene, which encodes the histone H3 lysine 4 (H3K4) methyltransferase MLL4. MLL4 catalyzes H3K4 monomethylation (H3K4me1) and acts as a key epigenetic regulator. Recent studies have highlighted how MLL4 dysfunction leads to a compensatory reinforcement of Polycomb-associated condensates and cause in mesenchymal stem cell models of KS1 increased nuclear stiffness, altered nuclear mechanics, and impaired differentiation.
Despite KS being associated with intellectual disability, the impact of KMT2D mutations on human neurodevelopment remains poorly understood. Most evidence derives from animal models, showing impaired neurogenesis and functions in the dentate gyrus (DG) of the hippocampus.
Here, we investigated the molecular, cellular, and nuclear mechanical consequences of KMT2D mutation during hippocampal neuronal differentiation using human induced pluripotent stem cells (hiPSCs) derived from a KS1 patient and a parental control. Morphometric analysis revealed increased nuclear volume and surface area in KS hiPSCs, indicating altered nuclear properties. Neurosetta Rosette Array analysis showed abnormal neural rosette formation, with reduced rosette area and perimeter and increased rosette number.
Both KS and control hiPSCs were differentiated into DG neurons, as confirmed by immunofluorescence and RT-qPCR for lineage-specific markers. While early differentiation was largely preserved, KS cultures showed reduced maturation into glutamatergic neurons and a decreased number of DG neurons at later stages. Altered nuclear morphology persisted throughout differentiation.
These results suggest that KMT2D mutations affect nuclear architecture in addition to epigenetic regulation, potentially contributing to hippocampal neurodevelopmental defects in KS1.