EXPRESSION OF THE EPILEPSY AND CANDIDATE DYSLEXIA SUSCEPTIBILITY GENE <EM>TANC2</EM> IN THE FETAL FOREBRAIN AND HUMAN GLUTAMATERGIC NEURONS

TANC2, a scaffolding protein, is involved in dense core granule cytoskeletal transport, regulation of dendritic spine development, and dendritic morphogenesis. Mutations in TANC2 have been implicated in epilepsy, language delay, and dyslexia. We explored TANC2 expression in the early human forebrain to better understand how mutations in this gene might contribute to neurodevelopmental conditions. Analysis of human tissue (hdbr.org/expression) and single-cell RNAseq (scRNAseq) data (nemoanalytics.org) revealed that TANC2 mRNA levels ranked within the top 50% of protein-coding genes in the fetal cerebral cortex and increased between 7.5-17 post-conceptual weeks. Cortical and thalamic scRNAseq analyses indicated enrichment in more mature cells, especially in glutamatergic neurons. Immunohistochemistry on human fetal forebrain sections from the Human Developmental Biology Resource (hdbr.org) supported the scRNAseq findings, showing colocalisation with the neuronal marker β3-tubulin in the cortical plate. Expression was limited to cell bodies and was not seen in GAP43-positive growing axons. A TANC2 heterozygous knockdown line was generated using CRISPR-Cas-9 in IBJ4 iPSCs and differentiated into glutamatergic neurons. TANC2 knockdown glutamatergic neurons displayed an increased number of neurites per cell compared to controls. Calcium imaging, using Calbryte dye, revealed a significant (p<0.0001) doubling in frequency of spontaneous calcium events, alongside apparent reduced network synchrony. We are currently pharmacologically blocking gap junctions at glutamatergic synapses to investigate how TANC2 knockdown affects network activity. In conclusion, these findings indicate that TANC2 is highly expressed throughout the human fetal forebrain, and that its loss leads to substantial alterations in neuronal morphology and network functionality.