Investigating Primary Cilium Defects in Joubert Syndrome via iPSC-Derived Neural Stem Cells

Background: Joubert Syndrome is a rare neurodevelopmental disorder classified within the group of ciliopathies, characterized by defects in the cerebellar vermis and malformations of the brainstem. To date, all mutations responsible for the disease lead to defects in the structure or function of the primary cilium. This organelle is involved in various cellular processes and plays a crucial role in several pathways essential for neurogenesis. However, the specific role of the primary cilium in the onset of Joubert Syndrome and how its dysfunction leads to cerebellar malformations remains poorly understood. Aim: To investigate the link between the primary cilium and Joubert Syndrome, we employ patient-specific iPSC-derived Neural Stem Cells as a model to gain insights into the primary cilium's characteristics and its impact on neural differentiation in the context of Joubert Syndrome. Results: "Biopsies were collected from two Joubert Syndrome patients, each harboring distinct mutations in the AHI1 gene. Primary fibroblast cultures revealed altered protein levels, and immunofluorescence analysis showed a reduction in ciliated cells alongside an increase in axoneme length. Both cell lines were reprogrammed into iPSCs and differentiated into NSCs, then cultured under starvation conditions to promote ciliogenesis. Despite this, most JS-derived NSCs failed to form primary cilia. Further differentiation into the three neural populations confirmed significant changes in the percentage of ciliated cells." Conclusion: The reduced ciliogenesis in Neural Stem Cells and neuronal/glial precursors may highlight a critical role of the primary cilium in early neurogenesis, impacting the timing of cell proliferation and differentiation in Joubert Syndrome patients.