Abstracts

Rationale: A novel gene, EFHC1, mutated in juvenile myoclonic epilepsy (JME) encodes a protein with three DM10 domains of unknown function and one putative EF-hand motif. We previously showed that EFHC1 associates with the centrosome and the mitotic spindle. This strongly suggests a role of EFHC1 in either cell division and/or brain development. Methods: Classical cell biology technologies (cell culture and transfection, immunofluorescence con focal microscopy, immunoprecipitation, westernblotting etc) combined with both in vivo and ex-vivo electroporation were used. Results: We demonstrate that EFHC1 is a microtubule-associated-protein (MAP) that interacts directly with tubulin through a new microtubule-binding domain (MTBD) located at the N-terminus of EFHC1. Overexpression of this MTBD alone acts as a dominant-negative by displacing the endogenous EFHC1 from its binding sites to microtubules. Either depletion of endogenous EFHC1 by RNAi or ectopic expression of the dominant-negative in vitro induces aberrant mitotic spindles, disruption of M phase progression, MT bundling and apoptosis. Furthermore, EFHC1 loss of function in vivo interferes with proper neuronal migration in the embryonic brain. Conclusions: These results indicate that EFHC1 is involved in cell division and in cerebral cortex development. We hypothesise that the mutations of EFHC1 could induce subtle neuronal migration defects that could lead to abnormal epileptogenic circuitry during cortical maturation occurring at the adolescence.