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ABSTRACT: Heterozygous mutations in Myoclonin1/EFHC1 cause juvenile myoclonic epilepsy (JME), the most common form of genetic generalized epilepsies, while homozygous F229L mutation is associated with primary intractable epilepsy in infancy. Heterozygous mutations in adolescent JME patients produce subtle malformations of cortical and subcortical architecture, whereas homozygous F229L mutation in infancy induces severe brain pathology and death. However, the underlying pathological mechanisms for these observations remain unknown. We had previously demonstrated that EFHC1 is a microtubule-associated protein (MAP) involved in cell division and radial migration during cerebral corticogenesis. Here, we show that JME mutations, including F229L, do not alter the ability of EFHC1 to colocalize with the centrosome and the mitotic spindle, but act in a dominant-negative manner to impair mitotic spindle organization. We also found that mutants EFHC1 expression disrupted radial and tangential migration by affecting the morphology of radial glia and migrating neurons. These results show how Myoclonin1/EFHC1 mutations disrupt brain development and potentially produce structural brain abnormalities on which epileptogenesis is established.
Human Molecular Genetics 08/2012; · 7.64 Impact Factor
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ABSTRACT: EFHC1, a gene mutated in juvenile myoclonic epilepsy, encodes EFHC1, a protein with three DM10 domains and one EF-hand motif. We recently demonstrated that this molecule is a microtubule-associated protein (MAP) implicated in neuronal migration. Because some controversies persist about the precise localization in the CNS, we studied the neuroanatomical distribution of EFHC1 in mature and developing mouse brain. In the adult, low mRNA expression was detected in several brain structures such as cortex, striatum, hippocampus and cerebellum. At E16, EFHC1 mRNA was shown to be expressed in cortex and not only in cells lining ventricles. Using a purified polyclonal antibody, EFHC1 staining was observed in all cortical layers, in piriform cortex, in hippocampus and in Purkinje cells of cerebellum. In the cortex, the majority of EFHC1 positive cells correspond to neurons, however some glial cells were also stained. In agreement with a previous study, we demonstrated strong EFHC1 expression in cilia of ependymal cells lining cerebral ventricles. Moreover, at E16, the protein was observed at the borders of brain ventricles, in choroid plexus, but also, although to a lesser extent, in piriform and neocortex. In these latter structures, the pattern of expression seems to correspond to the extensions of the radial glia fibers as demonstrated by BLBP immunostaining. Finally, we confirmed that EFHC1 was also expressed and co-localized with the mitotic spindle of neural stem cells. These results confirm that EFHC1 is a protein with a likely low expression level in mouse brain but detectable both in adult and embryonic brain supporting our previous data and hypothesis that EFHC1 could play an important role during brain development. As discussed, this opens the door to a new conceptual approach viewing some idiopathic generalized epilepsies as developmental diseases instead of classical channelopathies.
Epilepsy research 12/2009; 88(2-3):196-207. · 2.48 Impact Factor
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ABSTRACT: Mutations in the EFHC1 gene are linked to juvenile myoclonic epilepsy (JME), one of the most frequent forms of idiopathic generalized epilepsies. JME is associated with subtle alterations of cortical and subcortical architecture, but the underlying pathological mechanism remains unknown. We found that EFHC1 is a microtubule-associated protein involved in the regulation of cell division. In vitro, EFHC1 loss of function disrupted mitotic spindle organization, impaired M phase progression, induced microtubule bundling and increased apoptosis. EFHC1 impairment in the rat developing neocortex by ex vivo and in utero electroporation caused a marked disruption of radial migration. We found that this effect was a result of cortical progenitors failing to exit the cell cycle and defects in the radial glia scaffold organization and in the locomotion of postmitotic neurons. Therefore, we propose that EFHC1 is a regulator of cell division and neuronal migration during cortical development and that disruption of its functions leads to JME.
Nature Neuroscience 10/2009; 12(10):1266-74. · 15.53 Impact Factor
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ABSTRACT: 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. To study the properties of EFHC1, we expressed EGFP-tagged protein in various cell lines. In interphase cells, the fusion protein was present in the cytoplasm and in the nucleus with specific accumulation at the centrosome. During mitosis EGFP-EFHC1 colocalized with the mitotic spindle, especially at spindle poles and with the midbody during cytokinesis. Using a specific antibody, we demonstrated the same distribution of the endogenous protein. Deletion analyses revealed that the N-terminal region of EFHC1 is crucial for the association with the mitotic spindle and the midbody. Our results suggest that EFHC1 could play an important role during cell division.
Experimental Cell Research 10/2006; 312(15):2872-9. · 3.58 Impact Factor
