Abstracts

Periventricular nodular heterotopia (PVNH) is a congenital malformation of human cerebral cortex frequently associated with mutations in the Filamin-A (FLN-A) gene but the pathogenetic mechanisms remain unclear. Both loss and gain of FLN-A function have been proposed to disrupt the migration initiation of cortical neurons. Here we show that MEKK4 (a MAP3K member of the mitogen-activated protein kinase pathway) is involved in Fln-A regulation and PVNH formation., We performed histological analyses on the brains of MEKK4-deficient mice. Additionally, we designed short interference RNA (siRNA) constructs targeting MEKK4, incorporated these constructs into the developing cerebral cortex by in utero electroporation and analyzed the fates of transfected cells. Immunocytochemistry, in situ hybridization, electron microscopy, GST-pulldown and western blot analyses were also performed, MEKK4-/- mice develop bilateral PVNH in the cerebral cortex that arise from breaches in ventricular surface lining. Using neuronal markers, we show that cells within PVNH have differentiated and failed to migrate into the cortical plate. In utero electoporation of MEKK4 siRNA at E14.5 and analysis at P0 revealed dramatic disruption of migration-initiation of cortical neurons compared to control. Analysis of Fln-A expression in MEKK4-/- forebrain revealed elevated and ectopic Fln-A, while MEKK4 RNAi increased Fln-A phosphorylation in vitro. Finally, recombinant-MKK4/SEK1 protein precipitated a complex containing MEKK4 and Fln-A suggesting that MKK4/SEK1 bridges these molecules during development., Disrupted migration initiation in MEKK4-deficient cells may be related to both defects of the ventricular surface lining and dysregulated Fln-A. Our data demonstrate an essential role for MEKK4 in the migration of developing cortical neurons and provide insight into the pathogenesis of human PVNH., (Supported by the Epilepsy Foundation of America postdoctoral fellowship (to M.R.S), an under-represented minority fellowship (to C.M.B) on U.S. Public Health Service grants (to P.R.), a Child Health Research Grant from the Charles H. Hood Foundation, Inc. (Boston) (to H.C.). R.A.F. is an Investigator of the Howard Hughes Medical Institute.)