Molecular and cellular causes of severe heterotopia: Identifying new genes playing a role in radial glial cell

ROMERO DM; BAHI-BUISSON, N; POIRIER, K; LE MOING, A.G; CHELLY, J; DELEUZE JF; FRANCIS F

Paris

Congreso; ISN-ESN Meeting 2017; 2017

ISN

Subcortical heterotopias are malformations of cortical development associated with epilepsy and intellectual disability, and characterized by the presence of ectopic neurons in the white matter. Mouse models of this disorder are rare, although mutations were iden­tified in the microtubule binding protein Eml1/EML1 in the spontaneous HeCo (heterotopic cortex) mouse, and in patients exhibiting giant ribbon-like hetero­topia. HeCo mice have misplaced radial glial cell (RG) progenitors and ectopic proliferation during cortical development, which are likely to initiate non-cell autonomous migration defects. To explore the bases of this disorder, a cohort of patients showing anEML1-like phenotype was selected for further investigation. These patients showed giant heterotopia with polymicrogyria, or periventricular heterotopia and partial agenesis of the corpus callosum. Patient DNA samples were analyzed by exome sequencing identifying novel mutant genes. Candidate genes andpathways are being studied, particularly DLGAP4, which belongs to amembrane-associated guanylate kinase family known to function in synapses. Studying the consequences of a de novo frameshift mutation using the I-Tasser method, a severe modification of DLGAP4s functions was predicted. Expression analyses confirmed its presence in the ventricular zone (VZ) from early corticogenesis in the mouse brain. The role of this gene in progenitors during neurodevelopment has not been previously studied. Using different approaches, potential partners of Dlgap4 were identified, including Eml1. To further test its role in RGs during cortical development in utero electroporation of different Dlgap4 constructs was performed in mouse embryos. Our results reveal a strong VZ phenotype and strongly suggest that Dlgap4 is involved in the maintenance of RG cell polarity. When Dlgap4 is mis-regulated, changes in the ventricular surface are observed, as well as a periventricular heterotopia-like phenotype. This work reveals unsuspected molecular mechanisms important for the function of cortical progenitors, which when perturbed pro­duce severeEML1-like heterotopia phenotypes in mouse and human.