Malformations of cortical development (MCD) are recognized as a significant cause of epilepsy, developmental delay, and mental retardation. Periventricular heterotopia (PH) is one such MCD characterized by 1) ectopic neuronal nodule formation along the lateral ventricles of the brain suggesting defects in neuronal migration 2) microcephaly, suggesting defects in neural proliferation 3) dyslexia, suggesting abberent cortical connectivity. The most common form of PH is X-linked and due to mutations in the Filamin A (encodes FLNA) gene. A rarer autosomal recessive form of PH with microcephaly has been attributed to mutations in the vesicle transport gene Arfgef2 (encodes BIG2). The overall goal of this proposal is to 1) understand the pathogenic mechanisms giving rise to the various developmental abnormalities seen in affected individuals with PH and 2) address any shared cellular and molecular pathways between the two known causative genes Filamin A and Arfgef2, in giving rise to this disorder.
Specific Aim I will test the hypothesis that FLNA regulates neuroepithelial cell proliferation, migration, and differentiation during cortical development. We will use a null FLNA mouse (Dilp2) to assess impairments in: 1.1) neuroepithelial cell proliferation (BrdU, PHS, Ki-67), thickness of cortical plate, intermediate and ventricular/subventricular zones (Dapi), 1.2) neural migration by BrdU birthdating, and neuroepithelial lining integrity by staining for apical (Palsl, aPKC, Par3/6) and basolateral (B-catenin, N-cadherin) proteins, 1.3) neural differentiation in situ by staining for axonal organization (neurofilament, golgi stain) and in vitro by examining neuritogenesis (F-actin), axonogenesis (MAP2), and dendritogenesis (Tau-1).
Specific Aim II will test the hypothesis that FLNA-BIG2 binding regulates BIG2 subcellular localization and BIG2-dependent Sec7 activity. FLNA is a scaffolding protein whose PKA-phosphorylation (S2152) regulates its distribution to the membrane. Our data shows that FLNA binds BIG2 and is responsible for PKA- dependent localization of BIG2 to membrane ruffles. BIG2 is an A-kinase anchoring protein (AKAP) whose Sec7 function is dependent on PKA. Our binding studies implicate FLNA in the regulation of BIG2-Sec7 activity by PKA.
Specific Aim II will address whether 2.1) FLNA regulates BIG2 distribution, 2.2) PKA phosp- horylation sites on BIG2 (S614 and S1678) regulate FLNA-BIG2 binding and consequent Sec7 function. Malformations of cortical development represent up to 40% of pediatric epilepsy cases. Many of the genes causal for these disorders have been identified, yet their functions are not yet clear. This study provides a framework with which to understand the role of PH-associated genes in cortical development.
