Abstracts

Focal cortical dysplasias (FCD) are characterized by a localized malformation of the neocortex and the underlying white matter. Balloon cells, similar to those observed in tuberous sclerosis (TSC) are present in a significant number of cases (FCDIIb). Histopathological similarities indicate that FCDIIb may be pathogenetically related to the tuberous sclerosis complex (TSC), caused by mutations in either TSC1 or TSC2, that normally constitute a tumor suppressor mechanism. Accumulation of coding allelic variants affecting exons 5 and 17 of TSC1 as well as loss of heterozygosity of the second TSC1 allele have been observed in many FCDIIb patients (Becker et al., Ann Neurol 2002). Here, we have studied the potential functional relevance of coding allelic variants of TSC1 found in FCDIIb with respect to the interaction of the TSC1/TSC2 complex., Sequence variants of the TSC1 allele found in FCDIIb patients were introduced in the full-length TSC1 cDNA (kindly provided by Dr. M. Nellist, Amsterdam) by site-directed mutagenesis. We have further generated TSC1 cDNA variants with mutations found in TSC patients, i.e. by introducing premature stop codons. Protein interaction assays were performed to analyze a potentially compromised interaction between the TSC1/2 proteins hamartin and tuberin., TSC1 sequence variants were successfully introduced by site-directed mutagenesis. Compromised interaction of the hamartin-tuberin complex was most pronounced in TSC1 mutants bearing the premature stop codon at position R692X (p[lt]0,01). Sequence alterations of TSC1 present in FCDIIb (H732Y) also resulted in significantly compromised TSC1/2-interaction compared to wild-type TSC1 (p[lt]0,05). The latter was comparable to findings obtained by the expression of the TSC-determining allele variant R786X., Our data suggest, that allelic variants with amino acid exchange of the TSC1 gene in FCDIIb may be associated with compromised TSC1/TSC2 interaction. The functional relevance is currently studied in cell culture and animal systems., (Supported by DFG (SFB TR3, Emmy-Noether-Program), BONFOR, the BMBF German Israeli program and the Deutsche Krebshilfe.)