title: Minute amounts of hamartin wildtype rescue the emergence of tuber-like lesions in conditional Tsc1 ablated mice.
abstract: Tuberous sclerosis (TSC) is a phacomatosis associated with highly differentiated malformations including tubers in the brain. Those are composed of large dysplastic neurons and 'giant cells'. Cortical tubers are frequent causes of chronic seizures and resemble neuropathologically focal cortical dysplasias (FCD) type IIb. Patients with FCDIIb, however, lack additional stigmata of TSC. Mutations and allelic variants of the TSC1 gene have been observed in patients with tubers as well as FCDIIb. Those include hamartin(R692X) and hamartin(R786X), stop mutants frequent in TSC patients and hamartin(H732Y) frequent in FCDIIb. Expression of these variants in cell culture led to aberrant distribution of corresponding proteins. We here scrutinized morphological and structural effects of these TSC1 variants by intraventricular in utero electroporation (IUE), genetically mimicking the discrete focal character and a somatic postzygotic mosaicism of the lesion, focusing on the gene dosage required for tuber-like lesions to emerge in Tsc1(flox/flox) mice. Expression of only hamartin(R692X) as well as hamartin(R786X) led to a 2-fold enlargement of neurons with high pS6 immunoreactivity, stressing their in vivo pathogenic potential. Co-electroporation of the different aberrant alleles and varying amounts of wildtype TSC1 surprisingly revealed already minimal amounts of functional hamartin to be sufficient for phenotype rescue. This result strongly calls for further studies to unravel new mechanisms for substantial silencing of the second allele in cortical tubers, as proposed by Knudson's '2-hit hypothesis'. The rescuing effects may provide a promising basis for gene therapies aiming at reconstituting hamartin expression in tubers.
authors.affiliation: Section for Translational Epilepsy Research, Dept. of Neuropathology, Germany.
authors.forename: Barbara K
authors.initials: BK
authors.lastname: Robens
authors.affiliation: Neurosurgery, Bonn Univ. Clinic, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Grote
authors.affiliation: Section for Translational Epilepsy Research, Dept. of Neuropathology, Germany.
authors.forename: Julika
authors.initials: J
authors.lastname: Pitsch
authors.affiliation: Section for Translational Epilepsy Research, Dept. of Neuropathology, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Schoch
authors.affiliation: INSERM, Institut de Neurobiologie de la Méditerranée, Marseille, France; Aix-Marseille University, UMR 901 Marseille, France.
authors.forename: Carlos
authors.initials: C
authors.lastname: Cardoso
authors.affiliation: Section for Translational Epilepsy Research, Dept. of Neuropathology, Germany. Electronic address: albert_becker@uni-bonn.de.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Becker
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D001932:Brain Neoplasms / Q000235:genetics / Q000473:pathology; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics*; D009474:Neurons / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics; D012640:Seizures / Q000235:genetics / Q000473:pathology; D014402:Tuberous Sclerosis / Q000235:genetics*; D000077004:Tuberous Sclerosis Complex 1 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D012097:Repressor Proteins; C000624651:Tsc1 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D025521:Tumor Suppressor Proteins
keywords: Cortical tuber; Focal cortical dysplasia; In utero electroporation; Mammalian target of rapamycin; TSC1; Tuberous sclerosis