Tuberous sclerosis complex (TSC) is an autosomal dominant, tumor predisposition disorder characterized by significant neurodevelopmental brain lesions, such as tubers and subependymal nodules. The neuropathology of TSC is often associated with seizures and intellectual disability. To learn about the developmental perturbations that lead to these brain lesions, we created a mouse model that selectively deletes the Tsc2 gene from radial glial progenitor cells in the developing cerebral cortex and hippocampus. These Tsc2 mutant mice were severely runted, developed post-natal megalencephaly and died between 3 and 4 weeks of age. Analysis of brain pathology demonstrated cortical and hippocampal lamination defects, hippocampal heterotopias, enlarged dysplastic neurons and glia, abnormal myelination and an astrocytosis. These histologic abnormalities were accompanied by activation of the mTORC1 pathway as assessed by increased phosphorylated S6 in brain lysates and tissue sections. Developmental analysis demonstrated that loss of Tsc2 increased the subventricular Tbr2-positive basal cell progenitor pool at the expense of early born Tbr1-positive post-mitotic neurons. These results establish the novel concept that loss of function of Tsc2 in radial glial progenitors is one initiating event in the development of TSC brain lesions as well as underscore the importance of Tsc2 in the regulation of neural progenitor pools. Given the similarities between the mouse and the human TSC lesions, this model will be useful in further understanding TSC brain pathophysiology, testing potential therapies and identifying other genetic pathways that are altered in TSC.

Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder with variable expressivity. Heterozygous mutations in either of two genes, TSC1 (hamartin) or TSC2 (tuberin), are responsible for most cases. Hamartin and tuberin form a heterodimer that functions as a major cellular inhibitor of the mammalian target of rapamycin complex 1 (mTORC1) kinase. Genotype-phenotype studies suggest that TSC2 mutations are associated with a more severe neurologic phenotype, although the biologic basis for the difference between TSC1- and TSC2-based disease is unclear. Here we performed a study to compare and contrast the brain phenotypes of Tsc1 and Tsc2 single and double mutants. Using Tsc1 and Tsc2 floxed alleles and a radial glial transgenic Cre driver (FVB-Tg(GFAP-cre)25Mes/J), we deleted Tsc1 and/or Tsc2 in radial glial progenitor cells. Single and double mutants had remarkably similar phenotypes: early postnatal mortality, brain overgrowth, laminar disruption, astrogliosis, a paucity of oligodendroglia, and myelination defects. Double Tsc1/Tsc2 mutants died earlier than single mutants, and single mutants showed differences in the location of heterotopias and the organization of the hippocampal stratum pyramidale. The differences were not due to differential mTORC1 activation or feedback inhibition on Akt. These data provide further genetic evidence for individual hamartin and tuberin functions that may explain some of the genotype-phenotype differences seen in the human disease.

Intercenter variation exists in the management of hypoxic-ischemic encephalopathy (HIE). It is unclear whether increased resource utilization translates into improved neurodevelopmental outcomes.