The Role of TSC Genes During Brain Development

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DESCRIPTION (PROVIDED BY APPLICANT): The goals of this proposal are to 1) define mechanisms used by the TSC genes to control the generation of neurons and then glia from neural progenitor cells and 2) determine how defects in these processes result in cortical malformations in Tuberous Sclerosis Complex (TSC). TSC is caused by mutation of either the TSC1 or TSC2 genes and is the most common genetic cause of epilepsy and autism. These features are very likely due to cortical brain malformations (tubers) that are found in almost all patients. Previous work has demonstrated severe laminar disruptions within tubers with abnormal glia, dysmorphic neurons, and "giant" cells expressing neuronal as well as glia markers. These findings suggest that the TSC genes play a critical role during the generation of specific neuronal populations as well as the switch from neuronal to glia production by neural progenitor cells. Mechanisms that normally control this process are not well understood but appear linked to cell cycle exit and the length of G1. Proliferation, total cell cycle length, and G1 duration are mediated by cyclins, cyclin-dependent kinases (cdk), and cdk inhibitors such as p27kip1 (p27). Notably, while Tsc1 or Tsc2-deficient fibroblasts have decreased levels and activity of p27, similar alterations in Tsc1 or Tsc2-deficient neural progenitor cells have not been reported. Our Specific Aims are: 1) Determine the role of the Tsd gene on the timing of neuronal and glia production from neural progenitor cells, 2) determine G1 duration and proliferation in 7sc1-deficient neural progenitor cells, and 3) determine p27 expression, subcellular localization, and function in 7sc7-deficient neural progenitor cells. We will achieve these aims by studying 7sc1-deficient neural progenitor cells both in vivo and in vitro. The ability of these neural progenitor cells to differentiate will be determined using lineage specific markers. In addition, we will use S phase tracers to measure cell cycle length, G1 duration, and the proportion of cells that are actively proliferating in mice with Tsc1-deficient neural progenitor cells. Finally, p27 expression, subcellular localization, and function will be determined. The candidate will utilize this K08 Award to gain expertise in developmental neurobiology though interactions with his mentor, the Neuroscience research community at Vanderbilt University, and active involvement with national and international leaders in Developmental Neurobiology. Overall, this award should position him to become an independent physician-scientist who will successfully compete for future extramural NIH funding. Relevance: Tuberous Sclerosis Complex (TSC) is a genetic disease whose manifestations include seizure disorders, brain tumors, autism and developmental delay. This proposal seeks to understand the role of abnormal neural progenitor cells to TSC. These findings will likely have broad therapeutic implications for individuals with TSC as well as non-TSC patients with seizure disorders and autism.