Tuberous sclerosis complex (TSC) is an inherited disease with a wide range of features and severity. The signs and symptoms of TSC can include neurologic symptoms and benign tumors or hamartomas. The most frequent neurologic symptoms are seizures, mental retardation, and autism. The most common sites of hamartomas are the brain (cerebral cortical tubers and subependymal giant cell astrocytomas), the skin (facial angiofibromas), the lungs (lymphangiomyomatosis), the heart (rhabdomyomas), and the kidney (angiomyolipomas). Mutations in two genes, TCS1 and TCS2, cause TSC in humans. The protein products of these genes, hamartin and tuberin, bind to each other within the cell. In order to develop specific treatments for TSC, it is critical to understand the functions of hamartin and tuberin. Currently, there are no specific treatments for TSC.

Our goal is to use yeast to understand the functions of human hamartin and tuberin. S. pombe is a species of yeast that is often used for medical research. When genes are conservedbetween yeast and mammals, the most important and fundamental cellular functions of their protein products are also often conserved. The importance of S. pombe as a model system was underscored by the awarding of the 2001 Nobel Prize in Physiology to Paul Nurse. There are many advantages to using yeast model systems to study human disease. Yeast grow quickly and are easily manipulated genetically. Therefore, experiments that would take years in other model systems can be performed in weeks or months in yeast. Yeast provide an in vivo model of protein function (within the context of a living cell), which are an important complement to studies performed in cell culture systems. Finally, yeast are amenable to genetic screens. Genetic screens allow the rapid identification of genes that function in the same or related pathways to a gene of interest.

S. pombe contains genes that are highly similar to human TCS1 and TCS2, called gene homologs. In preliminary studies we have separately knocked out, or removed, these genes from S. pombe. The knockout yeast have defects that suggest that they are unable to correctly regulate their growth. In this project, we will determine the kinetics of this incorrect regulation of cell growth (Aim 1), determine how cell growth is affected by patient-derived mutations in the TCS2 gene (Aim 2), and perform a genetic screen to identify genes and proteins in the same pathway astuberin and hamartin (Aim 3). Our findings using yeast as a model system will be translated into mammalian cells, with the goal of elucidating the pathways through which tuberin and hamartin lead to human disease.