Investigating the Requirement for the Gene TSC2 in Early Human Neurodevelopment

Abstract

Tuberous sclerosis complex (TSC) is a multi-organ genetic disorder caused by mutations in either TSC1 or TSC2 which encode hamartin and tuberin, respectively. Hamartin and tuberin form a protein complex that indirectly, negatively regulates mammalian/mechanistic target of rapamycin complex 1 (mTORC1), a signaling hub that can regulate several cellular processes. When mTORC1 is hyperactive during development like in TSC, there can be severe consequences for patients such as benign brain tumors and debilitating neurological symptoms like epilepsy. It is thought that the epilepsy can be due to the presence of tubers located in the cerebral cortex which arise during development. Tubers are characterized by cortical mislamination, dysmorphic neurons, and giant cells that can co-express multiple, fate exclusive identity protein markers. These tuber characteristics indicate aberrant development of the cerebral cortex with changes in cell fate decisions that potentially are linked to abnormal epigenetic regulation. While TSC neurological phenotypes are well-documented, it is not yet known how early in neural development TSC1/2-mutant cells diverge from the typical developmental trajectory, whether such phenotypes are seen in the heterozygous-mutant populations comprising the majority of cells in patients, and if changes in neurodevelopment are accompanied by aberrant epigenetic regulation. To examine early neurodevelopmental phenotypes, TSC patient-derived induced pluripotent stem cells (iPSCs) harboring a disease-causing heterozygous microdeletion mutation in TSC2 were utilized. The following dissertation uses these TSC iPSC models derived into neural progenitor cells (NPC) to explore atypical neurodevelopment seen in TSC patients. Protein expression, RNA transcripts, and DNA methylation were studied in TSC2 mutant NPCs. Further, non-canonical roles for tuberin in mitotic division in iPSCs were explored.