<p>Liposarcoma (LPS) arises from adipocytes and is a rare malignancy among all cancer types, but represents the most common form of soft tissue sarcoma, with approximately 2,000 new cases reported annually. Clinically, liposarcomas are classified into four subtypes based on histological analysis: well-differentiated liposarcoma (WDLPS), dedifferentiated liposarcoma (DDLPS), myxoid/round cell liposarcoma, and pleomorphic liposarcoma. Although histological analysis provides useful information for identifying various liposarcoma subtypes, treatment options rely on a fundamental understanding of driver mutations and molecular mechanisms underlying tumorigenesis. This thesis focuses on elucidating important driver mutations and therapeutic targets to eradicate DDLPS. Notch signaling is an evolutionarily conserved signaling pathway essential for organ development and stem cell function. Aberrant Notch signaling underlies the tumorigenesis of many cancers including LPS. However, the specific role of Notch signaling in development of LPS remains elusive. In Chapter 2, I provide evidence demonstrating that Notch signaling plays a key role in cancer stem cells (CSCs), also referred to as tumor-initiating cells (TICs), that drive aggressive DDLPS. I used serial transplantation to enrich and generate a murine DDLPS cell line with constitutively activated Notch signaling (NICDOE). My analyses revealed that NICDOE DDLPS cells are heterogeneous and contain TICs that express cancer stem cell markers. Chapter 3 elucidates how Notch signaling regulates CSCs of LPS. I analyzed human LPS samples to establish a strong correlation between Notch signaling activation and tumor marker expression and prognosis. I further performed gene expression and metabolic analyses of NICDOE DDLPS cells. These assays revealed that NICDOE reduced mitochondrial respiration in DDLPS cells, which was associated with diminished expression of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), a master regulator of mitochondrial biogenesis. CRISPR/CAS9-mediated deletion of the NICDOE cassette rescued the expression of PGC-1α and mitochondrial respiration in DDLPS cells. Similarly, overexpression of PGC-1α was sufficient to rescue mitochondrial biogenesis in DDLPS cells. Together, these data demonstrate that Notch signaling regulates CSCs, at least partially by controlling PGC-1α mediated mitochondria biogenesis.</p>