UCLA

Pluripotent Stem Cells (PSCs) have the unique ability to divide indefinitely and self-renew in vitro, as well as differentiate into all cell types of the body. These cells present intriguing opportunities to study development and biology in novel ways, and can be utilized to produce large amounts of cells with therapeutic applications. In order to safely use PSCs to model difficult to study diseases, or to replace injured or diseased tissues in patients, we need to ensure that the in vitro differentiation process is effective. However, the field has encountered great difficulty in making fully differentiated, mature cells in vitro from PSCs. While it is currently possible to differentiate PSCs into many types of central nervous system (CNS) cells, we and others have shown that CNS cells derived from PSCs are immature and are most epigenetically and functionally similar to cells from the CNS at a mid-gestational time point. Since the developing nervous system is tightly temporally regulated in terms of division, differentiation, organization, and connection, this roadblock currently poses a challenge to the utility of PSC-derived CNS cells.

We have identified a molecular circuit consisting of LIN28 proteins and the let-7 microRNAs that regulates differentiation and maturation in the CNS and other organ systems. In this dissertation I present data to demonstrate that manipulation of the LIN28/let-7 circuit can induce functional maturation in CNS progenitors by acting through structural epigenetic protein HMGA2 and the Notch signaling pathway. Furthermore, by exploring the regulation of the let-7 miRNAs at the level of transcription, I propose that dynamic temporal regulation of some let-7 family members is an important driver of change in the LIN28/let-7 circuit. Finally, I describe efforts to generate PSC-derived inhibitory interneurons and to characterize their aging and maturation in vitro and in vivo, with the aim of understanding the mechanisms of post-mitotic neuronal functional maturation. These studies will pave the way for the generation of appropriately mature PSC-derived CNS cells, and may be broadly applicable toward generating mature cells from PSCs for the purposes of biological study or therapeutic utility.