UCLA

Induced pluripotent stem cells (iPSCs) are generated by overexpression of a combination of transcription factors. While this method to reprogram cells to the pluripotent state starts off using a defined number of factors, the complex cascade of events that it initiates during the inefficient process is far from being well defined. Therefore, many efforts are underway to characterize the molecular events involved in reprogramming to iPSCs. The work presented here aims to understand the mechanistic basis of reprogramming by examining biological processes that affect the maintenance of pluripotent cell populations. We find that the Wnt signaling pathway, which promotes the self-renewal of embryonic stem cells (ESCs), affects reprogramming efficiency in a stage-specific manner. We also find that while ESCs require the Polycomb repressive complexes (PRC1) and PRC2 to maintain the pluripotent state, components of the PRC1 and PRC2 are dispensable for reprogramming, revealing potential differences between how Polycomb group proteins may function in ESCs and during reprogramming. Finally, using a novel, single-cell secretion profiling platform, we discover that human ESC colonies are comprised of heterogeneous subpopulations that may serve to coordinate colony growth and self-renewal. Together, these findings reveal complexities of regulating the establishment and maintenance of pluripotency that should be considered in future reprogramming studies.