Objective

The development of metazoan organisms involves extensive cellular proliferation during embryogenesis, followed by gradual cellular differentiation over time. The acquisition of terminally differentiated cell states is typically associated with proliferation arrest, prompting a global inverse correlation between embryonic proliferation and cellular differentiation. Embryonal tumors, a type of pediatric brain tumor, are characterized by overall poorly differentiated histological features and a large embryonic/stem cell-like compartment within the tumor. Molecular studies indicate that the initiation events driving tumorigenesis occur during embryonic development. Given the inverse relationship between embryonic cellular proliferation and differentiation, as well considering the distinct molecular signature of pediatric brain tumors, we hypothesized that perturbations in developmental trajectories within the neural embryonic compartment can result in a loss of differentiation capacity and sustained proliferative potential of neural progenitor cells. The abnormal persistence of cells in an embryonic-like proliferative state could thus be a potent driver of tumorigenesis.

Methods

To investigate our hypothesis we induced the expression of the reprogramming factor POU5F1/OCT4 in cerebral organoid models and human cultured neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs). We achieved this through PiggyBAC transposon-mediated overexpression and by reactivating the endogenous locus using CRISPR activator constructs. The cells were then implanted intracerebrally in mice to assess their tumorigenic capacities. The histological, transcriptomic, and methylomic features of the resulting tumors were analyzed.

Results

Inhibiting the normal differentiation capacities of neural stem cells both in 2D culture and in cerebral organoids resulted in the development of cells capable of potently forming tumors in vivo. These tumors retained a strong neural stem identity and displayed histological, transcriptional and epigenetic features specific to embryonal brain tumors.

Conclusion

Our findings indicate that the loss of differentiation potential within the neural embryonic compartment is a significant mechanism driving tumorigenesis. The models we have developed will facilitate the study of mechanisms that may be common to a wide range of pediatric tumors, both within the nervous system and in other anatomical locations.