UCSF

Human pluripotent stem cells have opened up unprecedented opportunities to model human development and disease. Critical to these models is differentiation of stem cells toward relevant cell identities. Axial elongation of the neural tube is crucial during mammalian embryogenesis for anterior-posterior body axis formation and spinal cord development, but these processes cannot be interrogated directly in humans as they occur early post-implantation. However, this developmental period of regionalization significantly influences downstream cell fate. Here, I explore how models of axial patterning influence neural development and how these developmental models can influence engineered neural systems. First, I report an organoid model of neural tube extension derived from human pluripotent stem cell aggregates which recapitulate aspects of the morphological and temporal gene expression patterns of neural tube development. Next, I investigate the effect of early progenitor regionalization on mature V2a interneurons which reside in the hindbrain and spinal cord. Using a multiomic approach, I identify lasting epigenetic and transcriptional differences as a result of early developmental regionalization. The epigenetic differences suggest that uniquely open regions of chromatin are accessed by different transcription factor families, while the differences in transcription point to differences in axonal extension and synapse formation. I also observe differences in spontaneous activity produced from regionally distinct neuron populations. Computational modeling and knockdown validation studies identify CREB5 and TCF7L2 as mediators of some of the region-specific differences in gene expression. Finally, I show that attempting to ‘skip’ developmental patterning by induced transcription factor expression yields a population unlike either developmentally relevant V2a population, highlighting the importance of following developmental steps in establishing cell identities in vitro. This observation leads me to explore ways to achieve cell type specificity by contrasting directed and induced differentiation strategies and proposing ways they can complement one another to better recapitulate target cell type identity.