Retinoic Acid Delivery within Embryoid Bodies Induces an Early Streak Phenotype in vitro

During embryogenesis, cell specification and tissue formation is directed by the concentration and temporal presentation of morphogens, and similarly, pluripotent embryonic stem cells differentiate in vitro into various phenotypes in response to morphogen treatment. Embryonic stem cells are commonly differentiated as three dimensional spheroids called embryoid bodies (EBs); however, differentiation within EBs is typically heterogeneous and disordered. Here we show that spatiotemporal control of microenvironmental cues embedded directly within EBs enhances the homogeneity, synchrony and organization of differentiation. Degradable polymer microspheres releasing retinoic acid within EBs induce the formation of cystic spheroids closely resembling the early streak mouse embryo, with an exterior of visceral endoderm enveloping an epiblast layer. These results demonstrate that controlled morphogen presentation to stem cells more efficiently directs cell differentiation and tissue formation, thereby improving developmental biology models and enabling the development of regenerative medicine therapies and cell diagnostics. ESCs (D3 line) were maintained in an undifferentiated state on gelatin-coated tissue culture plates in LIF-containing media as described previously. EBs were formed from 2x106 ESCs inoculated in LIF-free media and cultured under rotary conditions. EBs containing microspheres were produced by coating CellTracker Red (CONTROLs) or RA-loaded (EXPERIMENTs) microspheres in 0.1% gelatin solution for 3 hours prior to mixing with ESCs in various microsphere to cell ratios and a range of rotary speeds. EB media was exchanged every 1-2 days as needed. Triplicate control and experiment EBs were processed for microarray.