Figure 1. The indirect co-culture model. A,

Morphology of undifferentiated ESC colonies cultured without feeder layer. B, Scheme of the indirect co-culture system: a facile cell expansion and stem cell differentiation system with continuous medium conditioning while preventing mixing of stem cells and co-culture cells by hanging culture inserts. Two cell populations are co-cultured in different compartments (insert and well) but can communicate via paracrine signaling through the pores of the membrane. C, The morphology of EKs. D, Reporter-based fluorescence-activated cell sorting (FACS) for purifying GFP⁺ cardiomyocytes isolated from neonatal αMHC-GFP transgenic mice. E, The morphology of the purified cardiomyocytes. Scale bars = 100 µm.