Figure 2. Strategies to develop universal ‘ground state’ defined culture that can support many different human pluripotent stem cell lines under an identical formula.

Optimization of a combinatorial small molecule library and surface cues using a human PSC line will lead to a set of necessary cues to maintain undifferentiated status of that specific line. Repeating the same process on a number of representative cell lines (e.g., 20 human PSC lines from various sources) will lead to the same number of cell line-specific customized culture systems and a systematic knowledge base on necessary signaling cues of various lines. Such a knowledge base could be used to develop a robust defined culture system by summing up small molecules and surface cues required by various human PSC lines, providing a wide range of signaling, that is, strategy X. On the other hand, detailed investigations of individually customized culture could lead to elucidation of molecular mechanisms governing the universal ‘ground state’ of human PSC lines. Such a discovery will then lead to identification of novel small molecules and surface cues that, when combined together, can be used to develop a robust defined culture with minimal number of components, that is, strategy Y.

PSC: Pluripotent stem cell.