Microcolonies of human embryonic stem cells as models of early embryonic patterning

Human embryonic stem cells when confined within two dimensional micropatterns with diameters in the 0.5-1mm range and subject to uniform Wnt or BMP stimulation, will spontaneously form radially symmetric spatial patterns that recapitulate the proximal-distal axis of the mammalian embryo at the time of gastrulation. This assay, when combined with inducible cell lines that express the canonical morphogens or inhibitors, becomes a very powerful technique to understand how an epithelium with ~2000 cells can self organize. To eliminate the boundaries that are inherent in 2D culture we have extended the assay to cells in defined hydrogels. They form closed apical-basal polarized shells that form a localized primitive streak in response to suitable morphogens. Stem cell systems enable the development of quantitative dynamic models for secreted morphogens and their inhibitors. Its anticipated they will facilitate the engineering of stem cell derived tissues for regenerative medicine