Dynamic Heterogeneity of Brachyury in Mouse Epiblast Stem Cells Mediates Distinct Response to Extrinsic Bone Morphogenetic Protein (BMP) Signaling.

Mouse pluripotent cells, such as embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs), provide excellent in vitro systems to study imperative pre- and postimplantation events of in vivo mammalian development. It is known that mouse ESCs are dynamic heterogeneous populations. However, it remains largely unclear whether and how EpiSCs possess heterogeneity and plasticity similar to that of ESCs. Here, we show that EpiSCs are discriminated by the expression of a specific marker T (Brachyury) into two populations. The T-positive (T(+)) and the T-negative (T(-)) populations can be interconverted within the same culture condition. In addition, the two populations display distinct responses to bone morphogenetic protein (BMP) signaling and different developmental potentials. The T(-) EpiSCs are preferentially differentiated into ectoderm lineages, whereas T(+) EpiSCs have a biased potential for mesendoderm fates. Mechanistic studies reveal that T(+) EpiSCs have an earlier and faster response to BMP4 stimulation than T(-) EpiSCs. Id1 mediates the commitment of T(-) EpiSCs to epidermal lineage during BMP4 treatment. On the other hand, Snail modulates the conversion of T(+) EpiSCs to mesendoderm fates with the presence of BMP4. Furthermore, T expression is essential for epithelial-mesenchymal transition during EpiSCs differentiation. Our findings suggest that the dynamic heterogeneity of the T(+)/T(-) subpopulation primes EpiSCs toward particular cell lineages, providing important insights into the dynamic development of the early mouse embryo.