Competence of in vitro cultured mouse embryonic stem cells for myogenic differentiation and fusion with myoblasts.

Pluripotent stem cells are a potential source of various cell types for use in regenerative medicine. Despite accumulating knowledge, there is currently no efficient and reproducible protocol that does not require genetic manipulation for generation of myogenic cells from pluripotent stem cells. Here, we examined whether mouse embryonic stem (ES) cells are able to undergo myogenic differentiation and fusion in response to signals released by differentiating myoblasts. Using ES cells expressing the histone 2B-green fluorescent fusion protein, we were able to detect hybrid myotubes formed by ES cells and differentiating myoblasts. ES cells that fused with myoblasts downregulated the expression of pluripotency markers and induced the expression of myogenic markers, while unfused ES cells did not exhibit this expression pattern. Thus, the signals released by myoblasts were not sufficient to induce myogenic differentiation of ES cells. Although ES cells synthesize many proteins involved in myoblast adhesion and fusion, we did not observe any myotubes formed exclusively by ES cells. We found that ES cells lacked M-cadherin and vascular cell adhesion molecule-1, which may account for the low frequency of hybrid myotube formation in ES cell-myoblast co-cultures and the inability of ES cells alone to form myotubes.