Rationale Primary Heart field progenitor generation observed in previous studies has resulted in heterogeneous and immature populations of cells that require sorting and are inadequate for developmental studies or human therapeutic applications.

Objective We are using human embryonic stem cells (hESCs) to model early mesoderm specification and its progressive commitment towards cardiac mesoderm. In particular, we are interested in the role of β-Catenin-dependent and -independent Wnt signalling on cardiogenic mesoderm differentiation and the expansion of primary heart field progenitors.

Methods and Results We report here that Wnt signalling plays stage-specific roles in mesoderm patterning and, more prevalently, in cardiac mesoderm specification. We discovered that multiphasic Wnt/β-Catenin-dependent signalling enhances the efficiency and homogeneity of the early cardiac mesoderm differentiation and expansion that is promoted by bone morphogenetic protein-4 and fibroblast growth factor-2 signalling. Key cardiac transcription factor genes NKX2.5 and TBX5 were expressed in greater than 90% of cells after 4 days of differentiation. Moreover, structural cardiac marker genes α-MYHv and MLCv were highly upregulated after only 6 days in completely chemically defined conditions.

Conclusions Stage-specific Wnt signalling enhances cardiogenic mesoderm generation in a chemically defined 2D hESC culture system. These findings establish a strong platform for studying primary heart field progenitor development, which could aid our understanding of key aspects of congenital and acquired heart disease.