Rb and LEK1: a "pas de deux" in cardiogenesis.

Cardiogenesis results from activation of a complex transcriptional network. The transcription factors work in a combinatorial manner to transactivate expression of constitutive genes. Embryonic stem (ES) cells are capable to recapitulate the early stages of cardiac cell differentiation. So far only the Bone Morphogenetic Protein (BMP)-dependent pathway switching on expression of Nkx2.5, one of the earliest cardiac transcription factor, has been described as the canonical cardiogenic pathway. Recently, using Rb-/- and LEK1-downregulated ES cells, we described a novel BMP-independent cardiogenic pathway implicating both Rb and LEK1, a mammalian homolog of the chicken cardiomyogenic factor 1(CMF1). Here, I discuss the role of Rb pathways in cell differentiation and the potential mechanisms underlying the effect of Rb/LEK1 interaction on cardiac specification of stem cells.