Methods for identifying factors for differentiating definitive endoderm

A method of identifying a factor that promotes the differentiation of human definitive endoderm cells, said method comprising the steps of:

• obtaining a human cell population comprising human definitive endoderm cells, wherein said human definitive endoderm cells comprise at least 10% of the human cells in said cell population;
• providing a candidate differentiation factor to said cell population;
• determining expression of a marker of a cell differentiated from definitive endoderm in said cell population at a first time point;
• determining expression of the same marker in said cell population at a second time point, wherein said second time point is subsequent to said first time point and wherein said second time point is subsequent to providing said cell population with said candidate differentiation factor;
• and
• determining if expression of the marker in said cell population at said second time point is increased as compared to the expression of the marker in said definitive endoderm cell population at said first time point, wherein an increase in expression of said marker in said cell population indicates that said candidate differentiation factor promotes the differentiation of said human definitive endoderm cells.