Fig. 8. A model of Nkx2.2 activity in the developing pancreas. Nkx2.2 functions as a repressor to specify and differentiate the glucagon-producing -cell population. Nkx2.2 also functions as a repressor to specify the early insulin-positive population and/or the immature Pdx1^low, Nkx6.1⁺, MafA^-, Glut2^- insulin-producing ß-cells, but this activity is not sufficient to produce a fully differentiated mature Pdx1^high, Nkx6.1⁺, MafA⁺, Glut2⁺ ß-cell. We propose that Nkx2.2-activator function will be required for this later differentiation step.