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 α-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 β-cells, but this activity is not sufficient to produce a fully differentiated mature Pdx1^high, Nkx6.1⁺, MafA⁺, Glut2⁺ β-cell. We propose that Nkx2.2-activator function will be required for this later differentiation step.