Fig. 8. Model for redundant functions of NKX6.1 and NKX6.2 in pancreatic endocrine cell differentiation. NKX6.1 represses NKX6.2 in PDX1⁺ pancreatic progenitors. Absence of NKX6.1 results in derepression of Nkx6.2, which partially compensates for loss of NKX6.1 function. Both NKX6.1 and NKX6.2 positively regulate expression of Myt1. As Myt1 is enriched in NGN3⁺ progenitors, while NKX6.2 is expressed only in PDX1⁺ progenitors, NKX6 factors may regulate Myt1 expression through a non-cell-autonomous mechanism. A factor (X) that mediates the signal between PDX1⁺ and NGN3⁺ progenitors remains to be identified. Myt1 in NGN3⁺ progenitors is required for their differentiation into - and ß-cells.