Pax genes, which encode a family of transcription factors, ave essentially
required for the formation of several tissues from all germ layers in the m
ammalian embryo. Specifically, in organogenesis, they ave involved in trigg
ering early events of cell differentiation. The differentiation of endoderm
-derived endocrine pancreas is mediated through Pax4 and Pax6. In the thyro
id gland, Pax8 is essential for the formation of thyroxine-producing follic
ular cells, also of endodermal origin. The analysis of loss-of-function mut
ants revealed a common function of Pax genes in organogenesis.