The Foxa subfamily of winged helix/forkhead box (Fox) transcription factors has 
been the subject of genetic and biochemical study for over 15 years. During this 
time its three members, Foxa1, Foxa2 and Foxa3, have been found to play 
important roles in multiple stages of mammalian life, beginning with early 
development, continuing during organogenesis, and finally in metabolism and 
homeostasis in the adult. Foxa2 is required for the formation of the node and 
notochord, and in its absence severe defects in gastrulation, neural tube 
patterning, and gut morphogenesis result in embryonic lethality. Foxa1 and Foxa2 
cooperate to establish competence in foregut endoderm and are required for 
normal development of endoderm-derived organs such as the liver, pancreas, 
lungs, and prostate. In post-natal life, members of the Foxa family control 
glucose metabolism through the regulation of multiple target genes in the liver, 
pancreas, and adipose tissue. Insight into the unique molecular basis of Foxa 
function has been obtained from recent genetic and genomic data, which identify 
the Foxa proteins as 'pioneer factors' whose binding to promoters and enhancers 
enable chromatin access for other tissue-specific transcription factors.