Clinical Science (2005) 108, 195–204 (Printed in Great Britain) 195 R E V I E W Winged-helix transcription factors and pancreatic development Kristen A. LANTZ * † and Klaus H. KAESTNER * † ∗ Department of Genetics, University of Pennsylvania Medical School, 560 Clinical Research Building, 415 Curie Blvd, Philadelphia, PA 19104, U.S.A., and †Penn Diabetes Center, University of Pennsylvania Medical School, 501 Stemmler Hall, 36th and Hamilton Walk, Philadelphia, PA 19104, U.S.A. A B S T R A C T The forkhead gene family, named after the founding gene member in Drosophila, is characterized by a unique DNA-binding domain. This so-called forkhead box encodes a winged-helix DNA-binding motif, the name of which describes the structure of the domain when bound to DNA. The three Fox (forkhead box) group A genes, Foxa1, Foxa2 and Foxa3, are expressed in embryonic endoderm, the germ layer that gives rise to the digestive system, and contribute to the specification of the pancreas and the regulation of glucose homoeostasis. Deletion of the Foxa2 gene in pancreatic β -cells in mice results in a phenotype resembling PHHI (persistent hyperinsulinaemic hypogly- caemia of infancy). Molecular analyses have demonstrated that Foxa2 is an important regulator of the genes encoding Sur1, Kir6.2 and Schad (short chain L-3-hydroxyacyl-CoA dehydrogenase), mutation of which causes PHHI in humans. Foxa1 was shown to be an essential activator of glucagon gene expression in vivo. An additional winged-helix protein, Foxo1, contributes to pancreatic β -cell function by regulating the Pdx1 gene, which is required for pancreatic develop- ment in cooperation with Foxa2. HISTORY OF THE FORKHEAD GENE FAMILY The Drosophila forkhead (fkh) gene was identified in a screen for embryonic-lethal mutations nearly 20 years ago, and was later cloned by chromosome walking [1,2]. Expression analysis in Drosophila revealed not only a strict nuclear localization of the fkh protein, but also sug- gested a function for the gene in embryonic gut devel- opment. In the absence of forkhead, head involution is blocked and the terminal domains that normally give rise to the anterior and posterior regions of the gut under- go homoeotic transformations, resulting in the spiked head structures (or ‘forks’) that gave rise to the gene name [1,2]. More detailed phenotype analyses of fkh mutant flies revealed important additional roles for the gene in the developing midgut and salivary glands [1,2]. At the time of discovery, the predicted protein displayed no previously characterized motifs or structural charac- teristics. Without significant amino acid similarity to any known proteins, forkhead became the founding member of a novel class of nuclear regulatory proteins. In unrelated studies of regulation of gene expression in the mammalian liver, a new protein, HNF-3A (hepa- tocyte nuclear factor 3A), was identified based on its ability to bind specific DNA sequences in the promoters of the transthyretin and α1-antitrypsin genes [3,4]. Muta- tion of these HNF-3 sites resulted in decreased expres- sion of promoter/reporter constructs of both of these important liver genes [3]. Shortly after these discoveries, sequence comparisons revealed a striking similarity Key words: DNA binding, forkhead, glucose homoeostasis, hepatocyte nuclear factor (HNF), pancreatic development, winged-helix transcription factor. Abbreviations: E6.5 etc., embryonic day 6.5 etc; EB, embryoid body; Fox, forkhead box; HNF-3, hepatocyte nuclear factor 3; MODY, maturity-onset diabetes of the young; P1 etc., postnatal day 1 etc.; Pdx1, pancreatic–duodenal homoeobox 1; PHHI, persistent hyperinsulinaemic hypoglycaemia of infancy; Schad, short chain l-3-hydroxyacyl-CoA dehydrogenase. Correspondence: Dr Klaus H. Kaestner, Department of Genetics, University of Pennsylvania Medical School, 560 Clinical Research Building, 415 Curie Blvd, Philadelphia, PA 19104, U.S.A. (email kaestner@mail.med.upenn.edu). C  2005 The Biochemical Society