Structural characterization of the mouse Foxf1a gene

Members in the superfamily of the forkhead/winged-helix transcription factors are known to play a critical role in the control of cell differentiation and tissue development. To understand the regulation and function of these genes, we have initially isolated and characterized the mouse Foxf1a gene, a novel forkhead gene predominantly expressed in the lung. The mouse gene consists of two exons with the forkhead domain contained in exon 1, and is located at band E1 on chromosome 8. Amino acid sequence of the mouse protein shares a high degree of homology to that of the corresponding human protein. The tissue specificity of expression of the mouse gene also resembles that found in the human gene. This gene is primarily expressed in the lung, and to a lesser extent in placenta and tissues in gastrointestinal tract. The transcription start site was mapped to 113 nucleotides upstream from the putative translation initiation site. The promoter of the mouse gene is highly GC rich and contains neither a CAAT nor a TATA box. A series of luciferase report constructs driven by the promoter and various deletions in the 5' flanking region of the gene were constructed and employed in transient transfection studies using a line of SV40 transformed mouse lymph node endothelial cells (SVEC4-10), which express the endogenous Foxf1a gene, and a line of mouse hepatoma cells (Hepa 1-6), in which Foxf1a is not expressed. To our surprise, these reporter genes are equally active in both cell lines. Further studies have shown that the proximal 5' flanking sequence and exon 1 of the endogenous gene are highly methylated in Hepa 1-6 cells but not in SVEC4-10 cells, suggesting that DNA methylation but not cell-specific transcription factor(s) regulates cell specificity of gene expression in these cultured cells.