Structural analysis of human and murine flt3 ligand genomic loci.

Both the murine and human genomic loci that encode flt3 ligand have been cloned. flt3 ligand is a hematopoietic growth factor that stimulates the proliferation of stem and progenitor cells. The portions of the murine and human flt3 ligand genomic loci encompassing the coding region of the protein are approximately 4.0 kb and 5.9 kb, respectively. The human genomic locus is larger as a result of the presence of repeated sequences within introns I, II, IV, V and VI. The transmembrane isoform of the murine and human flt3 ligand proteins are each encoded within seven exons (1-5 + 7 and 8). Analyses of flt3 ligand cDNA clones show that alternative splicing of a putative sixth exon results in the generation of a soluble form of the flt3 ligand protein. The sizes of each of the exons are well conserved between species. Murine and human flt3 genomic loci have a similar exon: intron structure compared to the genomic loci encoding Steel factor and colony stimulating factor 1. These proteins, which appear to be ancestrally related, are hematopoietic growth factors that stimulate cells via specific and structurally related tyrosine kinase receptors on the cell surface.