Flt-3 Ligand

Flt3 Ligand, also known as FL, is an α-helical cytokine that promotes the differentiation of multiple hematopoietic cell lineages. Mature mouse Flt3 Ligand consists of a 161 amino acid (aa) extracellular domain (ECD) with a cytokinelike domain and a juxtamembrane tether region, a 21 aa transmembrane segment, and a 22 aa cytoplasmic tail. Within the ECD, mouse Flt3 Ligand shares 71% and 81% aa sequence identity with human and rat Flt3 Ligand, respectively. Mouse and human Flt3 Ligand show cross-species activity. Flt3 Ligand is expressed as a non-covalently-linked dimer by T cells and bone marrow and thymic fibroblasts. Each 36 kDa chain carries approximately 12 kDa of N- and O-linked carbohydrates. Alternate splicing and proteolytic cleavage of the transmembrane form can generate a soluble 30 kDa fragment that includes the cytokine domain. Alternate splicing of mouse Flt3 Ligand also generates a membrane-associated isoform with a 57 aa substitution following the cytokine domain. Both transmembrane and soluble Flt3 Ligand signal through the tyrosine kinase receptor Flt3/ Flk2.