Stem Cell Factor (SCF) which binds to the c-Kit receptor is produced by fibroblasts and endothelial cells. The soluble and transmembrane forms of the protein are formed by alternative splicing of the same RNA transcript and the presence of both soluble and transmembrane SCF is required for normal hematopoietic function. SCF plays an important role in hematopoiesis, spermatogenesis, and melanogenesis. In addition, it also promotes mast cell adhesion, migration, proliferation, and survival 3. Rat SCF shares 75 % 90 % a.a. sequence identity with canine, feline, mouse, and human SCF. Furthermore, rat SCF is active on mouse and human cells, but human SCF is only weakly active on mouse cells.