We have cloned a partial cDNA encoding murine stem cell factor (SCF) and show that the gene is syntenic with the SI locus on mouse chromosome 10. Using retroviral vectors to immortalize fetal liver stromal cell lines from mice harboring lethal mutations at the SI locus (S//S/), we have shown that SCF genomic sequences are deleted in these lines. Furthermore, two other mutations at 3, Sfd and S1i2H, are associated with deletions or alterations of SCF genomic sequences. In vivo administration of SCF can reverse the macrocytic anemia and locally repair the mast cell deficiency of SIISP mice. We have also provided biological and physical evidence that SCF is a ligand for the c-kit receptor.

Mice harboring mutations at the dominant white spotting (W)(Russell, 1949) or steel (S/)(Sarvella and Russell, 1958) loci express similar pleiotropic abnormalities. Affected homozygous or compound heterozygous (eg, W/WV or S//Se mice are black eyed with white coats and exhibit severe deficiencies in hematopoiesis and fertility (reviewed in Russell, 1979). The development of neural crest-derived melanocytes is defective in mice with mutant W or SI genes, and this results in a lack of pigmentation in the coat hairs and skin (Mayer and Green, 1988; Sil-