The cloning and expression of the cDNA for ovine stem cell factor (kit-ligand) and characterization of its in vitro haematopoietic activity.

The cDNA encoding the soluble form of ovine stem cell factor (SCF) has been cloned and expressed. The soluble protein is predicted to be 165/166 amino acids in length, one more than the human and murine SCFs with which it shares 87% and 81% identity respectively. Ovine SCF has 98.5%, 95% and 91% identity with cattle, pig and dog SCF, respectively. The recombinant ovine (rov) SCF protein has been expressed in Chinese hamster ovary (CHO) cells, purified, and its biological activity on ovine bone marrow cells compared with that of interleukin 3 (rovIL-3), granulocyte-macrophage colony-stimulating factor (rovGM-CSF), interleukin 5 (rovIL-5), human macrophage colony-stimulating factor (M-CSF) and human erythropoietin (epo). On its own rovSCF supported the development of small numbers of neutrophil, macrophage, eosinophil, granulocyte-macrophage, mixed cell phenotype, haemopoietic blast cell and basophilic granular cell colonies in a soft agar clonogenic assay. In combination with each of the above cytokines rovSCF supported an increase in the number and size of the lineage-specific colony types that were stimulated by the other cytokines on their own. In an assay for precursors of multipotential colony-forming cells (multi-CFC), rovSCF in combination with rovIL-3 (but neither cytokine alone) supported the development of these early haematopoietic progenitor cells.