Functional and ultrastructural studies on the burst of c-kit ligand containing secretory cytoplasmatic vesicles

A fibroblast-like cell line (D064) was established from canine marrow long-term cultures. These cells start to differentiate into hematopoietic progenitor precursors under the influence of c-kit ligand, functioning in an autocrine and paracrine fashion. The message for c-kit ligand is transcribed in the fibroblast-like cell line and the ligand for the tyrosine-kinase c-kit is expressed on the cell surface as well as secreted in its soluble form. With a monoclonal antibody directed against all isoforms of c-kit ligand, the expression of c-kit ligand was investigated functionally and topographically by electron microscopy. Ultrastructural analysis revealed c-kit ligand in electron dense vesicles which were transported to the cell surface and burst to release the soluble, non-membrane bound isoform of c-kit ligand. A membrane bound isoform of c-kit ligand was also present on the cell membrane.