Membrane growth factors which are processed to produce soluble ligands may function both as soluble factors and as membrane factors. Important questions concerning membrane growth factors include the role of soluble and membrane forms in vivo and the elucidation of mechanisms governing their production.
The Kit and PDGFRa receptor tyrosine kinases are encoded in close proximity at the murine white spotting (W) and patch (Ph) loci. While W mutations affect hematopoiesis, melanogenesis, and gametogenesis, the Ph mutation affects melanogenesis and causes early lethality in homozygotes.
The receptor tyrosine kinase Kit plays critical roles in hematopoiesis, gametogenesis, and melanogenesis. In mast cells, Kit receptor activation mediates several cellular responses, including cell proliferation and suppression of apoptosis induced by growth factor deprivation and gamma-irradiation.