THE FPS FES TYROSINE KINASE IS EXPRESSED IN MYELOID, VASCULAR ENDOTHELIAL, EPITHELIAL, AND NEURONAL CELLS AND IS LOCALIZED IN THE TRANS-GOLGI NETWORK/

The fps/fes proto-oncogene encodes a cytoplasmic protein tyrosine kina se that is thought to participate in signaling pathways involving memb ers of the cytokine receptor superfamily, including those for erythrop oietin, granulocyte-macrophage colony-stimulating factor, leukemia inh ibitory factor, oncostatin M, ciliary neurotropic factor, and interleu kins 3, 4, 6, and 11. Expression of fps/fes has been detected in hemat opoietic cells, vascular endothelial cells, and cell types arising fro m all three germ layers during early development, Here, we describe fp s/fes expression in developing and adult tissues from normal mice or f rom transgenic animals overexpressing wild-type or activated mutant fp s/fes alleles, The highest levels of fps/fes expression were seen in a ngioblasts of early yolk sac blood islands, chondrocytes, vascular end othelial cells, neuronal cells, and several epithelial cell types, inc luding those of the choroid plexus and the uterus, Fps/Fes protein was concentrated in the perinuclear region of cultured neuronal, myeloid, epithelial, and vascular endothelial cells, and a chimeric Fps/Fes-gr een fluorescence protein colocalized with gamma-adaptin, a marker for the trans-Golgi apparatus, These observations suggest the involvement of Fps/Fes in vesicle transport processes in cells with prominent secr etory functions.