CD34 is a heavily glycosylated, transmembrane glycoprotein that is expressed on the surface of lymphohematopoietic stem and progenitor cells, small-vessel endothelial cells, embryonic fibroblasts and some cells in fetal and adult nervous tissue. CD34 associates with CrkL but not CrkII, is a substrate for PKC, and activation of PKC is coupled with surface expression of CD34. Since different patterns of glycosylation of the molecule are seen with different cell types, this might explain the wide range of CD34 molecular mass.
