Tie-1 and tie-2 define another class of putative receptor tyrosine kinase genes expressed in early embryonic vascular system.

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Abstract
We report the molecular cloning and characterization of two structurally related putative receptor tyrosine kinases, encoded by distinct genes (tie-1 and tie-2) on mouse chromosome 4. Both tie-1 and tie-2 encode receptor proteins possessing unique multiple extracellular domains: two immunoglobulin-like loop domains flanking three epidermal growth factor repeats followed by three fibronectin-type III repeats. Both genes are expressed in early embryonic vascular system and in maternal decidual vascular endothelial cells, where the vasculature undergoes an active angiogenesis. tie-2, but not tie-1, expression was also detected in extraembryonic mesoderm of the amnion. tie-1, but not tie-2, is expressed in an acute myelogenic cell line in vitro. tie-1 and tie-2 may form another class within the receptor tyrosine kinase gene family, and further characterization of these genes and identification of their putative ligands should define the nature of the signal-transduction cascades underlying early vascular system development, as well as their differential roles in mesodermal cells of the amniotic and myeloid lineages.