Molecular cloning and characterization of mouse TIE and TEK receptor tyrosine kinase genes and their expression in hematopoietic stem cells.

To identify receptor tyrosine kinases (RTKs) critical to early hematopoiesis, we performed polymerase chain reaction-based cloning from yolk sac and highly enriched bone marrow hematopoietic stem cells (HSCs). Characterization of two novel genes of their full-length cDNA sequences revealed that they were mouse homologues of the endothelial cell RTK genes, TIE and TEK. They shared a unique structural property of coexistent immunoglobulin-like domain, epidermal growth factor-like repeats, and fibronectin type III repeats in their extracellular domains. Both genes were expressed in a similar fashion in adult tissues and primitive hematopoietic cells, predominantly in the bone marrow HSCs.