Isolation of tyrosine kinase related genes expressed in the early hematopoietic system

Transmembrane tyrosine kinase receptors are involved in cellular interactions which promote proliferation and differentiation of many cell types. To identify receptor tyrosine kinases important in embryonic hematopoietic cell development we have utilized the polymerase chain reaction (PCR) and degenerate oligonucleotides for isolation of such genes from mouse yolk sac and fetal liver. Sequence analysis of PCR amplified cDNAs from these hematopoietic sites of day 8 and 14 embryos, resulted in the isolation of nine tyrosine kinase and three serine/threonine kinase related clones. Two of these receptors, tek and flk-1, are expressed in both yolk sac and fetal liver and have been shown previously to be important for endothelial cell development. Two other clones, 9B4 and 9A2 appeared novel upon isolation but have been recently described as ryk and SK2 (rat homologue). Here we describe the twelve isolated kinases, the specific expression patterns of flk-1, tek and ryk kinases and their potential relationship to the development of the hematopoietic system.