ISOLATION OF A RECEPTOR TYROSINE KINASE (DTK) FROM EMBRYONIC STEM-CELLS - STRUCTURE, GENETIC-MAPPING AND ANALYSIS OF EXPRESSION

Analysis of receptor tyrosine kinases expressed during mouse embryonic stem cell differentiation resulted in the cloning of a receptor designated developmental tyrosine kinase (DTK). The 850 amino acid mature receptor protein comprises an extracellular domain with two immunoglobulin-like motifs and two fibronectin type III modules, a 25 amino acid transmembrane domain and a cytoplasmic region with a catalytic kinase domain. In embryonic stem cells growing in the presence of leukemia inhibitory factor DTK is abundantly expressed, and this level of expression is maintained in differentiating embryonic stem cells and cystic embryoid bodies. In mid-gestational embryos (E14.5), DTK RNA is expressed in many tissues including brain, eye, thymus, lung, heart, gut, liver, testis and limbs. In contrast, expression of DTK in adult mice becomes restricted to brain, portions of the gastrointestinal tract, bladder, testis and ovary. There is enrichment of transcripts encoding DTK in purified fetal liver hematopoietic stem cells, when compared with unfractionated fetal liver. The DTK gene maps to mouse chromosome 2, band F.