Bmx Tyrosine Kinase Is Specifically Expressed in the Endocardium and the Endothelium of Large Arteries

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Abstract
Background The growth and differentiation of endothelial cells are regulated by signal transduction through tyrosine protein kinases. Recently, a novel cytoplasmic tyrosine kinase gene, Bmx (Bone Marrow tyrosine kinase gene in chromosome X), was identified in human bone marrow RNA and found to be expressed predominantly in myeloid hematopoietic cell lineages. Our preliminary analyses indicated that the Bmx gene was also highly expressed in human heart. Methods and Results Mouse Bmx cDNA was isolated, sequenced, and found to encode a polypeptide ≈91% identical to the human Bmx tyrosine kinase. Northern blotting and in situ hybridization of tissue sections indicated that Bmx mRNA is specifically expressed in the endocardium of the developing heart as well as in the endocardium of the left ventricle and in the endothelium of large arteries in adult mice. A weak signal was seen also in coronary arterial endothelium. Conclusions Bmx shows a unique specificity of expression among tyrosine kinase genes and may be involved in signal transduction in endocardial and arterial endothelial cells. The results suggest that specific signal transduction mechanisms are present in such endothelia.