Expression of a gene encoding a unique protein-tyrosine kinase within specific fetal- and adult-derived hematopoietic lineages

A gene encoding a unique protein-tyrosine kinase was isolated by PCR from undifferentiated embryonic stem (ES) cells. The gene, Emsk (embryonic stem cell kinase), is expressed in a number of different lymphoid and myeloid hematopoietic lineages and has been shown to be identical to the recently isolated focal adhesion-associated kinase gene (Fadk). Within the nonlymphoid lineages analyzed, Emsk/Fadk was found to be expressed in primitive and definitive erythroid cells but not in mast cells or macrophages. All CD5⁺ (B-1a) B cells tested, as well as freshly isolated conventional (B-2) B cells, expressed readily detectable levels of Emsk/Fadk. Within the T-cell lineage, Emsk/Fadk was expressed in V_γ5 γ/δ cells as well as in immature α/β cells found within the thymus. As the α/β T-cell population matures and exits the thymus, expression of Emsk/Fadk appears to be down regulated. The expression pattern outlined here suggests a role for Emsk/Fadk in multiple stages of hematopoietic development and raises the possibility that the kinase encoded by this gene has a broader spectrum of activities than was initially suggested.