Thrombopoietin and its alternatively spliced form are expressed in human amygdala and hippocampus.

Thrombopoietin (TPO) is a newly cloned and characterized cytokine that stimulates megakaryocytopoiesis and platelet production.'" Recent studies have shown that TPO speeds up platelet recovery after cytoreductive the rap^^,^ and, thus, holds great potential for the treatment of thrombocytopenia of various etiologies. Human mature TPO is composed of 353 amino acids. The N-terminal 153 amino acid sequence of TPO is highly conserved among the mouse, pig, and human and shares a significant homology with erythropoietin (EPO), a hematopoietic growth factor stimulating red blood cell production. In fact, the product derived from the N-terminal 153 amino acid sequence of TPO is fully functionaL2 However, further deletion of this 153 amino acid peptide at the C-terminus results in nonfunctional TPO derivatives.6 Recently, we have noticed that a 39 amino acid stretch within TPO's N-terminal half shares a significant homology with neurotrophins.'