Fig. 7. Schematic model of the TPO-induced signaling pathway in megakaryocytopoiesis. (A) The sites of inhibition in the MAPK and PI3K pathways are shown with particular emphasis on the proposed mechanism, through PI3K-AKT-mTOR-p70S6K-cyclin D3, mediating MK polyploidization (green). (B) The phospho-ERK (p-ERK) and phospho-AKT (p-AKT) expression are inversely correlated in promoting MK proliferation and endomitosis, respectively.