Stem Cells and Midkine

Midkine (MK) is expressed in embryonic stem (ES) cells and neural precursor cells including neural stem cells, and promotes their growth and survival. Because of the strong expression of MK in neural precursor cells, the role of MK in these cells has been clarified by analyzing cells derived from MK-deficient embryos. On the other hand, exogenously added MK promotes the self-renewal of ES cells cultured either on a feeder layer of embryonic fibroblasts without leukemia inhibitory factor (LIF) or on gelatin-coated dishes together with LIF. Pleiotrophin (PTN), which forms a family with MK, enhances the growth of hematopoietic stem cells, and promotes the dopaminergic differentiation of ES cells, in both cases in the presence of other growth factors. The use of MK or PTN either alone or in combination with other growth factors is a choice to be examined to enhance the growth, survival, and differentiation of various kinds of stem cells.