Localization of pleiotrophin and midkine in the postnatal developing cerebellum.

We demonstrated that pleiotrophin (PTN) and midkine (MK), proteins which constitute a novel heparin-binding growth factor family, are expressed in the postnatal developing cerebellar cortex by an immunohistochemical method. The expression patterns of both factors were quite similar both temporally and spatially; the levels of protein expression reached a peak at P7, and strong immunoreactivities were localized primarily in the premigratory zone of the external granular layer, the molecular layer, and the white matter. These findings suggest that PTN and MK are co-localized and thereby exert synergistic functions in the developmental events such as the migration of granule cells and the process outgrowth of neurons.