MIDKINE (MK) EXPRESSION IN EXTRAEMBRYONIC TISSUES, AMNIOTIC-FLUID, AND CEREBROSPINAL-FLUID DURING MOUSE EMBRYOGENESIS

Midkine (MK) and pleiotrophin (PTN) constitute a new family of heparin -binding growth factors. Extraembryonic membranes and the placenta of the mouse expressed MK mRNA at 11.5 days gestation. While the MK mRNA level in extraembryonic membranes decreased during embryogenesis, that in the placenta remained unchanged, Immunohistochemical studies showe d that MK was located in the yolk sac and in the amnion at 11.5 days g estation, PTN mRNA expression was weak in extraembryonic membranes and was scarcely detectable in the placenta, Western blot analysis reveal ed the presence of MK in amniotic fluid and cerebrospinal fluid, in am ounts of more than 1 mu g/ml, raising the possibility that MK delivere d by these fluids participates in the regulation of organogenesis. Tra nsport of MK from the site of its synthesis appears to also occur in t he adult kidney, since MK mRNA and the MK protein are localized in dif ferent regions of the kidney.