Divergent expression of midkine in the human fetal liver and kidney: immunohistochemical analysis of developmental changes in hilar primitive bile ducts and hepatocytes.

BACKGROUND/AIMS: Midkine (MK) is a novel heparin-binding growth factor whose gene has been identified in embryonal carcinoma cells in early stages of retinoic acid-induced differentiation. In this study, we investigated the developmental expression of MK protein in the human fetal liver and kidney.

METHODS

Twenty-one specimens each of the liver and kidney from fetuses (gestational weeks from 9 to 40) and neonates less than 4 weeks old were examined. Immunohistochemical and Western blot analyses were performed using a rat IgG2a monoclonal antibody against the carboxyl terminal region of human MK.

RESULTS

Immunohistochemical analysis revealed MK expression in the human fetal liver and kidney. The MK expression in the fetal liver showed a strong reaction from 9 to 16 gestational weeks. MK was expressed in the ductal plate, migrating biliary cells and newly formed bile ducts, and in hepatocytes of the hilar region in all specimens in the first and second trimesters. By contrast, the MK expression decreased gradually and was weak or not detected in the third trimester and neonatal period. However, MK expression in the kidney was found at 16 gestational weeks, as well as during both gestation and the neonatal period.

CONCLUSIONS

Divergent MK-expression was detected in the human fetal liver and kidney, and its expression may be related to fetal development, maturation, and functions of the liver and kidney.