A new family of heparin binding growth/differentiation factors: differential expression of the midkine (MK) and HB-GAM genes during mouse development.

MK (midkine) and HB-GAM (heparin-binding growth-associated molecule) constitute a new family of heparin-binding growth differentiation factors. The modes of expression of MK and HB-GAM during mouse development were quantitatively examined by mRNA hybridization. The following three distinct patterns of expression were observed in the brain/head region. On the 11th-13th days of gestation, MK was intensely, but HB-GAM relatively weakly expressed; on the 15th-19th days, both MK and HB-GAM expression became weaker; and in the neonatal period, HB-GAM was intensely expressed and MK expression increased slightly. The level of HB-GAM expression was lower than that of MK in the whole embryo on the 11th to 13th days of gestation. HB-GAM mRNA was detected in the kidney of newborn and young mice, where MK was more highly expressed. The identity of the weakly expressed MK and HB-GAM signals was confirmed by means of the polymerase chain reaction in the neonatal brain (MK), the head of 13-day embryos (HB-GAM), and the kidney of 7-day-old mice (HB-GAM). In conclusion, MK and HB-GAM are frequently co-expressed in the same cells and anatomic regions of the fetus or new born mouse, while their modes of expression differ.