Mitsiadis,T.A., Salmivirta,M., Muramatsu,T., Muramatsu,H., Rauvala,H., Lehtonen,E., Jalkanen,M., and, Thesleff,I.
Expression of the heparin-binding cytokines, midkine (MK) and HB-GAM (pleiotrophin) is associated with epithelial-mesenchymal interactions during fetal development and organogenesis.
Development 121(1):37-51 (1995).
Midkine (MK) and heparin binding-growth associated molecule (HB-GAM or pleiotrophin), constitute a new family of heparin- binding proteins implicated in the regulation of growth and differentiation (T. Muramatsu (1993) Int. J. Dev. Biol. 37, 183- 188). We used affinity- purified antibodies against MK and HB-GAM to analyze their distribution during mouse embryonic development. From 9 to 14.5 day post-coitum (dpc), both proteins were detected in central and peripheral nervous systems, facial processes, limb buds, sense organs, respiratory, digestive, urogenital, and skeletal systems. MK and HB-GAM were often localized on the surface of differentiating cells and in basement membranes of organs undergoing epithelial-mesenchymal interactions. The level of MK protein decreased considerably in the 16.5 dpc embryo, whereas HB-GAM staining persisted in many tissues. Our in situ hybridization results revealed a widespread expression of MK transcripts that was not always consistent with the distribution of MK protein in developing tissues. In many epithelio- mesenchymal organs MK and HB-GAM were codistributed with syndecan- 1, a cell surface proteoglycan. In limb buds and facial processes, MK, HB-GAM, and syndecan-1 were localized to the apical epithelium and the adjacent proliferating mesenchyme. Both MK and HB-GAM bound syndecan-1 in solid- phase assays in a heparan sulfate-dependent manner. The biological effects of MK and HB-GAM on limb and facial mesenchyme were studied in vitro by application of beads preloaded with the proteins. Neither MK nor HB-GAM stimulated mesenchymal cell proliferation or induced syndecan-1 expression. Taken together these results indicate that MK and HB-GAM may play regulatory roles in differentiation and morphogenesis of the vertebrate embryo, particularly in epithelio- mesenchymal organs, and suggest molecular interactions with syndecan-1.

Last edited 10.12.2004 by P.N.