Mouse insulin-like growth factor binding protein-6: expression, purification, characterization and histochemical localization.

The mitogenic and metabolic activities of insulin-like growth factors (IGF) are modulated by a family of six high affinity IGF binding proteins (IGFBPs). This study describes the expression of the mouse IGFBP-6 which is unique among IGFBPs in its preferential binding of IGF II, in insect cells using the baculovirus system. The purified, O-glycosylated IGFBP-6 was functional as shown by IGF binding and by inhibition of IGF II-stimulated DNA synthesis in human fibroblasts. Specific antibodies generated in chicken against the recombinant IGFBP-6 were used for Western blotting analysis and immunohistochemistry. Strong immunoreactivity was found in ossifying bones of the cranial base, in cell clusters of the pancreas anlage, in the trigeminal ganglion, on myoblasts, on motoneurons of the spinal cord of embryonic mice. In tissues of adult mouse, strong IGFBP-6 immunostaining was present in epidermal and peridermal layers of the skin, in meningeal layers, in long-striated skeletal muscle, and in the Langerhans' islets of the pancreas. No immunopositive staining was observed in lung and liver indicating that sites of synthesis and IGFBP action are different.