OSTEOBLASTIC CELLS REGULATE MI GENE-EXPRESSION IN CULTURED BONE-MARROW CELLS

The microphthalmia (mi) gene encodes a bHLH-Zip protein and certain mu tations in this gene are known to result in osteopetrosis. We examined mi gene expression in murine bone marrow (BM) cells and calvaria-deri ved osteoblastic (OB) cells. The mi message level in BM cells was thre e-to four-fold higher than that in OB cells. The mi message level in B M cells alone was not enhanced by 1,25(OH)(2) vitamin D-3 (vitamin D) which induces TRAP-positive multinucleated cells, but was enhanced two -fold by the addition of conditioned medium obtained from cultures of OB cells. The mi message levels in BM cells were also enhanced by macr ophage colony-stimulating factor (M-CSF). The mi message levels in coc ultures of BM cells and osteoblastic MC3T3-E1 cells, which do not supp ort osteoclastogenesis, were similar to those in the cocultures of BM cells and OB cells. Cocultures of BM cells with MC3T3-E1 cells did not yield TRAP-positive multinucleated cells, but they did maintain osteo clast progenitor cells. These findings suggest that mi is expressed in BM cells that may be under the control of OB cells. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.