EXPRESSION AND REGULATION OF LY-6 DIFFERENTIATION ANTIGENS BY MURINE OSTEOBLASTS

Osteoblasts arise from mesenchymal stem cells and differentiate to bec ome osteoid-secreting cells. However, little is known about these cell s during their stages of differentiation. One reason for this lack of information is that there is no reliable method to identify osteoblast s as they mature. One method that has been used successfully with othe r cell types is the identification of plasma membrane-expressed differ entiation antigens. The Ly-6 multigene family encodes differentiation antigens originally detected on lymphoid cells. Primary murine osteobl asts and the osteoblast-like MC3T3 cell line were examined for express ion of Ly-6 antigens by flow cytometry. Primary osteoblasts and MC3T3 cells constitutively expressed both Ly-GA and LSI-GC antigens, althoug h Ly-GC was much less abundant. Antigen expression was markedly increa sed by pretreating the cells with interferon-alpha/beta or -gamma. Nor thern blot analysis revealed constitutive expression of Ly-6 messenger RNA that was up-regulated by interferon treatment. Pretreatment of th e cells with transforming growth factor-beta 1 or 1,25-dihydroxyvitami n D-3 diminished constitutive Ly-6 expression. Ly-6 was localized intr acellularly to the Golgi complex. The current results demonstrate that mature osteoblasts express on their cell surface specific Ly-6 antige ns in a pattern that distinguishes them from the surrounding bone marr ow cells. These studies represent the first identification of osteobla st differentiation antigens that can be directly related to cells with in the hematopoietic lineage. By identifying similar antigens, osteobl asts at various stages of differentiation may be identified, isolated, and characterized.