| Objective: to discuss the mechanism and the function of NS by differentiating rat bone marrow stem cells into osteoblasts in vitro.Methods: The BMSCs isolated from the femur and tibia of 4~6-week-old male SD rat were cultured in vitro. The BMSCs of passage 3 were divided into two parts and cultured in different medium. Part A was sub cultured by L-DMEM medium and Part B added mineralization condition medium as the inducers. The morphological characters of BMSCs and cell proliferation were observed with phase contrast microscope and MTT test. Osteoblasts activities of the sub culturing cells were detected by alkaline phosphatase staining and alizarin red S staining. The expression of NS in BMSCs and induced cells were showed and compared by Immunohistochemical and immunofluorescence staining.Results: NS was abundantly expressed when BMSCs were proliferating in the early state, but it abruptly and almost entirely disappeared at the start of differentiation. BMSCs which was induced by mineralization hightly expressed medium NS than the cells which was cultured by L-DMEM medium, and expressed time dependence attenuation. BMSCs under the mineralized liquid could be induced to pack the distribution of osteoblast group. The BMSCs could be induced into osteoblasts in mineralization condition medium.The Immunohistochemical staining showed that the longer BMSCs induced the lower expression of NS. NS was negative expressed in osteoblasts. Alkaline phosphatase staining and alizarin red S staining were both positive.Conclusions: NS is a nucleolar protein predominantly associated with proliferating in BMSCs. It was mainly localized in the nucleoli. When bone marrow stem cells were differentiated into osteocytes, NS expression hightly decreased compared to the undifferentiated cells. In SD rat , NS which is involved in the regulation of proliferation of these cells is problely a marker of undifferentiated BMSCs.
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