SP7 and osteosarcoma: Moreover, Ocn expression level also decreased in a similar fashion as Nell-1 at 2 days post-transfection in primary human osteoblasts (Fig. 6B), but Opn expression patterns were different between Saos-2 osteosarcoma cells and normal primary human osteoblast cells, which may indicate that overexpression of Osterix plays a transient and more complicated role with variable effects on bone marker gene levels at different stages of maturation of human osteoblasts.