URB expression in human bone marrow stromal cells and during mouse development

Seven genes preferentially expressed in undifferentiated human bone marrow stromal cells (BMSC) with respect to BMSC-derived osteoblasts were previously identified by differential display. Here we characterize the expression of one of these genes, URB, belonging to the sushi-repeat-containing protein superfamily. In culture, URB is expressed in both human primary and cloned BMSC, and is drastically downregulated during osteoblastic differentiation of these cells. Here we show that in mouse tissues a single 3.8 kb Urb transcript is detected and that the mouse Urb protein is secreted as a 150 kDa glycoprotein. During mouse development Urb RNA is barely detectable in 9 dpc embryos and increases at later stages. Both in situ hybridization and immunohistochemistry analysis show Urb expression in mouse embryos starting from 14 dpc mostly in cartilage. The temporal and spatial expression pattern of Urb suggests its role in mouse skeletogenesis.