Objectives      To determine the role of Notch ligand

Delta-like 1 (DLL1) in bone morphogenetic proteins 9 (BMP9)-mediated osteogenesis in mesenchymal stem cells (MSCs) and investigate its possible mechanisms.       Methods      Recombinant adenoviruses were used to over-express DLL1 in immortalized mouse embryonic fibroblasts (iMEF). Cytochemical staining was used to evaluate the early-stage osteogenetic index

alkaline phosphatase (ALP) and the late-stage osteoblastic indicator

calcium deposits. Ectopic bone formation assay was conducted in nude mice

then HE staining and micro-CT scanning were employed to analyze osteogenetic status so as to determine the role of DLL1 in the process. qRT-PCR

Western blotting and luciferase reporter assay were conducted to detect the expression levels of BMP receptors

p-Smad1/5/8

and activity of Smad-binding element (SBE).       Results      Compared with control group

DLL1 in vitro treatment obviously enhanced the osteogenic indicators ALP and calcium deposits

and in vivo promoted ectopic bone formation in nude mice. ALK2 in BMP signal pathway was significantly elevated

but no change was seen in the level of ALK1. There were also no obvious changes in the total protein levels of Smad1/5/8

but those of phosphorylated Smad1/5/8 were increased. SBE activity was also enhanced (P0.05).       Conclusion      DLL1 enhances BMP-induced osteogenesis in MSCs both in vitro and in vivo

and it might exert the effect through BMP-Smad pathway.