Differentiation and osteoprotegerin secretion of human osteoblasts: R-spondin 1 effect via Wnt/beta-catenin signal pathway  
Wu Si-min, Liu Qing-mei, Ma Yan-yun, Wang Jiu-cun, Zhao Dong-bao
Chinese Journal of Tissue Engineering Research . 2015, (37): 5923 -5927 .  DOI: 10.3969/j.issn.2095-4344.2015.37.004