A "cytoldne-less" in vitro differentiation method would be promising for cost-effective mass production of cells used for regenerative medicine. In this study, we developed a differentiation signalobody S-RANK, in which the extracellular domain of receptor activator of nuclear factor kappa-B (RANK) is replaced with a single-chain variable fragment (scFv) to attain signaling in response to an inexpensive antigen. A murine macrophage cell line RAW264, which is known to differentiate into an osteoclast by RANK ligand (RANKL), was lentivirally transduced with S-RANK. When the resultant cells were cultured with a specific antigen, the cells differentiated into multinucleated tartrate-resistant acid phosphatase-positive osteoclasts. The differentiation efficiency was almost comparable to those induced by RANKL. In addition, the signaling analysis demonstrated that nuclear factor kappa-B and mitogen-activated protein kinase signaling pathways, which are the major signaling pathways downstream of wild-type RANK, were also activated by S-RANK. These results demonstrate that S-RANK sufficiently mimics signal transduction of wild-type RANK. Differentiation signalobodies may be applied for controlling differentiation of other cell types by using appropriate signaling domains. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.