WD repeat domain 5 (WDR5) is a member of the WD repeat protein family, which is involved in a variety of cellular processes, including cell cycle progression, signal transduction, apoptosis, and gene regulation. WDR5, also known as BIG-3, is expressed in the developing growth plate, accelerates chondrocyte and osteoblast differentiation in vitro, and regulates osteoblast differentiation during embryonic bone development. WDR5 interacts with the pluripotency factor Oct4/POU5F1 and is required for the efficient formation of induced pluripotent stem (iPS) cells.