The DKK (Dickkopf) family of secreted proteins includes DKK-1 through -4, and a related protein, Soggy (DKK-11). DKK-1 is an antagonist of the Wnt signaling pathway, forming inhibitory complexes with Wnt co-receptors LRP5 or LRP6 along with Kremen-1 or Kremen-2. DKK-1 is expressed during development and, in the adult, is expressed in osteoblasts and osteocytes. Over- or under-expression of DKK-1 can result in decreased or increased bone density.