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The bone remodelling cycle (see Poster panel “The bone remodelling cycle”) maintains the integrity of the skeleton through the balanced activities of its constituent cell types. These are the bone-forming osteoblast, a cell that produces the organic bone matrix and aids its mineralisation (Karsenty et al., 2009); the bonedegrading osteoclast, a unique type of exocrine cell that dissolves bone mineral and enzymatically degrades extracellular matrix (ECM) proteins (Teitelbaum, 2007); and the osteocyte, an osteoblast-derived post-mitotic cell within bone matrix that acts as a mechanosensor and an endocrine cell (Bonewald and Johnson, 2008). A fourth cell type, the bone lining cell, is thought to have a specific role in coupling bone resorption to bone formation (Everts et al., 2002), perhaps by physically defining bone remodelling compartments (Andersen et al., 2009). Molecular dissection of genetic disorders of highly …