Movie S5.

FIB-SEM images (EsB) and 3D reconstruction of a small distal tendon region comprised of an interface between unmineralized and mineralized tissue zones. The specimen is viewed in transverse profile to the longitudinal direction of the tissue prepared by protocol 1. The region is comprised of mineralized (white) and unmineralized (grey) collagen bundles together with a few intervening cells. 3D rendering shows tenocytes (tangerine) in linear disposition closely associated with mineralized collagen (blue) as the protein is secreted from the cells to form fibril bundles. The movie also suggests that there are many individual mineralized collagen fibrils in apparent units separated within a fibril bundle by dark thin structures yet to be identified; they may originate from the canaliculi but further work is required to establish their source.