Movie S7.

FIB-SEM images (SE) and 3D reconstruction of a proximal tendon containing an interface between unmineralized and mineralized tissue zones. The specimen is viewed in longitudinal profile following the long axis of the tissue prepared by protocol 2. The region is characterized by numerous collagen fibrils of various diameters and separated from one another by dark spaces, some of which contain mineral deposits (white and pseudo-colored red) of different sizes and shapes. The dark spaces are thought to represent the secondary channels that pervade the tendon and provide the space for fluid transport of mineral ion and mineral precursors. The mineral deposits in the interfibrillar collagen spaces are presumed to originate in association with putative matrix vesicles residing in secondary channels. Sites of intrafibrillar mineral deposition are marked by blue. In this movie and several others reconstructed from stacks of FIB-SEM images, intrafibrillar mineral sites are found in very close proximity to interfibrillar mineral sites, which are arranged linearly and in abundance near each intrafibrillar mineral deposit.