Jean E Aaron
The following personal viewpoint is a retrospective from diverse histological and elemental microanalytical techniques applied to mineralogenesis that repeatedly suggested a similarity of the inorganic phase of bone to indigenous populations of microbe-like objects (0.1 -1.0 µm) calcified with phosphate. There is evidence that the microspherical particles are fabricated in the “young” osteocyte golgi apparatus by a process common to unicellular organisms. Inside pre-programmed golgi saccules the “nascent” mineral is contained and controlled by envelopes of specific proteins and lipids in an advancement over a rudimentary version found in calcifying prokaryotes. An intracellular bio-inorganic interface (silicon, calcium and phosphate-rich) is central, primed by carbonate and tempered by trace elements (Mg, Al, Fe). To a lesser extent soft tissues also perform this inherent golgi-directed activity (with potential clinical aberrations). With age the organelle produces calcified microspheres that may be too large (osteoarthritis) or too small (osteoporosis), while “switching off” to allow hard tissues to weaken and “switching on” making soft ones stiffen. Historically the bony biospheres may return to sedimentary rocks to be mined as fertiliser, fuelling an ancient cycle driven by distant golgi bodies with a cargo of bone salt resembling vestigial prokaryotes and primordial “pre-prokaryotes”.