The architecture of microtubular network and Golgi orientation in osteoclasts--major differences between avian and mammalian species

In the present study, we analyze multinuclear osteoclasts obtained from several avian and mammalian species and describe the reorganization of their microtubular architecture and Golgi complex orientation during osteoclast differentiation and activation for bone resorption. In nonresorbing quail and chicken multinuclear osteoclasts, microtubules radiate from multiple centrosomal microtubule-organizing centers (MTOCs), whose number is equal to the number of nuclei. However, centrosomal MTOCs disappear at the time of cell activation for bone resorption and the Golgi membranes redistribute to circumscribe nuclei. In contrast to avian osteoclasts, both resorbing and nonresorbing rat, rabbit, and human osteoclasts have no or few centrosomal MTOCs. Instead, after cold-induced depolymerization, regrowing microtubules nucleate from the perinuclear area where immunofluoresce and immunoelectron scanning microscopy reveal pericentriolar matrix protein pericentrin associated with vimentin filaments. Furthermore, the circumnuclear reorganization of MTOCs and the Golgi is a result of mammalian osteoclast maturation and occur before any resorptive activity of the mononuclear osteoclasts and their fusion into multinucleated cells. Our results show that unlike previously suggested, the nuclear surfaces of mammalian osteoclasts act as the microtubule anchoring sites similarly to nuclear surfaces in multinucleated myotubes and suggest the role of perinuclear intermediate filament network in orchestrating the microtubular cytoskeleton.