２００６年 ９月 ４日（月曜日） 12：30～
Lynda F. Bonewald&s_comma; Ph.D.
Lefkowitz Professor of Oral Biology
Director of the Bone Biology Research Program&s_comma;
School of Dentistry&s_comma; University of Missouri at Kansas City&s_comma; U.S.A.
As the matrix producing osteoblast differentiates into a mature osteocyte surrounded by mineralized matrix&s_comma; a dramatic transformation takes place.
Morphology rapidly changes from cuboidal to dendritic. The mature osteocyte loses 70% of its cytoplasm as an osteoblast. For the osteoblast to embed in osteoid&s_comma; the cytoskeleton must be dramatically rearranged. Proteins known to be responsible for reorganization of the cytoskeleton&s_comma; destrin and CapG&s_comma; are elevated in early embedding cells as well as E11/gp38&s_comma; a molecule involved in dendrite elongation. Mineralized structures (50-100 nm) appear on newly forming dendrites as the earliest indication of initiation of biomineralization. Our observations suggest that the embedding of osteocytes and the formation of dendrites may be a highly dynamic process that is accomplished through the actions of actin degrading proteins destrin and CapG&s_comma; and the dendrite inducing protein E11/gp38. Once the extensions form&s_comma; small calcified&s_comma; spherical structures bud from the cell membrane&s_comma; then dissociate from the dendrite to associate with collagen fibers in order to initiate the mineralization process. In this manner&s_comma; the cell not only initiates and controls the biomineralization process&s_comma; but also protects itself while establishing the lacuno-canalicular syncytium essential for viability&s_comma; communication&s_comma; and most likely efficient mechanotransduction of mature osteocytes.