The Three-Dimensional Morphometry and Cell–Cell Communication of the Osteocyte Network in Chick and Mouse Embryonic Calvaria

The study of osteocytes has progressed in chicks. We examined whether chick osteocyte data can be applied to other species. We used mice for comparison because they are common clinical tools in biomedical research and useful for future study. We analyzed the three-dimensional (3D) osteocyte network and gap junctional intercellular communication (GJIC) in living embryonic calvaria for the anatomical features. Embryonic parietal bones were stained with fluorescently labeled phalloidin and observed using confocal laser scanning microscopy. GJIC between osteocytes in chick and mouse parietal bone was assessed using fluorescence recovery after photobleaching (FRAP). The values for one chick and mouse osteocyte, respectively, were calculated as follows: cell processes 1,131 ± 139 μm, 2,668 ± 596 μm; surface area 1,128 ± 358 μm², 2,654 ± 659 μm²; and cell volume 455 ± 90 μm³, 1,328 ± 210 μm³. The density of 3D osteocyte processes in the bone matrix was not significantly different. FRAP analysis showed dye coupling among osteocytes in chick and mouse bone. The fluorescence intensity recovered to 49.0 ± 2.4% in chicks and 39.9 ± 2.4% in mice after 5 minutes. Fluorescence recovery was similar within 4 minutes. The difference in osteocyte size between the two species might have affected their functions. Osteocyte processes in the two species may sense similarly changes in the exterior environment. We successfully conducted morphological and functional analyses of the osteocyte network in chicks and mice. The size of the osteocytes in bone differed between the two species.