Development and mineralization of embryonic avian scleral ossicles

PURPOSE To investigate the development and mineralization of avian scleral ossicles using fluorescence microscopy in combination with field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). METHODS The anterior halves of whole eyeballs from chickens on embryonic (E) days E10 to E21 and Japanese quail on embryonic days E8 to E17 were fixed in 100% methanol for 1 min, stained with Giemsa solution for 5 min, destained with distilled water for 30 min, and then viewed by epifluorescence. Propidium iodide (PI) was used to detect the nuclei of osteocytes in scleral ossicles. FESEM and EDS were then used to show areas of mineralization and to identify differences in the elemental composition of different regions of the ossicles. RESULTS Using Giemsa as a fluorescence stain, it was possible to observe the detailed morphology and development of both chicken and quail scleral ossicles. In chickens, bone microporosities first became visible at E15. Each microporosity contained a single nucleus, likely that of an osteocyte. The amount of carbon in ossicles steadily decreased during embryogenesis and post-hatching, while the concentration of oxygen showed a distinct increase over this time period. Calcium and phosphate levels in the ossicles increased gradually during embryonic and post-hatching stages. CONCLUSIONS A novel approach to study the development and mineralization of avian scleral ossicles during embryogenesis is presented. This methodology was validated by studying two different species, both important models for avian developmental research.