Microfibril formation in chick notochordal cells.

The central parts of the chick notochord at Hamburger and Hamilton's stages 20-22 were investigated by electron microscopy. Electron-dense bodies of various sizes and shapes and bounded by a limiting membrane were found in the central cells the notochord. These dense bodies contained fibrous material or microfibrils which ranged from 120 to 600 A in diameter. The large microfibrils often exhibited a typical repeating period with an interval of about 320 A. These dense bodies were always located near the cell membrane, which is rough or irregular in the central parts of the notochord at these stages. The fibrous core material of the dense body frequently shows striking similarities to amorphous fibrous material in the intercellular space of the central parts of the notochord, where they are situated at a considerable distance from the perinotochordal sheath space. From these results, it seems reasonable to suggest that the central cells as well as the peripheral cells of the notochord are capable of forming microfibrils similar to those observed in the perinotochordal sheath space. Moreover, they may play an important role in the total fibrillogenesis of the notochord.