Figure 2.

Cartoon of an axon and an oligodendrocyte cell that shows a schematic of the cellular anatomy of axonal degeneration in transgenic mice that have knockouts of genes for the two iron regulatory proteins IRP1 and IRP2 (adapted from reference [23]). The small brown dots represent ferritin particles, the molecular structure of which is shown. The inset shows an actual image from such a region in the brain that was stained to visualize ferritin and then was recorded by optical microscopy. The optical microscopic investigations suggest that there is a large increase in ferritin in the presumptive axonal regions (thick diagonal brown line in the inset) of the IRP-knockout mice. However, electron tomographic studies reveal that the most of the excess ferritin is localized to regions in the interior of the axon that are generated by invaginations of neighbouring oligodendrocyte cells into the axon.