Figure: Immunofluorescent localization of axon.
Immunofluorescent localization of recently assembled & old microtubules in a newly formed axon.  Prior to extending an axon, the neuron was microinjected with biotin-labeled tubulin.  The neuron was then stimulated to extend an axon & then fixed & stained to reveal microtubules containing biotin-tubulin (orange) & microtubules without biotin-tubulin (green).  Biotin-tubulin-containing microtubules assembled at some time after injection of biotin-tubulin, whereas microtubules without biotin-tubulin existed in the cell before injection & also before initiation of axon growth.  The presence of these latter microtubules in the newly formed axon is strong evidence that the were transported from the cell body into the newly formed axon.  For a full account, see Slaughter et al 1997, Microtubule   transport from the cell body into  the axons of growing neurons. J.   Neurosci.17: 5807-5819.