EXPERIMENTAL FIGURE 18-13 Spacing of microtubules depends on the length of the projection domains of microtubule-associated proteins. (a) Insect cells transfected to express MAP2, which has a long arm, or to express tau protein, which has a short arm, grow long axon-like processes. These electron micrographs show cross sections through the processes induced by the expression of MAP2 (left) and tau (right) in transfected cells. Note that the spacing between microtubules (MTs) in MAP2-containing cells is greater than in tau-containing cells. Both cell types contain approximately the same number of microtubules, but the effect of MAP2 is to enlarge the caliber of the axon-like process. (b) Diagrams of association between microtubules and MAPs. Note the difference between the lengths of the projection domains in MAP2 and in tau.

[Part (a) reprinted by permission from Macmillan Publishers Ltd: J. Chen et al., “Projection domains of MAP2 and tau determine spacings between microtubules in dendrites and axons,” Nature 1992, 360:6405, pp. 674-676.]