Projection domains of MAP2 and tau determine spacings between microtubules in dendrites and axons

Neurons develop a highly polarized morphology consisting of dendrites and a long axon. Both axons and dendrites contain microtubules and microtubule-associated proteins (MAPs) with characteristic structures. Among MAPs, MAP2 is specifically expressed in dendrites whereas MAP2C and tau are abundant in the axon. But the influence of MAP2, MAP2C and tau on the organization of microtubule domains in dendrites versus axons is unknown. Both MAP2 and tau induce microtubule bundle formation in fibroblasts after transfection of complementary DNAs, and a long process resembling an axon is extended in Sf9 cells infected with recombinant baculovirus expressing tau. We have now expressed MAP2 and MAP2C in Sf9 cells in order to compare their morphology and the arrangement of their microtubules to that found in Sf9 cells expressing tau. We report here that the spacing between microtubules depends on the MAP expressed: in cells expressing MAP2, the distance is similar to that found in dendrites, whereas the spacing between microtubules in cells expressing MAP2C or tau is similar to that found in axons.