Evolution of the multi-tubulin hypothesis.

Microtubules are organized into diverse cellular structures in multicellular organisms. How is such diversity generated? Although highly conserved overall, variable regions within alpha- and beta-tubulins show divergence from other alpha- and beta-tubulins in the same species, but show conservation among different species. Such conservation raises the question of whether diversity in tubulin structure mediates diversity in microtubule organization. Recent studies probing the function of beta-tubulin isotypes in axonemes of insects suggest that tubulin structure, through interactions with extrinsic proteins, can direct the architecture and supramolecular organization of microtubules.