The growth mechanism of complex microtubule structures, such as cilia and sperm tails, remained unknown for decades despite ‘hook assay’ studies in the 1980s. Using cryo-electron tomography, we confirmed that microtubules can directly bind to each other despite strong surface electrostatic repulsion. Computational simulations identified key structures enabling side growth, and live tracking of microtubule doublets revealed the self-assembly process. This research addressed long-standing inquiries within microtubule and cilia research communities. It represents excellent research and an example of a well-working collaboration. It grounded me in the principles of a bottom-up research approach using the in vitro reconstruction of cellular processes from purified components.

Credit: Debec et al., 2010

The microtubule seed should have the tubulin C-termini removed from one of its protofilaments. 

In vitro, tubulin assemblies form doublets by initiating from the outer junction. 

The C-terminus of the A11 protofilament must be occluded to permit the lateral bonding of the B1 protofilament. 

Live imaging demonstrated that microtubule doublet formation initiates stochastically along the entire length of the seed microtubule. This bidirectional assembly process was observed to be significantly faster than the rate of canonical microtubule elongation.