Galati et al. identify a protein that helps cilia basal bodies (BBs) respond to mechanical force so that they maintain their organization in multiciliated Tetrahymena cells.
Cilia are organized by BBs docked at the cell cortex. In order to swim efficiently, Tetrahymena align their BBs into arrays that run from the front to the back of the cell, and each BB is oriented so that its attached cilium beats in the same direction as all the others. This organization is lost in disA-1 mutant cells, but the identity of the mutated gene and the function of the protein that it encodes are unknown.
Galati et al. used next-generation sequencing to identify the disA-1 mutation and found that it results in a truncated version of a protein the researchers called DisAp. DisAp localized to the kinetodesmal fibers (KFs) that protrude from the anterior side of BBs and control the structures’ positioning and orientation. Galati et al. found that KFs grew when cilia experienced more mechanical force (either because they were beating faster or were pushing against a more viscous medium). KFs were shorter in disA-1 cells and didn’t elongate in response to increased force. This reduced the fibers’ contacts with the cell cortex, which might otherwise prevent BBs from reorienting.
The researchers also discovered that newly assembled BBs dock in the correct position by moving along the KF of the mother BB from which they formed. The shorter KFs of disA-1 cells likely inhibit this process as well.
DisAp is not conserved in vertebrates, but structures analogous to KFs, known as striated rootlets, orient BBs in multiciliated vertebrate cells. Senior author Chad Pearson now wants to investigate if these structures also elongate in response to increased mechanical force.
Text by Ben Short