Intraflagellar transport balances continuous turnover of outer doublet microtubules

TLDR

Flagellar length control is used to study organelle size regulation, yet previous models assumed flagella were static after assembly. Recent evidence shows flagella continuously turn over at their tips via intraflagellar transport, and blocking this transport stops tubulin incorporation and causes resorption, supporting a steady‑state model in which balanced assembly and disassembly regulate flagellar length.

Abstract

A central question in cell biology is how cells determine the size of their organelles. Flagellar length control is a convenient system for studying organelle size regulation. Mechanistic models proposed for flagellar length regulation have been constrained by the assumption that flagella are static structures once they are assembled. However, recent work has shown that flagella are dynamic and are constantly turning over. We have determined that this turnover occurs at the flagellar tips, and that the assembly portion of the turnover is mediated by intraflagellar transport (IFT). Blocking IFT inhibits the incorporation of tubulin at the flagellar tips and causes the flagella to resorb. These results lead to a simple steady-state model for flagellar length regulation by which a balance of assembly and disassembly can effectively regulate flagellar length.