How do cells control the length of their flagella?

Cells assemble a number of filamentous structures which have a specific length. The question of how cells control the length has been studied extensively in model organism Chlamydomonas reinhardtii which has two flagella of the same length.

Past studies have shown that when one of the flagella is severed, its length increases over time while, remarkably, the other flagellum shortens. Upon reaching a common length, the two flagella grow together until reaching their steady state length. Although we know the molecular players involved in the process, the mechanism is not well understood.

Previously, several models have suggested length-control to occur via the length-dependent assembly of the flagella. Here, we show that within a wide class of models, length-control of multiple flagella can only occur if the disassembly (depolymerization) of the flagella is length-dependent. We provide concrete examples to show how such length-dependent-depolymerization can occur within simple biophysical models.