Fig 3. Flagellar size regulation.

(A) Flagellum assembly in C. reinhardtii is regulated by IFT particles that incorporate tubulin dimers at the flagellum tip. This assembly process combined with the conservation of IFT amount in flagellum gives rise to an assembly rate that decreases with flagellum length. (B) Decrease in flagellar size with increasing number of flagella while the cell size is kept constant. (C, Left) We model the flagellar re-growth experiment [28], where one of the two flagella is amputated and regrowth is observed. The intact flagellum starts shrinking immediately after the amputation, indicating a shared pool of building blocks. (C, Right) Fit to the experimental data for the length dynamics of the two flagella with the growth curves from simulation show good quantitative agreement. The plotted time shows the duration after amputation. Parameters: tubulin concentration = 5 μM, α = 1, β = 0, tubulin size = 10 nm, k⁺ = 120 μm³ min⁻¹, k⁻ = 100 min⁻¹, t₀ = 1000 min, production rate of new subunits r_p = 0.0016 min⁻¹.