Figure 1.

Microtubule-severing proteins have very different effects on microtubules, depending on the preference of the particular severing protein for stable or labile domains of microtubules.

Microtubules in the axon consist of a stable domain toward the minus end of the microtubule and a labile domain toward the plus end. Shown in the figure are microtubules with stable and labile domains indicated in red and yellow respectively. Severing proteins are shown as scissors. Severing in the stable domain would increase microtubule number, while severing in the labile domain would pare down the labile domain without creating more microtubules. Katanin and spastin preferentially sever stable domains whereas we posit that fidgetins preferentially sever labile domains. Figure prepared by Andrew Matamoros.