Figure 1. Two mechanisms for contraction: buckling and end clustering.

Top: When two anti-parallel actin filaments are bridged by a myosin motor (blue) and a crosslink (green), their relative movement forces one filament to buckle, resulting in the contraction of the network. Bottom: Microtubule contraction seems to depend on the affinity of dynein motors (red) for the ends of the filaments. For a recent review on the topic of contraction, see Clark et al., 2014.